WEBVTT
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rc3 prerol music
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Herald: All right, fellow creatures, to be
honest, I never thought that I would be
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introducing a talk on measuring
radioactivity like ever in my life, but
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then again, considering the world stage,
current state at large, it might be not
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such a bad idea to be prepared for these
things. Right? And gladly, our next
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speaker, Oliver Keller, is an expert in
detecting radioactive stuff. Oliver is a
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physicist and works at one of the most
prominent nerd happy places. The CERN
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since 2013 is also doing a PhD project
about novel instruments and experiments on
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natural radioactivity at the University of
Geneva and to even more to add even more
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C3 pizzazz. Oliver is active in the open
science community and passionate about
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everything open source. All that sounds
really cool to me. So without further ado,
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let's give a warm, virtual welcome to
Oliver and let's hear what he has to say
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about measuring radioactivity with using
low cost silicon sensors. Oliver, the
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stream is yours.
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Oliver: Thanks. That was a very nice
introduction. I'm really happy to have the
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chance to present here. I'm a member since
quite some years and this is my first CCC
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talk, so I'm quite excited. Yeah, you can
follow me on Twitter or I'm also on
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Mastodon, not so active, and most of my
stuff is on GitHub. OK, so what will we
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talk about in this talk? I'll give you a
short overview, also about the
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radioactivity, because yeah, it's a topic
with many different details and then we
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will look at the detector more in detail
and how that works in terms of the physics
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behind it and the electronics. And then
finally, we look at things that can be
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measured, how the measurement actually
works, what are interesting objects to
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check and how this relates to silicon
detectors being used at CERN. So the
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project is on GitHub called DIY Particle
Detector. It's an electronic design, which
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is open hardware. There's a wiki with lots
of further details for building and for
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troubleshooting. There is a little web
browser tool I will show later, briefly,
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and there are scripts to record and nicely
plot the measurements. Those scripts are
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BSD-licensed and written in Python. There
are two variants of this detector. One is
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called electron detector, the other one
alpha spectrometer. They use the same
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circuit board, but one is using four
diodes, the other one one photodiode...
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There's a small difference between them,
but in general it's pretty similar. But
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the electron detector is much easier to
build and much easier to get started
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using. Then you have complete part lists
and even a complete kit can be bought on
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kitspace.org, which is an open hardware
community repository, and I really
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recommend you to check it out. It's a
great community platform and everyone can
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register their own GitHub project quite
easily. Now, this is a particle detector
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in a tin box, so you can use the famous
Altoids tin box or something for Swiss
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chocolate, for example. You can see it's
rather small, the board about the size of
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a nine volt block battery. And then you
need, in addition, about 20 resistors,
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capacitors and these silicon
diodes plus an operational amplifier,
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which is this little chip here, this
little black chip here on the right side,
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you can see is all old school large
components. This is on purpose, so it's
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easy to soldier for complete electronic
beginners. And this by the way, this
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picture is already one user of this
project who posted their own build on
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Twitter. OK, so natural radioactivity. So
I would say it's a story of many
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misconceptions. Let's imagine we are this
little stick figure here on the ground.
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Below us we have uranium and thorium. We
also have Potassium-40 in the ground and
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Potassium-40 is is pretty specific and
peculiar. It actually makes all of us a
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little bit radioactive. Every human has
about 4000 to 5000 radioactive decays
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every second because of the natural
potassium and natural potassium comes with
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a radioactive isotope, which is just
everywhere, it's in bananas. But it's also
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in us because we need it for our body
chemistry. It's really important and even
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some of those decays are even
producing anti-matter. So how cool is
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that? OK, so what would we be measuring on
the on ground? Well, there could be some
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gamma rays or electrons. Those are from
beta-decays. Or from the Uranium, there is
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one radionuclide appearing in the decay
chain, which is called Radon, and Radon is
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actually a gas. So from the ground the
Radon can diffuse upwards and travel with
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air and spread around. So it's a bit like
a vehicle for radioactivity from
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the ground to spread to other places. And
that Radon would decay with alpha
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particles producing electrons and beta-
decays and also gamma radiation further
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down in the decay chain. So just to
recapitulate, I've said it already twice,
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so alpha particles are actually helium
nuclei, so it's just two protons and two
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neutrons and the electrons are missing.
