When you think about radioactivity, you often think about… this. So today we’re going to try and scientifically understand this phenomenon, see if it’s really as dangerous and creepy as you think, and do some experiments that will show invisible particles. Let’s go. So you know what it’s like on YouTube now, I first have to tell you about the sponsor of this video, which is… NordVPN, yes! The last French YouTuber who hadn’t talked about NordVPN yet! So what’s a VPN? Well it’s a computer, a server to which you’ll connect and that will serve as a bridge between you and the internet / the informations and website you’re searching. How useful can it be to use a VPN, well first it’s for safety, because NordVPN uses encrypted tunnels so your data is totally unreadable. It’s mostly handy when using a public WiFi as this of restaurants or airports for instance. 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If the nucleus contains 1 proton then it’s hydrogen, 8 and it’s oxygen, 26 for iron, 80 for mercury, etc. The nucleus of a chemical element can contain a bit more or less neutrons, and those different versions are called isotopes. But some configurations are not stable and radioactivity is the natural process in which the nucleus of an atom disintegrates and spontaneously transforms into another element, until it gets back to a stable configuration. And as this transformation occurs, the nucleus releases energy and particles, and that’s called radiation. Radioactivity naturally happens everywhere, whether it’s from Earth, the surrounding air that contains Radon, space with cosmic rays, even if it’s just a little bit. Also you are radioactive, the human body contains Carbon 14 and Potassium 40 which are radioactive, Potassium 40 is also found in food like bananas… Anyway, it’s absolutely everywhere. OMG we’re gonna die! This radioactivity is used in nuclear energy (fission) to produce heat that will boil water, and then make vapor that will drive turbins that produce electricity; in medical domain it’s used to make CT scans, treat cancer cells… and..! In the mid-1800s though 1920s they used to make what’s called uranium glass which contains uranium in the shape of oxides, that’s what gives its yellow / green fluorescent tint. And when you light it up with UV light it starts glowing, it’s beautiful. Up until the 50s they used to make clocks with needles painted in Radium, that’s what helped them glow in the dark. And there was a time when Radium was also famous for cosmetics. Everything is fine! Oh and don’t worry, the radioactive rocks are here, we’ll get there in a minute. The radiations we talked about earlier exist in many forms, but there are 3 main types: Alpha, beta, and gamma rays. Alpha ray is a particle, made of 2 protons and 2 neutrons. It interacts a lot with matter, it’s the most dangerous one, but it naturally stops after a few centimeters of air, or instantly when it hits a paper layer or the skin. Beta ray is either the emission of an electron – then it’s beta minus – or a position – beta plus. These react a bit less with matter but they can run through a longer distance. And they can be stopped with tinfoil, plastic, or glass. And finally gamma rays, they’re actually an electromagnetic wave – just like light – but with a bit more energy and a higher frequency, close to X-rays. Those can get through matter easily, but they interact way less. All these radiation types have a thing in common, which is to be ionizing. Everywhere they go, they disturb the electric balance of matter and create ions, which means atoms or molecules that are charged either positively or negatively. This can induce chemical reactions that are not supposed to happen and this is where it gets toxic, but with a high dose. On the opposite, radiation from visible light, cellphones, WiFi, antennas, radios or even microwave are non-ionizing and they do not damage tissues or DNA. By the way, the exact moment a disintegration happens is random, but when you look at a bigger set of atoms, you can see that the activity rapidly drops, following an exponential decay. There is what’s called the half-life, which is the duration after which half of the atoms of a sample will have decayed. So after 2 half-lives there’s only 1/4 left, 1/8th, etc. To measure radioactivity, I have this Geiger counter, the Radiascan 701. It comes with a pro sensor, and can detect gamma, beta, and alpha rays. So as you can see there’s already a certain rate of radiation in the air, that’s the background radiation I was talking about earlier, coming from the Earth, air, etc. And each time a particle interacts with the sensor on the back, the device beeps, and that’s where the typical sound of Geiger counters come from. This background radiation has an average value of 0.2 microsieverts per hour, so we’ll have to talk about units, but first I have a few rocks to show you. This are all minerals with the same property, which is to contain… Uranium! First here is called autunite, it’s a quite beautiful mineral, crystalline, that contains Uranium in the middle of its molecule and has a color between fluorescent green and yellow. So when I say florescent you say… Yes, look at what happens when you shine it with UV light. It starts glowing with a magnificent and intense green light, you can easily see all the details and crystals, it’s crazy. But hey, it really looks like the typical radioactive stuff you see in cartoons, when it shines green, you know! Here I have a tobernite, which is another mineral compound that contains uranium, this one is a bit darker. And here I have autunite again, but agglomerated as small crystals on a granite mineral. So Uranium equals radioactivity… And even though Uranium by itself isn’t very radioactive… Let’s measure. Getting closer… Ha ha! 301 microsieverts per hour, wow! And for this one… 150 again, let’s go! And the small tobernite? 