WEBVTT - How Does a Geiger Counter Work? 0:00:01.890 --> 0:00:07.930 Welcome to BrainStuff, a production of iHeartRadio. Hey, BrainStuff. Lauren 0:00:07.950 --> 0:00:12.379 Vogelbaum here. The closest that lots of us ever get 0:00:12.440 --> 0:00:16.020 to a Geiger counter is the movies. In all kinds 0:00:16.060 --> 0:00:19.760 of media, from Atomic Age horror films to tragic dramas 0:00:19.840 --> 0:00:25.030 like Chernobyl to 1984's sewer monster classic Chud, you may 0:00:25.050 --> 0:00:27.990 have gotten a chill down your spine when a character 0:00:28.130 --> 0:00:31.630 pointed a boxy gadget into the darkness and was alerted 0:00:31.690 --> 0:00:34.710 to the presence of some yet unseen danger by an 0:00:34.890 --> 0:00:40.350 ominous clicking sound. But Geiger counters aren't just a conveniently 0:00:40.479 --> 0:00:44.480 spooky audio prop, nor an obsolete technology that went out 0:00:44.520 --> 0:00:47.320 of fashion when people stopped building atomic bomb shelters in 0:00:47.340 --> 0:00:51.820 their backyards. The Geiger counter, which in these scientific and 0:00:51.900 --> 0:00:55.330 engineering worlds is more precisely known as the Geiger-Muller counter— 0:00:55.970 --> 0:00:59.650 is still frequently used to detect radiation in various settings. 0:01:00.630 --> 0:01:04.030 The Nuclear Regulatory Commission says it's the most commonly used 0:01:04.130 --> 0:01:08.980 portable radiation instrument. The origins of this technology date back 0:01:09.000 --> 0:01:12.880 to the early 1900s. A young German physicist by the 0:01:12.920 --> 0:01:16.280 name of Hans Geiger had just written his PhD thesis 0:01:16.400 --> 0:01:20.350 on how electrical discharges move through gases and got himself 0:01:20.370 --> 0:01:22.890 a fellowship to join the physics lab at the University 0:01:22.930 --> 0:01:27.000 of Manchester in England. There, he worked as an assistant 0:01:27.030 --> 0:01:31.780 to one Ernest Rutherford, starting in 1907. This was an 0:01:31.840 --> 0:01:35.320 exciting time in the fields of physics and chemistry. We 0:01:35.360 --> 0:01:38.179 humans were just starting to figure out how atoms work. 0:01:39.340 --> 0:01:42.920 Rutherford had recently made the discovery that atoms don't necessarily 0:01:43.010 --> 0:01:46.429 last forever in the same state, that they can break 0:01:46.530 --> 0:01:51.790 down or transform under particular circumstances. This was wild at 0:01:51.810 --> 0:01:54.630 the time. This was a tiny grain of truth in 0:01:54.670 --> 0:01:58.870 what alchemists were after for centuries, the transmutation of elements. 0:02:00.410 --> 0:02:04.590 Rutherford was working specifically with radioactive elements like uranium and 0:02:04.650 --> 0:02:07.870 radium and looking at how they decay. That's how he 0:02:07.890 --> 0:02:11.630 wound up winning the 1908 Nobel Prize in Chemistry. His 0:02:11.730 --> 0:02:14.250 work was also nominated for the Prize in Physics, but 0:02:14.290 --> 0:02:16.910 the committee decided it pertained more to chemistry because it 0:02:16.950 --> 0:02:21.650 had to do with chemical elements. Anyway, we understand today 0:02:21.710 --> 0:02:25.230 that radioactive elements are made up of unstable atoms that 0:02:25.270 --> 0:02:29.160 will spontaneously decay into atoms of another element in a 0:02:29.240 --> 0:02:33.359 predictable way. The nucleus of such an unstable atom will 0:02:33.540 --> 0:02:37.579 throw off a particle or split, leaving behind a different 0:02:37.639 --> 0:02:41.030 element or two and giving off some particle and or 0:02:41.050 --> 0:02:46.029 a radioactive ray. Rutherford was laying the groundwork for this 0:02:46.070 --> 0:02:50.000 understanding and starting to put together that atoms have a 0:02:50.080 --> 0:02:54.320 dense nucleus made up of even smaller particles, and further, 0:02:54.560 --> 0:02:57.480 that an atom's nucleus