And in beta decay basically one neutron is
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transformed into a proton and an electron.
And there's also an electron-anti-neutrino
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generated. But this is super hard to
measure. So we're not measuring those.
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Mostly we will be measuring electrons from
beta-decays. That's why you see all these
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little e's indicating betadecays. Ok, if
you would go to the hospital here on the
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left side, we would probably find some x
rays from checking our bones or something
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like this, or even gamma rays or alpha
particles being used in treatments or very
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modern even proton beams are sometimes
generated for medical applications. Now,
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here on the right side, if you go close to
a nuclear power plant, we probably measure
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nothing unless there's a problem in this
case, most likely we would find some gamma
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radiation. But only if there is a problem.
OK, and then actually that's not the whole
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story. This is terrestrial radiation. But
we also have radiation coming from
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upwards, showering down on us every
minute, and there's actually nothing we
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can do against it. So protons are
accelerated from in the universe.
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Basically, the biggest particle
accelerator nature has. And once they hit
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our atmosphere they break apart into less
energetic particles and it's many of them.
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So in the first stage there's lots of pions
generated and also neutrons. But neutrons
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are really hard to measure, so I'll ignore
them for most of the talk. Then those
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pions can decay into gamma rays and then
trigger a whole chain of positron electron
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decays, which again create gamma rays and
so forth. And this goes actually the whole
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way down to the earth. We will have a
little bit of that on the sea level.
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And the other more known part of
atmospheric radiation is actually muons.
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So some pions decay into muons, which is
kind of a heavy electron and also
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neutrinos. But neutrinos are, again, very
hard to measure. So I'll ignore them for
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most of this talk. And if you look here on
the right side on this altitude scale,
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you'll see an airplane would be basically
traveling where most of the atmospheric
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radiation is produced. And this is why if
you go on such an airplane, you have
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actually several times more radiation
in there than here on earth. And, of
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course, on the ground, it also depends
where you are. There are different amounts
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of uranium and thorium in the ground and
this is just naturally there. So but it
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depends on the geology, of course. OK, so
I've talked quite a bit about radiation,
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and I'm saying I want to use silicon to
detect it. So what radiation exactly?
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Maybe. Let's let's take a step back and
think about what we know maybe from
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school. So we have this rainbow for
visible light. Right. This is in terms of
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wavelength. We have 800 to 400 nanometers
spanning from the infrared/red area to all
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the green to blue and into the violet. And
lower down those wavelengths or let's say
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bigger millimeter waves, meter waves and
even kilometer, that would be radio waves,
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radio frequencies for our digital
communication systems, wi-fi, mobile
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devices and so forth. But I want to look
actually more towards the right because
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that's what we are measuring with these
detectors. It's shorter wavelength, which
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actually means higher energy. So on the
right side, we would be having ultraviolet
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radiation, which is kind of at the border
to what we can measure. And these 800 to
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400nm translate into 1.5 to 3 eV, which is
a unit that particle physicists really
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prefer because it basically relates the
energy of an electron after it has been
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accelerated by 1 Volt and makes it
much easier to work with nuclear
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particle physics, because everything, all
the energy is always related to an
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electron. And this energy, this formula
here is just a reminder that the
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wavelengths can be always converted into
energy and it's inversely proportional. So
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wavelength increases to the left and the
energy to right. And if you increase
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energy more from from the visible range,
so let's say thousands of electron volts,
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then we arrive here. Millions - mega
electron volts, even GeV. And there is now
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a pretty important distinction between
those two areas, and that is the right one
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is ionizing radiation and the left one is
non ionizing radiation. UV is a little bit
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in the middle of that. So some parts of
the UV spectrum can be ionizing. It also
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depends a lot on the material that the
radiation is interacting with. For these
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detectors I'm talking about today and
alpha, beta, gamma radiation, this is all
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ionizing, so some examples, lowest energy
on the lower spectrum would be x rays than
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electrons, gamma rays from radioactive
nuclides that already talked about in the
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previous slide, alpha particles, and that
muons from the atmosphere would be more on
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the GeV range and so forth. And for these
higher energies, of course, you need
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something like the LHC to accelerate
particles to really high energies. And
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then you can even access the TeV regime.
