n Risks from Nuclear Radiation Radiafion’s dangerous and useful al the same fime — it ean both cause and cure cancer, for instance. " Ionising Radiation Can Damage Cells and Tissues 1) Bele and gamma oan penetrate the kin and eof fiseues to reach the delicate organs inside the body. This makes beta and gamma sources more hazardous than alpha when outside the body. If they get inside (e.g. swallowed or breathed in), theit radiation mostly passes straight out without doing much damage. 2) Alpha radiation can't penetrate tho ckin, but it's very dangerous if it gets incide the body. Alpha sources do all their damage in a very looalised area. MUTATE The properties oF ala, beta 3) When radiation enters your body, it wil collide with moleoules in your oa. = od gonna ne cree sy = These collisions cause ionisation. which damages or destroys the molecules. "1 iii vitae The extent of the harmful effects depends on how much exposure ‘you have to the radiation, and its energy and penetration. jee uw weal 4) Lower doses tend to cause minor damage without killing the cell. This can cause mutations in cells which then divide uncontrollably — this is cancer. 5) Higher doses tend to kill celle completely, causing radiation sickness if a large part of your body is affected at the same time. DP ead cll Exposure to Radiation is called Irradiation 1) Objects near @ radioactive source are jtradiated by if. This simply means they're exposed to it (we're ahvays being irradiated by background radiation sources). . 2) Irradiating something does not make it radioactive (and won't turn you into @ superhero). 8) Keeping sources in lead-lined boxes, standing behind barriers or being in a different room t ‘and using remote-controlled arme are all ways of reducing the risk of irradiation. | Contamination is Radioactive Particles Getting onto Objects 1) Hf unwanted radioactive atoms get onto or info an object, the object is said to be contaminated. E.g. if you {ouch a radioactive source without wearing gloves, your hands would be contaminated. 2) These contamineting atoms might then decay, releasing radiation which could cause you herm. 2) Contamination is especially dangerous because radioactive particles could get inside your body. 4) Gloves and tongs should be used when handling sources, to avoid patticles getting stuck to your ckin or under your nails. Some industrial workers wear protective sults and masks to stop them breathing in particles. | Radioactive Waste is Difficult to Dispose of Safely 1) Most radioactive waste from nuclear power stations and hospitals is ‘low-level’ (slightly radioactive) — ‘things like clothing, syringes, ete. This kind of waste can be dieposed of by buruing it in secure landfil sites. 2) High-level waste is the really dangerous stuff — a lot of it stays highly radioactive for tens. of thousands of years, and so has to be treated very carefully. It's often sealed into glass blocks, which are then sealed in metal canisters. These could then be buried deep underground. 8) However, difficult to find suitable places to bury high-level waste. The site has to be geologically stable (e.g. not suffer from earthquakes), since big movements in the rock could listurb the canisters and allow radioactive material to leak out. If this material gets into the groundwater, it could contaminate the soil, plants, rivers, etc., and get into our drinking water. Failing your exams would be a high-level waste of time... Make sure you ean describe how to reduce the risks of nuclear radiation, and why its so important that you do. QU Explain the difference between contamination and irradiation [1 mark] Q2 Give three safety measures that should be followed to avoid the risk of irradiation [2 marks} Section 7 — Radioactivity and Particles72 Nuclear Fission and Fusion Loads of energy's released either when you break apart really big nuclei or join together really small nuclei. | Nuclear Power Stations use Nuclear Fission Chain Reactions | 1) Nuclear fission is the eplifting of an atom, which releases eneray. If can be spontaneous, but reactor i's made to happen — e.g. to uraniuim-235. 2) a slow-moving neutron is absorbed by @ uranium-235 nucleus, the nucleus ean split. 8) Each time this happens, it spits out a small number of neutrons. These might go on to hit other uranium-286 nuolei, causing them to eplit also... and go on and 0 on. T 4) When uranium-235 splits in two it will form {wo new daushter nuclei, both lighter elements than uranium. 5) These now nuclei are usually radioactive. This ie the big problem with nuclear power — radioaotive waste. 6) Each nucleus splitting gives out » lot of enerey — this energy is in the kinetic energy stores of the fission products (the daughter nuclei and the neutrons). 