1 00:00:00,000 --> 00:00:13,630 *rc3 prerol music* 2 00:00:13,630 --> 00:00:19,840 Herald: All right, fellow creatures, to be honest, I never thought that I would be 3 00:00:19,840 --> 00:00:25,440 introducing a talk on measuring radioactivity like ever in my life, but 4 00:00:25,440 --> 00:00:30,480 then again, considering the world stage, current state at large, it might be not 5 00:00:30,480 --> 00:00:35,600 such a bad idea to be prepared for these things. Right? And gladly, our next 6 00:00:35,600 --> 00:00:42,000 speaker, Oliver Keller, is an expert in detecting radioactive stuff. Oliver is a 7 00:00:42,000 --> 00:00:47,040 physicist and works at one of the most prominent nerd happy places. The CERN 8 00:00:47,040 --> 00:00:53,760 since 2013 is also doing a PhD project about novel instruments and experiments on 9 00:00:53,760 --> 00:01:00,800 natural radioactivity at the University of Geneva and to even more to add even more 10 00:01:00,800 --> 00:01:06,480 C3 pizzazz. Oliver is active in the open science community and passionate about 11 00:01:06,480 --> 00:01:12,960 everything open source. All that sounds really cool to me. So without further ado, 12 00:01:12,960 --> 00:01:18,400 let's give a warm, virtual welcome to Oliver and let's hear what he has to say 13 00:01:18,400 --> 00:01:24,800 about measuring radioactivity with using low cost silicon sensors. Oliver, the 14 00:01:24,800 --> 00:01:28,070 stream is yours. 15 00:01:28,070 --> 00:01:32,560 Oliver: Thanks. That was a very nice introduction. I'm really happy to have the 16 00:01:32,560 --> 00:01:38,310 chance to present here. I'm a member since quite some years and this is my first CCC 17 00:01:38,310 --> 00:01:44,438 talk, so I'm quite excited. Yeah, you can follow me on Twitter or I'm also on 18 00:01:44,438 --> 00:01:50,156 Mastodon, not so active, and most of my stuff is on GitHub. OK, so what will we 19 00:01:50,156 --> 00:01:55,695 talk about in this talk? I'll give you a short overview, also about the 20 00:01:55,695 --> 00:02:02,035 radioactivity, because yeah, it's a topic with many different details and then we 21 00:02:02,035 --> 00:02:08,183 will look at the detector more in detail and how that works in terms of the physics 22 00:02:08,183 --> 00:02:13,160 behind it and the electronics. And then finally, we look at things that can be 23 00:02:13,160 --> 00:02:19,156 measured, how the measurement actually works, what are interesting objects to 24 00:02:19,156 --> 00:02:28,122 check and how this relates to silicon detectors being used at CERN. So the 25 00:02:28,122 --> 00:02:33,400 project is on GitHub called DIY Particle Detector. It's an electronic design, which 26 00:02:33,400 --> 00:02:39,437 is open hardware. There's a wiki with lots of further details for building and for 27 00:02:39,437 --> 00:02:45,363 troubleshooting. There is a little web browser tool I will show later, briefly, 28 00:02:45,363 --> 00:02:52,115 and there are scripts to record and nicely plot the measurements. Those scripts are 29 00:02:52,115 --> 00:02:58,056 BSD-licensed and written in Python. There are two variants of this detector. One is 30 00:02:58,056 --> 00:03:03,094 called electron detector, the other one alpha spectrometer. They use the same 31 00:03:03,094 --> 00:03:08,471 circuit board, but one is using four diodes, the other one one photodiode... 32 00:03:08,471 --> 00:03:14,180 There's a small difference between them, but in general it's pretty similar. But 33 00:03:14,180 --> 00:03:18,509 the electron detector is much easier to build and much easier to get started 34 00:03:18,509 --> 00:03:25,678 using. Then you have complete part lists and even a complete kit can be bought on 35 00:03:25,678 --> 00:03:31,638 kitspace.org, which is an open hardware community repository, and I really 36 00:03:31,638 --> 00:03:36,366 recommend you to check it out. It's a great community platform and everyone can 37 00:03:36,366 --> 00:03:44,105 register their own GitHub project quite easily. Now, this is a particle detector 38 00:03:44,105 --> 00:03:51,025 in a tin box, so you can use the famous Altoids tin box or something for Swiss 39 00:03:51,025 --> 00:03:57,342 chocolate, for example. You can see it's rather small, the board about the size of 40 00:03:57,342 --> 00:04:03,615 a nine volt block battery. And then you need, in addition, about 20 resistors, 41 00:04:03,615 --> 00:04:10,356 capacitors and these silicon diodes plus an operational amplifier, 42 00:04:10,356 --> 00:04:15,117 which is this little chip here, this little black chip here on the right side, 43 00:04:15,117 --> 00:04:19,520 you can see is all old school large components. This is on purpose, so it's 44 00:04:19,520 --> 00:04:24,635 easy to soldier for complete electronic beginners. And this by the way, this 45 00:04:24,635 --> 00:04:30,176 picture is already one user of this project who posted their own build on 46 00:04:30,176 --> 00:04:38,084 Twitter. OK, so natural radioactivity. So I would say it's a story of many 47 00:04:38,084 --> 00:04:44,080 misconceptions. Let's imagine we are this little stick figure here on the ground. 