OK, silicon diodes. What kind of silicon
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diodes? I'm using in this project, low
local silicon pin diodes, one is called
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BPW34 it's manufactured from Vishay or
Osram, costs about 50 cents. So that's what
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I mean with low cost. There's another one
called BPX61 from Osram. It's quite a bit
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more expensive. This is the lower one here
on the right. It has a metal case, which
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is the main reason why it's more
expensive. But it's quite interesting
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because that one we can use for the alpha
detector. If you look closely, there is a
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glass on top, but we can remove that. We
have a sensitive area. So this chip is
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roughly 7mm² large and it has a thickness,
a sensitive thickness of about 50
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micrometer, which is not a lot. So it's
basically the half of the width of a human
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hair. And in total, it's a really small,
sensitive volume. But it's it's enough to
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measure something. And just as a reminder,
how much of gamma rays or X-rays we will
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detect with this, not a lot because it's
high, energetic photon radiation kind
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doesn't interact very well in any kind of
matter. And because a sensitive area is so
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thin, it would basically permeate through
it and most of the times not interact and
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doesn't make a signal. OK, what's really
important, since we don't want to measure
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light, we have to shield light away. We
need to block all of the light, that means
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easiest way to do it is to put it in a
metal case. There is electromagnetically
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shielded and completely protected from
light as well. Electromagnetic radiation
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or radiowaves can also influence these
detectors because they are super
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sensitive. So this sould be a complete
Faraday cage, complete metal structure
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around it. There's a lot of hints and tips
how to achieve that on the wiki on the on
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the GitHub of this project. OK, let's
think about one of those PIN diodes,
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normally there is one part in the
silicon which is n-doped
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negatively doped, and the other part
usually, which is positively dropped. And
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then you arrive at a simple so called p-n-
junction, which is a regular
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semiconducting diode. Now, pin diodes add
another layer of so-called intrinsic
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layer, here shown with the i. And that
actually is the main advantage. Why this
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kind of detector works quite well and have
a relatively large sensitive Sigma's. So
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if you think about, let's say, a photon
from an x ray or gamma-decay or an
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electron hitting the sensor. So by the
way, this is a cross-section view from the
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side, but that doesn't really matter. But
let's say they come here from the top into
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the... into the diode and we're looking
at the side then we have actually
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ionization because this is ionizing
radiation, so we get free charges in the
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form of electron-hole pairs. So electrons,
which here the blue ball and the red
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circle would be the holes. And depending
on the radiation kind, how this ionization
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takes place is quite different, but the
result is if you get a signal, it means
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there was ionization. Now, if just this
would happen, we could not measure
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anything. Those charges would quickly
recombine and on the outside of the diode,
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it would be a little signal. But what we
can do is we can apply actually a voltage
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from the outside. So here we just put a
battery. So we have a positive voltage
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here, a couple of volts. And then what
happens is that the electrons would be
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attracted by the positive voltage and the
holes will travel to the negative
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potential. And we end up with a little net
current or a small bunch of charges that
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can be measured across the diode as a
tiny, tiny current. The sensitive volume
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is actually proportional to the voltage,
so the more voltage we put, the more the
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bigger is our volume and the more we can
actually measure with certain limits, of
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course, because the structure of the pin
diode has a maximum thickness just
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according how it is manufactured. And
these properties can be estimated with
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C-V-measurements. So here you see an
example of a couple of diodes, a few of
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the same type. The two that I've
mentioned, they're different versions. One
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has a transparent plastic case. One has a
black plastic case. Doesn't really matter.
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You see, basically in all the cases, more
or less the same curve. And as you
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increase the voltage, the capacitance goes
down. So it's great and basically shows us
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those silicon chips are very similar, if
not exactly the same chip. Those
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differences are easily explained by
manufacturing variances. And then because
00:18:34.880 --> 00:18:39.280
this actually, if you think about it, it
looks a bit like a parallel plate
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capacitor and actually you can treat it as
one. And if you know the capacitance and
00:18:45.120 --> 00:18:50.240
the size, the area, you can actually
calculate the distance of these two plates
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or basically width or the thickness of the
diode. And then we arrive at about 50
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
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current, now we need to amplify it, so we
have a couple of diodes, I'm explaining
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now the electron detector, because it's
easier. We have four diodes at the input
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and this is the symbol for an operational
amplifier. There are two of those in the
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circuit. The first stage is really the
special one. So if you have a particle
00:19:25.840 --> 00:19:31.200
striking the diode, we get a little charge
current hitting the amplifier. And then we
00:19:31.200 --> 00:19:34.880
have here this important feedback
circuit. So the output is fed back into
00:19:34.880 --> 00:19:40.880
the input, which in this case makes a
negative amplification. And the
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amplification is defined actually by this
capacitance here. The resistor has a
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secondary role with the small capacitance.
