September 9, 2026 • 12 mins
The Geiger counters we use to detect harmful radiation today are 100-year-old technology that works based on simple behaviors of electrons and ions. Learn about ionizing radiation and the invention of the Geiger-Müller counter (including why it clicks) in today's episode of BrainStuff, based on this article: https://science.howstuffworks.com/geiger-counter.htm
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Speaker 1 (00:01):
Welcome to BrainStuff, a production of iHeartRadio. Hey, BrainStuff. Lauren
Vogelbaum here. The closest that lots of us ever get
to a Geiger counter is the movies. In all kinds
of media, from Atomic Age horror films to tragic dramas
like Chernobyl to 1984's sewer monster classic Chud, you may
(00:25):
have gotten a chill down your spine when a character
pointed a boxy gadget into the darkness and was alerted
to the presence of some yet unseen danger by an
ominous clicking sound. But Geiger counters aren't just a conveniently
spooky audio prop, nor an obsolete technology that went out
of fashion when people stopped building atomic bomb shelters in
(00:47):
their backyards. The Geiger counter, which in these scientific and
engineering worlds is more precisely known as the Geiger-Muller counter—
is still frequently used to detect radiation in various settings.
The Nuclear Regulatory Commission says it's the most commonly used
portable radiation instrument. The origins of this technology date back
(01:09):
to the early 1900s. A young German physicist by the
name of Hans Geiger had just written his PhD thesis
on how electrical discharges move through gases and got himself
a fellowship to join the physics lab at the University
of Manchester in England. There, he worked as an assistant
to one Ernest Rutherford, starting in 1907. This was an
(01:31):
exciting time in the fields of physics and chemistry. We
humans were just starting to figure out how atoms work.
Rutherford had recently made the discovery that atoms don't necessarily
last forever in the same state, that they can break
down or transform under particular circumstances. This was wild at
the time. This was a tiny grain of truth in
(01:54):
what alchemists were after for centuries, the transmutation of elements.
Rutherford was working specifically with radioactive elements like uranium and
radium and looking at how they decay. That's how he
wound up winning the 1908 Nobel Prize in Chemistry. His
work was also nominated for the Prize in Physics, but
the committee decided it pertained more to chemistry because it
(02:16):
had to do with chemical elements. Anyway, we understand today
that radioactive elements are made up of unstable atoms that
will spontaneously decay into atoms of another element in a
predictable way. The nucleus of such an unstable atom will
throw off a particle or split, leaving behind a different
(02:37):
element or two and giving off some particle and or
a radioactive ray. Rutherford was laying the groundwork for this
understanding and starting to put together that atoms have a
dense nucleus made up of even smaller particles, and further,
that an atom's nucleus can break apart and give off
those particles. So, he and his assistant Geiger were observing
(03:03):
samples of these radioactive elements and saw that when an
atom of uranium decays into thorium, it gives off what
they called an alpha particle. Geiger worked with Rutherford to
develop a radiation measuring device, a counter to detect these
alpha particles. Geier continued this research back in Germany. His
(03:24):
career was interrupted during World War I, in which he
served as an artillery officer in the German army. But afterward,
he returned to research and eventually teaching at the University
of Kiel in 1925. There, he teamed with Walter Muller,
one of his graduate students, to improve his counter. they
were looking to make it more sensitive, more reliable, more durable,
(03:48):
and to make it detect not only alpha particles, but
other types of radiation as well, including beta particles and
gamma radiation. The device they created, the Geiger-Muller tube, is
pretty much the same technology that's used today. But okay,
a quick overview here of how radiation works. Radiation can
(04:10):
be a confusing term because all waves in the electromagnetic
spectrum are types of radiation, including the light that's bouncing
into your eyeballs right now and the microwaves that heat
up your frozen burrito. The dangerous category of radiation, your
Fukushima or, I don't know, a chud category, is what's
called ionizing radiation, like gamma rays. These are photons that
(04:35):
have enough energy that when they hit an atom, they
can knock electrons clear off. It's called ionizing because this
disrupts the balance of positive and negative electrical charge within
the atom, making it an ion. This can change the
form and function of whatever those atoms are a part of,
including your squishy human body. Subatomic particles can also cause
(05:00):
ionizing radiation when they're moving fast enough. And, for example,
an alpha particle being emitted from a decaying radioactive atom
can be moving at 10,000 miles a second, which is
16,000 kilometers a second, which is fast. Now, alpha particles
are made up of two protons and two neutrons. It's
(05:22):
basically a helium-4 nucleus. Metaparticles are single electrons, and neither
of those can really penetrate your body very well. So
they're really only a danger to people if you eat
or inhale material that's emitting them. But you should avoid that.
