February 12, 2020 • 46 mins
What exactly is radiation? How is electromagnetic radiation different from particle radiation? What is ionizing radiation? And how do Geiger counters work?
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Episode Transcript
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Speaker 1 (00:04):
Welcome to tech Stuff, a production of I Heart Radios
How Stuff Works. Hey there, and welcome to tech Stuff.
I'm your host, Jonathan Strickland. I'm an executive producer with
iHeart Radio and a love of all things tech, and
inspired by my last episode about smoke detectors, I thought
(00:25):
I would do an episode about radiation and radiation detectors.
And I want to define terms like radiation and radioactivity,
to talk about the different types of radiation there are,
and to differentiate between ionizing and non ionizing radiation and
chat about the technology around it. So first, what is radiation. Well,
(00:47):
it's a fairly broad term with lots of different meanings
as it turns out, but I think that's part of
why there's frequently a lot of confusion around the concept
of radiation. But there are a couple of definitions that
for our purpose as we want to focus on, and
really the one that we're truly interested in is the
process of admitting radiant energy in the form of waves
(01:09):
or particles as a definition I took from the Miriam
Webster Dictionary. By the way, so radiation can involve electromagnetic
waves or it might involve sub atomic particles. Uh, some
radiation has the potential to be harmful, even deadly in
sufficient intensities and length of exposure. Some radiation is relatively safe,
(01:30):
particularly under specific controls. So let's start with some early
discoveries of electro magnetic radiation, as those predate our understanding
of particle based radiation. So our story begins in eighteen
hundred with an early scientist named William Herschel. And Willie
(01:51):
was interested in learning more about the spectrum of light,
and it was already understood that if you were to
pass light through a prism, you could separate light into
different colors. You know, the good old roy g BIV spectrum,
which stands for red, orange, yellow, green, blue, indigo, and violet.
The spectrum will always be in that order. Anytime you
(02:11):
pass light through a prism, it's going to break into
those bands in that order, and those bands actually represent
bands of frequencies of light waves. Herschel was wondering if
the different colors of light produced different amounts of heat,
So is one type of light warmer than another, So
(02:32):
he set up a system in which he positioned thermometers
at each color displayed from light passing through a prism.
So he sets up a prism in his window, lights
coming through it, and it's hitting a table, and it
divides up into different bands of color. He sets the
thermometers in each band of color, and he happened to
(02:53):
have an extra thermometer just beyond the red end of
the spectrum, so it's actually in the dark. It was
beyond the range of the visible light. He had no
way of knowing it, but he had, by happy coincidence,
placed a thermometer right where the infrared band was. And
we can't see infrared light, but that light does transmit heat.
(03:16):
In fact, Herschel was surprised to see that it was
that thermometer, the one that was in the darkness, just
beyond the red range, that actually registered the highest temperature
out of all the thermometers he had set out. And
we often talked about heat radiating outward from a source.
In eighteen o one, another big thinker named Johann Wilhelm
(03:37):
Ritter built upon Herschel's experiment. He decided to see if
perhaps there was anything beyond the other end of the spectrum,
a k a. The violet end. In fact, he really
discovered it sort of by accident. Ritter experimented by using
a substance called silver chloride, and this is a chemical
that turns black if it's exposed to sunlight. Ritter built
(04:01):
on the understanding that blue light would produce a greater
reaction in silver chloride than red light, so he did
a variation on Herschel's experiment. He again used a prism
to break the light into bands of color, and then
within each band of color he placed a vile a
silver chloride to see if the reactions were different across
(04:23):
the spectrum of light. He could see that, indeed, the
reaction did vary across the spectrum. The closer you got
to the violet side of the spectrum, the more intense
the reaction was, and it was most evident just beyond
the violet side, in an area where there was no
visible light at all. So clearly there was something going
(04:47):
on on that end of the spectrum. So on the
red end you were getting some sort of heat which
we now know is infrared, and on the violet end
there's something else that was really reacting to silver chloride.
So Ritter would call this chemical raise, which to this
very day we don't do anymore. Now today we call
it ultraviolet light. Herschel and Ritter had made the first
(05:11):
steps to increase our understanding of the electromagnetic spectrum, of
which visible light is just one tiny part, and as
we would build on that understanding, we'd also gain more
information about what effects these types of radiation can have
on us. Some of them have very little effect on us,
some of them can have a drastic effect on us.
(05:33):
And it would take a lot more time, but we
would gradually begin to understand that if you look at
the spectrum, it includes everything from radio waves on one
extreme end of it to gamma raise on the other
end of it, and these waves vary in wavelength, frequency,
and energy. So on one extreme end you've got those
(05:55):
radio waves. These can have really long wavelengths, measuring hens
of miles, like sixty two miles or a hundred kilometers
for wavelengths of certain radio frequencies. So if you had
a perfectly steady radio wave, like just imagine, it's a
perfect signal you. If you were to map it out,
it would be a beautiful sign wave. If you measured
(06:17):
from the peak at one point to the next peak,
that's the wavelength. That's what would have been a hundred
kilometers in distance an enormous wave. The frequency of a
wave refers to how frequently a specific point on a wavelength,
you know, like that peak, how frequently you could see
(06:39):
that point on each wave pass a given reference point
within a second. So with the longest radio waves at
the lowest frequencies, you're talking about a frequency of around
three thousand cycles per second, meaning that in one seconds time,
three thousand peaks past that given point of reference. Now,
(07:00):
one thing to keep in mind is that this is
electromagnetic radiation. An electromagnetic radiation all travels at the same speed,
that being the speed of light. Now, we do have
to remember the speed of light isn't a constant across
all media. It's a constant within each media. So we
we usually when we're talking about the speed of light,
(07:21):
we're talking about within the vacuum of space. But if
light is traveling through an atmosphere or through water or something,
it actually does travel at a different speed than that
because it it's all dependent upon the medium. Still, electromagnetic
radiation travels at that speed. So a wavelength of uh,
(07:42):
you know, one wavelength of of a radio wave is
traveling at the speed of light, as is one wavelength
of gamma radiation. However, because the radio waves are so
long and the gamma rays are so short in wavelength,
the frequency has to be different, right. The frequency of
the radio waves has to be lower than the frequency
(08:04):
of gamma rays because you get way more gamma rays
passing within a frame of a second, even though they're
both traveling at the same speed. All right, That gets confusing, right,
So I like to explain this with an analogy. Imagine
you've got two identical straight roads, one lane wide, and
they're right next to each other. Down one road, you
(08:25):
have a series of buses, and each bus super long,
measures eighteen meters in length, traveling down the road at
fifty KOs per hour, and there's one meter of space
in between each bus. So bus number one eighteen meters
long than you have a meter, and a bus number
two is eighteen meters long than you have a meter.
(08:46):
That's dangerous, but whatever, they're traveling down at fifty an hour,
perfectly in sync with each other. On the other road,
do you have a series of zippy little smart cars
and each smart car measures just three meters in length.
They're also going down the road at fifty kilometers per
hour with a meter of space in between each pair
of cars. Now, individual vehicles are all traveling at the
(09:08):
same speed, they're all traveling at fifty kilometers per hour.
But the smart cars aren't as long as the buses.
So if you were to have a accounter, there's someone
standing by the bus lane and there's someone standing by
the smart car lane, and they're holding a little counter
in their hands. The person next to the smart cars
is going to count way more smart cars in the
(09:29):
same amount of time as the person counting the buses.
And it's not because smart cars are traveling faster. They're not.
They're just smaller, so more of them can go by
within that given amount of time. The same thing is
true with wavelengths of the electromagnetic spectrum red light, blue light,
X rays, radio waves. They're all traveling at the same speed.
They just have different wavelengths, so they have to have
(09:51):
different frequencies. Now, as I said earlier, in those early
days in the nineteenth century, we didn't have this level
of understanding. We weren't aware of different wavelengths and frequencies,
and we didn't know that longer wavelengths and lower frequencies
of electromagnetic radiation carry less energy, whereas high frequencies and
(10:11):
very small wavelengths of electromagnetic radiation can pack way more energy.
If you were to look at the experiments of Herschel
and Ritter, you might actually think that that's not the case,
because the invisible light off the red end of the
spectrum was carrying a lot of heat. It was heating
up a thermometer more than the others, so maybe it
carries more energy. And whereas the violet side you just
(10:34):
saw silver chloride change color. So it would take a
lot more experimentation to get a deeper understanding of the
actual nature of electromagnetic radiation. Now to go into the
full history of how that understanding would unfold is the
stuff of college lecture series, So I'll just give very
brief summaries to get us kind of closer to our objective.