It is what makes the output voltage here
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large. The smaller the capacitance, the
larger the output and it's inverted. Then
00:19:57.200 --> 00:20:02.320
in the next amplifier step, we just
increase the voltage again to a level that
00:20:02.320 --> 00:20:08.160
is useful for using it later. But all of
the signal quality that has been
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
00:20:13.120 --> 00:20:18.880
first stage. The second one is just to
better adapt it to the input of the
00:20:18.880 --> 00:20:24.480
measurement device that's connected. So
here, this is a classic inverting
00:20:24.480 --> 00:20:29.120
amplifier with just these two resistors
define the amplification factor. It's very
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
00:20:35.360 --> 00:20:39.760
the charge pulse and this, the circuit
here is sensitive, starting from about
00:20:39.760 --> 00:20:50.320
1000 liberated charges in those diodes as
a result from ionization. We get something
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like 320 micro Volt at this first output,
and this is a spike that quickly
00:20:55.920 --> 00:21:01.600
decreases. Basically these capacitors are
charged and quickly discharged with this
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resistor and this is what we see here. And
then that is amplified again by a factor
00:21:07.360 --> 00:21:14.080
of 100. And then we arrive at something
like at least 32 mV, which is conveniently
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a voltage that is compatible with most
microphone or headset inputs of computers
00:21:20.000 --> 00:21:25.600
or mobile phones, so that the regular
headset here has these four connectors and
00:21:25.600 --> 00:21:31.520
the last ring actually connects the
microphone. The other is ground and reft.
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
00:21:39.360 --> 00:21:46.400
1000 pulses overlayed and measured on an
oscilloscope here. So it's a bit more
00:21:46.400 --> 00:21:52.400
accurate. You see the deposits a bit
better, kind of like the persistence mode
00:21:52.400 --> 00:21:58.160
of an oscilloscope. And the size of the
pulse is proportional to energy that was
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
00:22:03.680 --> 00:22:08.560
enough such that regular sampling
frequency of a sound card can actually
00:22:08.560 --> 00:22:14.800
catch it and measure it. Yeah, this is
Potassium Salt. This is cut here. This is
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
00:22:18.720 --> 00:22:26.320
it in the pharmacy or in certain organic
food stores as a replacement salt.
00:22:26.320 --> 00:22:33.120
On the right side is an example from this
small Columbite Stone, which has traces of
00:22:33.120 --> 00:22:38.720
uranium on it. And this is measured with
the alpha spectrometer. And you see those
00:22:38.720 --> 00:22:42.640
pulses are quite a bit bigger here. We
have 50 microseconds and here we have more
00:22:42.640 --> 00:22:52.880
like one milliseconds of pulse width. Now
there's a software on a browser. This is
00:22:52.880 --> 00:23:00.720
something I wrote using the Web Audio API
and it works on most browsers, best is
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
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
00:23:13.120 --> 00:23:18.560
with the alpha spectrometer circuit, you
get these nice large pulses. In case of
00:23:18.560 --> 00:23:22.800
the electron detector the pulse is much
shorter and you see it, you see the noise
00:23:22.800 --> 00:23:28.880
much more amplified. This red line is kind
of the minimum level that the pulse needs
00:23:28.880 --> 00:23:32.240
to trigger. This would be better. And
that's like the trigger level of an
00:23:32.240 --> 00:23:38.160
oscilloscope. And you can set that with
those buttons in the browser. You need to
00:23:38.160 --> 00:23:42.960
find a good value. Of course, if you
change your input volume settings, for
00:23:42.960 --> 00:23:49.840
example, this will change. So you have to
remember which, with which settings it
00:23:49.840 --> 00:23:55.600
works well. And it is pulsed, for example,
is even oscillating here. So for electron
00:23:55.600 --> 00:24:01.440
detector, it's basically nice to count
particles. For the alpha detector it's
00:24:01.440 --> 00:24:06.240
really the case where the size of the
pulse can be nicely evaluated and we can
00:24:06.240 --> 00:24:11.120
actually do energy measurements. And these
energy measurements can be also called
00:24:11.120 --> 00:24:17.520
spectrometry. So if you look closer at
these many pulses that have been recorded
00:24:17.520 --> 00:24:26.560
and we find that there is really like much
more intensity, which means many more same
00:24:26.560 --> 00:24:32.160