48 00:04:44,080 --> 00:04:50,644 Below us we have uranium and thorium. We also have Potassium-40 in the ground and 49 00:04:50,644 --> 00:04:56,809 Potassium-40 is is pretty specific and peculiar. It actually makes all of us a 50 00:04:56,809 --> 00:05:05,138 little bit radioactive. Every human has about 4000 to 5000 radioactive decays 51 00:05:05,138 --> 00:05:10,258 every second because of the natural potassium and natural potassium comes with 52 00:05:10,258 --> 00:05:14,979 a radioactive isotope, which is just everywhere, it's in bananas. But it's also 53 00:05:14,979 --> 00:05:20,320 in us because we need it for our body chemistry. It's really important and even 54 00:05:20,320 --> 00:05:26,224 some of those decays are even producing anti-matter. So how cool is 55 00:05:26,224 --> 00:05:32,432 that? OK, so what would we be measuring on the on ground? Well, there could be some 56 00:05:32,432 --> 00:05:39,429 gamma rays or electrons. Those are from beta-decays. Or from the Uranium, there is 57 00:05:39,429 --> 00:05:46,956 one radionuclide appearing in the decay chain, which is called Radon, and Radon is 58 00:05:46,956 --> 00:05:53,320 actually a gas. So from the ground the Radon can diffuse upwards and travel with 59 00:05:53,320 --> 00:06:01,137 air and spread around. So it's a bit like a vehicle for radioactivity from 60 00:06:01,137 --> 00:06:08,183 the ground to spread to other places. And that Radon would decay with alpha 61 00:06:08,183 --> 00:06:14,148 particles producing electrons and beta- decays and also gamma radiation further 62 00:06:14,148 --> 00:06:21,683 down in the decay chain. So just to recapitulate, I've said it already twice, 63 00:06:21,683 --> 00:06:29,828 so alpha particles are actually helium nuclei, so it's just two protons and two 64 00:06:29,828 --> 00:06:38,150 neutrons and the electrons are missing. And in beta decay basically one neutron is 65 00:06:38,150 --> 00:06:43,095 transformed into a proton and an electron. And there's also an electron-anti-neutrino 66 00:06:43,095 --> 00:06:47,694 generated. But this is super hard to measure. So we're not measuring those. 67 00:06:47,694 --> 00:06:54,524 Mostly we will be measuring electrons from beta-decays. That's why you see all these 68 00:06:54,524 --> 00:07:00,334 little e's indicating betadecays. Ok, if you would go to the hospital here on the 69 00:07:00,334 --> 00:07:08,965 left side, we would probably find some x rays from checking our bones or something 70 00:07:08,965 --> 00:07:16,484 like this, or even gamma rays or alpha particles being used in treatments or very 71 00:07:16,484 --> 00:07:22,814 modern even proton beams are sometimes generated for medical applications. Now, 72 00:07:22,814 --> 00:07:28,179 here on the right side, if you go close to a nuclear power plant, we probably measure 73 00:07:28,179 --> 00:07:33,886 nothing unless there's a problem in this case, most likely we would find some gamma 74 00:07:33,886 --> 00:07:40,639 radiation. But only if there is a problem. OK, and then actually that's not the whole 75 00:07:40,639 --> 00:07:46,886 story. This is terrestrial radiation. But we also have radiation coming from 76 00:07:46,886 --> 00:07:50,863 upwards, showering down on us every minute, and there's actually nothing we 77 00:07:50,863 --> 00:07:56,571 can do against it. So protons are accelerated from in the universe. 78 00:07:56,571 --> 00:08:02,416 Basically, the biggest particle accelerator nature has. And once they hit 79 00:08:02,416 --> 00:08:10,159 our atmosphere they break apart into less energetic particles and it's many of them. 80 00:08:10,159 --> 00:08:15,850 So in the first stage there's lots of pions generated and also neutrons. But neutrons 81 00:08:15,850 --> 00:08:21,625 are really hard to measure, so I'll ignore them for most of the talk. Then those 82 00:08:21,625 --> 00:08:29,045 pions can decay into gamma rays and then trigger a whole chain of positron electron 83 00:08:29,045 --> 00:08:34,877 decays, which again create gamma rays and so forth. And this goes actually the whole 84 00:08:34,877 --> 00:08:40,183 way down to the earth. We will have a little bit of that on the sea level. 85 00:08:40,183 --> 00:08:46,040 And the other more known part of atmospheric radiation is actually muons. 86 00:08:46,040 --> 00:08:52,374 So some pions decay into muons, which is kind of a heavy electron and also 87 00:08:52,374 --> 00:08:57,639 neutrinos. But neutrinos are, again, very hard to measure. So I'll ignore them for 88 00:08:57,639 --> 00:09:03,464 most of this talk. And if you look here on the right side on this altitude scale, 89 00:09:03,464 --> 00:09:08,420 you'll see an airplane would be basically traveling where most of the atmospheric 90 00:09:08,420 --> 00:09:13,323 radiation is produced. And this is why if you go on such an airplane, you have 91 00:09:13,323 --> 00:09:19,879 actually several times more radiation in there than here on earth. And, of 92 00:09:19,879 --> 00:09:24,210 course, on the ground, it also depends where you are. There are different amounts 93 00:09:24,210 --> 00:09:30,140 of uranium and thorium in the ground and this is just naturally there. So but it 94 00:09:30,140 --> 00:09:36,773 depends on the geology, of course. OK, so I've talked quite a bit about radiation, 95 00:09:36,773 --> 00:09:43,045 and I'm saying I want to use silicon to detect it. So what radiation exactly? 96 00:09:43,045 --> 00:09:48,514 Maybe. Let's let's take a step back and think about what we know maybe from 97 00:09:48,514 --> 00:09:54,840 school. So we have this rainbow for visible light. Right. This is in terms of 98 00:09:54,840 --> 00:10:03,000 wavelength. We have 800 to 400 nanometers spanning from the infrared/red area to all 99 00:10:03,000 --> 00:10:12,857 the green to blue and into the violet. And lower down those wavelengths or let's say 100 00:10:12,857 --> 00:10:17,744 bigger millimeter waves, meter waves and even kilometer, that would be radio waves, 101 00:10:17,744 --> 00:10:22,370 radio frequencies for our digital communication systems, wi-fi, mobile 102 00:10:22,370 --> 00:10:27,720 devices and so forth. But I want to look actually more towards the right because 103 00:10:27,720 --> 00:10:33,441 that's what we are measuring with these detectors. It's shorter wavelength, which 104 00:10:33,441 --> 00:10:39,797 actually means higher energy. So on the right side, we would be having ultraviolet 105 00:10:39,797 --> 00:10:47,328 radiation, which is kind of at the border to what we can measure. And these 800 to 106 