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{
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"text": "<i>rc3 prerol music</i>",
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{
"start": 13630,
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"text": "Herald: All right, fellow creatures, to be<br>honest, I never thought that I would be",
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"position": 2
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{
"start": 19840,
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"text": "introducing a talk on measuring<br>radioactivity like ever in my life, but",
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{
"start": 25440,
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"text": "then again, considering the world stage,<br>current state at large, it might be not",
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},
{
"start": 30480,
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"text": "such a bad idea to be prepared for these<br>things. Right? And gladly, our next",
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{
"start": 35600,
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"text": "speaker, Oliver Keller, is an expert in<br>detecting radioactive stuff. Oliver is a",
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{
"start": 42000,
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"text": "physicist and works at one of the most<br>prominent nerd happy places. The CERN",
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{
"start": 47040,
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"text": "since 2013 is also doing a PhD project<br>about novel instruments and experiments on",
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{
"start": 53760,
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"text": "natural radioactivity at the University of<br>Geneva and to even more to add even more",
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"position": 9
},
{
"start": 60800,
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"text": "C3 pizzazz. Oliver is active in the open<br>science community and passionate about",
"meta": {
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},
"position": 10
},
{
"start": 66480,
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"text": "everything open source. All that sounds<br>really cool to me. So without further ado,",
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"position": 11
},
{
"start": 72960,
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"text": "let's give a warm, virtual welcome to<br>Oliver and let's hear what he has to say",
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"position": 12
},
{
"start": 78400,
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"text": "about measuring radioactivity with using<br>low cost silicon sensors. Oliver, the",
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"position": 13
},
{
"start": 84800,
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"text": "stream is yours.",
"meta": {
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{
"start": 88070,
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"text": "Oliver: Thanks. That was a very nice<br>introduction. I'm really happy to have the",
"meta": {
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},
"position": 15
},
{
"start": 92560,
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"text": "chance to present here. I'm a member since<br>quite some years and this is my first CCC",
"meta": {
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},
"position": 16
},
{
"start": 98310,
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"text": "talk, so I'm quite excited. Yeah, you can<br>follow me on Twitter or I'm also on",
"meta": {
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"region": null
},
"position": 17
},
{
"start": 104438,
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"text": "Mastodon, not so active, and most of my<br>stuff is on GitHub. OK, so what will we",
"meta": {
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},
"position": 18
},
{
"start": 110156,
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"text": "talk about in this talk? I'll give you a<br>short overview, also about the",
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{
"start": 115695,
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"text": "radioactivity, because yeah, it's a topic<br>with many different details and then we",
"meta": {
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},
"position": 20
},
{
"start": 122035,
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"text": "will look at the detector more in detail<br>and how that works in terms of the physics",
"meta": {
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"region": null
},
"position": 21
},
{
"start": 128183,
"end": 133160,
"text": "behind it and the electronics. And then<br>finally, we look at things that can be",
"meta": {
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},
"position": 22
},
{
"start": 133160,
"end": 139156,
"text": "measured, how the measurement actually<br>works, what are interesting objects to",
"meta": {
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},
"position": 23
},
{
"start": 139156,
"end": 148122,
"text": "check and how this relates to silicon<br>detectors being used at CERN. So the",
"meta": {
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"region": null
},
"position": 24
},
{
"start": 148122,
"end": 153400,
"text": "project is on GitHub called DIY Particle<br>Detector. It's an electronic design, which",
"meta": {
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},
"position": 25
},
{
"start": 153400,
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"text": "is open hardware. There's a wiki with lots<br>of further details for building and for",
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},
"position": 26
},
{
"start": 159437,
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"text": "troubleshooting. There is a little web<br>browser tool I will show later, briefly,",
"meta": {
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"region": null
},
"position": 27
},
{
"start": 165363,
"end": 172115,
"text": "and there are scripts to record and nicely<br>plot the measurements. Those scripts are",
"meta": {
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},
"position": 28
},
{
"start": 172115,
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"text": "BSD-licensed and written in Python. There<br>are two variants of this detector. One is",
"meta": {
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"region": null
},
"position": 29
},
{
"start": 178056,
"end": 183094,
"text": "called electron detector, the other one<br>alpha spectrometer. They use the same",
"meta": {
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"region": null
},
"position": 30
},
{
"start": 183094,
"end": 188471,
"text": "circuit board, but one is using four<br>diodes, the other one one photodiode...",
"meta": {
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},
"position": 31
},
{
"start": 188471,
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"text": "There's a small difference between them,<br>but in general it's pretty similar. But",
"meta": {
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},
"position": 32
},
{
"start": 194180,
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"text": "the electron detector is much easier to<br>build and much easier to get started",
"meta": {
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"position": 33
},
{
"start": 198509,
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"text": "using. Then you have complete part lists<br>and even a complete kit can be bought on",
"meta": {
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"region": null
},
"position": 34
},
{
"start": 205678,
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"text": "kitspace.org, which is an open hardware<br>community repository, and I really",
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},
"position": 35
},
{
"start": 211638,
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"text": "recommend you to check it out. It's a<br>great community platform and everyone can",
"meta": {
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},
"position": 36
},
{
"start": 216366,
"end": 224105,
"text": "register their own GitHub project quite<br>easily. Now, this is a particle detector",
"meta": {
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"region": null
},
"position": 37
},
{
"start": 224105,
"end": 231025,
"text": "in a tin box, so you can use the famous<br>Altoids tin box or something for Swiss",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 38
},
{
"start": 231025,
"end": 237342,
"text": "chocolate, for example. You can see it's<br>rather small, the board about the size of",
"meta": {
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"region": null
},
"position": 39
},
{
"start": 237342,
"end": 243615,