pulses were detected, we can relate it to
radium and radon. If we use a reference
00:24:32.160 --> 00:24:35.920
alpha source and I have done this, I have
measured the whole circuit with the reference
00:24:35.920 --> 00:24:41.360
sources and provide the calibration on
GitHub and you can reuse the GitHub
00:24:41.360 --> 00:24:47.280
calibration if you use exactly the same
sound settings that I have used for
00:24:47.280 --> 00:24:53.600
recording. And for example, these two very
weak lines here from two very distinctive
00:24:53.600 --> 00:25:02.560
polonium isotopes from the uranium decay
chain. The top part here which is really
00:25:02.560 --> 00:25:08.240
dark, corresponds basically in the
histogram view to this side on the left,
00:25:08.240 --> 00:25:12.160
which is electrons. Most of these
electrons will actually enter the chip and
00:25:12.160 --> 00:25:18.800
leave it without being completely
absorbed by it, but alpha particles
00:25:18.800 --> 00:25:22.960
interact so strongly that they are
completely absorbed within the 50
00:25:22.960 --> 00:25:29.520
micrometers of sensitive volume of these
diodes and OK here is a bit difficult to
00:25:29.520 --> 00:25:35.440
see peaks. But the far end of the high
energy spectrum, you see two really clear
00:25:35.440 --> 00:25:40.560
peaks and those can only stem from
polonium, actually. I mean, we know it's
00:25:40.560 --> 00:25:46.960
uranium and that can only be polonium,
which is that isotope that produces the
00:25:46.960 --> 00:25:56.080
most energetic alpha particles and
which is natural. And I said, if you use
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
00:25:59.840 --> 00:26:04.560
same soundcard because they're if you put
it to hundred percent input sensitivity,
00:26:04.560 --> 00:26:08.880
you will have exactly the same result,
like in my calibration case. And this
00:26:08.880 --> 00:26:13.120
soundcard is pretty cheap, but also pretty
good. It costs just two dollars and has a
00:26:13.120 --> 00:26:18.560
pretty range and resolves quite well, 16
bits and think, oh, you could do that with
00:26:18.560 --> 00:26:24.640
Arduino as well, is actually a bit hard to
do. A really well defined 16 bit
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
00:26:31.280 --> 00:26:34.960
straightforward. And you can have just
some Python scripts on the computer to
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
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
00:26:44.720 --> 00:26:50.160
the metal frame and then the glass breaks
away easily. Is not a problem, there's
00:26:50.160 --> 00:26:56.800
more on that on the wiki. Now we
can kind of compare alpha and gamma
00:26:56.800 --> 00:27:03.920
spectrometry. Here's an example. This is
the uranium glazed ceramics. The red part
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.
00:27:09.840 --> 00:27:15.040
And in the spectrum we have two very
distinctive peaks and nothing in the high
00:27:15.040 --> 00:27:20.800
energy regime. Only this low energy range
has a signal. And this corresponds
00:27:20.800 --> 00:27:27.920
actually to uranium 238 and 234 because
they use actually purified uranium. So all
00:27:27.920 --> 00:27:33.920
of the high energy progeny or daughters of
uranium, they're not present here because
00:27:33.920 --> 00:27:38.720
it was purified uranium. And this
measurement doesn't even need vacuum, I
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
00:27:43.280 --> 00:27:48.400
would improve this peaks by a lot. So this
widening here to the left, basically, that
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
00:27:55.200 --> 00:28:00.960
air pressure, which already interacts a
lot with the particles and absorbs a lot
00:28:00.960 --> 00:28:06.960
of energy before the particles hit the
sensor. So in terms of pros and cons, I
00:28:06.960 --> 00:28:12.080
would say the small sensor is quite
interesting here in an alpha spectrometry
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
00:28:18.400 --> 00:28:25.280
very precisely on specific spots. And on
the other hand, of course, the conditions
00:28:25.280 --> 00:28:29.440
of the object influence the measurement a
lot. So, for example, if there's some
00:28:29.440 --> 00:28:34.560
additional paint on top, the alpha
particles might not make it through. But
00:28:34.560 --> 00:28:40.560
in most of these kind of samples, alpha
radiation actually makes it through the
00:28:40.560 --> 00:28:46.800
top, a transparent paint layer. In terms
of gamma spectrometry, you would usually
00:28:46.800 --> 00:28:51.760
have these huge and really expensive
sensors. And then the advantage, of
00:28:51.760 --> 00:28:56.800
course, is that you can measure,
regardless of your object, you don't
00:28:56.800 --> 00:29:01.040
really need to prepare the object a lot.