00:10:47,328 --> 00:10:54,085 400nm translate into 1.5 to 3 eV, which is a unit that particle physicists really 107 00:10:54,085 --> 00:11:02,931 prefer because it basically relates the energy of an electron after it has been 108 00:11:02,931 --> 00:11:09,270 accelerated by 1 Volt and makes it much easier to work with nuclear 109 00:11:09,270 --> 00:11:15,385 particle physics, because everything, all the energy is always related to an 110 00:11:15,385 --> 00:11:21,208 electron. And this energy, this formula here is just a reminder that the 111 00:11:21,208 --> 00:11:25,937 wavelengths can be always converted into energy and it's inversely proportional. So 112 00:11:25,937 --> 00:11:30,551 wavelength increases to the left and the energy to right. And if you increase 113 00:11:30,551 --> 00:11:35,962 energy more from from the visible range, so let's say thousands of electron volts, 114 00:11:35,962 --> 00:11:43,400 then we arrive here. Millions - mega electron volts, even GeV. And there is now 115 00:11:43,400 --> 00:11:51,810 a pretty important distinction between those two areas, and that is the right one 116 00:11:51,810 --> 00:11:58,020 is ionizing radiation and the left one is non ionizing radiation. UV is a little bit 117 00:11:58,020 --> 00:12:03,150 in the middle of that. So some parts of the UV spectrum can be ionizing. It also 118 00:12:03,150 --> 00:12:09,567 depends a lot on the material that the radiation is interacting with. For these 119 00:12:09,567 --> 00:12:13,820 detectors I'm talking about today and alpha, beta, gamma radiation, this is all 120 00:12:13,820 --> 00:12:21,326 ionizing, so some examples, lowest energy on the lower spectrum would be x rays than 121 00:12:21,326 --> 00:12:29,440 electrons, gamma rays from radioactive nuclides that already talked about in the 122 00:12:29,440 --> 00:12:34,877 previous slide, alpha particles, and that muons from the atmosphere would be more on 123 00:12:34,877 --> 00:12:40,302 the GeV range and so forth. And for these higher energies, of course, you need 124 00:12:40,302 --> 00:12:46,184 something like the LHC to accelerate particles to really high energies. And 125 00:12:46,184 --> 00:12:56,415 then you can even access the TeV regime. OK, silicon diodes. What kind of silicon 126 00:12:56,415 --> 00:13:02,592 diodes? I'm using in this project, low local silicon pin diodes, one is called 127 00:13:02,592 --> 00:13:09,034 BPW34 it's manufactured from Vishay or Osram, costs about 50 cents. So that's what 128 00:13:09,034 --> 00:13:15,167 I mean with low cost. There's another one called BPX61 from Osram. It's quite a bit 129 00:13:15,167 --> 00:13:19,555 more expensive. This is the lower one here on the right. It has a metal case, which 130 00:13:19,555 --> 00:13:23,451 is the main reason why it's more expensive. But it's quite interesting 131 00:13:23,451 --> 00:13:28,523 because that one we can use for the alpha detector. If you look closely, there is a 132 00:13:28,523 --> 00:13:35,800 glass on top, but we can remove that. We have a sensitive area. So this chip is 133 00:13:35,800 --> 00:13:43,076 roughly 7mm² large and it has a thickness, a sensitive thickness of about 50 134 00:13:43,076 --> 00:13:49,681 micrometer, which is not a lot. So it's basically the half of the width of a human 135 00:13:49,681 --> 00:13:55,401 hair. And in total, it's a really small, sensitive volume. But it's it's enough to 136 00:13:55,401 --> 00:14:02,200 measure something. And just as a reminder, how much of gamma rays or X-rays we will 137 00:14:02,200 --> 00:14:09,057 detect with this, not a lot because it's high, energetic photon radiation kind 138 00:14:09,057 --> 00:14:15,471 doesn't interact very well in any kind of matter. And because a sensitive area is so 139 00:14:15,471 --> 00:14:21,399 thin, it would basically permeate through it and most of the times not interact and 140 00:14:21,399 --> 00:14:28,400 doesn't make a signal. OK, what's really important, since we don't want to measure 141 00:14:28,400 --> 00:14:35,120 light, we have to shield light away. We need to block all of the light, that means 142 00:14:35,120 --> 00:14:40,080 easiest way to do it is to put it in a metal case. There is electromagnetically 143 00:14:40,080 --> 00:14:44,880 shielded and completely protected from light as well. Electromagnetic radiation 144 00:14:44,880 --> 00:14:49,840 or radiowaves can also influence these detectors because they are super 145 00:14:49,840 --> 00:14:55,360 sensitive. So this sould be a complete Faraday cage, complete metal structure 146 00:14:55,360 --> 00:15:03,120 around it. There's a lot of hints and tips how to achieve that on the wiki on the on 147 00:15:03,120 --> 00:15:10,080 the GitHub of this project. OK, let's think about one of those PIN diodes, 148 00:15:10,080 --> 00:15:18,720 normally there is one part in the silicon which is n-doped 149 00:15:18,720 --> 00:15:23,920 negatively doped, and the other part usually, which is positively dropped. And 150 00:15:23,920 --> 00:15:28,080 then you arrive at a simple so called p-n- junction, which is a regular 151 00:15:28,080 --> 00:15:33,840 semiconducting diode. Now, pin diodes add another layer of so-called intrinsic 152 00:15:33,840 --> 00:15:41,920 layer, here shown with the i. And that actually is the main advantage. Why this 153 00:15:41,920 --> 00:15:50,800 kind of detector works quite well and have a relatively large sensitive Sigma's. So 154 00:15:50,800 --> 00:15:58,320 if you think about, let's say, a photon from an x ray or gamma-decay or an 155 00:15:58,320 --> 00:16:03,920 electron hitting the sensor. So by the way, this is a cross-section view from the 156 00:16:03,920 --> 00:16:09,840 side, but that doesn't really matter. But let's say they come here from the top into 157 00:16:09,840 --> 00:16:16,480 the... into the diode