150 too, come on! Of course it’s a bit scary to hear the counter go wild, at 1,500 times the background value, but it’s not necessarily dangerous to hold them in hands, I mean… HOLY SH** WHAT IS THIS CRAP! By the way it’s very important to know that radioactivity decreases by following an inverse-square law, so every time you double the distance you stand from something radioactive, the intensity of radiation divides by 4, so if you triple the distance it’s divided by 9, etc. So even though I have a super high value on contact, if I barely take the sensor away, it drops… it drops very fast, until about 50cm (2ft) where there’s almost nothing. Oh an also, stories about contamination as soon as something touches anything radioactive, well, this little box has been in contact with the rock for days… And there’s nothing at all, rays only go through of course. Therefore, are these radiation dangerous, and just how much? There are tons of units, but we mainly use those: the Gray, 1 Gray equals 1 joule of energy brought to 1kg of matter, then the Becquerel, which defines the amount of disintegrations per second, and finally Sievert, or microsievert, that takes body effect into account. You have to know that the impact of radiation on the human body depends on the particle you consider, and the organ exposed. Alpha particles have 20 times more effect than beta or gamma, but because they’re blocked by the surface of the skin, you’d need to eat or breathe a radioactive substance that emits alpha for it to be harmful. Also, every part of the body doesn’t react the same when exposed to radiation, the most sensitive are lungs, bone marrow, and the… *cling cling* And a dose received at once or spread in time won’t have the same effects, so it’s a bit hard to define thresholds of danger. But basically, you have high chances of death if you receive a dose of 2Sv at once, no observable effects on blood below 100mSv, and generally, you shouldn’t be exposed to something that emits more than 1mSv per hour. Naturally, we all receive between 2500 and 3500 microsieverts of radiation per year, that’s equal to 2.5 to 3.5 millisieverts. For comparison, an arm x-ray gives a dose of about 1µSv, just about as much as eating 10 bananas. A Paris – NY flight is equal to 40µSv, and a thorax CT scan can climb up to 5,000 or 12,000 µSv. So that’s about 3 to 4 years of natural radiation. It’s not dangerous, but don’t do that several times a year, huh. A nuclear worker in France can receive up to 500mSv of radiation per year on his hands, and 20mSv on his body (50mSv in the USA). But that’s a dose an astronaut receives in about 4 weeks in the international space station, who received about 130 to 160mSv during a 6 month mission. So if you get the calculation right… that’s about 50 to 80 years of radiation. In 6 months. Still, astronauts are just tine. Who else is also more exposed than the average? Smokers! Yes, because there’s polonium 210 and lead 210 in cigarettes, and they’re both radioactive isotopes that will gently get in the lungs and emit from the inside on the organ that’s 12 times more sensitive than skin for instance. Aight, imma head out, bye! Anyway, even though radiation can damage tissues and DNA and cause cancers, it’s all a matter of dose and exposure. So no, holding radioactive rocks from time to time in my hands doesn’t mean something will happen to me. Now that your brains are melting with all this theory, let’s go back to a bit of practice. No, I haven’t built a nuclear bomb. Not yet. •ᴗ• But we’ve built 2 machines that allow to see the path of particles coming from radioactivity. First up we have here a massive cloud chamber. Basically, this machine works by first creating a cold surface. So here we have a copper sheet, under which are a lot of Peltier modules, than can create heat on one side, and cold on the other. Necessarily we need to evacuate the head, so that’s why we have a lot of water-cooling and fans down there. On top of this aquarium I will place a piece of foam soaked in isopropanol. And slowly the vapors will fall and accumulate on the cold plate until they reach a state of supersaturation. We also have high voltage applied between those wire and the sheet, which allows for a better visualization of…the effect. This machine took us about 2 weeks to build, it’s really tough and I could even make an entire video about it. Still, it works partially, I mean it gets cold but not cold enough yet. So for this we had to take out the machine outside where it’s cold, and finally we got some results. So the machine is outside, right now it’s about 3°C, inside the chamber it’s about -32°C, and I placed the autunite rock as you can see, so let’s help it now with a bit of high voltage. Look what happens when I flip the switch… Wow, check it out! It’s beautiful! All these trails you can see in the chamber are only visible because of radioactivity. The Uranium atoms contained in the autunite decay by emitting an alpha particle that ionizes the air and alcohol vapors on its way and this allows the supersaturated alcohol vapors to condense and form tiny droplets that fall. When you see short and thick tracks, these are from alpha particles, because remember they only go for a few centimeters in air. When you see thinner tracks that swirl around, these are electrons so beta minus particles. And by placing a needle from a radium clock, you can also see its alpha radiation. If you let the chamber run without any radioactive material inside, you can see all the natural background radiation in the fog. And if you’re lucky you can even see an atom of Radon decaying, and emitting an alpha particle too. It’s gorgeous but there’s even more simple. This little device called a spark chamber. This one took only 2 hours to build with components you can find on Banggood it’s very easy and works all the time. Inside is a high voltage component that will generate over 30kV, and I’m applying this voltage across the wires and this aluminum plate right there. And as you can see… both are separated by just a few millimeters. The goal is for the spark not to form naturally because there are no spikes between the poles. So when I turn the machine on, there’s no arcing as you can see. And when I bring the rock close to the wires… Now you can see that every time an alpha particle is emitted and crosses the space between the wires and the sheet, it ionizes are on its way and creates a path on which the electrical current can flow much more easily. As a more energetic source of alpha particles, I have this capsule from an old smoke detector that contains Americium. Look what happens when I bring it close. The radiation is a lot more intense, and you can really see that the sparks only from right under the capsule. And when I lift up the radioactive source slowly, you can se that above a certain height, no particles reach the machine because they can only go through a few centimeters of air. You can also demonstrate the fact that alpha particles are stopped by a sheet of paper. Well, people always think it’s creepy but I think radioactivity is pretty cool! This deserves a Like, right? SUBSCRIBE to the channel if you like experiments, and write your ideas in the comments. I could even make a video about these machines, or tutorials to build them because they’re so interesting to watch. Big thanks again to NordVPN for sponsoring this video. Alright I’m out, I have some uranium to stow. Happy Science to all, bye!