You might want some lead shielding around
00:29:01.040 --> 00:29:06.400
it. That's again, expensive, but you can
do it. You can improve the measurement
00:29:06.400 --> 00:29:14.000
like that. And it's basically costly
because the sensor is quite expensive.
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
00:29:19.680 --> 00:29:28.160
here you're looking at several hundred to
several thousand euros. OK, now measuring
00:29:28.160 --> 00:29:34.880
I have to be a bit quicker now, I noticed.
So I talked about the potassium
00:29:34.880 --> 00:29:39.440
salt. There's also fertilizer based on
potassium baking powder. Uranium glass is
00:29:39.440 --> 00:29:44.800
quite nice. You can find that easily on
flea markets. Often also old radium
00:29:44.800 --> 00:29:50.080
watches. Here's another example of a
uranium glaze, the kitchen tile in this
00:29:50.080 --> 00:29:54.400
case, this was actually in the kitchen. So
the chances are that you at home find
00:29:54.400 --> 00:29:58.240
actually some of those things in the
cupboards of your parents or your
00:29:58.240 --> 00:30:01.840
grandparents. It is an example of
thoriated glass, which has this
00:30:01.840 --> 00:30:08.400
distinctive brownish color, which actually
is from the radiation. And a nice little
00:30:08.400 --> 00:30:12.720
experiment that I can really recommend you
to look up is radioactive balloon
00:30:12.720 --> 00:30:17.920
experiment. Here, you charge the balloon
electrostaticly and then it would catch
00:30:17.920 --> 00:30:21.840
polonium from the air. And it's really
great. You basically get a radioactive
00:30:21.840 --> 00:30:30.803
balloon after it was just left for 15
minutes in a normal regular room. OK, now
00:30:30.803 --> 00:30:36.928
the last kind of context of all of
this to end this presentation, I want to
00:30:36.928 --> 00:30:43.280
quickly remind how important these silicon
detectors are for places like CERN. It's a
00:30:43.280 --> 00:30:48.815
cross-section of the ATLAS detector. And
here you have basically the area where the
00:30:48.815 --> 00:30:53.950
collisions happen in the ATLAS detector.
So this is just a fraction of a meter. And
00:30:53.950 --> 00:31:02.049
you have today 50 to 100 head on collisions
of two protons happening every 25
00:31:02.049 --> 00:31:08.380
nanoseconds. Not right now, but soon
again, machines will be started again next
00:31:08.380 --> 00:31:15.112
year. And you also can, by the way, build
a similar project which has a slightly
00:31:15.112 --> 00:31:19.492
different name. It's called Build Your Own
Particle Detector. This is Atlas and made
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,
00:31:25.210 --> 00:31:32.504
how to build it from LEGO to better
visualize the size and interact more with
00:31:32.504 --> 00:31:38.434
particle physics. In case of the CMS
detector. This is the second biggest
00:31:38.434 --> 00:31:43.648
detector at CERN. Here you see nicely that
in the middle, at the core of the
00:31:43.648 --> 00:31:49.362
collision, you have many, many pixel and
microstrip detectors which are made of
00:31:49.362 --> 00:31:59.464
silicon. And these are actually 16 m² of
silicon pixel detectors and 200m² of
00:31:59.464 --> 00:32:04.870
microstrip detectors also made of silicon.
So without basically that silicon
00:32:04.870 --> 00:32:10.649
technology modern detectors wouldn't work
because this fine segmentation is really
00:32:10.649 --> 00:32:16.611
required to distinguish all of these newly
created particles as a result of the
00:32:16.611 --> 00:32:24.609
collision. So to summarize the website is
on GitHub, there is really this big wiki,
00:32:24.609 --> 00:32:29.349
which you should have a look at, and
there's a gallery of pictures from users.