can break apart and give off 0:02:57.580 --> 0:03:02.920 those particles. So, he and his assistant Geiger were observing 0:03:03.020 --> 0:03:06.590 samples of these radioactive elements and saw that when an 0:03:06.770 --> 0:03:10.810 atom of uranium decays into thorium, it gives off what 0:03:10.830 --> 0:03:15.090 they called an alpha particle. Geiger worked with Rutherford to 0:03:15.130 --> 0:03:19.500 develop a radiation measuring device, a counter to detect these 0:03:19.630 --> 0:03:24.919 alpha particles. Geier continued this research back in Germany. His 0:03:24.980 --> 0:03:27.799 career was interrupted during World War I, in which he 0:03:27.860 --> 0:03:31.220 served as an artillery officer in the German army. But afterward, 0:03:31.340 --> 0:03:34.320 he returned to research and eventually teaching at the University 0:03:34.340 --> 0:03:39.540 of Kiel in 1925. There, he teamed with Walter Muller, 0:03:39.940 --> 0:03:44.290 one of his graduate students, to improve his counter. they 0:03:44.310 --> 0:03:47.920 were looking to make it more sensitive, more reliable, more durable, 0:03:48.640 --> 0:03:51.420 and to make it detect not only alpha particles, but 0:03:51.540 --> 0:03:55.040 other types of radiation as well, including beta particles and 0:03:55.300 --> 0:04:00.430 gamma radiation. The device they created, the Geiger-Muller tube, is 0:04:00.730 --> 0:04:05.050 pretty much the same technology that's used today. But okay, 0:04:05.330 --> 0:04:10.010 a quick overview here of how radiation works. Radiation can 0:04:10.050 --> 0:04:13.589 be a confusing term because all waves in the electromagnetic 0:04:13.650 --> 0:04:17.609 spectrum are types of radiation, including the light that's bouncing 0:04:17.630 --> 0:04:20.590 into your eyeballs right now and the microwaves that heat 0:04:20.630 --> 0:04:25.570 up your frozen burrito. The dangerous category of radiation, your 0:04:25.670 --> 0:04:29.300 Fukushima or, I don't know, a chud category, is what's 0:04:29.330 --> 0:04:35.730 called ionizing radiation, like gamma rays. These are photons that 0:04:35.830 --> 0:04:38.670 have enough energy that when they hit an atom, they 0:04:38.690 --> 0:04:43.250 can knock electrons clear off. It's called ionizing because this 0:04:43.310 --> 0:04:46.930 disrupts the balance of positive and negative electrical charge within 0:04:46.950 --> 0:04:51.250 the atom, making it an ion. This can change the 0:04:51.350 --> 0:04:54.410 form and function of whatever those atoms are a part of, 0:04:55.270 --> 0:05:00.650 including your squishy human body. Subatomic particles can also cause 0:05:00.810 --> 0:05:05.270 ionizing radiation when they're moving fast enough. And, for example, 0:05:05.510 --> 0:05:09.039 an alpha particle being emitted from a decaying radioactive atom 0:05:09.380 --> 0:05:14.080 can be moving at 10,000 miles a second, which is 0:05:14.080 --> 0:05:18.960 16,000 kilometers a second, which is fast. Now, alpha particles 0:05:19.100 --> 0:05:21.940 are made up of two protons and two neutrons. It's 0:05:22.060 --> 0:05:28.200 basically a helium-4 nucleus. Metaparticles are single electrons, and neither 0:05:28.240 --> 0:05:31.380 of those can really penetrate your body very well. So 0:05:31.580 --> 0:05:34.360 they're really only a danger to people if you eat 0:05:34.480 --> 0:05:39.180 or inhale material that's emitting them. But you should avoid that. 0:05:39.560 --> 0:05:43.669 And also, other types of ionizing radiation can easily penetrate 0:05:43.730 --> 0:05:47.349 our bodies and cause cell death and cancer and other 0:05:47.450 --> 0:05:51.110 unpleasant issues, which is why having a way to detect 0:05:51.170 --> 0:05:55.880 that radiation can be so useful. A Geiger counter is 0:05:55.940 --> 0:05:59.470 a relatively simple and inexpensive device that works through two 0:05:59.529 --> 0:06:05.190 basic principles. First, that ionizing radiation knocks electrons off of atoms. 