(10:54):
In the nineteenth century you had numerous scientists and inventors
who were observing all sorts of interesting stuff that would
later become integrated into our knowledge of electromagnetism. So Michael
Faraday did a great deal of work exploring the relationship
between electric and magnetic fields. For example, his work would
inspire a Scottish physicist named James Clerk Maxwell to look
(11:19):
into the matter further, and Maxwell made predictions about electromagnetic
radiation based on those early experiments and observation, saying, well,
based on what we know, I expect that will eventually
find something that fits this mathematical uh example of what
should be there, and his predictions proved to be accurate,
(11:39):
and they in turn would serve as an important foundation
for Albert Einstein's special theory of relativity, as the one
that gives us the famous equation equals mc squared, which
tells us that energy and mass are related at an
intrinsic level. And Maxwell's observations about electromagnetic radiation would lead
to a theory about heat radiation that in turn would
(12:00):
be overturned by Max Planck, whose formulation of quantum hypothesis
to describe how heat radiates would become the predominant one.
But all of that is a little outside of our scope.
So the point I wanted to make is that the
nineteenth century was a boom time for scientific observations and discoveries,
and the things we would learn would serve us well
(12:21):
as we moved into the next phase of understanding of radiation.
And what it's all about. So the other big discoveries
that relate to this episode came about at the end
of the nineteenth century, so we get to look at
both ends of the eighteen hundreds. In eight Vilhelm runjeon
which I mentioned him in the last episode, he was
experimenting with a cathode ray tube, and I talked about
(12:43):
that again in the Smoke Detective episode. Essentially, these are
devices that produce streams of electrons by heating up a
filament inside a glass vacuum tube, kind of similar to
a light bulb. Runjen found that as he applied an
electric voltage to the cathode ray tube a light detection
screen in his lab that was made out of barium
(13:04):
platina cyanide fluorest, it actually lit up. It detected light
even though there was no visible light there. So he
began to experiment with this phenomenon, this invisible light that
was causing this this detector to light up, and that
included putting objects between the cathode ray tube and the screen,
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and he saw that whatever was coming out of the
tube seemed to be penetrating through objects and it was
still hitting the screen on the other side. He found
that if he put photographic film, the energy would interact
with the photographic film, and if you put something in
between the film and the cathode ray tube, he could
get a really interesting image of it. Uh, it's like
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you could see through certain stuff pretty clearly. So, for example,
his hand, he put his hand in front of it
and he took a photo. Then the picture would show
the skeleton in hand. It would it would show through
the soft tissues of his hand, and he thought, well,
this is interesting. He discovered a new type of radiation
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and he called it the X ray because what the
heck was going to call it? It was an unknown quantity,
and in mathematics we often refer to unknown quantities as X,
like solve for X. So it was meant to be
a placeholder. X rays just it turned into the permanent
name for the stuff. Now. Initially, no one was aware
(14:32):
that X ray radiation was potentially dangerous with its shorter
wavelength and higher frequency and energy than visible light. In fact,
no one was even sure that was another form of light.
They thought it might be, but they weren't certain, and
that wouldn't be proven until nineteen twelve. But people began
to understand that there was some potential danger the X
(14:54):
rays fairly early on. In eighteen nineties six, the year
after Runton's UH discovery, the journal Nature published an article
with the title The Harmful Effects of X rays. And
in that article there was a story about a guy
who had worked as an X ray demonstrator in London,
(15:15):
and he described the effects of X ray exposure that
he experienced, particularly on his hands, after working for a
full summer doing demonstrations with X ray machines for several
hours a day, I'm going to quote an excerpt. In
the first two or three weeks, I felt no inconvenience,
(15:37):
but after a while appeared on the fingers of my
right hand many dark spots which pierced under the skin,
and gradually they became very painful. The rest of the
skin was red and strongly inflamed. My hand was so
bad that I was constantly forced to bathe it in
very cold water. An ointment momentarily on the pain. But
(16:01):
the epidermist had dried up, had become hard and yellow
like parchment, and completely insensible, so I was not surprised
when my hand began to peel. From that point, the
guy goes on to describe how things got even worse,
like he began to lose fingernails and stuff. But I'm
gonna leave out the rest of the grizzly details. The
(16:24):
point is people are starting to notice that the longer
someone was exposed to X rays, the more severe the
consequences seemed to be. Short exposures did not appear to
be as serious, but this was something that people were
starting to get a little concerned about that would grow
in the years to come. But first, let's take a
quick break before we jump into that discussion. Okay, so
(16:55):
before we took our break, I was talking about how
people were beginning to understand that X rays could be dangerous.
That didn't stop early irresponsible implementations of X ray machines. However,
people thought of these as curiosities. They were things to
be celebrated and experienced. Thomas Edison thought everyone would have
one in their own home and thought perhaps they should
(17:17):
have them, because again, they didn't understand the dangers yet.
People would even have X ray parties in which guests
would take X ray photos of themselves, you know, of
their foot, or their hand, or even their face, and
they would get to keep the photographs at the end
of the party. Shoe stores installed X ray fluoroscopes to
(17:38):
get a look at a person's foot, And while a
person visiting the store wouldn't likely walk away with a
lethal dose of radiation, the folks who were working at
the store were exposed to X rays much more frequently
and for longer durations, and many of them would suffer
the consequences. But all of those awful discoveries would take
(17:59):
some times, so people didn't immediately notice the issues. Meanwhile,
let's get back to the discovery of radioactivity by talking
about the other kind of radiation, not the electro magnetic type.
So in eighteen ninety six, which was that same year
that the Nature article about the dangers of X rays
came out, there was a physicist named al Marie Beccarel
(18:22):
who was wondering if some materials he was working with
might produce the same sort of energy that Rundgen's X
rays seemed to create. One of those materials that Beckerel
was working with was a crystal made up of uranium salts. Now,
the various materials Beccarel had interest in all shared a
common trait. They were all phosphorescent, so they could all glow,
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and he wondered if they were giving off the same
sort of invisible light stuff that run Gen was observing
with X rays. So Beckarel set up an experiment. He
put down a photographic plate. He totally covered it so
that one of it would be exposed to light because
that would activate the photoreactive chemicals on the plate. And
on top of the covering he put a selection of
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his phosphorescent crystals to see if any of them would
interact with the photo reactive chemicals. And he exposed the
whole thing to the sun, you know, thinking that the
sun would charge these various crystals. And at the end
of the experiment he discovered that out of all the
different things he was testing, only one seemed to have
any effect at all, and that was the rock crystal
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that was actually made up of uranium salt, and that
was the only one that seemed to have fogged up
the the photoplate. So he thought, well, I'll do a
longer test. I'll leave it out in the sun longer,
see if I get a bigger, more clear result. But
the weather at that point wasn't cooperating. It had gotten cloudy,
so he couldn't put it out in the sun. So
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he takes his photographic plates and his uranium salts and
he stores them away and waits for the weather to
get better. So they were actually stored next to each
other in a dark cabinet. Several days later, as the
weather was starting to finally clear out, he was getting
ready to conduct his experiment, but he decided, you know what,
before I do this, I better make sure these photographic
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plates are still good, because the chemicals can actually expire,
and I'd be wasting my time if they aren't working anymore.
So he picks one and develops it, and it happened
to be one that was close to the iranium salts.
Rock He was surprised to discover that the bits of
the photographic plate that had been close to those uranium
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salts had images on them, even though the salts had
not been exposed to sunlight. They've been stored in a
dark cupboard, and he concluded that the uranium salts themselves
were giving off some sort of emission that was being
captured on this photographic plate. Henri Becarel had a couple
of enterprising and brilliant assistants. One was Pierre Curie and
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the other was Marie Sklodowska, who would marry Pierre and
become Marie Curie. She uh really was fascinated by radioactivity,
and together with her husband, they began to study the
ranium salts as well as looking for other similar materials
that seemed to display this radioactive phenomena. They tested some
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mining operation waste. It's called a pitch blend. The mining
operations were happy to get rid of it because it
was just run off from their operations, and they found
that it could contained traces of radioactive material, and eventually
they were able to separate a small amount of it
from the rest of the pitch blend, and it would
later be called radium. It was far more radioactive than
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the uranium salts they had already worked with. The Curies
and Beckrel would receive the Nobel Prize in Physics for
their discoveries. Runen also received one earlier for his discovery
of X rays, and then Pierre Curie would later tragically
die in a traffic accident. Marie would go on to
discover another radioact development, this one called polonium, and she
(22:00):
would receive a second Nobel Prize, though that second one
was in chemistry. She's one of only a few people
who have ever received more than one Nobel Prize. Now,
one thing Beckerel did with his own research was proved
that the energy coming out of this uranium salt was
not the same thing as X rays, and he did
this by testing the uranium salts against X rays with
(22:23):
a device that could generate a magnetic field. So X
rays would pass through the magnetic field unimpeded. And that's
because X ray radiation has no electric charge, and thus
it has no magnetic field of its own, so it's
not affected by magnetic field. It just passes through. Is
that there's nothing else there but the radiation coming from
the uranium salts bent upon encountering the magnetic field, and
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that told Beckarel that whatever was coming out of the
uranium salts had an electric charge to it, because it
had to have an electric charge in or to have
its own magnetic field and thus be either attracted or
repelled by the magnetic field and his testing vice. So
Beckerel tested numerous types of radioactive substances using this approach
and observed three basic results. Either radiation would bend one
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way using certain radioactive materials, and he would conclude, this
is a positive radiation material because it is being attracted
to the negative side of the magnetic field and repelled
by the positive side, or it would bend the other way,
so he would have the opposite conclusion. Okay, this is
negative radiation because it's being attracted to the positive side
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and repelled by the negative side, or it passed straight
through like X rays, and it would have no electrical
charge at all, so it would be neutral. So you
had positive, negative, and electrically neutral radiation. In their work,
the Curies and Beckarel noted that prolonged exposure to some
of these radioactive materials would result in injuries and ailments,
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like if you handled some of the more radioactive stuff
like radium for any length of time, you could actually
get burns on your skin, and you could suffer radiation sickness,
which includes symptoms like nausea, but the extent of the
damage was unknown for years. Marie cry died in nineteen
thirty four of a plastic anemia, which was probably a
(24:16):
consequence of her exposure to radioactive material over the years.