"text": "a nine volt block battery. And then you<br>need, in addition, about 20 resistors,",
"meta": {
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"region": null
},
"position": 40
},
{
"start": 243615,
"end": 250356,
"text": "capacitors and these silicon<br>diodes plus an operational amplifier,",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 41
},
{
"start": 250356,
"end": 255117,
"text": "which is this little chip here, this<br>little black chip here on the right side,",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 42
},
{
"start": 255117,
"end": 259520,
"text": "you can see is all old school large<br>components. This is on purpose, so it's",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 43
},
{
"start": 259520,
"end": 264635,
"text": "easy to soldier for complete electronic<br>beginners. And this by the way, this",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 44
},
{
"start": 264635,
"end": 270176,
"text": "picture is already one user of this<br>project who posted their own build on",
"meta": {
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"region": null
},
"position": 45
},
{
"start": 270176,
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"text": "Twitter. OK, so natural radioactivity. So<br>I would say it's a story of many",
"meta": {
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"region": null
},
"position": 46
},
{
"start": 278084,
"end": 284080,
"text": "misconceptions. Let's imagine we are this<br>little stick figure here on the ground.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 47
},
{
"start": 284080,
"end": 290644,
"text": "Below us we have uranium and thorium. We<br>also have Potassium-40 in the ground and",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 48
},
{
"start": 290644,
"end": 296809,
"text": "Potassium-40 is is pretty specific and<br>peculiar. It actually makes all of us a",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 49
},
{
"start": 296809,
"end": 305138,
"text": "little bit radioactive. Every human has<br>about 4000 to 5000 radioactive decays",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 50
},
{
"start": 305138,
"end": 310258,
"text": "every second because of the natural<br>potassium and natural potassium comes with",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 51
},
{
"start": 310258,
"end": 314979,
"text": "a radioactive isotope, which is just<br>everywhere, it's in bananas. But it's also",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 52
},
{
"start": 314979,
"end": 320320,
"text": "in us because we need it for our body<br>chemistry. It's really important and even",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 53
},
{
"start": 320320,
"end": 326224,
"text": "some of those decays are even<br>producing anti-matter. So how cool is",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 54
},
{
"start": 326224,
"end": 332432,
"text": "that? OK, so what would we be measuring on<br>the on ground? Well, there could be some",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 55
},
{
"start": 332432,
"end": 339429,
"text": "gamma rays or electrons. Those are from<br>beta-decays. Or from the Uranium, there is",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 56
},
{
"start": 339429,
"end": 346956,
"text": "one radionuclide appearing in the decay<br>chain, which is called Radon, and Radon is",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 57
},
{
"start": 346956,
"end": 353320,
"text": "actually a gas. So from the ground the<br>Radon can diffuse upwards and travel with",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 58
},
{
"start": 353320,
"end": 361137,
"text": "air and spread around. So it's a bit like<br>a vehicle for radioactivity from",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 59
},
{
"start": 361137,
"end": 368183,
"text": "the ground to spread to other places. And<br>that Radon would decay with alpha",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 60
},
{
"start": 368183,
"end": 374148,
"text": "particles producing electrons and beta-<br>decays and also gamma radiation further",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 61
},
{
"start": 374148,
"end": 381683,
"text": "down in the decay chain. So just to<br>recapitulate, I've said it already twice,",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 62
},
{
"start": 381683,
"end": 389828,
"text": "so alpha particles are actually helium<br>nuclei, so it's just two protons and two",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 63
},
{
"start": 389828,
"end": 398150,
"text": "neutrons and the electrons are missing.<br>And in beta decay basically one neutron is",
"meta": {
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},
"position": 64
},
{
"start": 398150,
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"text": "transformed into a proton and an electron.<br>And there's also an electron-anti-neutrino",
"meta": {
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"region": null
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"position": 65
},
{
"start": 403095,
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"text": "generated. But this is super hard to<br>measure. So we're not measuring those.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 66
},
{
"start": 407694,
"end": 414524,
"text": "Mostly we will be measuring electrons from<br>beta-decays. That's why you see all these",
"meta": {
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"region": null
},
"position": 67
},
{
"start": 414524,
"end": 420334,
"text": "little e's indicating betadecays. Ok, if<br>you would go to the hospital here on the",
"meta": {
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"region": null
},
"position": 68
},
{
"start": 420334,
"end": 428965,
"text": "left side, we would probably find some x<br>rays from checking our bones or something",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 69
},
{
"start": 428965,
"end": 436484,
"text": "like this, or even gamma rays or alpha<br>particles being used in treatments or very",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 70
},
{
"start": 436484,
"end": 442814,
"text": "modern even proton beams are sometimes<br>generated for medical applications. Now,",
"meta": {
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"region": null
},
"position": 71
},
{
"start": 442814,
"end": 448179,
"text": "here on the right side, if you go close to<br>a nuclear power plant, we probably measure",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 72
},
{
"start": 448179,
"end": 453886,
"text": "nothing unless there's a problem in this<br>case, most likely we would find some gamma",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 73
},
{
"start": 453886,
"end": 460639,
"text": "radiation. But only if there is a problem.<br>OK, and then actually that's not the whole",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 74
},
{
"start": 460639,
"end": 466886,
"text": "story. This is terrestrial radiation. But<br>we also have radiation coming from",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 75
},
{
"start": 466886,
"end": 470863,
"text": "upwards, showering down on us every<br>minute, and there's actually nothing we",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 76
},
{
"start": 470863,
"end": 476571,
"text": "can do against it. So protons are<br>accelerated from in the universe.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 77
},
{
"start": 476571,
"end": 482416,
"text": "Basically, the biggest particle<br>accelerator nature has. And once they hit",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 78
},
{
"start": 482416,
"end": 490159,
"text": "our atmosphere they break apart into less<br>energetic particles and it's many of them.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 79
},
{
"start": 490159,
"end": 495850,
"text": "So in the first stage there's lots of pions<br>generated and also neutrons. But neutrons",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 80
},
{
"start": 495850,
"end": 501625,
"text": "are really hard to measure, so I'll ignore<br>them for most of the talk. Then those",
"meta": {
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"region": null
},
"position": 81
},
{
"start": 501625,
"end": 509045,
"text": "pions can decay into gamma rays and then<br>trigger a whole chain of positron electron",
"meta": {
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"region": null
},
"position": 82
},
{
"start": 509045,
"end": 514877,
"text": "decays, which again create gamma rays and<br>so forth. And this goes actually the whole",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 83
},
{
"start": 514877,
"end": 520183,
"text": "way down to the earth. We will have a<br>little bit of that on the sea level.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 84
},
{
"start": 520183,
"end": 526040,
"text": "And the other more known part of<br>atmospheric radiation is actually muons.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 85
},
{
"start": 526040,