and we're looking at the side then we have actually 158 00:16:16,480 --> 00:16:22,000 ionization because this is ionizing radiation, so we get free charges in the 159 00:16:22,000 --> 00:16:26,960 form of electron-hole pairs. So electrons, which here the blue ball and the red 160 00:16:26,960 --> 00:16:34,240 circle would be the holes. And depending on the radiation kind, how this ionization 161 00:16:34,240 --> 00:16:39,760 takes place is quite different, but the result is if you get a signal, it means 162 00:16:39,760 --> 00:16:45,520 there was ionization. Now, if just this would happen, we could not measure 163 00:16:45,520 --> 00:16:53,120 anything. Those charges would quickly recombine and on the outside of the diode, 164 00:16:53,120 --> 00:16:58,720 it would be a little signal. But what we can do is we can apply actually a voltage 165 00:16:58,720 --> 00:17:06,320 from the outside. So here we just put a battery. So we have a positive voltage 166 00:17:06,320 --> 00:17:12,000 here, a couple of volts. And then what happens is that the electrons would be 167 00:17:12,000 --> 00:17:18,480 attracted by the positive voltage and the holes will travel to the negative 168 00:17:18,480 --> 00:17:26,720 potential. And we end up with a little net current or a small bunch of charges that 169 00:17:26,720 --> 00:17:35,200 can be measured across the diode as a tiny, tiny current. The sensitive volume 170 00:17:35,200 --> 00:17:41,040 is actually proportional to the voltage, so the more voltage we put, the more the 171 00:17:41,040 --> 00:17:44,880 bigger is our volume and the more we can actually measure with certain limits, of 172 00:17:44,880 --> 00:17:49,520 course, because the structure of the pin diode has a maximum thickness just 173 00:17:49,520 --> 00:17:56,800 according how it is manufactured. And these properties can be estimated with 174 00:17:56,800 --> 00:18:02,720 C-V-measurements. So here you see an example of a couple of diodes, a few of 175 00:18:02,720 --> 00:18:06,240 the same type. The two that I've mentioned, they're different versions. One 176 00:18:06,240 --> 00:18:11,360 has a transparent plastic case. One has a black plastic case. Doesn't really matter. 177 00:18:11,360 --> 00:18:16,800 You see, basically in all the cases, more or less the same curve. And as you 178 00:18:16,800 --> 00:18:21,760 increase the voltage, the capacitance goes down. So it's great and basically shows us 179 00:18:21,760 --> 00:18:26,960 those silicon chips are very similar, if not exactly the same chip. Those 180 00:18:26,960 --> 00:18:34,880 differences are easily explained by manufacturing variances. And then because 181 00:18:34,880 --> 00:18:39,280 this actually, if you think about it, it looks a bit like a parallel plate 182 00:18:39,280 --> 00:18:45,120 capacitor and actually you can treat it as one. And if you know the capacitance and 183 00:18:45,120 --> 00:18:50,240 the size, the area, you can actually calculate the distance of these two plates 184 00:18:50,240 --> 00:18:58,080 or basically width or the thickness of the diode. And then we arrive at about 50 185 00:18:58,080 --> 00:19:06,800 micrometer, if you put something like 8 or 10 volts. OK, now we have a tiny charge 186 00:19:06,800 --> 00:19:11,600 current, now we need to amplify it, so we have a couple of diodes, I'm explaining 187 00:19:11,600 --> 00:19:16,640 now the electron detector, because it's easier. We have four diodes at the input 188 00:19:16,640 --> 00:19:21,360 and this is the symbol for an operational amplifier. There are two of those in the 189 00:19:21,360 --> 00:19:25,840 circuit. The first stage is really the special one. So if you have a particle 190 00:19:25,840 --> 00:19:31,200 striking the diode, we get a little charge current hitting the amplifier. And then we 191 00:19:31,200 --> 00:19:34,880 have here this important feedback circuit. So the output is fed back into 192 00:19:34,880 --> 00:19:40,880 the input, which in this case makes a negative amplification. And the 193 00:19:40,880 --> 00:19:46,320 amplification is defined actually by this capacitance here. The resistor has a 194 00:19:46,320 --> 00:19:51,360 secondary role with the small capacitance. It is what makes the output voltage here 195 00:19:51,360 --> 00:19:57,200 large. The smaller the capacitance, the larger the output and it's inverted. Then 196 00:19:57,200 --> 00:20:02,320 in the next amplifier step, we just increase the voltage again to a level that 197 00:20:02,320 --> 00:20:08,160 is useful for using it later. But all of the signal quality that has been 198 00:20:08,160 --> 00:20:13,120 achieved in the first stage will stay like that. So signal to noise is defined by the 199 00:20:13,120 --> 00:20:18,880 first stage. The second one is just to better adapt it to the input of the 200 00:20:18,880 --> 00:20:24,480 measurement device that's connected. So here, this is a classic inverting 201 00:20:24,480 --> 00:20:29,120 amplifier with just these two resistors define the amplification factor. It's very 202 00:20:29,120 --> 00:20:35,360 simple. It's just a factor of hundred in this case. And so if you think again about 203 00:20:35,360 --> 00:20:39,760 the charge pulse and this, the circuit here is sensitive, starting from about 204 00:20:39,760 --> 00:20:50,320 1000 liberated charges in those diodes as a result from ionization. We get something 205 00:20:50,320 --> 00:20:55,920 like 320 micro Volt at this first output, and this is a spike that quickly 206 00:20:55,920 --> 00:21:01,600 decreases. Basically these capacitors are charged and quickly discharged with this 207 00:21:01,600 --> 00:21:07,360 resistor and this is what we see here. And then that is amplified again by a factor 208 00:21:07,360 --> 00:21:14,080 of 100. And then we arrive at something like at least 32 mV, which is conveniently 209 