It certainly would have increased the odds of her developing that,
and that's something that is is good to just mention
in general is that when we think of radiation, we
often think of the radiation sickness, the sort of acute
symptoms you can have if you have a sudden exposure
(24:38):
to an intense amount of radiation. But in many ways,
the consequences of exposure to radiation are really more about
the increased risk of developing UH conditions like cancer. UH.
And it doesn't necessarily mean that if you do develop cancer,
that it was a direct result of that exposure to radiation,
(24:59):
but rather or that the exposure to radiation increased the
odds that you would develop cancer. It's a complicated thing
to look at because without knowing all the variables, you
cannot say conclusively that X caused why, but you can't
say that X made Y way more likely. That's what
we think with Currie, that she probably developed a plastic
(25:23):
anemia as a consequence of this exposure to stuff like
radium over the years. Many of her belongings and even
a cookbook she used, are actually stored in shielded containers
to this day because they're still radioactive dangerously. So the
lack of understanding about the consequences of radiation exposure would
(25:44):
have many more nasty consequences, just as it had with
the X ray fad. For example, because radium is phosphorescent,
it was seen as a useful material for stuff like
the hands of watches, like analog watches. He would paint
an analog watches minute and our hands with radium, and
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that would make it glow in the dark and made
it really easy to read the time, even if you
were in low lighting. While the amount of radium on
these watches was very very small and not likely to
harm somebody who was wearing the watch, the employees responsible
for painting the watch hands received way more radiation exposure. Colloquially,
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they were called radium girls, and the management positions at
these facilities frequently had significant protection from radiation, but the
same could not be said for the women on the
front lines, the women actually doing the work painting the
radium onto these watch hands. It also wasn't uncommon for
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a worker to lick the end of her brush to
shape it so that she could more easily paint the
watch hand. So that meant these workers were occasionally depositing
little amounts of radium directly on their tongues. They were
ingesting radium. Radium when ingested, will deposit itself in bone,
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much like calcium would, so several of the workers would
ultimately grow ill with radiation sickness. A group of five
of them later brought a lawsuit against their company. That
company was the United States Radium Company. They charged them
with being irresponsible in areas of health and safety, and
in turn that prompted a detailed study into what the
(27:32):
long term effects of radium exposure are and it's awful
that our knowledge came at such a steep price. At
the same time, the results of that study would lead
to massive changes in health and safety regulations for the
benefit of workers in the United States. From these discoveries,
physicists began to learn more about the nature of radioactive
(27:54):
material in general. They observed that there were different kinds
of radiation beyond just calling it positive, negative, or electrically neutral.
Some radiation seem to have more penetrative abilities. They could
penetrate further into solid matter than other types of radiation.
So you might have one type of radiation that isn't
(28:16):
able to penetrate solid matter effectively, and another one seems
to go right through stuff as if there's no problem.
A physicist named Ernest Rutherford conducted numerous experiments with radioactive
material and at this point we were beginning to understand
that radioactivity was a process in which certain materials undergo
a process called decay, and that is the form that
(28:38):
they are in. The radioactive form is inherently unstable. You
can if you want to think of it in terms
of want, I mean putting motivation is ridiculous because we're
talking about atomic particles here. But it's a form of
an atom that does not want to be that form.
It's unstable. So these materials will spontaneously but not necessary early,
(29:00):
quickly break apart and give off energy and subatomic particles
as they decay to a more stable form. Rutherford classified
three types of radiation. He said this was all based
off the penetrative properties of radiation, how far they could
penetrate into matter. The three types he classified were alpha radiation,
(29:21):
beta radiation, and gamma radiation. Alpha particles had the least
amount of ability to penetrate matter, and gamma rays were
the opposite. They could very easily penetrate matter. Upon further study,
scientists discovered that an alpha particle is relatively massive on
the atomic scale of things. It actually consists of an
(29:43):
ejected helium nucleus. A helium nucleus is two protons and
two neutrons. This is the type of radiation given off
by a mera sirium to forty one. That's the radioactive
material that's inside smoke detectors that I talked about in
the last episode. The ionization chambers have this type of
radioactive material in them, so you probably have some of
(30:03):
the stuff in your house right now. Alpha particles are
not able to penetrate matter very well, and they're big
enough and slow enough that they can't really get through skin,
at least not most of the time, so they're not
likely to have it affects you. Uh. They can't even
go through very much air. After a couple of inches,
(30:24):
they've lost the energy to move forward. Breathing in alpha
particles would be a real risk, and you wouldn't want
to swallow any of it either, so you don't want
to come into contact with the stuff, But having it
enclosed in a smoke detector in its own little chamber
in the smoke detector is more than enough protection that
you wouldn't receive any sort of significant radiation exposure from
(30:48):
the ameer sirium inside a smoke detector. You would receive
way more if you just went outside for a few hours.
So it's not that big. It's it's it's like background
levels of radiation UM. Beta particles are lighter than alpha particles,
and they move fast. They're actually ejected electrons. They can
(31:08):
travel further than alpha particles through the air. An alpha particle,
like I said, I can only move a couple of inches,
but beta particles can move several feet. They're also moderately penetrating.
They can pass through human skin, at least under the
surface level of human skin, So if you're in contact
with beta emitting material for a prolonged amount of time,
you could suffer a skin injury like a skin burn. UH.
(31:31):
Stuff that emits beta radiation includes carbon fourteen, sulfur thirty five,
and strontium ninety UH. Those numbers at the ends of
those names are important that designates isotopes. Isotopes are forms
of an atom that have a different number of neutrons,
but of course they have the same number of protons
and electrons. If you start having different number of protons,
(31:52):
then you end up with a different element. So the
most common form of carbon is carbon twelve. Carbon twelve
has six proto ons and six neutrons, but you can
also find carbon fourteen that has six protons and eight neutrons,
but it's unstable. It will undergo radioactive decay over time,
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so it will spontaneously decay and give off beta emissions.
Gamma radiation, like X ray radiation, is a form of
electromagnetic radiation. If you were to look at the full
spectrum of electromagnetic radiation, radio waves are on one end
with a very long, low frequency low energy waves. Gamma
rays are on the opposite, so this is the very
(32:33):
very very short wavelengths incredibly high frequencies. They pack a
ton of energy in them. X rays are slightly less energetic,
but there are still far more powerful than visible light,
which is why they can penetrate through solid objects better
than visible light could, and gamma rays are even better
at it than X rays are. These rays are electrically neutral,
(32:55):
so magnetic fields won't cause them to change their paths.
They'll just keep going straight. They can travel many feet
through the air. They can penetrate several inches into human tissue.
In fact, it requires significant shielding to protect against gamma radiation.
Radium two twenty six amidst gamma radiation, as do several
other radioactive materials, And this is really dangerous stuff. It
(33:19):
will not turn you into the Incredible Hulk, but it
might cause nasty, nasty problems for you. Now, in addition
to all these observations and the growing realization that some
forms of radioactivity posed a serious health hazard to humans,
scientists discovered that these forms of radiation would interact with
other particles and ionize them. That is, when the interaction
(33:42):
would happen, the particles would have electrons split off of them,
and by particles, I'm really talking about atoms and molecules,
I shouldn't use the word particle. I should say these
atoms are molecules. When they would encounter this kind of radiation,
they would have electrons stripped away, and the remaining molecule
or atom would end up having a net positive charge
(34:03):
because it just lost electrons. Electrons have a negative charge.
Were referred to this general type of radiation as ionizing radiation.
