[MUSIQUE] >> In this video, we'll introduce you to the handling of radioactive sources of type α, β and γ, and radiation protection measures to protect both the people who handle sources and the environment. Let me present Dr. Alessandro Bravar, who is senior lecturer in our particle physics department, and who directs the nuclear physics lab course for our students. Dr. Bravar is an active member of the neutrinos research group in our department, and he prepares an experiment on muon physics at the Paul Scherrer Institute in Villigen, near Zurich. Alessandro, can you explain to us what the rules of the game are, when handling radioactive sources? >> First, in this laboratory, we are using several radioactive sources. In general, they are stored in a safe, to block all the radiation, and also to restrict access to the sources because we cannot allow anyone to use radioactive sources, unless they have had adequate preparation. So, I will take out some radioactive sources, a β source, and a γ source, and we will see how they are protected, how they are stored, and also how we measure the radiation coming out, with shielding and without shielding. >> Very good. So let's go! [BIP] [BIP] So, first thing, I open the safe. This is a first source, a β source, here we have a γ source, and as I'll show you an old watch, where one used radium to make the needles visible. [NO AUDIO] >> So, that's three sources, you see there β- source, 90Sr, you see a γ source, 137Cs, and an old alarm clock that incorporates a very, very weak source of radium. >> So, Alessandro, can you explain why the sources are packaged like this and how students are protected from excessive radiation? >> Okay. So I begin with the first source, it's a β- source, which emits electrons. So all the sources we use here are sealed sources. That is to say that there is a small layer of protection around the source to avoid physical contact and thus contamination. But the protective layer is not sufficient to block all radiations. Depending on the type of radiation, different materials and also materials of different thickness are used to block the radiation. In this case, there is a β- source so it emits electrons. To stop the electrons, one needs about 2cm of plastic, and therefore, the source is contained in this plastic object. Here, if you look, you can see the silvery part, it is the radioactive part that emits electrons. To show that the source is well shielded, you can use a Geiger counter to measure the radiation level. So I turn on the counter, and as we see, there are not many counts coming from the source. On the contrary, if I remove the protection (as I said, 2cm of plastic), and placing the counter on the source, we see compteur sur la source et on voit que on that the count rate goes up a lot, say several thousand hits per second. So I put the cap back on and we see that there is no more radiation from the source. The second source I will show you is a γ source, gammas are photons of a certain energy, rather high energy compared to visible light photons. To protect photon sources, one needs a lead shielding. To stop the photons, it takes a rather heavy material with a rather high Z, such as lead. Here is the lead container, inside we have a second lead container, the source is hidden inside. To remove the source, I use a pair of tweezers, I do not touch the source with my fingers.Inside there is this little piece of lead, which contains the source in its tip. So if I place a Geiger counter just in front of the source, we see that the count rate is quite high. On the contrary, if I put the source in its containers almost no radiation comes out. So to protect from a source of γ-type, one does not just choose the good material, but also a thickness of the shielding according to the intensity of the source. The more the source intense, the more lead I need to stop all photons emerging from the source. >> In fact, we did a little calculation of the absorption of photons in the minimum of their cross section, in a previous video. In the old times, in the 1950s, everyone was much more relaxed with respect to radioactive sources, right? One even put them into objects of every day use. Can you explain what was the purpose of the radioactive source in this clock? >> This is an old alarm clock, and to make the hands visible during the night, they used radium to make them phosphorescent. Today, we use different materials, such as phosphorus, but in the past, people used radium, and this is a very, very dangerous substance. The reason why the radium is so dangerous is that it decyas into radon. Radon is a radioactive element, it is a gas, which is everywhere in nature, and we can breathe radon. Breathing air one also takes in a portion of radon in our lungs, where radon decays by emitting alpha particles, which come in direct contact with the tissues of our body and can do much damage. In fact, radon is one of the concerns we have around the world, in homes, also in Switzerland.There are regions in Switzerland, especially the Alps and the Jura, where there are rocks outgassing a lot of radon, while in big cities, like in Geneva or Zurich etc., there is not much radon. >> That is to say that one should not spend the night in a basement in the Alps. in a basement in the Alps. >> Exactly. Houses must be properly ventilated. >> And, that's why we have banned the use of radium since a long time. To show the effect, although there is a minimum amount of radium, which has been deposited on the clock, with the same Geiger counter, which I used before, one can reach a certain number of counts, which tells us that there is a lot of radium decays from this clock And so it's not a good idea to sleep with such a clock by the bedside. >> And that's why, we have long since banned using radium in clocks. Thank you very much. [MUSIQUE]