00:21:14,080 --> 00:21:20,000 a voltage that is compatible with most microphone or headset inputs of computers 210 00:21:20,000 --> 00:21:25,600 or mobile phones, so that the regular headset here has these four connectors and 211 00:21:25,600 --> 00:21:31,520 the last ring actually connects the microphone. The other is ground and reft. 212 00:21:31,520 --> 00:21:39,360 Left, right for the earbuds. OK, how do we record those pulses? This is an example of 213 00:21:39,360 --> 00:21:46,400 1000 pulses overlayed and measured on an oscilloscope here. So it's a bit more 214 00:21:46,400 --> 00:21:52,400 accurate. You see the deposits a bit better, kind of like the persistence mode 215 00:21:52,400 --> 00:21:58,160 of an oscilloscope. And the size of the pulse is proportional to energy that was 216 00:21:58,160 --> 00:22:03,680 absorbed. And the circuit is made in such a way that the width of the pulse is big 217 00:22:03,680 --> 00:22:08,560 enough such that regular sampling frequency of a sound card can actually 218 00:22:08,560 --> 00:22:14,800 catch it and measure it. Yeah, this is Potassium Salt. This is cut here. This is 219 00:22:14,800 --> 00:22:18,720 called a low salt in the UK. There is also a german variance, you can also just buy 220 00:22:18,720 --> 00:22:26,320 it in the pharmacy or in certain organic food stores as a replacement salt. 221 00:22:26,320 --> 00:22:33,120 On the right side is an example from this small Columbite Stone, which has traces of 222 00:22:33,120 --> 00:22:38,720 uranium on it. And this is measured with the alpha spectrometer. And you see those 223 00:22:38,720 --> 00:22:42,640 pulses are quite a bit bigger here. We have 50 microseconds and here we have more 224 00:22:42,640 --> 00:22:52,880 like one milliseconds of pulse width. Now there's a software on a browser. This is 225 00:22:52,880 --> 00:23:00,720 something I wrote using the Web Audio API and it works on most browsers, best is 226 00:23:00,720 --> 00:23:06,640 Chrome, on iOs, of course, you have to use Safari and that records once you plug the 227 00:23:06,640 --> 00:23:13,120 detector, it records from the input at 48 or 44.1kHz the pulses. Here's an example 228 00:23:13,120 --> 00:23:18,560 with the alpha spectrometer circuit, you get these nice large pulses. In case of 229 00:23:18,560 --> 00:23:22,800 the electron detector the pulse is much shorter and you see it, you see the noise 230 00:23:22,800 --> 00:23:28,880 much more amplified. This red line is kind of the minimum level that the pulse needs 231 00:23:28,880 --> 00:23:32,240 to trigger. This would be better. And that's like the trigger level of an 232 00:23:32,240 --> 00:23:38,160 oscilloscope. And you can set that with those buttons in the browser. You need to 233 00:23:38,160 --> 00:23:42,960 find a good value. Of course, if you change your input volume settings, for 234 00:23:42,960 --> 00:23:49,840 example, this will change. So you have to remember which, with which settings it 235 00:23:49,840 --> 00:23:55,600 works well. And it is pulsed, for example, is even oscillating here. So for electron 236 00:23:55,600 --> 00:24:01,440 detector, it's basically nice to count particles. For the alpha detector it's 237 00:24:01,440 --> 00:24:06,240 really the case where the size of the pulse can be nicely evaluated and we can 238 00:24:06,240 --> 00:24:11,120 actually do energy measurements. And these energy measurements can be also called 239 00:24:11,120 --> 00:24:17,520 spectrometry. So if you look closer at these many pulses that have been recorded 240 00:24:17,520 --> 00:24:26,560 and we find that there is really like much more intensity, which means many more same 241 00:24:26,560 --> 00:24:32,160 pulses were detected, we can relate it to radium and radon. If we use a reference 242 00:24:32,160 --> 00:24:35,920 alpha source and I have done this, I have measured the whole circuit with the reference 243 00:24:35,920 --> 00:24:41,360 sources and provide the calibration on GitHub and you can reuse the GitHub 244 00:24:41,360 --> 00:24:47,280 calibration if you use exactly the same sound settings that I have used for 245 00:24:47,280 --> 00:24:53,600 recording. And for example, these two very weak lines here from two very distinctive 246 00:24:53,600 --> 00:25:02,560 polonium isotopes from the uranium decay chain. The top part here which is really 247 00:25:02,560 --> 00:25:08,240 dark, corresponds basically in the histogram view to this side on the left, 248 00:25:08,240 --> 00:25:12,160 which is electrons. Most of these electrons will actually enter the chip and 249 00:25:12,160 --> 00:25:18,800 leave it without being completely absorbed by it, but alpha particles 250 00:25:18,800 --> 00:25:22,960 interact so strongly that they are completely absorbed within the 50 251 00:25:22,960 --> 00:25:29,520 micrometers of sensitive volume of these diodes and OK here is a bit difficult to 252 00:25:29,520 --> 00:25:35,440 see peaks. But the far end of the high energy spectrum, you see two really clear 253 00:25:35,440 --> 00:25:40,560 peaks and those can only stem from polonium, actually. I mean, we know it's 254 00:25:40,560 --> 00:25:46,960 uranium and that can only be polonium, which is that isotope that produces the 255 00:25:46,960 --> 00:25:56,080 most energetic alpha particles and which is natural. And I said, if you use 256 00:25:56,080 --> 00:25:59,840 the same setting like me, you can use it. So the best is if you use actually the 257 00:25:59,840 --> 00:26:04,560 same soundcard because they're if you put it to hundred percent input sensitivity, 258 00:26:04,560 --> 00:26:08,880 you will have exactly the same result, like in my calibration case. And this 259 00:26:08,880 --> 00:26:13,120 soundcard is pretty cheap, but also pretty good. It costs just two dollars and has a 260 00:26:13,120 --> 00:26:18,560 