It has created ions. Not all radiation is ionizing. Radio
waves for example, are not ionizing radiation, nor are microwaves
or visible light. These types of radiation don't have enough
(34:27):
energy to ionize other particles, and it's why it's safe
for us to broadcast radio waves and to walk around
with radio waves going all over the place. They don't
affect us, we don't interact with them. Makes sense that
we would evolve in such a way where the radio
waves wouldn't affect us. This is why if you were
to live next to a cell phone tower, you would
(34:48):
not receive harmful radiation in the form of ionizing radiation,
because that's not the type that cell phone towers can emit. Uh,
they just don't pack the punch at ionizing radiation like alpha,
beta and gamma radiation as a different story, That stuff
really can mess us up, and for that reason, it's
(35:09):
a good thing to be able to detect it so
that we can remove ourselves or the radioactive material from
the environment that otherwise would pose a real threat to
our long term health. So when we come back, I'll
talk more about what is actually going on with the
radioactive interactions in our bodies, as well as the device
used to detect it, and it's typically called a Geiger counter.
(35:32):
But we'll be right back and I'll talk about then. Okay,
So radiation interacting with the human body that ionizing radiation
can damage the cells in our body. Now, we have
(35:52):
systems in our body that are really good at repairing damage,
So it's entirely possible to encounter radiation suffer some damage
as long as the damage. As long as the radiation
wasn't so intense and the exposure so extreme that you
didn't have uh, mortal wounds from acute exposure, you might
(36:14):
very well recover without any issue. But radiation can damage
the d n A inside ourselves, and occasionally that can
lead to other big problems, such as the development of cancer,
which is why we say exposure to radiation increases your
risk of developing cancer. It doesn't necessarily mean that we
(36:36):
can easily draw a line from exposure to development, but
we certainly know that it increases your risk of developing it.
It could be the reason that someone develops cancer. But
there's so many variables it's impossible to say in any
you know, given case, uh, specific cases, you might be
(36:57):
able to trace it down, but now in general, you
can't just easily make that that conclusion. It is clear
that acute exposure to high levels of of ionizing radiation
will cause injury and sickness and increase risk of more
serious health problems further down the line. So we want
(37:17):
to be able to detect that stuff early before we
risk having a longer exposure to it. Radiations invisible frequently
exposure to lower levels of it could be very harmful,
but they might not be noticeable. We might not register
it just from our own personal experience. So how do
(37:39):
we detect it? And that's where we get to the
Geiger Counter. It's named after a guy named Hans Geiger Counter.
Now I'm just kidding, it's actually just Hans Geiger. Some
people actually call these devices Geiger Mueller counters, because another
guy named Valter Mueller took Geiger's design and tweaked it
a bit about two decades after the initial invention of
(38:02):
the Geiger counter to improve its performance. Some folks just
shorten this down to GM counters. But Hans Geiger was
a physicist who worked very closely with Ernest Rutherford, whom
I mentioned earlier as being the smarty pants who was
classifying radiation as alpha, beta, and gamma, and Geiger came
up with a device that initially was meant to detect
(38:23):
alpha particles. He would eventually expand it so he could
detect other types of radiation too, and he did it
with a pretty clever approach. Al Right, so I mentioned
that these types of radiation have enough energy to ionize
particles right to create electrically charged particles by stripping away electrons.
So ions have a net electrical charge there. It's either
(38:45):
positive or negative in general, but in this case we're
talking about positive ions. And the movement of electrically charged
particles has a name. It's electricity. That's what that is.
So thought Geiger. If I can create a device that
detects the presence of ions, then it stands to reason
that something in the area is causing these ions to
(39:07):
form something like radioactive material over time. Geiger counters, like
I said, would be able to detect all sorts of
different types of radiation, but initially it was all about
alpha radiation. And here's how it would work. A typical
Geiger counter has a meter that's connected to a wand
or tube. So the meter is your indicator. The meter
(39:28):
is what tells you if you get a hit, if
there's a spike that indicates radiation. Inside the tube or
the wand is a chamber, and inside the chamber is
a low pressure gas and typically there's a a window
made out of plastic on one side of this chamber.
Also in that same chamber with the low pressure gas
(39:52):
is a thin metal wire of tungsten. You can almost
think of it as like the filament on a light bulb,
and the fire runs to the end of the tube
that leads into the the cable that in turn attaches
to the meter, and at the end of that wire
there is an electrode with a high positive voltage. Now
(40:15):
the other end of the wire is not connected to
another contact. There's no complete circuit here, so you just
have a very high positive voltage on the wire. But
it creates an electric field between the metal wire and
the outside of the tube. So if the gas inside
the tube, this low pressure gas, encounters ionizing radiation, then
(40:42):
that radiation will strip electrons away from the gas molecules
inside the chamber. The stripped electrons, because of their negative charge,
will immediately zap the toungusten wire inside this one because
again we've applied a strong positive voltage to that wire.
(41:02):
So the electrons having the negative charge are attracted to
the positive charge of the tungsten wire. UH This usually
means that there's a big rush of electrons. As electrons
are moving, they will bash into other molecules, which will
strip over other electrons, so you'll get a quick zap.
Then you typically have to quench the Geiger counter, but
(41:23):
that really doesn't matter for the rest of this discussion.
I mean, it matters, but we're gonna focus on how
this is detecting things. So you get a bunch of
electrons that hit this tungsten wire that creates a pulse
of electricity, and the pulse is what feeds through a
cable that goes to the meter, and the meter registers
that there's been a pulse of electricity, which means that
(41:44):
there's been the generation of ions inside this chamber, which
in turn means you've encountered some sort of ionizing radiation. Uh.
The wire might also pass the signal through an amplifier.
The amplifier will increase the power of that signal and
send it to a loud speaker, and that's where you
get that clicking noise. So if you've ever seen a
(42:05):
movie where someone's using a Geiger counter and you're hearing
a series of clicks, that's because the idea is that
the wires picking up electric pulses due to ions, and
then that's being sent to a loud speakers, so that's
what's making the clicking noise. The beauty of this design
is that it isolates the ions source from the environment.
(42:26):
Right the source of the ions is this gas inside
a chamber. The gas is kept separate from the surrounding environment,
so you don't have to worry about somehow encountering ions
out in the wild, Like if you were standing next
to an ion generator. Let's say you've gotten ionization purifier,
something that's meant to purify the air in your room,
(42:48):
you shouldn't get a readoubt from your Geiger counter because
the ions being generated by this ionization chamber would not
be interacting with the gas inside the Geiger counters chamber. Instead,
the only time the gas and the Giger counter should
be ionizing at all is if you're coming into range
(43:09):
of ionizing radiation. So dependent upon the intensity of the
readelts you're getting, you would know kind of how much
radiation you were experiencing at any given moment. And again,
radiation exposure on its own does not immediately mean that
you mutate or you you know, suffer terrible injuries unless
(43:30):
it's an incredibly intense amount of radiation uh at very
high energies. But it does mean that you need to,
you know, get out of there and to find some
other place to be. One thing I didn't really talk
about in this episode was the concept of half life's
and that is important because half life's also give us
(43:51):
an idea of how long radioactive material could potentially remain dangerous.
And when you're looking at half lives that are on
thousands of years, you're talking about uh, time that extends
beyond that which humans have been on Earth right as
at least as human beings as we understand them, but
(44:13):
we might trace it back to an earlier evolutionary form
of humans. But you start looking at some of these
materials and you realize, wow, this stuff is going to
be radioactive for longer than humans have been walking around
on Earth as human beings. Uh. That's why you get
people who are concerned about things like nuclear power, where
(44:33):
one of the byproducts of nuclear power tends to be
nuclear waste that is radioactive. Some of that nuclear waste
will be radioactive and dangerously so for a relatively short time.
But there are other types of nuclear waste that will
be radioactive for a very long time and sure in
uh it's not emitting radiation at a level high enough
(44:56):
for it to you know, be dangerous if we don't
treat it carefully, but it's persistent and and long time
exposure to it will increase our risk of developing really
nasty diseases like cancer, So that's where that concern comes in. Now.
There are a lot of different approaches to nuclear power
(45:17):
to mitigate the creation of nuclear waste, and there are
a lot of plans on what to do with that
nuclear waste to try and keep it far enough away
from people to not be a problem, but that all
runs into a lot of other social issues that are
harder to solve than technical issues. Um. On the flip side,
we're also looking at possibilities like fusion power, which is
(45:40):
very different from the fission process that generates a lot
of nuclear waste, but those are topics for a different episode.
I hope you have a greater understanding of how radiation
works and what it actually means, as well as how
Geiger counters work. Again, I think it's a very elegant
way to try and detect radiation it's not so much
(46:03):
detecting the radiation directly, but rather the effects of radiation
on something that we can more easily observe directly. And
I think that's a very clever approach to uh to
creating a meter. If you guys have suggestions for future
episodes of tech Stuff, reach out to me and let
(46:23):
me know. On social media, the handle at both Twitter
and Facebook is exactly the same. That handle is text
stuff H s W and I'll talk to you again
really soon. Text Stuff is a production of I Heart
Radio's How Stuff Works. For more podcasts from I heart Radio,
(46:46):
visit the I heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Welcome to tech Stuff, a production of I Heart Radios
How Stuff Works. Hey there, and welcome to tech Stuff.