"end": 532374,
"text": "So some pions decay into muons, which is<br>kind of a heavy electron and also",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 86
},
{
"start": 532374,
"end": 537639,
"text": "neutrinos. But neutrinos are, again, very<br>hard to measure. So I'll ignore them for",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 87
},
{
"start": 537639,
"end": 543464,
"text": "most of this talk. And if you look here on<br>the right side on this altitude scale,",
"meta": {
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"region": null
},
"position": 88
},
{
"start": 543464,
"end": 548420,
"text": "you'll see an airplane would be basically<br>traveling where most of the atmospheric",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 89
},
{
"start": 548420,
"end": 553323,
"text": "radiation is produced. And this is why if<br>you go on such an airplane, you have",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 90
},
{
"start": 553323,
"end": 559879,
"text": "actually several times more radiation<br>in there than here on earth. And, of",
"meta": {
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"region": null
},
"position": 91
},
{
"start": 559879,
"end": 564210,
"text": "course, on the ground, it also depends<br>where you are. There are different amounts",
"meta": {
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},
"position": 92
},
{
"start": 564210,
"end": 570140,
"text": "of uranium and thorium in the ground and<br>this is just naturally there. So but it",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 93
},
{
"start": 570140,
"end": 576773,
"text": "depends on the geology, of course. OK, so<br>I've talked quite a bit about radiation,",
"meta": {
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"region": null
},
"position": 94
},
{
"start": 576773,
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"text": "and I'm saying I want to use silicon to<br>detect it. So what radiation exactly?",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 95
},
{
"start": 583045,
"end": 588514,
"text": "Maybe. Let's let's take a step back and<br>think about what we know maybe from",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 96
},
{
"start": 588514,
"end": 594840,
"text": "school. So we have this rainbow for<br>visible light. Right. This is in terms of",
"meta": {
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"region": null
},
"position": 97
},
{
"start": 594840,
"end": 603000,
"text": "wavelength. We have 800 to 400 nanometers<br>spanning from the infrared/red area to all",
"meta": {
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"region": null
},
"position": 98
},
{
"start": 603000,
"end": 612857,
"text": "the green to blue and into the violet. And<br>lower down those wavelengths or let's say",
"meta": {
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"region": null
},
"position": 99
},
{
"start": 612857,
"end": 617744,
"text": "bigger millimeter waves, meter waves and<br>even kilometer, that would be radio waves,",
"meta": {
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"region": null
},
"position": 100
},
{
"start": 617744,
"end": 622370,
"text": "radio frequencies for our digital<br>communication systems, wi-fi, mobile",
"meta": {
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"region": null
},
"position": 101
},
{
"start": 622370,
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"text": "devices and so forth. But I want to look<br>actually more towards the right because",
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"start": 627720,
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"text": "that's what we are measuring with these<br>detectors. It's shorter wavelength, which",
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"start": 633441,
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"text": "actually means higher energy. So on the<br>right side, we would be having ultraviolet",
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"start": 639797,
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"text": "radiation, which is kind of at the border<br>to what we can measure. And these 800 to",
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{
"start": 647328,
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"text": "400nm translate into 1.5 to 3 eV, which is<br>a unit that particle physicists really",
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"start": 654085,
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"text": "prefer because it basically relates the<br>energy of an electron after it has been",
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"position": 107
},
{
"start": 662931,
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"text": "accelerated by 1 Volt and makes it<br>much easier to work with nuclear",
"meta": {
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},
"position": 108
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{
"start": 669270,
"end": 675385,
"text": "particle physics, because everything, all<br>the energy is always related to an",
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"position": 109
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{
"start": 675385,
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"text": "electron. And this energy, this formula<br>here is just a reminder that the",
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{
"start": 681208,
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"text": "wavelengths can be always converted into<br>energy and it's inversely proportional. So",
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"position": 111
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{
"start": 685937,
"end": 690551,
"text": "wavelength increases to the left and the<br>energy to right. And if you increase",
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"position": 112
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{
"start": 690551,
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"text": "energy more from from the visible range,<br>so let's say thousands of electron volts,",
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{
"start": 695962,
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"text": "then we arrive here. Millions - mega<br>electron volts, even GeV. And there is now",
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"position": 114
},
{
"start": 703400,
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"text": "a pretty important distinction between<br>those two areas, and that is the right one",
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"position": 115
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{
"start": 711810,
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"text": "is ionizing radiation and the left one is<br>non ionizing radiation. UV is a little bit",
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"position": 116
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{
"start": 718020,
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"text": "in the middle of that. So some parts of<br>the UV spectrum can be ionizing. It also",
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{
"start": 723150,
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"text": "depends a lot on the material that the<br>radiation is interacting with. For these",
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{
"start": 729567,
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"text": "detectors I'm talking about today and<br>alpha, beta, gamma radiation, this is all",
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{
"start": 733820,
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"text": "ionizing, so some examples, lowest energy<br>on the lower spectrum would be x rays than",
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{
"start": 741326,
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"text": "electrons, gamma rays from radioactive<br>nuclides that already talked about in the",
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},
"position": 121
},
{
"start": 749440,
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"text": "previous slide, alpha particles, and that<br>muons from the atmosphere would be more on",
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"position": 122
},
{
"start": 754877,
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"text": "the GeV range and so forth. And for these<br>higher energies, of course, you need",
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"position": 123
},
{
"start": 760302,
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"text": "something like the LHC to accelerate<br>particles to really high energies. And",
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},
"position": 124
},
{
"start": 766184,
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"text": "then you can even access the TeV regime.<br>OK, silicon diodes. What kind of silicon",
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},
"position": 125