0:06:05.850 --> 0:06:12.390 And second, that moving electrons transmit electrical energy. A Geiger-Muller 0:06:12.450 --> 0:06:16.969 tube consists of a sealed, usually cylindrical chamber containing a 0:06:17.110 --> 0:06:21.070 stable gas, usually argon or xenon, that's held at a 0:06:21.110 --> 0:06:25.150 low pressure. with a thin wire running lengthwise through the cylinder. 0:06:26.190 --> 0:06:28.330 Some tubes have a window on one end to allow 0:06:28.470 --> 0:06:32.080 alpha and beta particles in more easily. The chamber also 0:06:32.220 --> 0:06:35.560 acts as an electrical circuit. The wire is the anode, 0:06:35.880 --> 0:06:39.200 or the bit where electricity enters the device, and the 0:06:39.279 --> 0:06:42.000 outer shell of the chamber is the cathode, or the 0:06:42.020 --> 0:06:47.360 bit where electricity leaves the device. When ionizing radiation enters 0:06:47.400 --> 0:06:50.159 the chamber, it does what it says on the tin 0:06:50.400 --> 0:06:54.710 and ionizes the gas there, knocking negatively charged electrons off 0:06:54.730 --> 0:06:58.240 of atoms and creating positive ions from the part of 0:06:58.260 --> 0:07:03.159 the atom that remains. In a Geiger-Muller counter, a high-voltage 0:07:03.260 --> 0:07:07.419 electrical charge is then applied to the circuit, which causes 0:07:07.480 --> 0:07:12.010 the free electrons to travel to the now positively charged anode. 0:07:13.150 --> 0:07:16.910 This alone might not be enough to register the reaction 0:07:16.930 --> 0:07:20.850 that's happening, but there's an amplification that happens in the 0:07:20.870 --> 0:07:25.720 gas around the anode The initial free electrons collide with 0:07:25.760 --> 0:07:29.820 more atoms of the gas, creating a cascade or avalanche 0:07:29.920 --> 0:07:34.220 of ionization along the wire. When this charge reaches a 0:07:34.260 --> 0:07:37.800 certain threshold, it generates an electric pulse that can be 0:07:37.840 --> 0:07:42.680 registered by an attached device. This might be a mechanical 0:07:42.800 --> 0:07:46.380 needle indicator that moves along a visual display, or some 0:07:46.430 --> 0:07:50.420 kind of digital readout. But either way is usually accompanied 0:07:50.580 --> 0:07:54.280 by an audio output that's just a little speaker that 0:07:54.600 --> 0:07:59.250 clicks with the pulses. Geiger counters also have a built-in 0:07:59.290 --> 0:08:02.810 method of dissipating or quenching the charge in the tube 0:08:03.190 --> 0:08:05.970 so that it doesn't just avalanche over and over again, 0:08:06.570 --> 0:08:10.120 but will rather reset and be able to accurately register 0:08:10.200 --> 0:08:15.320 radioactivity again. This is accomplished by manufacturers adding a little 0:08:15.360 --> 0:08:17.640 bit of what's called a quenching vapor to the tube 0:08:17.680 --> 0:08:21.370 as well, something like halogen or an alcohol that will 0:08:21.410 --> 0:08:26.929 neutralize the reaction. This all happens over the course of microseconds. 0:08:27.950 --> 0:08:31.110 The number of clicks that you hear indicates how many 0:08:31.170 --> 0:08:35.030 times it's happening in a minute. The visual display will 0:08:35.070 --> 0:08:38.190 also indicate the counts per minute, or sometimes per second. 0:08:39.720 --> 0:08:42.160 When you turn on a Geiger counter, you'll usually hear 0:08:42.210 --> 0:08:45.810 some clicks right away, no matter where you are. That's 0:08:45.890 --> 0:08:50.270 because of naturally occurring background radioactivity that comes from the sun, 0:08:50.830 --> 0:08:54.370 natural uranium deposits in the soil, certain types of rock, 0:08:54.950 --> 0:08:59.720 and a naturally occurring radioactive gas called radon, among other sources. 