I'm your host, Jonathan Strickland. I'm an executive producer with
iHeart Radio and a love of all things tech, and
inspired by my last episode about smoke detectors, I thought
(00:25):
I would do an episode about radiation and radiation detectors.
And I want to define terms like radiation and radioactivity,
to talk about the different types of radiation there are,
and to differentiate between ionizing and non ionizing radiation and
chat about the technology around it. So first, what is radiation. Well,
(00:47):
it's a fairly broad term with lots of different meanings
as it turns out, but I think that's part of
why there's frequently a lot of confusion around the concept
of radiation. But there are a couple of definitions that
for our purpose as we want to focus on, and
really the one that we're truly interested in is the
process of admitting radiant energy in the form of waves
(01:09):
or particles as a definition I took from the Miriam
Webster Dictionary. By the way, so radiation can involve electromagnetic
waves or it might involve sub atomic particles. Uh, some
radiation has the potential to be harmful, even deadly in
sufficient intensities and length of exposure. Some radiation is relatively safe,
(01:30):
particularly under specific controls. So let's start with some early
discoveries of electro magnetic radiation, as those predate our understanding
of particle based radiation. So our story begins in eighteen
hundred with an early scientist named William Herschel. And Willie
(01:51):
was interested in learning more about the spectrum of light,
and it was already understood that if you were to
pass light through a prism, you could separate light into
different colors. You know, the good old roy g BIV spectrum,
which stands for red, orange, yellow, green, blue, indigo, and violet.
The spectrum will always be in that order. Anytime you
(02:11):
pass light through a prism, it's going to break into
those bands in that order, and those bands actually represent
bands of frequencies of light waves. Herschel was wondering if
the different colors of light produced different amounts of heat,
So is one type of light warmer than another, So
(02:32):
he set up a system in which he positioned thermometers
at each color displayed from light passing through a prism.
So he sets up a prism in his window, lights
coming through it, and it's hitting a table, and it
divides up into different bands of color. He sets the
thermometers in each band of color, and he happened to
(02:53):
have an extra thermometer just beyond the red end of
the spectrum, so it's actually in the dark. It was
beyond the range of the visible light. He had no
way of knowing it, but he had, by happy coincidence,
placed a thermometer right where the infrared band was. And
we can't see infrared light, but that light does transmit heat.
(03:16):
In fact, Herschel was surprised to see that it was
that thermometer, the one that was in the darkness, just
beyond the red range, that actually registered the highest temperature
out of all the thermometers he had set out. And
we often talked about heat radiating outward from a source.
In eighteen o one, another big thinker named Johann Wilhelm
(03:37):
Ritter built upon Herschel's experiment. He decided to see if
perhaps there was anything beyond the other end of the spectrum,
a k a. The violet end. In fact, he really
discovered it sort of by accident. Ritter experimented by using
a substance called silver chloride, and this is a chemical
that turns black if it's exposed to sunlight. Ritter built
(04:01):
on the understanding that blue light would produce a greater
reaction in silver chloride than red light, so he did
a variation on Herschel's experiment. He again used a prism
to break the light into bands of color, and then
within each band of color he placed a vile a
silver chloride to see if the reactions were different across
(04:23):
the spectrum of light. He could see that, indeed, the
reaction did vary across the spectrum. The closer you got
to the violet side of the spectrum, the more intense
the reaction was, and it was most evident just beyond
the violet side, in an area where there was no
visible light at all. So clearly there was something going
(04:47):
on on that end of the spectrum. So on the
red end you were getting some sort of heat which
we now know is infrared, and on the violet end
there's something else that was really reacting to silver chloride.
So Ritter would call this chemical raise, which to this
very day we don't do anymore. Now today we call
it ultraviolet light. Herschel and Ritter had made the first
(05:11):
steps to increase our understanding of the electromagnetic spectrum, of
which visible light is just one tiny part, and as
we would build on that understanding, we'd also gain more
information about what effects these types of radiation can have
on us. Some of them have very little effect on us,
some of them can have a drastic effect on us.
(05:33):
And it would take a lot more time, but we
would gradually begin to understand that if you look at
the spectrum, it includes everything from radio waves on one
extreme end of it to gamma raise on the other
end of it, and these waves vary in wavelength, frequency,
and energy. So on one extreme end you've got those
(05:55):
radio waves. These can have really long wavelengths, measuring hens
of miles, like sixty two miles or a hundred kilometers
for wavelengths of certain radio frequencies. So if you had
a perfectly steady radio wave, like just imagine, it's a
perfect signal you. If you were to map it out,
it would be a beautiful sign wave. If you measured
(06:17):
from the peak at one point to the next peak,
that's the wavelength. That's what would have been a hundred
kilometers in distance an enormous wave. The frequency of a
wave refers to how frequently a specific point on a wavelength,
you know, like that peak, how frequently you could see
(06:39):
that point on each wave pass a given reference point
within a second. So with the longest radio waves at
the lowest frequencies, you're talking about a frequency of around
three thousand cycles per second, meaning that in one seconds time,
three thousand peaks past that given point of reference. Now,
(07:00):
one thing to keep in mind is that this is
electromagnetic radiation. An electromagnetic radiation all travels at the same speed,
that being the speed of light. Now, we do have
to remember the speed of light isn't a constant across
all media. It's a constant within each media. So we
we usually when we're talking about the speed of light,
(07:21):
we're talking about within the vacuum of space. But if
light is traveling through an atmosphere or through water or something,
it actually does travel at a different speed than that
because it it's all dependent upon the medium. Still, electromagnetic
radiation travels at that speed. So a wavelength of uh,
(07:42):
you know, one wavelength of of a radio wave is
traveling at the speed of light, as is one wavelength
of gamma radiation. However, because the radio waves are so
long and the gamma rays are so short in wavelength,
the frequency has to be different, right. The frequency of
the radio waves has to be lower than the frequency
(08:04):
of gamma rays because you get way more gamma rays
passing within a frame of a second, even though they're
both traveling at the same speed. All right, That gets confusing, right,
So I like to explain this with an analogy. Imagine
you've got two identical straight roads, one lane wide, and
they're right next to each other. Down one road, you
(08:25):
have a series of buses, and each bus super long,
measures eighteen meters in length, traveling down the road at
fifty KOs per hour, and there's one meter of space
in between each bus. So bus number one eighteen meters
long than you have a meter, and a bus number
two is eighteen meters long than you have a meter.
(08:46):
That's dangerous, but whatever, they're traveling down at fifty an hour,
perfectly in sync with each other. On the other road,
do you have a series of zippy little smart cars
and each smart car measures just three meters in length.
They're also going down the road at fifty kilometers per
hour with a meter of space in between each pair
of cars. Now, individual vehicles are all traveling at the
(09:08):
same speed, they're all traveling at fifty kilometers per hour.
But the smart cars aren't as long as the buses.
So if you were to have a accounter, there's someone
standing by the bus lane and there's someone standing by
the smart car lane, and they're holding a little counter
in their hands. The person next to the smart cars
is going to count way more smart cars in the
(09:29):
same amount of time as the person counting the buses.
And it's not because smart cars are traveling faster. They're not.
They're just smaller, so more of them can go by
within that given amount of time. The same thing is
true with wavelengths of the electromagnetic spectrum red light, blue light,
X rays, radio waves. They're all traveling at the same speed.
They just have different wavelengths, so they have to have
(09:51):
different frequencies. Now, as I said earlier, in those early
days in the nineteenth century, we didn't have this level
of understanding. We weren't aware of different wavelengths and frequencies,
and we didn't know that longer wavelengths and lower frequencies
of electromagnetic radiation carry less energy, whereas high frequencies and
(10:11):
very small wavelengths of electromagnetic radiation can pack way more energy.
If you were to look at the experiments of Herschel
and Ritter, you might actually think that that's not the case,
because the invisible light off the red end of the
spectrum was carrying a lot of heat. It was heating
up a thermometer more than the others, so maybe it
carries more energy. And whereas the violet side you just
(10:34):
saw silver chloride change color. So it would take a
lot more experimentation to get a deeper understanding of the
actual nature of electromagnetic radiation. Now to go into the
full history of how that understanding would unfold is the
stuff of college lecture series, So I'll just give very
brief summaries to get us kind of closer to our objective.
(10:54):
In the nineteenth century you had numerous scientists and inventors
who were observing all sorts of interesting stuff that would
later become integrated into our knowledge of electromagnetism. So Michael
Faraday did a great deal of work exploring the relationship
between electric and magnetic fields. For example, his work would
inspire a Scottish physicist named James Clerk Maxwell to look
(11:19):
into the matter further, and Maxwell made predictions about electromagnetic
radiation based on those early experiments and observation, saying, well,
based on what we know, I expect that will eventually
find something that fits this mathematical uh example of what
should be there, and his predictions proved to be accurate,
(11:39):
and they in turn would serve as an important foundation
for Albert Einstein's special theory of relativity, as the one
that gives us the famous equation equals mc squared, which
tells us that energy and mass are related at an
intrinsic level. And Maxwell's observations about electromagnetic radiation would lead
to a theory about heat radiation that in turn would
(12:00):
be overturned by Max Planck, whose formulation of quantum hypothesis
to describe how heat radiates would become the predominant one.