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
00:32:34.307 --> 00:32:38.920
wrote how to use it because the spectra
can sometimes be difficult to interpret.
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
00:32:44.440 --> 00:32:49.648
some discussions there on GitHub. And most
of the things I saw today are actually
00:32:49.648 --> 00:32:54.594
written in detail in a scientific article,
which is open access, of course. And I
00:32:54.594 --> 00:33:00.198
want to highlight two related citizen
science projects on the one hand, as the
00:33:00.198 --> 00:33:07.382
safecast, which is about a large, nice,
sensitive Geiger-Müller based detector
00:33:07.382 --> 00:33:12.640
that has the GPS and people upload their
measurements there. This is quite nice.
00:33:12.640 --> 00:33:17.318
And also opengeiger is another website,
mostly German content, but also some of it
00:33:17.318 --> 00:33:23.412
is English, that also uses diode
detectors, showed many nice places. He
00:33:23.412 --> 00:33:29.971
calls it Geiger caching, places around the
world where you can measure something,
00:33:29.971 --> 00:33:35.032
some old mines, things like this. And if
you want updates, I would propose to
00:33:35.032 --> 00:33:40.156
follow me on Twitter. I'm right now
writing up two other articles with more
00:33:40.156 --> 00:33:46.889
ideas for measurements and some of the
things you have seen today. Thanks a lot.
00:33:50.949 --> 00:33:57.840
Herald: Well, thanks a lot, Oliver. I hope
everyone can hear me now again. Yes,
00:33:57.840 --> 00:34:02.880
thanks for mentioning the citizen science
project as well. It's really cool I think.
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
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
00:34:18.240 --> 00:34:24.000
of the system? Did you pick particular
resistor values and or Opamps to optimize
00:34:24.000 --> 00:34:29.280
for noise? Was it a problem?
Oliver: Yeah, so noise is the big
00:34:29.280 --> 00:34:36.880
issue here. Basically, the amplifier is
one I found that this around four, four
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
00:34:45.040 --> 00:34:49.600
amplifier type, but this is the most
important one. And then actually the
00:34:49.600 --> 00:34:54.800
resistors, here, the resistance in the
first stage, sorry, the capacitors is the
00:34:54.800 --> 00:34:59.200
second important thing. They should be
really small since I'm limited here with
00:34:59.200 --> 00:35:07.520
hand soldarable capacitors. Basically I
choose the one that were just still
00:35:07.520 --> 00:35:11.200
available, let's say, and this is
basically what is available is basically a
00:35:11.200 --> 00:35:15.840
10 pF capacitor. If you put two of them,
one after another, you half the
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
00:35:20.800 --> 00:35:29.280
kind of tried to keep the same
resistor values as much as possible, and
00:35:29.280 --> 00:35:32.720
here at the output, for example, this is
to adjust the output signal for a
00:35:32.720 --> 00:35:37.680
microphone input in the alpha
spectrometer, I changed the values quite a
00:35:37.680 --> 00:35:43.440
bit to make a large pulse. But, yeah,
it's basically playing with the time
00:35:43.440 --> 00:35:47.670
constants of this network and this
network.
00:35:49.425 --> 00:35:56.000
Herald: All right, I hope that answers for
the person. Yeah, but people can get a
00:35:56.000 --> 00:36:02.480
contact to you right after the show maybe
as well. So there's another question. Have
00:36:02.480 --> 00:36:12.400
you considered using an I²S Codec with a
Raspberry Pi? radiation H80 should be
00:36:12.400 --> 00:36:17.120
almost no set up and completely
repeatable. So last ones are for comment.
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
00:36:25.280 --> 00:36:31.280
actually quite straightforward. But of
course there's many ways to get fancy.
00:36:31.280 --> 00:36:35.440
And this is really this should actually
attract teachers and high school students
00:36:35.440 --> 00:36:41.040
as well, this project. So this is one of
the main reasons why certain technologies
00:36:41.040 --> 00:36:45.399
have been chosen, rather simple than,
let's say, fancy.
