Detecting ANTIMATTER in food - DIY Gamma spectroscopy

today we're gonna be talking about antimatter so let me just get some really quick here we go and a little more perfect now at this point you're probably thinking that I've finally lost it and the quarantine is getting to me but fear not internet stranger I'm no crazier than I was before I'm not sure if that makes that better though anyway these items do actually contain antimatter albeit obviously very tiny amounts otherwise they'd explode and take out most of the neighbourhood as soon as they touched anything today we're gonna build a device that will let us detect the antimatter inside here and in other common items so first what is antimatter well everything you've ever interacted with iswell matter that is a collection of twelve fundamental particles that can be mixed and matched to make atoms and molecules and just about everything else these twelve particles make up the standard model of particle physics enter the basis for most modern physics but of the twelve these three are the ones that you encounter the most these two are called quarks and we get three of them together they form protons and neutrons which make up the cores of atoms and then this one is the humble electron which is responsible for holding different atoms together electricity and lots of other phenomena but as it turns out all of these particles actually come in two flavors matter and their antimatter counterparts the weird part is that antimatter and regular matter are almost indistinguishable they have the same mass and most of the same properties the only difference is that their charges are flipped so an electron which is normally negatively charged its antiparticle called a positron is well positively charged and if you get enough anti quarks together to form an antiproton it would be negatively charged rather than positive like a normal proton is but other than that that are identical you can actually make entire atoms using nothing but anti particles and their properties as far as anyone can tell are the same as normal atoms other than that charge flip scientists have made anti hydrogen for example using anti protons and positrons and when they looked at the spectrum of light it puts out when you excite it it was identical to normal hydrogen which personally I find fascinating and very very weird so now you're probably wondering well okay well how does that relate to my spinach and salt where's the antimatter in that the answer comes then to potassium in nature potassium comes in three forms known as isotopes basically these are atoms which have the same number of protons but different number of neutrons making some slightly lighter or heavier remember we classify elements by the number of protons so as long as that doesn't change they're all considered the same element one of these isotopes potassium-40 is ever so slightly radioactive and unstable so over time it'll eventually decay into either calcium 40 or argon 40 on the whole it mostly turns into calcium doing so about 89 percent of the time it does this via a process called beta decay one of the neutrons in the potassium course spontaneously turns into a proton and in the process ejects an electron and while this is cool it's not what we're interested in that other 11% of the time when it decays into argon is when things get exciting rather than one of the neutrons ejecting an electron in this case one of the protons can absorb an electron and goes the other way turning into a neutron but this leaves the core of the new argon atom with way too much energy and it needs to get rid of it somehow so it does this by emitting a very high-energy form of light called a gamma ray and it's that gamma ray where things get weird Einstein's famous equation equals MC squared shows that mass and energy can be sort of interchangeable but well that is the most famous version of the equation it only applies to very low energy situations the full equation is e squared is equal to MC squared squared plus PC squared basically this means that energy is actually proportional to both the mass and the momentum of a particle so in a sense if you can provide enough energy to cover the mass of a particle you can generate new particles basically out of nothing but there's a catch to make new particles you always have to make two at a time this is called pair production an electron has a rest mass of 511 Killah electron volts and a positron being otherwise identical to its Matter counterpart also has a mass of 511 kil electron volts during pair production you always make one matter particle in one antimatter particle so in this case all you need is something with combined energy of greater than one 20 to kill electron volts and you can make a pair of particles remember that gamma ray from the potassium decay it has an energy of 14 60 kill electron volts which means that it passes the threshold for pair production but some basic math shows that 14 60 minus 10 22 leaves 438 kill electron volts leftover so in order for a pair production to happen a third criteria needs to be accounted for the gamma ray needs to pass near an atom this way the particles can be formed and it can pass off that excess energy as momentum to the atom giving it a little shove when these conditions are met we occasionally get two new particles one of which is antimatter when I say occasionally though I mean it this does not happen with every single gamma ray there are basically four ways that a gamma ray can interact with matter and the probability of each method changes based on the energy of the gamma ray passed about a thousand kill electron volts or one mega electron volt well it is possible to get pair production the probability still isn't very high but as you approach 10 mega electron volts the probability climbs significantly so for your average banana for example which contains approximately 350 milligrams of potassium you get one positron every 75 minutes as you can imagine that would make detecting this very difficult so to make the probability higher and hopefully detectable I'll be using about two kilograms of various potassium salts to provide enough potassium 40 that I can more easily detect the positrons so now we've got our antimatter how do we detect it well antimatter doesn't tend to exist very long on earth because of the sheer number of matter particles everywhere as soon as that positron comes in contact with an electron from a nearby atom the pair annihilation release two more gamma rays this time each carrying 511 kill electron