But all of that is a little outside of our scope.
So the point I wanted to make is that the
nineteenth century was a boom time for scientific observations and discoveries,
and the things we would learn would serve us well
(12:21):
as we moved into the next phase of understanding of radiation.
And what it's all about. So the other big discoveries
that relate to this episode came about at the end
of the nineteenth century, so we get to look at
both ends of the eighteen hundreds. In eight Vilhelm runjeon
which I mentioned him in the last episode, he was
experimenting with a cathode ray tube, and I talked about
(12:43):
that again in the Smoke Detective episode. Essentially, these are
devices that produce streams of electrons by heating up a
filament inside a glass vacuum tube, kind of similar to
a light bulb. Runjen found that as he applied an
electric voltage to the cathode ray tube a light detection
screen in his lab that was made out of barium
(13:04):
platina cyanide fluorest, it actually lit up. It detected light
even though there was no visible light there. So he
began to experiment with this phenomenon, this invisible light that
was causing this this detector to light up, and that
included putting objects between the cathode ray tube and the screen,
(13:25):
and he saw that whatever was coming out of the
tube seemed to be penetrating through objects and it was
still hitting the screen on the other side. He found
that if he put photographic film, the energy would interact
with the photographic film, and if you put something in
between the film and the cathode ray tube, he could
get a really interesting image of it. Uh, it's like
(13:48):
you could see through certain stuff pretty clearly. So, for example,
his hand, he put his hand in front of it
and he took a photo. Then the picture would show
the skeleton in hand. It would it would show through
the soft tissues of his hand, and he thought, well,
this is interesting. He discovered a new type of radiation
(14:12):
and he called it the X ray because what the
heck was going to call it? It was an unknown quantity,
and in mathematics we often refer to unknown quantities as X,
like solve for X. So it was meant to be
a placeholder. X rays just it turned into the permanent
name for the stuff. Now. Initially, no one was aware
(14:32):
that X ray radiation was potentially dangerous with its shorter
wavelength and higher frequency and energy than visible light. In fact,
no one was even sure that was another form of light.
They thought it might be, but they weren't certain, and
that wouldn't be proven until nineteen twelve. But people began
to understand that there was some potential danger the X
(14:54):
rays fairly early on. In eighteen nineties six, the year
after Runton's UH discovery, the journal Nature published an article
with the title The Harmful Effects of X rays. And
in that article there was a story about a guy
who had worked as an X ray demonstrator in London,
(15:15):
and he described the effects of X ray exposure that
he experienced, particularly on his hands, after working for a
full summer doing demonstrations with X ray machines for several
hours a day, I'm going to quote an excerpt. In
the first two or three weeks, I felt no inconvenience,
(15:37):
but after a while appeared on the fingers of my
right hand many dark spots which pierced under the skin,
and gradually they became very painful. The rest of the
skin was red and strongly inflamed. My hand was so
bad that I was constantly forced to bathe it in
very cold water. An ointment momentarily on the pain. But
(16:01):
the epidermist had dried up, had become hard and yellow
like parchment, and completely insensible, so I was not surprised
when my hand began to peel. From that point, the
guy goes on to describe how things got even worse,
like he began to lose fingernails and stuff. But I'm
gonna leave out the rest of the grizzly details. The
(16:24):
point is people are starting to notice that the longer
someone was exposed to X rays, the more severe the
consequences seemed to be. Short exposures did not appear to
be as serious, but this was something that people were
starting to get a little concerned about that would grow
in the years to come. But first, let's take a
quick break before we jump into that discussion. Okay, so
(16:55):
before we took our break, I was talking about how
people were beginning to understand that X rays could be dangerous.
That didn't stop early irresponsible implementations of X ray machines. However,
people thought of these as curiosities. They were things to
be celebrated and experienced. Thomas Edison thought everyone would have
one in their own home and thought perhaps they should
(17:17):
have them, because again, they didn't understand the dangers yet.
People would even have X ray parties in which guests
would take X ray photos of themselves, you know, of
their foot, or their hand, or even their face, and
they would get to keep the photographs at the end
of the party. Shoe stores installed X ray fluoroscopes to
(17:38):
get a look at a person's foot, And while a
person visiting the store wouldn't likely walk away with a
lethal dose of radiation, the folks who were working at
the store were exposed to X rays much more frequently
and for longer durations, and many of them would suffer
the consequences. But all of those awful discoveries would take
(17:59):
some times, so people didn't immediately notice the issues. Meanwhile,
let's get back to the discovery of radioactivity by talking
about the other kind of radiation, not the electro magnetic type.
So in eighteen ninety six, which was that same year
that the Nature article about the dangers of X rays
came out, there was a physicist named al Marie Beccarel
(18:22):
who was wondering if some materials he was working with
might produce the same sort of energy that Rundgen's X
rays seemed to create. One of those materials that Beckerel
was working with was a crystal made up of uranium salts. Now,
the various materials Beccarel had interest in all shared a
common trait. They were all phosphorescent, so they could all glow,
(18:46):
and he wondered if they were giving off the same
sort of invisible light stuff that run Gen was observing
with X rays. So Beckarel set up an experiment. He
put down a photographic plate. He totally covered it so
that one of it would be exposed to light because
that would activate the photoreactive chemicals on the plate. And
on top of the covering he put a selection of
(19:08):
his phosphorescent crystals to see if any of them would
interact with the photo reactive chemicals. And he exposed the
whole thing to the sun, you know, thinking that the
sun would charge these various crystals. And at the end
of the experiment he discovered that out of all the
different things he was testing, only one seemed to have
any effect at all, and that was the rock crystal
(19:31):
that was actually made up of uranium salt, and that
was the only one that seemed to have fogged up
the the photoplate. So he thought, well, I'll do a
longer test. I'll leave it out in the sun longer,
see if I get a bigger, more clear result. But
the weather at that point wasn't cooperating. It had gotten cloudy,
so he couldn't put it out in the sun. So
(19:51):
he takes his photographic plates and his uranium salts and
he stores them away and waits for the weather to
get better. So they were actually stored next to each
other in a dark cabinet. Several days later, as the
weather was starting to finally clear out, he was getting
ready to conduct his experiment, but he decided, you know what,
before I do this, I better make sure these photographic
(20:12):
plates are still good, because the chemicals can actually expire,
and I'd be wasting my time if they aren't working anymore.
So he picks one and develops it, and it happened
to be one that was close to the iranium salts.
Rock He was surprised to discover that the bits of
the photographic plate that had been close to those uranium
(20:33):
salts had images on them, even though the salts had
not been exposed to sunlight. They've been stored in a
dark cupboard, and he concluded that the uranium salts themselves
were giving off some sort of emission that was being
captured on this photographic plate. Henri Becarel had a couple
of enterprising and brilliant assistants. One was Pierre Curie and
(20:54):
the other was Marie Sklodowska, who would marry Pierre and
become Marie Curie. She uh really was fascinated by radioactivity,
and together with her husband, they began to study the
ranium salts as well as looking for other similar materials
that seemed to display this radioactive phenomena. They tested some
(21:15):
mining operation waste. It's called a pitch blend. The mining
operations were happy to get rid of it because it
was just run off from their operations, and they found
that it could contained traces of radioactive material, and eventually
they were able to separate a small amount of it
from the rest of the pitch blend, and it would
later be called radium. It was far more radioactive than
(21:38):
the uranium salts they had already worked with. The Curies
and Beckrel would receive the Nobel Prize in Physics for
their discoveries. Runen also received one earlier for his discovery
of X rays, and then Pierre Curie would later tragically
die in a traffic accident. Marie would go on to
discover another radioact development, this one called polonium, and she
(22:00):
would receive a second Nobel Prize, though that second one
was in chemistry. She's one of only a few people
who have ever received more than one Nobel Prize. Now,
one thing Beckerel did with his own research was proved
that the energy coming out of this uranium salt was
not the same thing as X rays, and he did
this by testing the uranium salts against X rays with
(22:23):
a device that could generate a magnetic field. So X
rays would pass through the magnetic field unimpeded. And that's
because X ray radiation has no electric charge, and thus
it has no magnetic field of its own, so it's
not affected by magnetic field. It just passes through. Is
that there's nothing else there but the radiation coming from
the uranium salts bent upon encountering the magnetic field, and
(22:46):
that told Beckarel that whatever was coming out of the
uranium salts had an electric charge to it, because it
had to have an electric charge in or to have
its own magnetic field and thus be either attracted or
repelled by the magnetic field and his testing vice. So
Beckerel tested numerous types of radioactive substances using this approach
and observed three basic results. Either radiation would bend one
(23:10):
way using certain radioactive materials, and he would conclude, this
is a positive radiation material because it is being attracted
to the negative side of the magnetic field and repelled
by the positive side, or it would bend the other way,
so he would have the opposite conclusion. Okay, this is
negative radiation because it's being attracted to the positive side
(23:31):
and repelled by the negative side, or it passed straight
through like X rays, and it would have no electrical
charge at all, so it would be neutral. So you
had positive, negative, and electrically neutral radiation. In their work,
the Curies and Beckarel noted that prolonged exposure to some
of these radioactive materials would result in injuries and ailments,
(23:53):
like if you handled some of the more radioactive stuff
like radium for any length of time, you could actually
get burns on your skin, and you could suffer radiation sickness,
which includes symptoms like nausea, but the extent of the
damage was unknown for years. Marie cry died in nineteen
thirty four of a plastic anemia, which was probably a
(24:16):
consequence of her exposure to radioactive material over the years.