pretty range and resolves quite well, 16 bits and think, oh, you could do that with 261 00:26:18,560 --> 00:26:24,640 Arduino as well, is actually a bit hard to do. A really well defined 16 bit 262 00:26:24,640 --> 00:26:31,280 measurement, even at 48 kHz. It's not so easy and this keeps it cheap and kind of 263 00:26:31,280 --> 00:26:34,960 straightforward. And you can have just some Python scripts on the computer to 264 00:26:34,960 --> 00:26:40,960 read it out. And this is as a reminder, in order to measure alpha particles, we have 265 00:26:40,960 --> 00:26:44,720 to remove the glass here on top of the diode. So I'm doing it just cutting into 266 00:26:44,720 --> 00:26:50,160 the metal frame and then the glass breaks away easily. Is not a problem, there's 267 00:26:50,160 --> 00:26:56,800 more on that on the wiki. Now we can kind of compare alpha and gamma 268 00:26:56,800 --> 00:27:03,920 spectrometry. Here's an example. This is the uranium glazed ceramics. The red part 269 00:27:03,920 --> 00:27:09,840 is uranium oxide that was used to create this nice red color in the 50s, 60s, 70s. 270 00:27:09,840 --> 00:27:15,040 And in the spectrum we have two very distinctive peaks and nothing in the high 271 00:27:15,040 --> 00:27:20,800 energy regime. Only this low energy range has a signal. And this corresponds 272 00:27:20,800 --> 00:27:27,920 actually to uranium 238 and 234 because they use actually purified uranium. So all 273 00:27:27,920 --> 00:27:33,920 of the high energy progeny or daughters of uranium, they're not present here because 274 00:27:33,920 --> 00:27:38,720 it was purified uranium. And this measurement doesn't even need vacuum, I 275 00:27:38,720 --> 00:27:43,280 put it just like this in a regular box. Of course, if you would have vacuum, you 276 00:27:43,280 --> 00:27:48,400 would improve this peaks by a lot. So this widening here to the left, basically, that 277 00:27:48,400 --> 00:27:55,200 this peak is almost below the other one. That is due to the natural air at regular 278 00:27:55,200 --> 00:28:00,960 air pressure, which already interacts a lot with the particles and absorbs a lot 279 00:28:00,960 --> 00:28:06,960 of energy before the particles hit the sensor. So in terms of pros and cons, I 280 00:28:06,960 --> 00:28:12,080 would say the small sensor is quite interesting here in an alpha spectrometry 281 00:28:12,080 --> 00:28:18,400 because it's enough to have a small sensor. So it's cheap and you can measure 282 00:28:18,400 --> 00:28:25,280 very precisely on specific spots. And on the other hand, of course, the conditions 283 00:28:25,280 --> 00:28:29,440 of the object influence the measurement a lot. So, for example, if there's some 284 00:28:29,440 --> 00:28:34,560 additional paint on top, the alpha particles might not make it through. But 285 00:28:34,560 --> 00:28:40,560 in most of these kind of samples, alpha radiation actually makes it through the 286 00:28:40,560 --> 00:28:46,800 top, a transparent paint layer. In terms of gamma spectrometry, you would usually 287 00:28:46,800 --> 00:28:51,760 have these huge and really expensive sensors. And then the advantage, of 288 00:28:51,760 --> 00:28:56,800 course, is that you can measure, regardless of your object, you don't 289 00:28:56,800 --> 00:29:01,040 really need to prepare the object a lot. You might want some lead shielding around 290 00:29:01,040 --> 00:29:06,400 it. That's again, expensive, but you can do it. You can improve the measurement 291 00:29:06,400 --> 00:29:14,000 like that. And it's basically costly because the sensor is quite expensive. 292 00:29:14,000 --> 00:29:19,680 Vice versa in the set setup for 15 to 30 euro. You have everything you need and 293 00:29:19,680 --> 00:29:28,160 here you're looking at several hundred to several thousand euros. OK, now measuring 294 00:29:28,160 --> 00:29:34,880 I have to be a bit quicker now, I noticed. So I talked about the potassium 295 00:29:34,880 --> 00:29:39,440 salt. There's also fertilizer based on potassium baking powder. Uranium glass is 296 00:29:39,440 --> 00:29:44,800 quite nice. You can find that easily on flea markets. Often also old radium 297 00:29:44,800 --> 00:29:50,080 watches. Here's another example of a uranium glaze, the kitchen tile in this 298 00:29:50,080 --> 00:29:54,400 case, this was actually in the kitchen. So the chances are that you at home find 299 00:29:54,400 --> 00:29:58,240 actually some of those things in the cupboards of your parents or your 300 00:29:58,240 --> 00:30:01,840 grandparents. It is an example of thoriated glass, which has this 301 00:30:01,840 --> 00:30:08,400 distinctive brownish color, which actually is from the radiation. And a nice little 302 00:30:08,400 --> 00:30:12,720 experiment that I can really recommend you to look up is radioactive balloon 303 00:30:12,720 --> 00:30:17,920 experiment. Here, you charge the balloon electrostaticly and then it would catch 304 00:30:17,920 --> 00:30:21,840 polonium from the air. And it's really great. You basically get a radioactive 305 00:30:21,840 --> 00:30:30,803 balloon after it was just left for 15 minutes in a normal regular room. OK, now 306 00:30:30,803 --> 00:30:36,928 the last kind of context of all of this to end this presentation, I want to 307 00:30:36,928 --> 00:30:43,280 quickly remind how important these silicon detectors are for places like CERN. It's a 308 00:30:43,280 --> 00:30:48,815 cross-section of the ATLAS detector. And here you have basically the area where the 309 00:30:48,815 --> 00:30:53,950 collisions happen in the ATLAS detector. So this is just a fraction of a meter. And 310 00:30:53,950 --> 00:31:02,049 you have today 50 to 100 head on collisions of two protons happening every 25 311 00:31:02,049 --> 00:31:08,380 nanoseconds. Not right now, but soon again, machines will be started again next 