volts of energy using a device called a gamma ray spectrometer we can detect not only that first gamma ray from the potassium but also the resulting in violation gamma rays from the positrons that are formed so let's build one this is my gamma ray spectrometer and we actually used it in my last video to determine what sort of radioactive material is in these quack medicine negative ion bracelets if you haven't already seen that I'd highly recommend checking that video out the spectrometer is made of three pieces a crystal which turns any gamma rays that hit it visible-light a special vacuum tube which will turn the light into electrical signals and a box which takes those signals and feeds them into a computer so we can interpret them and make a spectrum let's start with the crystal there are a variety of different materials that will work for this and I actually built two probes using two different materials the first is called bicron and is actually a special type of plastic the other is sodium iodide doped with a small amount of thallium bicron is cheap so you can get huge chunks of it for not a lot of money but has a significant flaw that makes it basically useless for our purposes when a gamma ray hits one of these materials the flash of light that's emitted is approximately proportional to the energy of the gamma ray or at least it should be with bicron the flashes of light are kind of all over the place and while it almost always makes a flash of light you can't actually use them to figure out the energy of the incident gamma ray because it's just so sloppy sodium iodide on the other hand is much better but also more expensive and can be used to figure out what energy the gamma ray was as the flashes are proportional to within about six to eight percent still not perfect but very reasonable and sufficient for our purposes beyond sodium iodide the price of crystals shoots up very quickly but so does the quality of the spectrum they produce and the size of crystal you need to get a good spectrum decreases as well ultra pure germanium for example needs to be cooled with liquid nitrogen to work but gives flashes that are within point two percent accuracy here's two spectrums showing the difference between germanium and sodium iodide you can see how much sharper the peaks are with germanium but again for our purposes would cost thousands of dollars to set up whereas my sodium iodide crystal only cost about 150 because it had a small crack in it okay we've got our crystal now let's talk vacuum tubes this is a photomultiplier tube and they are amazing using some honestly really simple physics they can turn a single photon into a huge electrical signal which is very easy to then pick up and interpret with a computer inside there's a series of plates that are each charged with a high voltage that decreases with each plate when a photon hits the first plate it knocks a couple of electrons free which are accelerated at the next plate the electron hits the plate knocking even more electrons free this repeats all the way to the end we're at that point so many electrons crash into the plate all at once that there's a big spike of electricity what's really cool is that spike is also proportional so if more photons hit the first plate at once more initial electrons are knocked off and the end pulse is larger finally this box is where all the magic happens it's the GS USB Pro from a company called Gama spectacular my friend Steven sessile Minh runs the company and was kind enough to send me this one honestly I love this thing it's really easy to use and it's packed full of features and compared to the price of a gamma spectrometer normally it's really quite affordable so if you're interested I've put some links in the description I originally got the photomultiplier tube as a kit that came with all the instructions for setting it up and it was actually quite easy it was a little bit of soldering to setup the high voltage lines and then mounting the BNC connector in an end cap made of PVC pipe fittings then everything was held together with black electrical tape this not only holds everything together but also insulates the tube so that no stray light can get in and ruin your readings before it was totally taped up though the crystal or bicron was cleaned with a microfiber cloth and some silicon optical coupling grease was added to the face the crystal was then mounted onto the tube and carefully rubbed back and forth to distribute the grease before being taped down permanently then the whole thing was covered in a second layer of tape to really make sure it was light tight with the bike Ron there was actually an extra step in there where you have to wrap the outside in white teflon tape to make sure any photons that are emitted inside are reflected back into the tube that process was maybe the biggest pain-in-the-ass ever and took over an hour since the tape kept being statically attracted to my gloves and coming off once everything was taped up and sealed the last step to make this permanent is the add some heat shrink tubing to protect everything for the sodium crystal I added a little bit of thin cardboard to make the shape a little more even since the PVC was a little bit chunky then I just slid the heat shrink over it and hit it with the heat gun carefully I also added some foam to the crystal end to help protect it from bumps for the bike ron the heat shrink was a wee bit too small so getting it on was a nightmare and I ended up having to do it in two pieces but when everything was said and done I had two awesome probes ready for use I ended up picking up a special cable to connect the probe to the gamma spectacular since it uses a weird connector called safe high voltage but the cable only cost four fifteen or twenty bucks from China but other than that everything just connects together easily and the box is plugged into my laptop via the USB port the first thing I had to do was calibrate the detectors so I used one of the thorium laced bracelets from the last video to do that thorium or rather the things that decays into put out a variety of gamma rays of known energy so I can use them to calibrate my detector Stephen provided me with a little calibration sheet which I've linked to below that lets you adjust the voltage you're feeding into the tube until the peaks are spread out in a linear fashion across the whole spectrum this is important so that anything that I measure will give me an accurate reading of what energy the gamma ray was I'm using a program called PRA which takes the audio