It certainly would have increased the odds of her developing that,
and that's something that is is good to just mention
in general is that when we think of radiation, we
often think of the radiation sickness, the sort of acute
symptoms you can have if you have a sudden exposure
(24:38):
to an intense amount of radiation. But in many ways,
the consequences of exposure to radiation are really more about
the increased risk of developing UH conditions like cancer. UH.
And it doesn't necessarily mean that if you do develop cancer,
that it was a direct result of that exposure to radiation,
(24:59):
but rather or that the exposure to radiation increased the
odds that you would develop cancer. It's a complicated thing
to look at because without knowing all the variables, you
cannot say conclusively that X caused why, but you can't
say that X made Y way more likely. That's what
we think with Currie, that she probably developed a plastic
(25:23):
anemia as a consequence of this exposure to stuff like
radium over the years. Many of her belongings and even
a cookbook she used, are actually stored in shielded containers
to this day because they're still radioactive dangerously. So the
lack of understanding about the consequences of radiation exposure would
(25:44):
have many more nasty consequences, just as it had with
the X ray fad. For example, because radium is phosphorescent,
it was seen as a useful material for stuff like
the hands of watches, like analog watches. He would paint
an analog watches minute and our hands with radium, and
(26:06):
that would make it glow in the dark and made
it really easy to read the time, even if you
were in low lighting. While the amount of radium on
these watches was very very small and not likely to
harm somebody who was wearing the watch, the employees responsible
for painting the watch hands received way more radiation exposure. Colloquially,
(26:27):
they were called radium girls, and the management positions at
these facilities frequently had significant protection from radiation, but the
same could not be said for the women on the
front lines, the women actually doing the work painting the
radium onto these watch hands. It also wasn't uncommon for
(26:49):
a worker to lick the end of her brush to
shape it so that she could more easily paint the
watch hand. So that meant these workers were occasionally depositing
little amounts of radium directly on their tongues. They were
ingesting radium. Radium when ingested, will deposit itself in bone,
(27:09):
much like calcium would, so several of the workers would
ultimately grow ill with radiation sickness. A group of five
of them later brought a lawsuit against their company. That
company was the United States Radium Company. They charged them
with being irresponsible in areas of health and safety, and
in turn that prompted a detailed study into what the
(27:32):
long term effects of radium exposure are and it's awful
that our knowledge came at such a steep price. At
the same time, the results of that study would lead
to massive changes in health and safety regulations for the
benefit of workers in the United States. From these discoveries,
physicists began to learn more about the nature of radioactive
(27:54):
material in general. They observed that there were different kinds
of radiation beyond just calling it positive, negative, or electrically neutral.
Some radiation seem to have more penetrative abilities. They could
penetrate further into solid matter than other types of radiation.
So you might have one type of radiation that isn't
(28:16):
able to penetrate solid matter effectively, and another one seems
to go right through stuff as if there's no problem.
A physicist named Ernest Rutherford conducted numerous experiments with radioactive
material and at this point we were beginning to understand
that radioactivity was a process in which certain materials undergo
a process called decay, and that is the form that
(28:38):
they are in. The radioactive form is inherently unstable. You
can if you want to think of it in terms
of want, I mean putting motivation is ridiculous because we're
talking about atomic particles here. But it's a form of
an atom that does not want to be that form.
It's unstable. So these materials will spontaneously but not necessary early,
(29:00):
quickly break apart and give off energy and subatomic particles
as they decay to a more stable form. Rutherford classified
three types of radiation. He said this was all based
off the penetrative properties of radiation, how far they could
penetrate into matter. The three types he classified were alpha radiation,
(29:21):
beta radiation, and gamma radiation. Alpha particles had the least
amount of ability to penetrate matter, and gamma rays were
the opposite. They could very easily penetrate matter. Upon further study,
scientists discovered that an alpha particle is relatively massive on
the atomic scale of things. It actually consists of an
(29:43):
ejected helium nucleus. A helium nucleus is two protons and
two neutrons. This is the type of radiation given off
by a mera sirium to forty one. That's the radioactive
material that's inside smoke detectors that I talked about in
the last episode. The ionization chambers have this type of
radioactive material in them, so you probably have some of
(30:03):
the stuff in your house right now. Alpha particles are
not able to penetrate matter very well, and they're big
enough and slow enough that they can't really get through skin,
at least not most of the time, so they're not
likely to have it affects you. Uh. They can't even
go through very much air. After a couple of inches,
(30:24):
they've lost the energy to move forward. Breathing in alpha
particles would be a real risk, and you wouldn't want
to swallow any of it either, so you don't want
to come into contact with the stuff, But having it
enclosed in a smoke detector in its own little chamber
in the smoke detector is more than enough protection that
you wouldn't receive any sort of significant radiation exposure from
(30:48):
the ameer sirium inside a smoke detector. You would receive
way more if you just went outside for a few hours.
So it's not that big. It's it's it's like background
levels of radiation UM. Beta particles are lighter than alpha particles,
and they move fast. They're actually ejected electrons. They can
(31:08):
travel further than alpha particles through the air. An alpha particle,
like I said, I can only move a couple of inches,
but beta particles can move several feet. They're also moderately penetrating.
They can pass through human skin, at least under the
surface level of human skin, So if you're in contact
with beta emitting material for a prolonged amount of time,
you could suffer a skin injury like a skin burn. UH.
(31:31):
Stuff that emits beta radiation includes carbon fourteen, sulfur thirty five,
and strontium ninety UH. Those numbers at the ends of
those names are important that designates isotopes. Isotopes are forms
of an atom that have a different number of neutrons,
but of course they have the same number of protons
and electrons. If you start having different number of protons,
(31:52):
then you end up with a different element. So the
most common form of carbon is carbon twelve. Carbon twelve
has six proto ons and six neutrons, but you can
also find carbon fourteen that has six protons and eight neutrons,
but it's unstable. It will undergo radioactive decay over time,
(32:12):
so it will spontaneously decay and give off beta emissions.
Gamma radiation, like X ray radiation, is a form of
electromagnetic radiation. If you were to look at the full
spectrum of electromagnetic radiation, radio waves are on one end
with a very long, low frequency low energy waves. Gamma
rays are on the opposite, so this is the very
(32:33):
very very short wavelengths incredibly high frequencies. They pack a
ton of energy in them. X rays are slightly less energetic,
but there are still far more powerful than visible light,
which is why they can penetrate through solid objects better
than visible light could, and gamma rays are even better
at it than X rays are. These rays are electrically neutral,
(32:55):
so magnetic fields won't cause them to change their paths.
They'll just keep going straight. They can travel many feet
through the air. They can penetrate several inches into human tissue.
In fact, it requires significant shielding to protect against gamma radiation.
Radium two twenty six amidst gamma radiation, as do several
other radioactive materials, And this is really dangerous stuff. It
(33:19):
will not turn you into the Incredible Hulk, but it
might cause nasty, nasty problems for you. Now, in addition
to all these observations and the growing realization that some
forms of radioactivity posed a serious health hazard to humans,
scientists discovered that these forms of radiation would interact with
other particles and ionize them. That is, when the interaction
(33:42):
would happen, the particles would have electrons split off of them,
and by particles, I'm really talking about atoms and molecules,
I shouldn't use the word particle. I should say these
atoms are molecules. When they would encounter this kind of radiation,
they would have electrons stripped away, and the remaining molecule
or atom would end up having a net positive charge
(34:03):
because it just lost electrons. Electrons have a negative charge.
Were referred to this general type of radiation as ionizing radiation.