312 00:31:08,380 --> 00:31:15,112 year. And you also can, by the way, build a similar project which has a slightly 313 00:31:15,112 --> 00:31:19,492 different name. It's called Build Your Own Particle Detector. This is Atlas and made 314 00:31:19,492 --> 00:31:25,210 out of LEGO. And on this website, you find a nice plan, how to build or ideas, 315 00:31:25,210 --> 00:31:32,504 how to build it from LEGO to better visualize the size and interact more with 316 00:31:32,504 --> 00:31:38,434 particle physics. In case of the CMS detector. This is the second biggest 317 00:31:38,434 --> 00:31:43,648 detector at CERN. Here you see nicely that in the middle, at the core of the 318 00:31:43,648 --> 00:31:49,362 collision, you have many, many pixel and microstrip detectors which are made of 319 00:31:49,362 --> 00:31:59,464 silicon. And these are actually 16 m² of silicon pixel detectors and 200m² of 320 00:31:59,464 --> 00:32:04,870 microstrip detectors also made of silicon. So without basically that silicon 321 00:32:04,870 --> 00:32:10,649 technology modern detectors wouldn't work because this fine segmentation is really 322 00:32:10,649 --> 00:32:16,611 required to distinguish all of these newly created particles as a result of the 323 00:32:16,611 --> 00:32:24,609 collision. So to summarize the website is on GitHub, there is really this big wiki, 324 00:32:24,609 --> 00:32:29,349 which you should have a look at, and there's a gallery of pictures from users. 325 00:32:29,349 --> 00:32:34,307 There's some simulation software that I used as well. I didn't develop it, but I 326 00:32:34,307 --> 00:32:38,920 wrote how to use it because the spectra can sometimes be difficult to interpret. 327 00:32:38,920 --> 00:32:44,440 And there's a new discussion forum that I would really appreciate if some of you had 328 00:32:44,440 --> 00:32:49,648 some discussions there on GitHub. And most of the things I saw today are actually 329 00:32:49,648 --> 00:32:54,594 written in detail in a scientific article, which is open access, of course. And I 330 00:32:54,594 --> 00:33:00,198 want to highlight two related citizen science projects on the one hand, as the 331 00:33:00,198 --> 00:33:07,382 safecast, which is about a large, nice, sensitive Geiger-Müller based detector 332 00:33:07,382 --> 00:33:12,640 that has the GPS and people upload their measurements there. This is quite nice. 333 00:33:12,640 --> 00:33:17,318 And also opengeiger is another website, mostly German content, but also some of it 334 00:33:17,318 --> 00:33:23,412 is English, that also uses diode detectors, showed many nice places. He 335 00:33:23,412 --> 00:33:29,971 calls it Geiger caching, places around the world where you can measure something, 336 00:33:29,971 --> 00:33:35,032 some old mines, things like this. And if you want updates, I would propose to 337 00:33:35,032 --> 00:33:40,156 follow me on Twitter. I'm right now writing up two other articles with more 338 00:33:40,156 --> 00:33:46,889 ideas for measurements and some of the things you have seen today. Thanks a lot. 339 00:33:50,949 --> 00:33:57,840 Herald: Well, thanks a lot, Oliver. I hope everyone can hear me now again. Yes, 340 00:33:57,840 --> 00:34:02,880 thanks for mentioning the citizen science project as well. It's really cool I think. 341 00:34:02,880 --> 00:34:09,840 We do have a few minutes for the Q&A and also a lot of questions coming up in our 342 00:34:09,840 --> 00:34:18,240 instance at the IRC. So the first question was, can you talk a bit more about the SNR 343 00:34:18,240 --> 00:34:24,000 of the system? Did you pick particular resistor values and or Opamps to optimize 344 00:34:24,000 --> 00:34:29,280 for noise? Was it a problem? Oliver: Yeah, so noise is the big 345 00:34:29,280 --> 00:34:36,880 issue here. Basically, the amplifier is one I found that this around four, four 346 00:34:36,880 --> 00:34:45,040 euros, trying to find the slide. Yeah, you have to look it up on GitHub to the 347 00:34:45,040 --> 00:34:49,600 amplifier type, but this is the most important one. And then actually the 348 00:34:49,600 --> 00:34:54,800 resistors, here, the resistance in the first stage, sorry, the capacitors is the 349 00:34:54,800 --> 00:34:59,200 second important thing. They should be really small since I'm limited here with 350 00:34:59,200 --> 00:35:07,520 hand soldarable capacitors. Basically I choose the one that were just still 351 00:35:07,520 --> 00:35:11,200 available, let's say, and this is basically what is available is basically a 352 00:35:11,200 --> 00:35:15,840 10 pF capacitor. If you put two of them, one after another, you half the 353 00:35:15,840 --> 00:35:20,800 capacitance, so you get five. And this, by the way, is also then the capacitor. So I 354 00:35:20,800 --> 00:35:29,280 kind of tried to keep the same resistor values as much as possible, and 355 00:35:29,280 --> 00:35:32,720 here at the output, for example, this is to adjust the output signal for a 356 00:35:32,720 --> 00:35:37,680 microphone input in the alpha spectrometer, I changed the values quite a 357 00:35:37,680 --> 00:35:43,440 bit to make a large pulse. But, yeah, it's basically playing with the time 358 00:35:43,440 --> 00:35:47,670 constants of this network and this network. 359 00:35:49,425 --> 00:35:56,000 Herald: All right, I hope that answers for the person. Yeah, but people can get a 360 00:35:56,000 --> 00:36:02,480 contact to you right after the show maybe as well. So there's another question. Have 361 00:36:02,480 --> 00:36:12,400 you considered using an I²S Codec with a Raspberry Pi? radiation H80 should be 362 00:36:12,400 --> 00:36:17,120 almost no set up and completely repeatable. So last ones are for comment. 363 00:36:19,520 --> 00:36:25,280 Oliver: I don't know that component, but, yeah, as I said, using a sound card, it's 364 00:36:25,280 --> 00:36:31,280 actually quite straightforward. But of course there's many ways to get fancy. 