},
{
"start": 776415,
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"text": "diodes? I'm using in this project, low<br>local silicon pin diodes, one is called",
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},
"position": 126
},
{
"start": 782592,
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"text": "BPW34 it's manufactured from Vishay or<br>Osram, costs about 50 cents. So that's what",
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},
"position": 127
},
{
"start": 789034,
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"text": "I mean with low cost. There's another one<br>called BPX61 from Osram. It's quite a bit",
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},
"position": 128
},
{
"start": 795167,
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"text": "more expensive. This is the lower one here<br>on the right. It has a metal case, which",
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},
"position": 129
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{
"start": 799555,
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"text": "is the main reason why it's more<br>expensive. But it's quite interesting",
"meta": {
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},
"position": 130
},
{
"start": 803451,
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"text": "because that one we can use for the alpha<br>detector. If you look closely, there is a",
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"position": 131
},
{
"start": 808523,
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"text": "glass on top, but we can remove that. We<br>have a sensitive area. So this chip is",
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"position": 132
},
{
"start": 815800,
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"text": "roughly 7mm² large and it has a thickness,<br>a sensitive thickness of about 50",
"meta": {
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"position": 133
},
{
"start": 823076,
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"text": "micrometer, which is not a lot. So it's<br>basically the half of the width of a human",
"meta": {
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},
"position": 134
},
{
"start": 829681,
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"text": "hair. And in total, it's a really small,<br>sensitive volume. But it's it's enough to",
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},
"position": 135
},
{
"start": 835401,
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"text": "measure something. And just as a reminder,<br>how much of gamma rays or X-rays we will",
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},
"position": 136
},
{
"start": 842200,
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"text": "detect with this, not a lot because it's<br>high, energetic photon radiation kind",
"meta": {
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},
"position": 137
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{
"start": 849057,
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"text": "doesn't interact very well in any kind of<br>matter. And because a sensitive area is so",
"meta": {
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},
"position": 138
},
{
"start": 855471,
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"text": "thin, it would basically permeate through<br>it and most of the times not interact and",
"meta": {
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},
"position": 139
},
{
"start": 861399,
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"text": "doesn't make a signal. OK, what's really<br>important, since we don't want to measure",
"meta": {
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},
"position": 140
},
{
"start": 868400,
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"text": "light, we have to shield light away. We<br>need to block all of the light, that means",
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},
"position": 141
},
{
"start": 875120,
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"text": "easiest way to do it is to put it in a<br>metal case. There is electromagnetically",
"meta": {
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},
"position": 142
},
{
"start": 880080,
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"text": "shielded and completely protected from<br>light as well. Electromagnetic radiation",
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},
"position": 143
},
{
"start": 884880,
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"text": "or radiowaves can also influence these<br>detectors because they are super",
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},
"position": 144
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"start": 889840,
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"text": "sensitive. So this sould be a complete<br>Faraday cage, complete metal structure",
"meta": {
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},
"position": 145
},
{
"start": 895360,
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"text": "around it. There's a lot of hints and tips<br>how to achieve that on the wiki on the on",
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},
"position": 146
},
{
"start": 903120,
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"text": "the GitHub of this project. OK, let's<br>think about one of those PIN diodes,",
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"position": 147
},
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"start": 910080,
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"text": "normally there is one part in the<br>silicon which is n-doped",
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"start": 918720,
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"text": "negatively doped, and the other part<br>usually, which is positively dropped. And",
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"position": 149
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"start": 923920,
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"text": "then you arrive at a simple so called p-n-<br>junction, which is a regular",
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"start": 928080,
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"text": "semiconducting diode. Now, pin diodes add<br>another layer of so-called intrinsic",
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},
"position": 151
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{
"start": 933840,
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"text": "layer, here shown with the i. And that<br>actually is the main advantage. Why this",
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{
"start": 941920,
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"text": "kind of detector works quite well and have<br>a relatively large sensitive Sigma's. So",
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"position": 153
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{
"start": 950800,
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"text": "if you think about, let's say, a photon<br>from an x ray or gamma-decay or an",
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"start": 958320,
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"text": "electron hitting the sensor. So by the<br>way, this is a cross-section view from the",
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{
"start": 963920,
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"text": "side, but that doesn't really matter. But<br>let's say they come here from the top into",
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{
"start": 969840,
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"text": "the... into the diode and we're looking<br>at the side then we have actually",
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"position": 157
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"start": 976480,
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"text": "ionization because this is ionizing<br>radiation, so we get free charges in the",
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"position": 158
},
{
"start": 982000,
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"text": "form of electron-hole pairs. So electrons,<br>which here the blue ball and the red",
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"position": 159
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{
"start": 986960,
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"text": "circle would be the holes. And depending<br>on the radiation kind, how this ionization",
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"position": 160
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{
"start": 994240,
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"text": "takes place is quite different, but the<br>result is if you get a signal, it means",
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"start": 999760,