And also, other types of ionizing radiation can easily penetrate
(05:43):
our bodies and cause cell death and cancer and other
unpleasant issues, which is why having a way to detect
that radiation can be so useful. A Geiger counter is
a relatively simple and inexpensive device that works through two
basic principles. First, that ionizing radiation knocks electrons off of atoms.
(06:05):
And second, that moving electrons transmit electrical energy. A Geiger-Muller
tube consists of a sealed, usually cylindrical chamber containing a
stable gas, usually argon or xenon, that's held at a
low pressure. with a thin wire running lengthwise through the cylinder.
(06:26):
Some tubes have a window on one end to allow
alpha and beta particles in more easily. The chamber also
acts as an electrical circuit. The wire is the anode,
or the bit where electricity enters the device, and the
outer shell of the chamber is the cathode, or the
bit where electricity leaves the device. When ionizing radiation enters
(06:47):
the chamber, it does what it says on the tin
and ionizes the gas there, knocking negatively charged electrons off
of atoms and creating positive ions from the part of
the atom that remains. In a Geiger-Muller counter, a high-voltage
electrical charge is then applied to the circuit, which causes
(07:07):
the free electrons to travel to the now positively charged anode.
This alone might not be enough to register the reaction
that's happening, but there's an amplification that happens in the
gas around the anode The initial free electrons collide with
more atoms of the gas, creating a cascade or avalanche
(07:29):
of ionization along the wire. When this charge reaches a
certain threshold, it generates an electric pulse that can be
registered by an attached device. This might be a mechanical
needle indicator that moves along a visual display, or some
kind of digital readout. But either way is usually accompanied
(07:50):
by an audio output that's just a little speaker that
clicks with the pulses. Geiger counters also have a built-in
method of dissipating or quenching the charge in the tube
so that it doesn't just avalanche over and over again,
but will rather reset and be able to accurately register
radioactivity again. This is accomplished by manufacturers adding a little
(08:15):
bit of what's called a quenching vapor to the tube
as well, something like halogen or an alcohol that will
neutralize the reaction. This all happens over the course of microseconds.
The number of clicks that you hear indicates how many
times it's happening in a minute. The visual display will
also indicate the counts per minute, or sometimes per second.
(08:39):
When you turn on a Geiger counter, you'll usually hear
some clicks right away, no matter where you are. That's
because of naturally occurring background radioactivity that comes from the sun,
natural uranium deposits in the soil, certain types of rock,
and a naturally occurring radioactive gas called radon, among other sources.
(09:01):
Though there are a number of other radiation detection technologies available,
The Geiger counter is a fairly simple technology that's been
around for a while, and they're fairly inexpensive today, with
some low-end consumer versions on the market that cost less
than $ 100. Many industries still use Geiger counters for such
things as monitoring radioactive contamination in laboratories. Law enforcement personnel
(09:26):
may use sophisticated versions of the devices to detect the
transportation of illicit radioactive materials, and many emergency responders carry
them as well. In Japan, personal Geiger counters became hot
sellers after the 2011 accident at the Fukushima Daiichi nuclear
power plant. They're also used by prospectors to find uranium
(09:47):
and other minerals. But Geiger counters also have limitations. You're
not getting any information about what type of ionizing radiation
set it off. A basic one can't tell you anything
about the energy of the radiation affecting it, and a
higher magnitude of radiation will change the dose rate that
you receive. The counter is only telling you yes or
(10:11):
no ionizing radiation and how often it's detecting it, not
how strong it is. For the article this episode is
based on, Hasdaf Works spoke by email with the Los
Alamos National Laboratory. They explained, Geiger-Muller counters are used everywhere,
especially when a low-cost solution that doesn't require a distinguishing
(10:32):
radiation type or energy is desired. A GM counter is
inherently unable to discern what type of particle triggered the pulse,
or even the energy of a particle. Because every interaction
produces the same pulse strength, a Think of a set mousetrap.
When sprung, it produces the same response regardless if a
(10:53):
mouse or a human foot is responsible, though the consequences
may be much different. As I said above, the Geiger-Muller
counter is not the only type of radiation dosimeter out there.
A Geiger-Muller counter can be combined with or replaced by
other devices that are capable of giving you a more
(11:13):
detailed and or accurate display of the radiation present. including
the total dose received over time expressed in a unit
called a sievert, which is amazing for workers who have
occupational exposure to dangerous radiation. These devices often do lose
the fun clicking sound, but outside of specific types of
(11:34):
work and scary movies, that's probably a plus. Today's episode
is based on the article, How Do Geiger Counters Work?
on HowStuffWorks.com, written by Patrick J. Geiger. BrainStuff is a
production of iHeart Podcasts in partnership with HowStuffWorks.com and is
produced by Tyler Klang. For more shows from iHeart Podcasts,
(11:58):
visit the iHeart Radio app, Apple Podcasts, or wherever you
listen to your favorite shows.