365 00:36:31,280 --> 00:36:35,440 And this is really this should actually attract teachers and high school students 366 00:36:35,440 --> 00:36:41,040 as well, this project. So this is one of the main reasons why certain technologies 367 00:36:41,040 --> 00:36:45,399 have been chosen, rather simple than, let's say, fancy. 368 00:36:45,399 --> 00:36:51,612 Herald: Yeah, so it should work with a lot of people, I guess, and one another 369 00:36:51,612 --> 00:36:58,169 question was how consistent are the sound cards? Did you find the same calibration 370 00:36:58,169 --> 00:37:04,733 worked the same with several of them? Oliver: So if you want to use my 371 00:37:04,733 --> 00:37:11,701 calibration, you should really buy this two dollar card from eBay, CM108. I 372 00:37:11,701 --> 00:37:20,620 haven't seen a big difference from card to card in this one. But of course, like from 373 00:37:20,620 --> 00:37:25,790 one computer to the mobile phone, it's a huge difference in input, sensitivity and 374 00:37:25,790 --> 00:37:30,782 noise. And it's very difficult to reuse the calibration in this case. But you 375 00:37:30,782 --> 00:37:39,344 still can count particles and the electron detector is anyway, um, mostly it actually 376 00:37:39,344 --> 00:37:43,124 just makes sense for counting because the electrons are not completely absorbed. So 377 00:37:43,124 --> 00:37:47,526 you get an energy information, but it's not the complete energy of the electron. 378 00:37:47,526 --> 00:37:52,971 So yeah, you could use it for x rays, but then you need an x ray machine. So yeah. 379 00:37:52,971 --> 00:37:58,685 Herald: Who doesn't need an x ray machine, right? *laugs* So maybe one question I 380 00:37:58,685 --> 00:38:05,123 have, because I'm not very familiar with the tech stuff, but what actually can be 381 00:38:05,123 --> 00:38:11,881 done with it right in the field. So you mentioned some working with teachers with 382 00:38:11,881 --> 00:38:17,523 these detectors? What have you done with that in the wild so to say? 383 00:38:17,523 --> 00:38:23,800 Oliver: So what's quite nice is you can characterize stones with it, for example. 384 00:38:23,800 --> 00:38:29,840 So since you can connect it to a smartphone this is completely mobile and 385 00:38:29,840 --> 00:38:34,379 it goes quite well in combination with a Geiger counter in this case. So with a 386 00:38:34,379 --> 00:38:38,440 Geiger counter, you just look around, where are some hot spots and then you can 387 00:38:38,440 --> 00:38:44,665 go closer with the alpha spectrometer and actually be sure that there is some traces 388 00:38:44,665 --> 00:38:51,883 of thorium or uranium on the stone, for example. Or in this type of ceramic, these 389 00:38:51,883 --> 00:38:58,952 old ceramics, you can go to the flea market and just look for these very bright 390 00:38:58,952 --> 00:39:04,310 red ceramics and measure them on the spot and then decide which one to buy. 391 00:39:04,310 --> 00:39:12,072 Herald: OK, so that's what I'm going to do with it. Thanks for for highlighting a bit 392 00:39:12,072 --> 00:39:18,846 the practical side, I think it's really cool to educate people about scientific 393 00:39:18,846 --> 00:39:25,734 things as well. Another question from the IRC. Didn't you have problems with common 394 00:39:25,734 --> 00:39:30,999 mode rejection by connecting the device through the sound card? If yes have you 395 00:39:30,999 --> 00:39:38,345 tried to do a AD conversion digitization on the bord itself already? Transfer 396 00:39:38,345 --> 00:39:42,440 transfer wire SP dif? Oliver: Yeah, so, of course, I mean, this 397 00:39:42,440 --> 00:39:48,154 is the thing to do, if you want to make a like a super stable, rock solid 398 00:39:48,154 --> 00:39:54,224 measurement device, but it is really expensive. I mean, we are looking here at 399 00:39:54,224 --> 00:40:00,837 15 euros and yeah, that's the reason to have this separate soundcard just to 400 00:40:00,837 --> 00:40:08,206 enable with some very low resources to do this. But I'm looking for these pulses. So 401 00:40:08,206 --> 00:40:15,660 this common mode rejection is a problem. And also this is kind of Überschwinger - 402 00:40:15,660 --> 00:40:22,610 I'm missing the English term. This is kind of oscillations here. If you design a 403 00:40:22,610 --> 00:40:27,654 specific analog to digital conversion, of course, you would take all of that into 404 00:40:27,654 --> 00:40:32,671 account and it wouldn't happen. But here this happens because the circuit can never 405 00:40:32,671 --> 00:40:38,097 be exactly optimal for certain soundcard input. It will always be some mismatch of 406 00:40:38,097 --> 00:40:44,508 impedances and. Herald: All right, so maybe these special 407 00:40:44,508 --> 00:40:52,000 technical issues and details, this could be something you could discuss with Oliver 408 00:40:52,000 --> 00:41:00,112 on Twitter of maybe Oliver or want to join the IRC room for your talk as well. People 409 00:41:00,112 --> 00:41:07,120 were very engaged during your talk. So is this always a good sign. In that sense I'd 410 00:41:07,120 --> 00:41:14,680 say thank you for being part of this first remote chaos experience. Thanks again for 411 00:41:14,680 --> 00:41:21,433 for your talk and for taking the time and yeah, best for you and enjoy the rest of 412 00:41:21,433 --> 00:41:28,474 the conference of the Congress and a warm round of virtual applause and big thank 413 00:41:28,474 --> 00:41:33,024 you to you, Oliver. Oliver: Thanks, I will join the chat room 414 00:41:33,024 --> 00:41:34,553 right now. 415 00:41:34,553 --> 00:41:39,272 *rc3 postrol music* 416 00:41:39,272 --> 00:42:14,000 Subtitles created by c3subtitles.de in the year 2021. Join, and help us!