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"text": "there was ionization. Now, if just this<br>would happen, we could not measure",
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"position": 162
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{
"start": 1005520,
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"text": "anything. Those charges would quickly<br>recombine and on the outside of the diode,",
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"position": 163
},
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"start": 1013120,
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"text": "it would be a little signal. But what we<br>can do is we can apply actually a voltage",
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{
"start": 1018720,
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"text": "from the outside. So here we just put a<br>battery. So we have a positive voltage",
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"position": 165
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"start": 1026320,
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"text": "here, a couple of volts. And then what<br>happens is that the electrons would be",
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"position": 166
},
{
"start": 1032000,
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"text": "attracted by the positive voltage and the<br>holes will travel to the negative",
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"start": 1038480,
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"text": "potential. And we end up with a little net<br>current or a small bunch of charges that",
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"position": 168
},
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"start": 1046720,
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"text": "can be measured across the diode as a<br>tiny, tiny current. The sensitive volume",
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},
"position": 169
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{
"start": 1055200,
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"text": "is actually proportional to the voltage,<br>so the more voltage we put, the more the",
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},
"position": 170
},
{
"start": 1061040,
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"text": "bigger is our volume and the more we can<br>actually measure with certain limits, of",
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},
"position": 171
},
{
"start": 1064880,
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"text": "course, because the structure of the pin<br>diode has a maximum thickness just",
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"position": 172
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{
"start": 1069520,
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"text": "according how it is manufactured. And<br>these properties can be estimated with",
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"position": 173
},
{
"start": 1076800,
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"text": "C-V-measurements. So here you see an<br>example of a couple of diodes, a few of",
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},
{
"start": 1082720,
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"text": "the same type. The two that I've<br>mentioned, they're different versions. One",
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"position": 175
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{
"start": 1086240,
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"text": "has a transparent plastic case. One has a<br>black plastic case. Doesn't really matter.",
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"position": 176
},
{
"start": 1091360,
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"text": "You see, basically in all the cases, more<br>or less the same curve. And as you",
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"position": 177
},
{
"start": 1096800,
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"text": "increase the voltage, the capacitance goes<br>down. So it's great and basically shows us",
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"position": 178
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{
"start": 1101760,
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"text": "those silicon chips are very similar, if<br>not exactly the same chip. Those",
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"text": "differences are easily explained by<br>manufacturing variances. And then because",
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"position": 180
},
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"text": "this actually, if you think about it, it<br>looks a bit like a parallel plate",
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"text": "capacitor and actually you can treat it as<br>one. And if you know the capacitance and",
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"text": "the size, the area, you can actually<br>calculate the distance of these two plates",
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},
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"start": 1130240,
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"text": "or basically width or the thickness of the<br>diode. And then we arrive at about 50",
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{
"start": 1138080,
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"text": "micrometer, if you put something like 8 or<br>10 volts. OK, now we have a tiny charge",
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},
{
"start": 1146800,
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"text": "current, now we need to amplify it, so we<br>have a couple of diodes, I'm explaining",
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{
"start": 1151600,
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"text": "now the electron detector, because it's<br>easier. We have four diodes at the input",
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"text": "and this is the symbol for an operational<br>amplifier. There are two of those in the",
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"text": "circuit. The first stage is really the<br>special one. So if you have a particle",
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{
"start": 1165840,
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"text": "striking the diode, we get a little charge<br>current hitting the amplifier. And then we",
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{
"start": 1171200,
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"text": "have here this important feedback<br>circuit. So the output is fed back into",
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"start": 1174880,
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"text": "the input, which in this case makes a<br>negative amplification. And the",
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"start": 1180880,
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"text": "amplification is defined actually by this<br>capacitance here. The resistor has a",
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{
"start": 1186320,
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"text": "secondary role with the small capacitance.<br>It is what makes the output voltage here",
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{
"start": 1191360,
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"text": "large. The smaller the capacitance, the<br>larger the output and it's inverted. Then",
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},
{
"start": 1197200,
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"text": "in the next amplifier step, we just<br>increase the voltage again to a level that",
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{
"start": 1202320,
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"text": "is useful for using it later. But all of<br>the signal quality that has been",
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{
"start": 1208160,
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"text": "achieved in the first stage will stay like<br>that. So signal to noise is defined by the",
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},
{
"start": 1213120,
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"text": "first stage. The second one is just to<br>better adapt it to the input of the",
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"position": 199
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{
"start": 1218880,
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"text": "measurement device that's connected. So<br>here, this is a classic inverting",
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"position": 200
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{
"start": 1224480,