signal that the gamma Spectacular puts out and turns it into a spectrum first I calibrate the peak shape of the audio signal by collecting about a thousand pulses so that PRA knows what the pulses should look like then I capture a spectrum for about 15 minutes and since I'm using a thorium source I should get a series of Peaks I highlight each peak by clicking on it and then hitting either the F G or H key which will highlight more or less of the spectrum the goal here is to highlight just the peaks if that's being a bit glitchy I can just use the B and E keys to mark the beginning and end of a feature with the peaks highlighted the program gives me the mean values and standard deviation of each peak these can be fed into that spreadsheet so that I can see if I've got the right voltage if the graph is curved upwards I turn the voltage down and if the graph is curved downwards I turn the voltage up and I just repeat until the graph is flat from there I calibrate the actual energy of each peak by using the known values of the thorium decay chain and plugging the arbitrary unit values and known energies into the calibration window after that everything is set up and a spectrometer is ready to use to measure some actual samples let's start with the potassium salts to give the best chance of detecting the annihilation if we can see it then we can be sure that anything else that shows the potassium peak should be doing the same even if it's harder to detect here I've got a mix of potassium chloride and potassium phosphate for a total of 2.1 kilograms of salt i just piled everything around the detector and let it run for a day to give a nice clear spectrum but you'd see the potassium peak and even a minute of starting the recording sure enough there's a antek peek at 1460 kill electron volts from the gamma ray the potassium puts out just as we expected but now if we look at around 500 kill electron volts sure enough there's a tiny peek it's really tiny almost lost in the noise but the program does see it that is the annihilation peak one of the reasons it's so hard to see this is because I'm doing this without any shielding so the ambient background radiation makes this much more difficult to detect what's preferred is to do this experiment in a leadbox with anywhere from four to eight inches of lead on all sides here's another potassium-40 spectrum taken by peter dali with much better shielding and the peak is actually a little more visible but without either a big lead box or a more sensitive crystal or ideally both this is really right at the threshold for what's possible with this setup as I said before pair production is more likely the higher the gamma energy is so on a thorium spectrum for example you see the annihilation peak at 511 is much stronger since there's a lot of higher energy gamma rays which are more likely to undergo pair production which as a fun note means those quack medicine bracelets also put out a little bit of antimatter on top of all the rest of the radioactive garbage they emit but no matter what once we start getting gamma rays above the threshold we do slowly start getting a small amount of antimatter all of these pale in comparison to an isotope which just emits positrons directly sodium 22 for example decays directly via positron emission without undergoing power production so the annihilation peak that you get when analyzing it is massive comparatively another place where you'll see a very large annihilation peak is actually on an airplane the atmosphere is so thin where commercial planes fly that the levels of very high-energy gamma rays and other cosmic rays are much higher compared to sea level so you get lots of pair production and a very detectable annihilation peak if we now measure the spinach we see mostly the same thing though of course the annihilation peak is now way too small to see all living matter has potassium in it which means a small amount of potassium-40 and as such you'll always see the potassium-40 peak and as long as that peak is there we can be sure that we're getting a few positrons but the amount of potassium is so low in most things that detecting the positrons with this detector is just not possible however here spectrum taken from some wild-caught Atlantic salmon and analyzed with a vastly better detector we see the usual potassium-40 peak and the annihilation peak is now much clearer we also see some cesium 137 which is a little bit sketchy but not unexpected for something living in the oceans altogether I hope this demonstrates that since everything you eat has potassium in it you will always be eating a tiny amount of antimatter in fact there's actually a pretty decent quantity of potassium in you already so part of the radiation that you naturally emit is a miniscule amount of antimatter in an upcoming video we'll be revisiting gamma spectroscopy again to look at another interesting technique called coincidence detection basically we connect both probes together and only register pulses that set both off at the same time this gives directional information so one experiment is to simply stack them a name them skyward so we can detect cosmic rays and even perform some really cool measurements on them we'll be able to see them decay within the detector into different particles and should be able to use them to demonstrate time dilation and prove an aspect of special relativity I'm also looking at maybe modifying pipsqueak and turning it into a gamma ray camera at some point but that'll be for future videos and so I'll leave it there before I wrap up I need to say a huge thank you to my amazing patrons channel members and supporters on Kofi especially in these uncertain times it's your amazing support that helps me keep making videos and work on projects like this so I can't thank you all enough if you'd like to help keep the flow of science videos coming there's some links below if you enjoyed you know what to do hit the like button subscribe and of course ring the bell to see when I post new videos if you'd like to see updates on these projects long before they make it into videos be sure to head over to Instagram and Twitter where I post snapshots very regularly that's all for now and I'll see you next time

Channel: The Thought Emporium

Views: 357,118

Keywords: gamma ray, antimatter, positron, gamma spectroscopy, spectrum, gamma, radiation, nuclear, physics, particle physics, science, education, tutorial, photomultiplier, vacuum tube, cosmic ray

Id: K16uPl6_S7A

Length: 17min 25sec (1045 seconds)

Published: Mon Mar 30 2020