Welcome to BrainStuff, a production of iHeartRadio. Hey, BrainStuff. Lauren
Vogelbaum here. The closest that lots of us ever get
to a Geiger counter is the movies. In all kinds
of media, from Atomic Age horror films to tragic dramas
like Chernobyl to 1984's sewer monster classic Chud, you may
(00:25):
have gotten a chill down your spine when a character
pointed a boxy gadget into the darkness and was alerted
to the presence of some yet unseen danger by an
ominous clicking sound. But Geiger counters aren't just a conveniently
spooky audio prop, nor an obsolete technology that went out
of fashion when people stopped building atomic bomb shelters in
(00:47):
their backyards. The Geiger counter, which in these scientific and
engineering worlds is more precisely known as the Geiger-Muller counter—
is still frequently used to detect radiation in various settings.
The Nuclear Regulatory Commission says it's the most commonly used
portable radiation instrument. The origins of this technology date back
(01:09):
to the early 1900s. A young German physicist by the
name of Hans Geiger had just written his PhD thesis
on how electrical discharges move through gases and got himself
a fellowship to join the physics lab at the University
of Manchester in England. There, he worked as an assistant
to one Ernest Rutherford, starting in 1907. This was an
(01:31):
exciting time in the fields of physics and chemistry. We
humans were just starting to figure out how atoms work.
Rutherford had recently made the discovery that atoms don't necessarily
last forever in the same state, that they can break
down or transform under particular circumstances. This was wild at
the time. This was a tiny grain of truth in
(01:54):
what alchemists were after for centuries, the transmutation of elements.
Rutherford was working specifically with radioactive elements like uranium and
radium and looking at how they decay. That's how he
wound up winning the 1908 Nobel Prize in Chemistry. His
work was also nominated for the Prize in Physics, but
the committee decided it pertained more to chemistry because it
(02:16):
had to do with chemical elements. Anyway, we understand today
that radioactive elements are made up of unstable atoms that
will spontaneously decay into atoms of another element in a
predictable way. The nucleus of such an unstable atom will
throw off a particle or split, leaving behind a different
(02:37):
element or two and giving off some particle and or
a radioactive ray. Rutherford was laying the groundwork for this
understanding and starting to put together that atoms have a
dense nucleus made up of even smaller particles, and further,
that an atom's nucleus can break apart and give off
those particles. So, he and his assistant Geiger were observing
(03:03):
samples of these radioactive elements and saw that when an
atom of uranium decays into thorium, it gives off what
they called an alpha particle. Geiger worked with Rutherford to
develop a radiation measuring device, a counter to detect these
alpha particles. Geier continued this research back in Germany. His
(03:24):
career was interrupted during World War I, in which he
served as an artillery officer in the German army. But afterward,
he returned to research and eventually teaching at the University
of Kiel in 1925. There, he teamed with Walter Muller,
one of his graduate students, to improve his counter. they
were looking to make it more sensitive, more reliable, more durable,
(03:48):
and to make it detect not only alpha particles, but
other types of radiation as well, including beta particles and
gamma radiation. The device they created, the Geiger-Muller tube, is
pretty much the same technology that's used today. But okay,
a quick overview here of how radiation works. Radiation can
(04:10):
be a confusing term because all waves in the electromagnetic
spectrum are types of radiation, including the light that's bouncing
into your eyeballs right now and the microwaves that heat
up your frozen burrito. The dangerous category of radiation, your
Fukushima or, I don't know, a chud category, is what's
called ionizing radiation, like gamma rays. These are photons that
(04:35):
have enough energy that when they hit an atom, they
can knock electrons clear off. It's called ionizing because this
disrupts the balance of positive and negative electrical charge within
the atom, making it an ion. This can change the
form and function of whatever those atoms are a part of,
including your squishy human body. Subatomic particles can also cause
(05:00):
ionizing radiation when they're moving fast enough. And, for example,
an alpha particle being emitted from a decaying radioactive atom
can be moving at 10,000 miles a second, which is
16,000 kilometers a second, which is fast. Now, alpha particles
are made up of two protons and two neutrons. It's
(05:22):
basically a helium-4 nucleus. Metaparticles are single electrons, and neither
of those can really penetrate your body very well. So
they're really only a danger to people if you eat
or inhale material that's emitting them. But you should avoid that.
And also, other types of ionizing radiation can easily penetrate
(05:43):
our bodies and cause cell death and cancer and other
unpleasant issues, which is why having a way to detect
that radiation can be so useful. A Geiger counter is
a relatively simple and inexpensive device that works through two
basic principles. First, that ionizing radiation knocks electrons off of atoms.