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"text": "amplifier with just these two resistors<br>define the amplification factor. It's very",
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"start": 1229120,
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"text": "simple. It's just a factor of hundred in<br>this case. And so if you think again about",
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{
"start": 1235360,
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"text": "the charge pulse and this, the circuit<br>here is sensitive, starting from about",
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{
"start": 1239760,
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"text": "1000 liberated charges in those diodes as<br>a result from ionization. We get something",
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"start": 1250320,
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"text": "like 320 micro Volt at this first output,<br>and this is a spike that quickly",
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{
"start": 1255920,
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"text": "decreases. Basically these capacitors are<br>charged and quickly discharged with this",
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{
"start": 1261600,
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"text": "resistor and this is what we see here. And<br>then that is amplified again by a factor",
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{
"start": 1267360,
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"text": "of 100. And then we arrive at something<br>like at least 32 mV, which is conveniently",
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"position": 208
},
{
"start": 1274080,
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"text": "a voltage that is compatible with most<br>microphone or headset inputs of computers",
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"position": 209
},
{
"start": 1280000,
"end": 1285600,
"text": "or mobile phones, so that the regular<br>headset here has these four connectors and",
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"position": 210
},
{
"start": 1285600,
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"text": "the last ring actually connects the<br>microphone. The other is ground and reft.",
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},
"position": 211
},
{
"start": 1291520,
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"text": "Left, right for the earbuds. OK, how do we<br>record those pulses? This is an example of",
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},
"position": 212
},
{
"start": 1299360,
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"text": "1000 pulses overlayed and measured on an<br>oscilloscope here. So it's a bit more",
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},
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},
{
"start": 1306400,
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"text": "accurate. You see the deposits a bit<br>better, kind of like the persistence mode",
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"position": 214
},
{
"start": 1312400,
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"text": "of an oscilloscope. And the size of the<br>pulse is proportional to energy that was",
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{
"start": 1318160,
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"text": "absorbed. And the circuit is made in such<br>a way that the width of the pulse is big",
"meta": {
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},
{
"start": 1323680,
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"text": "enough such that regular sampling<br>frequency of a sound card can actually",
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"position": 217
},
{
"start": 1328560,
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"text": "catch it and measure it. Yeah, this is<br>Potassium Salt. This is cut here. This is",
"meta": {
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},
"position": 218
},
{
"start": 1334800,
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"text": "called a low salt in the UK. There is also<br>a german variance, you can also just buy",
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},
"position": 219
},
{
"start": 1338720,
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"text": "it in the pharmacy or in certain organic<br>food stores as a replacement salt.",
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},
"position": 220
},
{
"start": 1346320,
"end": 1353120,
"text": "On the right side is an example from this<br>small Columbite Stone, which has traces of",
"meta": {
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},
"position": 221
},
{
"start": 1353120,
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"text": "uranium on it. And this is measured with<br>the alpha spectrometer. And you see those",
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},
"position": 222
},
{
"start": 1358720,
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"text": "pulses are quite a bit bigger here. We<br>have 50 microseconds and here we have more",
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},
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},
{
"start": 1362640,
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"text": "like one milliseconds of pulse width. Now<br>there's a software on a browser. This is",
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},
"position": 224
},
{
"start": 1372880,
"end": 1380720,
"text": "something I wrote using the Web Audio API<br>and it works on most browsers, best is",
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},
"position": 225
},
{
"start": 1380720,
"end": 1386640,
"text": "Chrome, on iOs, of course, you have to use<br>Safari and that records once you plug the",
"meta": {
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},
"position": 226
},
{
"start": 1386640,
"end": 1393120,
"text": "detector, it records from the input at 48<br>or 44.1kHz the pulses. Here's an example",
"meta": {
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},
"position": 227
},
{
"start": 1393120,
"end": 1398560,
"text": "with the alpha spectrometer circuit, you<br>get these nice large pulses. In case of",
"meta": {
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},
"position": 228
},
{
"start": 1398560,
"end": 1402800,
"text": "the electron detector the pulse is much<br>shorter and you see it, you see the noise",
"meta": {
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},
"position": 229
},
{
"start": 1402800,
"end": 1408880,
"text": "much more amplified. This red line is kind<br>of the minimum level that the pulse needs",
"meta": {
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},
"position": 230
},
{
"start": 1408880,
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"text": "to trigger. This would be better. And<br>that's like the trigger level of an",
"meta": {
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},
"position": 231
},
{
"start": 1412240,
"end": 1418160,
"text": "oscilloscope. And you can set that with<br>those buttons in the browser. You need to",
"meta": {
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"region": null
},
"position": 232
},
{
"start": 1418160,
"end": 1422960,
"text": "find a good value. Of course, if you<br>change your input volume settings, for",
"meta": {
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},
"position": 233
},
{
"start": 1422960,
"end": 1429840,
"text": "example, this will change. So you have to<br>remember which, with which settings it",
"meta": {
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},
"position": 234
},
{
"start": 1429840,
"end": 1435600,
"text": "works well. And it is pulsed, for example,<br>is even oscillating here. So for electron",
"meta": {
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},
"position": 235
},
{
"start": 1435600,
"end": 1441440,
"text": "detector, it's basically nice to count<br>particles. For the alpha detector it's",
"meta": {
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},
"position": 236
},
{
"start": 1441440,
"end": 1446240,
"text": "really the case where the size of the<br>pulse can be nicely evaluated and we can",
"meta": {
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},
"position": 237
},
{
"start": 1446240,
"end": 1451120,
"text": "actually do energy measurements. And these<br>energy measurements can be also called",
"meta": {
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"region": null
},
"position": 238
},
{
"start": 1451120,
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"text": "spectrometry. So if you look closer at<br>these many pulses that have been recorded",
"meta": {
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},
"position": 239
},
{
"start": 1457520,
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"text": "and we find that there is really like much<br>more intensity, which means many more same",
"meta": {