00:36:45.399 --> 00:36:51.612
Herald: Yeah, so it should work with a lot
of people, I guess, and one another
00:36:51.612 --> 00:36:58.169
question was how consistent are the sound
cards? Did you find the same calibration
00:36:58.169 --> 00:37:04.733
worked the same with several of them?
Oliver: So if you want to use my
00:37:04.733 --> 00:37:11.701
calibration, you should really buy this
two dollar card from eBay, CM108. I
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
00:37:20.620 --> 00:37:25.790
one computer to the mobile phone, it's a
huge difference in input, sensitivity and
00:37:25.790 --> 00:37:30.782
noise. And it's very difficult to reuse
the calibration in this case. But you
00:37:30.782 --> 00:37:39.344
still can count particles and the electron
detector is anyway, um, mostly it actually
00:37:39.344 --> 00:37:43.124
just makes sense for counting because the
electrons are not completely absorbed. So
00:37:43.124 --> 00:37:47.526
you get an energy information, but it's
not the complete energy of the electron.
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.
00:37:52.971 --> 00:37:58.685
Herald: Who doesn't need an x ray machine,
right? laugs So maybe one question I
00:37:58.685 --> 00:38:05.123
have, because I'm not very familiar with
the tech stuff, but what actually can be
00:38:05.123 --> 00:38:11.881
done with it right in the field. So you
mentioned some working with teachers with
00:38:11.881 --> 00:38:17.523
these detectors? What have you done with
that in the wild so to say?
00:38:17.523 --> 00:38:23.800
Oliver: So what's quite nice is you can
characterize stones with it, for example.
00:38:23.800 --> 00:38:29.840
So since you can connect it to a
smartphone this is completely mobile and
00:38:29.840 --> 00:38:34.379
it goes quite well in combination with a
Geiger counter in this case. So with a
00:38:34.379 --> 00:38:38.440
Geiger counter, you just look around,
where are some hot spots and then you can
00:38:38.440 --> 00:38:44.665
go closer with the alpha spectrometer and
actually be sure that there is some traces
00:38:44.665 --> 00:38:51.883
of thorium or uranium on the stone, for
example. Or in this type of ceramic, these
00:38:51.883 --> 00:38:58.952
old ceramics, you can go to the flea
market and just look for these very bright
00:38:58.952 --> 00:39:04.310
red ceramics and measure them on the spot
and then decide which one to buy.
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
00:39:12.072 --> 00:39:18.846
the practical side, I think it's really
cool to educate people about scientific
00:39:18.846 --> 00:39:25.734
things as well. Another question from the
IRC. Didn't you have problems with common
00:39:25.734 --> 00:39:30.999
mode rejection by connecting the device
through the sound card? If yes have you
00:39:30.999 --> 00:39:38.345
tried to do a AD conversion digitization
on the bord itself already? Transfer
00:39:38.345 --> 00:39:42.440
transfer wire SP dif?
Oliver: Yeah, so, of course, I mean, this
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
00:39:48.154 --> 00:39:54.224
measurement device, but it is really
expensive. I mean, we are looking here at
00:39:54.224 --> 00:40:00.837
15 euros and yeah, that's the reason to
have this separate soundcard just to
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
00:40:08.206 --> 00:40:15.660
this common mode rejection is a problem.
And also this is kind of Überschwinger -
00:40:15.660 --> 00:40:22.610
I'm missing the English term. This is kind
of oscillations here. If you design a
00:40:22.610 --> 00:40:27.654
specific analog to digital conversion, of
course, you would take all of that into
00:40:27.654 --> 00:40:32.671
account and it wouldn't happen. But here
this happens because the circuit can never
00:40:32.671 --> 00:40:38.097
be exactly optimal for certain soundcard
input. It will always be some mismatch of
00:40:38.097 --> 00:40:44.508
impedances and.
Herald: All right, so maybe these special
00:40:44.508 --> 00:40:52.000
technical issues and details, this could
be something you could discuss with Oliver
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
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
00:41:07.120 --> 00:41:14.680
say thank you for being part of this first
remote chaos experience. Thanks again for
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
00:41:21.433 --> 00:41:28.474
the conference of the Congress and a warm
round of virtual applause and big thank
00:41:28.474 --> 00:41:33.024
you to you, Oliver.
Oliver: Thanks, I will join the chat room
00:41:33.024 --> 00:41:34.553
right now.
00:41:34.553 --> 00:41:39.272
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