(06:05):
And second, that moving electrons transmit electrical energy. A Geiger-Muller
tube consists of a sealed, usually cylindrical chamber containing a
stable gas, usually argon or xenon, that's held at a
low pressure. with a thin wire running lengthwise through the cylinder.
(06:26):
Some tubes have a window on one end to allow
alpha and beta particles in more easily. The chamber also
acts as an electrical circuit. The wire is the anode,
or the bit where electricity enters the device, and the
outer shell of the chamber is the cathode, or the
bit where electricity leaves the device. When ionizing radiation enters
(06:47):
the chamber, it does what it says on the tin
and ionizes the gas there, knocking negatively charged electrons off
of atoms and creating positive ions from the part of
the atom that remains. In a Geiger-Muller counter, a high-voltage
electrical charge is then applied to the circuit, which causes
(07:07):
the free electrons to travel to the now positively charged anode.
This alone might not be enough to register the reaction
that's happening, but there's an amplification that happens in the
gas around the anode The initial free electrons collide with
more atoms of the gas, creating a cascade or avalanche
(07:29):
of ionization along the wire. When this charge reaches a
certain threshold, it generates an electric pulse that can be
registered by an attached device. This might be a mechanical
needle indicator that moves along a visual display, or some
kind of digital readout. But either way is usually accompanied
(07:50):
by an audio output that's just a little speaker that
clicks with the pulses. Geiger counters also have a built-in
method of dissipating or quenching the charge in the tube
so that it doesn't just avalanche over and over again,
but will rather reset and be able to accurately register
radioactivity again. This is accomplished by manufacturers adding a little
(08:15):
bit of what's called a quenching vapor to the tube
as well, something like halogen or an alcohol that will
neutralize the reaction. This all happens over the course of microseconds.
The number of clicks that you hear indicates how many
times it's happening in a minute. The visual display will
also indicate the counts per minute, or sometimes per second.
(08:39):
When you turn on a Geiger counter, you'll usually hear
some clicks right away, no matter where you are. That's
because of naturally occurring background radioactivity that comes from the sun,
natural uranium deposits in the soil, certain types of rock,
and a naturally occurring radioactive gas called radon, among other sources.
(09:01):
Though there are a number of other radiation detection technologies available,
The Geiger counter is a fairly simple technology that's been
around for a while, and they're fairly inexpensive today, with
some low-end consumer versions on the market that cost less
than $ 100. Many industries still use Geiger counters for such
things as monitoring radioactive contamination in laboratories. Law enforcement personnel
(09:26):
may use sophisticated versions of the devices to detect the
transportation of illicit radioactive materials, and many emergency responders carry
them as well. In Japan, personal Geiger counters became hot
sellers after the 2011 accident at the Fukushima Daiichi nuclear
power plant. They're also used by prospectors to find uranium
(09:47):
and other minerals. But Geiger counters also have limitations. You're
not getting any information about what type of ionizing radiation
set it off. A basic one can't tell you anything
about the energy of the radiation affecting it, and a
higher magnitude of radiation will change the dose rate that
you receive. The counter is only telling you yes or
(10:11):
no ionizing radiation and how often it's detecting it, not
how strong it is. For the article this episode is
based on, Hasdaf Works spoke by email with the Los
Alamos National Laboratory. They explained, Geiger-Muller counters are used everywhere,
especially when a low-cost solution that doesn't require a distinguishing
(10:32):
radiation type or energy is desired. A GM counter is
inherently unable to discern what type of particle triggered the pulse,
or even the energy of a particle. Because every interaction
produces the same pulse strength, a Think of a set mousetrap.
When sprung, it produces the same response regardless if a
(10:53):
mouse or a human foot is responsible, though the consequences
may be much different. As I said above, the Geiger-Muller
counter is not the only type of radiation dosimeter out there.
A Geiger-Muller counter can be combined with or replaced by
other devices that are capable of giving you a more
(11:13):
detailed and or accurate display of the radiation present. including
the total dose received over time expressed in a unit
called a sievert, which is amazing for workers who have
occupational exposure to dangerous radiation. These devices often do lose
the fun clicking sound, but outside of specific types of
(11:34):
work and scary movies, that's probably a plus. Today's episode
is based on the article, How Do Geiger Counters Work?
on HowStuffWorks.com, written by Patrick J. Geiger. BrainStuff is a
production of iHeart Podcasts in partnership with HowStuffWorks.com and is
produced by Tyler Klang. For more shows from iHeart Podcasts,
(11:58):
visit the iHeart Radio app, Apple Podcasts, or wherever you
listen to your favorite shows.
BrainStuff News
Host
Lauren Vogelbaum
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