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},
"position": 240
},
{
"start": 1466560,
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"text": "pulses were detected, we can relate it to<br>radium and radon. If we use a reference",
"meta": {
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},
"position": 241
},
{
"start": 1472160,
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"text": "alpha source and I have done this, I have<br>measured the whole circuit with the reference",
"meta": {
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},
"position": 242
},
{
"start": 1475920,
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"text": "sources and provide the calibration on<br>GitHub and you can reuse the GitHub",
"meta": {
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},
"position": 243
},
{
"start": 1481360,
"end": 1487280,
"text": "calibration if you use exactly the same<br>sound settings that I have used for",
"meta": {
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},
"position": 244
},
{
"start": 1487280,
"end": 1493600,
"text": "recording. And for example, these two very<br>weak lines here from two very distinctive",
"meta": {
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},
"position": 245
},
{
"start": 1493600,
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"text": "polonium isotopes from the uranium decay<br>chain. The top part here which is really",
"meta": {
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},
"position": 246
},
{
"start": 1502560,
"end": 1508240,
"text": "dark, corresponds basically in the<br>histogram view to this side on the left,",
"meta": {
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},
"position": 247
},
{
"start": 1508240,
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"text": "which is electrons. Most of these<br>electrons will actually enter the chip and",
"meta": {
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},
"position": 248
},
{
"start": 1512160,
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"text": "leave it without being completely<br>absorbed by it, but alpha particles",
"meta": {
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},
"position": 249
},
{
"start": 1518800,
"end": 1522960,
"text": "interact so strongly that they are<br>completely absorbed within the 50",
"meta": {
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},
"position": 250
},
{
"start": 1522960,
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"text": "micrometers of sensitive volume of these<br>diodes and OK here is a bit difficult to",
"meta": {
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},
"position": 251
},
{
"start": 1529520,
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"text": "see peaks. But the far end of the high<br>energy spectrum, you see two really clear",
"meta": {
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},
"position": 252
},
{
"start": 1535440,
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"text": "peaks and those can only stem from<br>polonium, actually. I mean, we know it's",
"meta": {
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},
"position": 253
},
{
"start": 1540560,
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"text": "uranium and that can only be polonium,<br>which is that isotope that produces the",
"meta": {
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},
"position": 254
},
{
"start": 1546960,
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"text": "most energetic alpha particles and<br>which is natural. And I said, if you use",
"meta": {
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},
"position": 255
},
{
"start": 1556080,
"end": 1559840,
"text": "the same setting like me, you can use it.<br>So the best is if you use actually the",
"meta": {
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"region": null
},
"position": 256
},
{
"start": 1559840,
"end": 1564560,
"text": "same soundcard because they're if you put<br>it to hundred percent input sensitivity,",
"meta": {
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"region": null
},
"position": 257
},
{
"start": 1564560,
"end": 1568880,
"text": "you will have exactly the same result,<br>like in my calibration case. And this",
"meta": {
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"region": null
},
"position": 258
},
{
"start": 1568880,
"end": 1573120,
"text": "soundcard is pretty cheap, but also pretty<br>good. It costs just two dollars and has a",
"meta": {
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"region": null
},
"position": 259
},
{
"start": 1573120,
"end": 1578560,
"text": "pretty range and resolves quite well, 16<br>bits and think, oh, you could do that with",
"meta": {
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"region": null
},
"position": 260
},
{
"start": 1578560,
"end": 1584640,
"text": "Arduino as well, is actually a bit hard to<br>do. A really well defined 16 bit",
"meta": {
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"region": null
},
"position": 261
},
{
"start": 1584640,
"end": 1591280,
"text": "measurement, even at 48 kHz. It's not so<br>easy and this keeps it cheap and kind of",
"meta": {
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"region": null
},
"position": 262
},
{
"start": 1591280,
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"text": "straightforward. And you can have just<br>some Python scripts on the computer to",
"meta": {
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"region": null
},
"position": 263
},
{
"start": 1594960,
"end": 1600960,
"text": "read it out. And this is as a reminder, in<br>order to measure alpha particles, we have",
"meta": {
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"region": null
},
"position": 264
},
{
"start": 1600960,
"end": 1604720,
"text": "to remove the glass here on top of the<br>diode. So I'm doing it just cutting into",
"meta": {
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"region": null
},
"position": 265
},
{
"start": 1604720,
"end": 1610160,
"text": "the metal frame and then the glass breaks<br>away easily. Is not a problem, there's",
"meta": {
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"region": null
},
"position": 266
},
{
"start": 1610160,
"end": 1616800,
"text": "more on that on the wiki. Now we<br>can kind of compare alpha and gamma",
"meta": {
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"region": null
},
"position": 267
},
{
"start": 1616800,
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"text": "spectrometry. Here's an example. This is<br>the uranium glazed ceramics. The red part",
"meta": {
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},
"position": 268
},
{
"start": 1623920,
"end": 1629840,
"text": "is uranium oxide that was used to create<br>this nice red color in the 50s, 60s, 70s.",
"meta": {
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"region": null
},
"position": 269
},
{
"start": 1629840,
"end": 1635040,
"text": "And in the spectrum we have two very<br>distinctive peaks and nothing in the high",
"meta": {
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},
"position": 270
},
{
"start": 1635040,
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"text": "energy regime. Only this low energy range<br>has a signal. And this corresponds",
"meta": {
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},
"position": 271
},
{
"start": 1640800,
"end": 1647920,
"text": "actually to uranium 238 and 234 because<br>they use actually purified uranium. So all",
"meta": {
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},
"position": 272
},
{
"start": 1647920,
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"text": "of the high energy progeny or daughters of<br>uranium, they're not present here because",
"meta": {
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},
"position": 273
},
{
"start": 1653920,
"end": 1658720,
"text": "it was purified uranium. And this<br>measurement doesn't even need vacuum, I",
"meta": {
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"region": null
},
"position": 274
},
{
"start": 1658720,
"end": 1663280,
"text": "put it just like this in a regular box. Of<br>course, if you would have vacuum, you",
"meta": {
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"region": null
},
"position": 275
},
{
"start": 1663280,
"end": 1668400,
"text": "would improve this peaks by a lot. So this<br>widening here to the left, basically, that",
"meta": {
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"region": null
},
"position": 276
},
{
"start": 1668400,
"end": 1675200,
"text": "this peak is almost below the other one.<br>That is due to the natural air at regular",
"meta": {
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"region": null
},
"position": 277
},
{
"start": 1675200,
"end": 1680960,
"text": "air pressure, which already interacts a<br>lot with the particles and absorbs a lot",
"meta": {
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"region": null
},
"position": 278
},
{
"start": 1680960,
"end": 1686960,