It has created ions. Not all radiation is ionizing. Radio
waves for example, are not ionizing radiation, nor are microwaves
or visible light. These types of radiation don't have enough
(34:27):
energy to ionize other particles, and it's why it's safe
for us to broadcast radio waves and to walk around
with radio waves going all over the place. They don't
affect us, we don't interact with them. Makes sense that
we would evolve in such a way where the radio
waves wouldn't affect us. This is why if you were
to live next to a cell phone tower, you would
(34:48):
not receive harmful radiation in the form of ionizing radiation,
because that's not the type that cell phone towers can emit. Uh,
they just don't pack the punch at ionizing radiation like alpha,
beta and gamma radiation as a different story, That stuff
really can mess us up, and for that reason, it's
(35:09):
a good thing to be able to detect it so
that we can remove ourselves or the radioactive material from
the environment that otherwise would pose a real threat to
our long term health. So when we come back, I'll
talk more about what is actually going on with the
radioactive interactions in our bodies, as well as the device
used to detect it, and it's typically called a Geiger counter.
(35:32):
But we'll be right back and I'll talk about then. Okay,
So radiation interacting with the human body that ionizing radiation
can damage the cells in our body. Now, we have
(35:52):
systems in our body that are really good at repairing damage,
So it's entirely possible to encounter radiation suffer some damage
as long as the damage. As long as the radiation
wasn't so intense and the exposure so extreme that you
didn't have uh, mortal wounds from acute exposure, you might
(36:14):
very well recover without any issue. But radiation can damage
the d n A inside ourselves, and occasionally that can
lead to other big problems, such as the development of cancer,
which is why we say exposure to radiation increases your
risk of developing cancer. It doesn't necessarily mean that we
(36:36):
can easily draw a line from exposure to development, but
we certainly know that it increases your risk of developing it.
It could be the reason that someone develops cancer. But
there's so many variables it's impossible to say in any
you know, given case, uh, specific cases, you might be
(36:57):
able to trace it down, but now in general, you
can't just easily make that that conclusion. It is clear
that acute exposure to high levels of of ionizing radiation
will cause injury and sickness and increase risk of more
serious health problems further down the line. So we want
(37:17):
to be able to detect that stuff early before we
risk having a longer exposure to it. Radiations invisible frequently
exposure to lower levels of it could be very harmful,
but they might not be noticeable. We might not register
it just from our own personal experience. So how do
(37:39):
we detect it? And that's where we get to the
Geiger Counter. It's named after a guy named Hans Geiger Counter.
Now I'm just kidding, it's actually just Hans Geiger. Some
people actually call these devices Geiger Mueller counters, because another
guy named Valter Mueller took Geiger's design and tweaked it
a bit about two decades after the initial invention of
(38:02):
the Geiger counter to improve its performance. Some folks just
shorten this down to GM counters. But Hans Geiger was
a physicist who worked very closely with Ernest Rutherford, whom
I mentioned earlier as being the smarty pants who was
classifying radiation as alpha, beta, and gamma, and Geiger came
up with a device that initially was meant to detect
(38:23):
alpha particles. He would eventually expand it so he could
detect other types of radiation too, and he did it
with a pretty clever approach. Al Right, so I mentioned
that these types of radiation have enough energy to ionize
particles right to create electrically charged particles by stripping away electrons.
So ions have a net electrical charge there. It's either
(38:45):
positive or negative in general, but in this case we're
talking about positive ions. And the movement of electrically charged
particles has a name. It's electricity. That's what that is.
So thought Geiger. If I can create a device that
detects the presence of ions, then it stands to reason
that something in the area is causing these ions to
(39:07):
form something like radioactive material over time. Geiger counters, like
I said, would be able to detect all sorts of
different types of radiation, but initially it was all about
alpha radiation. And here's how it would work. A typical
Geiger counter has a meter that's connected to a wand
or tube. So the meter is your indicator. The meter
(39:28):
is what tells you if you get a hit, if
there's a spike that indicates radiation. Inside the tube or
the wand is a chamber, and inside the chamber is
a low pressure gas and typically there's a a window
made out of plastic on one side of this chamber.
Also in that same chamber with the low pressure gas
(39:52):
is a thin metal wire of tungsten. You can almost
think of it as like the filament on a light bulb,
and the fire runs to the end of the tube
that leads into the the cable that in turn attaches
to the meter, and at the end of that wire
there is an electrode with a high positive voltage. Now
(40:15):
the other end of the wire is not connected to
another contact. There's no complete circuit here, so you just
have a very high positive voltage on the wire. But
it creates an electric field between the metal wire and
the outside of the tube. So if the gas inside
the tube, this low pressure gas, encounters ionizing radiation, then
(40:42):
that radiation will strip electrons away from the gas molecules
inside the chamber. The stripped electrons, because of their negative charge,
will immediately zap the toungusten wire inside this one because
again we've applied a strong positive voltage to that wire.
(41:02):
So the electrons having the negative charge are attracted to
the positive charge of the tungsten wire. UH This usually
means that there's a big rush of electrons. As electrons
are moving, they will bash into other molecules, which will
strip over other electrons, so you'll get a quick zap.
Then you typically have to quench the Geiger counter, but
(41:23):
that really doesn't matter for the rest of this discussion.
I mean, it matters, but we're gonna focus on how
this is detecting things. So you get a bunch of
electrons that hit this tungsten wire that creates a pulse
of electricity, and the pulse is what feeds through a
cable that goes to the meter, and the meter registers
that there's been a pulse of electricity, which means that
(41:44):
there's been the generation of ions inside this chamber, which
in turn means you've encountered some sort of ionizing radiation. Uh.
The wire might also pass the signal through an amplifier.
The amplifier will increase the power of that signal and
send it to a loud speaker, and that's where you
get that clicking noise. So if you've ever seen a
(42:05):
movie where someone's using a Geiger counter and you're hearing
a series of clicks, that's because the idea is that
the wires picking up electric pulses due to ions, and
then that's being sent to a loud speakers, so that's
what's making the clicking noise. The beauty of this design
is that it isolates the ions source from the environment.
(42:26):
Right the source of the ions is this gas inside
a chamber. The gas is kept separate from the surrounding environment,
so you don't have to worry about somehow encountering ions
out in the wild, Like if you were standing next
to an ion generator. Let's say you've gotten ionization purifier,
something that's meant to purify the air in your room,
(42:48):
you shouldn't get a readoubt from your Geiger counter because
the ions being generated by this ionization chamber would not
be interacting with the gas inside the Geiger counters chamber. Instead,
the only time the gas and the Giger counter should
be ionizing at all is if you're coming into range
(43:09):
of ionizing radiation. So dependent upon the intensity of the
readelts you're getting, you would know kind of how much
radiation you were experiencing at any given moment. And again,
radiation exposure on its own does not immediately mean that
you mutate or you you know, suffer terrible injuries unless
(43:30):
it's an incredibly intense amount of radiation uh at very
high energies. But it does mean that you need to,
you know, get out of there and to find some
other place to be. One thing I didn't really talk
about in this episode was the concept of half life's
and that is important because half life's also give us
(43:51):
an idea of how long radioactive material could potentially remain dangerous.
And when you're looking at half lives that are on
thousands of years, you're talking about uh, time that extends
beyond that which humans have been on Earth right as
at least as human beings as we understand them, but
(44:13):
we might trace it back to an earlier evolutionary form
of humans. But you start looking at some of these
materials and you realize, wow, this stuff is going to
be radioactive for longer than humans have been walking around
on Earth as human beings. Uh. That's why you get
people who are concerned about things like nuclear power, where
(44:33):
one of the byproducts of nuclear power tends to be
nuclear waste that is radioactive. Some of that nuclear waste
will be radioactive and dangerously so for a relatively short time.
But there are other types of nuclear waste that will
be radioactive for a very long time and sure in
uh it's not emitting radiation at a level high enough
(44:56):
for it to you know, be dangerous if we don't
treat it carefully, but it's persistent and and long time
exposure to it will increase our risk of developing really
nasty diseases like cancer, So that's where that concern comes in. Now.
There are a lot of different approaches to nuclear power
(45:17):
to mitigate the creation of nuclear waste, and there are
a lot of plans on what to do with that
nuclear waste to try and keep it far enough away
from people to not be a problem, but that all
runs into a lot of other social issues that are
harder to solve than technical issues. Um. On the flip side,
we're also looking at possibilities like fusion power, which is
(45:40):
very different from the fission process that generates a lot
of nuclear waste, but those are topics for a different episode.
I hope you have a greater understanding of how radiation
works and what it actually means, as well as how
Geiger counters work. Again, I think it's a very elegant
way to try and detect radiation it's not so much
(46:03):
detecting the radiation directly, but rather the effects of radiation
on something that we can more easily observe directly. And
I think that's a very clever approach to uh to
creating a meter. If you guys have suggestions for future
episodes of tech Stuff, reach out to me and let
(46:23):
me know. On social media, the handle at both Twitter
and Facebook is exactly the same. That handle is text
stuff H s W and I'll talk to you again
really soon. Text Stuff is a production of I Heart
Radio's How Stuff Works. For more podcasts from I heart Radio,
(46:46):
visit the I heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.
TechStuff News
Hosts And Creators
Oz Woloshyn
Karah Preiss
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