0:09:01.120 --> 0:09:05.280 Though there are a number of other radiation detection technologies available, 0:09:05.870 --> 0:09:08.890 The Geiger counter is a fairly simple technology that's been 0:09:08.929 --> 0:09:12.370 around for a while, and they're fairly inexpensive today, with 0:09:12.550 --> 0:09:15.489 some low-end consumer versions on the market that cost less 0:09:15.510 --> 0:09:20.270 than $ 100. Many industries still use Geiger counters for such 0:09:20.350 --> 0:09:26.130 things as monitoring radioactive contamination in laboratories. Law enforcement personnel 0:09:26.170 --> 0:09:29.270 may use sophisticated versions of the devices to detect the 0:09:29.490 --> 0:09:34.480 transportation of illicit radioactive materials, and many emergency responders carry 0:09:34.500 --> 0:09:38.849 them as well. In Japan, personal Geiger counters became hot 0:09:38.929 --> 0:09:42.820 sellers after the 2011 accident at the Fukushima Daiichi nuclear 0:09:42.840 --> 0:09:47.319 power plant. They're also used by prospectors to find uranium 0:09:47.480 --> 0:09:52.730 and other minerals. But Geiger counters also have limitations. You're 0:09:52.760 --> 0:09:56.510 not getting any information about what type of ionizing radiation 0:09:56.550 --> 0:09:59.970 set it off. A basic one can't tell you anything 0:10:00.190 --> 0:10:03.329 about the energy of the radiation affecting it, and a 0:10:03.620 --> 0:10:06.660 higher magnitude of radiation will change the dose rate that 0:10:06.700 --> 0:10:11.220 you receive. The counter is only telling you yes or 0:10:11.360 --> 0:10:15.719 no ionizing radiation and how often it's detecting it, not 0:10:15.860 --> 0:10:19.590 how strong it is. For the article this episode is 0:10:19.630 --> 0:10:22.350 based on, Hasdaf Works spoke by email with the Los 0:10:22.450 --> 0:10:28.290 Alamos National Laboratory. They explained, Geiger-Muller counters are used everywhere, 0:10:28.710 --> 0:10:32.560 especially when a low-cost solution that doesn't require a distinguishing 0:10:32.660 --> 0:10:36.920 radiation type or energy is desired. A GM counter is 0:10:36.980 --> 0:10:40.940 inherently unable to discern what type of particle triggered the pulse, 0:10:41.340 --> 0:10:45.020 or even the energy of a particle. Because every interaction 0:10:45.140 --> 0:10:49.370 produces the same pulse strength, a Think of a set mousetrap. 0:10:49.990 --> 0:10:53.390 When sprung, it produces the same response regardless if a 0:10:53.470 --> 0:10:57.470 mouse or a human foot is responsible, though the consequences 0:10:57.670 --> 0:11:02.579 may be much different. As I said above, the Geiger-Muller 0:11:02.620 --> 0:11:06.260 counter is not the only type of radiation dosimeter out there. 0:11:07.200 --> 0:11:10.579 A Geiger-Muller counter can be combined with or replaced by 0:11:10.700 --> 0:11:13.339 other devices that are capable of giving you a more 0:11:13.660 --> 0:11:18.199 detailed and or accurate display of the radiation present. including 0:11:18.220 --> 0:11:21.240 the total dose received over time expressed in a unit 0:11:21.280 --> 0:11:25.089 called a sievert, which is amazing for workers who have 0:11:25.280 --> 0:11:30.990 occupational exposure to dangerous radiation. These devices often do lose 0:11:31.050 --> 0:11:34.790 the fun clicking sound, but outside of specific types of 0:11:34.850 --> 0:11:43.880 work and scary movies, that's probably a plus. Today's episode 0:11:43.940 --> 0:11:46.120 is based on the article, How Do Geiger Counters Work? 0:11:46.300 --> 0:11:50.260 on HowStuffWorks.com, written by Patrick J. Geiger. BrainStuff is a 0:11:50.260 --> 0:11:53.920 production of iHeart Podcasts in partnership with HowStuffWorks.com and is 0:11:53.960 --> 0:11:57.830 produced by Tyler Klang. For more shows from iHeart Podcasts, 0:11:58.010 --> 0:12:01.410 visit the iHeart Radio app, Apple Podcasts, or wherever you 0:12:01.450 --> 0:12:02.770 listen to your favorite shows.