"text": "of energy before the particles hit the<br>sensor. So in terms of pros and cons, I",
"meta": {
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"region": null
},
"position": 279
},
{
"start": 1686960,
"end": 1692080,
"text": "would say the small sensor is quite<br>interesting here in an alpha spectrometry",
"meta": {
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"region": null
},
"position": 280
},
{
"start": 1692080,
"end": 1698400,
"text": "because it's enough to have a small<br>sensor. So it's cheap and you can measure",
"meta": {
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"region": null
},
"position": 281
},
{
"start": 1698400,
"end": 1705280,
"text": "very precisely on specific spots. And on<br>the other hand, of course, the conditions",
"meta": {
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"region": null
},
"position": 282
},
{
"start": 1705280,
"end": 1709440,
"text": "of the object influence the measurement a<br>lot. So, for example, if there's some",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 283
},
{
"start": 1709440,
"end": 1714560,
"text": "additional paint on top, the alpha<br>particles might not make it through. But",
"meta": {
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"region": null
},
"position": 284
},
{
"start": 1714560,
"end": 1720560,
"text": "in most of these kind of samples, alpha<br>radiation actually makes it through the",
"meta": {
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"region": null
},
"position": 285
},
{
"start": 1720560,
"end": 1726800,
"text": "top, a transparent paint layer. In terms<br>of gamma spectrometry, you would usually",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 286
},
{
"start": 1726800,
"end": 1731760,
"text": "have these huge and really expensive<br>sensors. And then the advantage, of",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 287
},
{
"start": 1731760,
"end": 1736800,
"text": "course, is that you can measure,<br>regardless of your object, you don't",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 288
},
{
"start": 1736800,
"end": 1741040,
"text": "really need to prepare the object a lot.<br>You might want some lead shielding around",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 289
},
{
"start": 1741040,
"end": 1746400,
"text": "it. That's again, expensive, but you can<br>do it. You can improve the measurement",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 290
},
{
"start": 1746400,
"end": 1754000,
"text": "like that. And it's basically costly<br>because the sensor is quite expensive.",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 291
},
{
"start": 1754000,
"end": 1759680,
"text": "Vice versa in the set setup for 15 to 30<br>euro. You have everything you need and",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 292
},
{
"start": 1759680,
"end": 1768160,
"text": "here you're looking at several hundred to<br>several thousand euros. OK, now measuring",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 293
},
{
"start": 1768160,
"end": 1774880,
"text": "I have to be a bit quicker now, I noticed.<br>So I talked about the potassium",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 294
},
{
"start": 1774880,
"end": 1779440,
"text": "salt. There's also fertilizer based on<br>potassium baking powder. Uranium glass is",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 295
},
{
"start": 1779440,
"end": 1784800,
"text": "quite nice. You can find that easily on<br>flea markets. Often also old radium",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 296
},
{
"start": 1784800,
"end": 1790080,
"text": "watches. Here's another example of a<br>uranium glaze, the kitchen tile in this",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 297
},
{
"start": 1790080,
"end": 1794400,
"text": "case, this was actually in the kitchen. So<br>the chances are that you at home find",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 298
},
{
"start": 1794400,
"end": 1798240,
"text": "actually some of those things in the<br>cupboards of your parents or your",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 299
},
{
"start": 1798240,
"end": 1801840,
"text": "grandparents. It is an example of<br>thoriated glass, which has this",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 300
},
{
"start": 1801840,
"end": 1808400,
"text": "distinctive brownish color, which actually<br>is from the radiation. And a nice little",
"meta": {
"new_paragraph": false,
"region": null
},
"position": 301
},
{
"start": 1808400,
"end": 1812720,
"text": "experiment that I can really recommend you<br>to look up is radioactive balloon",
"meta": {
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"region": null
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"text": "the last kind of context of all of<br>this to end this presentation, I want to",
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"text": "quickly remind how important these silicon<br>detectors are for places like CERN. It's a",
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"text": "nanoseconds. Not right now, but soon<br>again, machines will be started again next",
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"text": "year. And you also can, by the way, build<br>a similar project which has a slightly",
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"text": "different name. It's called Build Your Own<br>Particle Detector. This is Atlas and made",
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"text": "out of LEGO. And on this website, you<br>find a nice plan, how to build or ideas,",
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"text": "collision. So to summarize the website is<br>on GitHub, there is really this big wiki,",
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"text": "ideas for measurements and some of the<br>things you have seen today. Thanks a lot.",
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"text": "Herald: Well, thanks a lot, Oliver. I hope<br>everyone can hear me now again. Yes,",
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"text": "Herald: All right, I hope that answers for<br>the person. Yeah, but people can get a",
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"text": "Herald: Yeah, so it should work with a lot<br>of people, I guess, and one another",
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"text": "of thorium or uranium on the stone, for<br>example. Or in this type of ceramic, these",
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"text": "old ceramics, you can go to the flea<br>market and just look for these very bright",
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"text": "Herald: OK, so that's what I'm going to do<br>with it. Thanks for for highlighting a bit",
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"text": "the practical side, I think it's really<br>cool to educate people about scientific",
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"text": "on Twitter of maybe Oliver or want to join<br>the IRC room for your talk as well. People",
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"video_title": "#rC3 - Measuring radioactivity using low-cost silicon sensors",
"video_description": "https://media.ccc.de/v/rc3-11546-measuring_radioactivity_using_low-cost_silicon_sensors\n\nA DIY particle physics detector in a tin box.\n\nThis talk gives a brief introduction to natural radioactivity and shows how a detector can be built from simple photodiodes. The electronics are easy to solder for beginners and provide a hands-on opportunity for entering the exciting world of modern particle physics with a practical DIY and citizen science approach.\n\nNatural radioactivity surrounds us everywhere and is composed of different kinds of ionising radiation or subatomic particles. This talk presents a DIY particle detector based on low-cost silicon photodiodes and its relations to modern detectors like the ones developed at CERN. \n\nThe project is open hardware, easy to solder for beginners, and intended for citizen science & educational purposes. In contrast to simpler Geiger-Müller counters, this detector measures the energy of impinging particles and can distinguish in particular between alpha particles and electrons from beta decays. A cheap USB sound card or smartphone headset connection can be employed for recording the signals. Corresponding data analysis scripts written in python and related tools from particle physics research will be briefly discussed.\n\nAn introduction about terrestrial and cosmic sources of radioactivity will be given together with details on the interaction of ionising radiation in silicon. I will conclude with a discussion of interesting every-day objects that are worthwhile targets for investigation and show example measurements of characteristic alpha particle energy spectra - without using expensive vacuum equipment.\n\nOliver Keller\n\nhttps://fahrplan.events.ccc.de/rc3/2020/Fahrplan/events/11546.html",
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