7) Ina reactor, this energy is transferred to thermal energy stores to produce sieam to drive a jurbine (see below). ‘a nuclear " Nuclear Reactors Have to Work Safely | 1) The neutrons released by fission reaotione in a nuclear reactor [Baron have a lot of energy. In order to be absorbed by uranium nuclei |eontrol and gustain the chain reaction, they need to be slowed down. 2) The moderator, usually graphite or water, slows down neutrons. 8) Control rods, often made of boron, limit the rate of fission by absorbing excess neutrons. 4) The high-energy neutrons and gamma rays (energy) released in fission are highly penetrating ionising radiation. Shielding has to be used to absorb the ionising radiation. ‘The shielding is usually a thick concrete structure, which may also contain lead or other metals. 5) A substance (e.g. CO,) pumped round the reactor transfers the energy (by heating) to the water in the heat ‘exchanger. The water turns to steam, which furne a turbine, which turns @ generator and generates electricity. | Nuclear Fusion ing Small Nucle: n is the opposite of nuclear fission. In nuclear fusion, two light nuclei collide at high speed and create a larger, heavier nucleus. E.g. hydrogen nuclei can fuse to produce a helium nucleus. nucleus doesn't have as much mass as the two separate, did. Some of the mass of the lighter nuclei is converted to energy (don't panic, you don't need to know how). This energy is then released es radiation. 8) Fusion releases a lot of energy (more than fission for a given mass of fuel) — all the energy released in stars comes from fusion. 4) The big problem i that fusion only happens at really high pressures and temperatures (about 10 000 000 °C). This is because the positively charged nuclei have to get very close to fuse, so they need to be moving very fact to overcome the strong force due to elecirostatio repulsion (p.28). 1s haven't found a way of using fusion to generate energy for us fo use. The jemperalures and pressures needed for fusion are so high that fusion reactors are really hard and expensive 40 build. / Pity they can’t release energy by confusion...* Nuclear reactors are carefully-designed to release energy safely, but we've not worked out how to do that with fusion yet. 1) Nuclear fusi join (fuse) 2) 5) | QI Draw a diagram showing how fission can lead to a chain reaction. [3 marks] Q2 Explain why fusion only occurs at high temperatures and pressures. [2 marks] Section 7 — Radioactivity and Particles “There'd be plenty of physi books to use as fue13 Revision Questions for Section 7 Well, that wraps up Section 7. Now a reward for ploughing through loads of pages of pretty intense ccience —a page of lovely questions. Okay, | know it seems a little daunting, but it's absolutely vital to check that ‘you've learnt all the right ctu. + Try these questions and fick off each one when you get it right. + When you've done all the questions for a topie and are completely happy with it, tok off the topic. Nuclear Radiation (p.66-68) [] 1) What ic the atomic number of a nucleus? 2) What is the mass number of a nucleus? 8) What are isotopes of an element? 4) Name four things that may be emitted during radioaotive decay. 5) Briefly describe what background radiation is and where it comes from. 8) Des 7), Which is the most ionising out of alpha, beta and gamma radiation? 8) Describe how the mass and atomic numbers of an atom change if it emits an alpha particle. what alpha, beta and gamma radi 9) In whet type of nuclear decay does @ neutron change into @ proton within the nucleus? 10) What type of nuclear decay doesn't change the mass or charge of the nucleus? I) What type of radiation is stopped by paper? 12) Give two ways you can deteot ionising rac 13) What quantities need to be the Half-life (p.69) 7] 14) What is meant by the ‘activity’ of a radioactive source? 15) Define half-life. 16) True or false? A short half-life means a small proportion of the atoms are decaying per second. Uses and Risks of Nuclear Radiation (p.70-71) [_] 17) Briefly describe ¢wo uses of nuclear radiation in medicine. ion. noooooooooo0o! ich side of @ nuclear equation? 18) Explain why alpha radiation could not be used to check the thickness of metal sheets. j00 OON 19) Other than thickness gauges, give one other use of nuclear radiation in industry. 20) Why is nuclear radiation dangerous to living organisms? Ol 21) Explain why radioactive waste ie difficult to dispose of eafely. Fusion and Fission (p.72) [_] 22) What are the products of the nuclear fission of uranium-2357 23) True or false? The fission products of uranium-235 are also radioactive. Oo 24) Briefly describe how a chain reaction is set up in a nuclear reactor. 25) What job do control rods, moderatore and shielding do in @ nuclear reactor? oo 26) State the conditions needed to create a fusion reaction. Section 7 — Radioactivity and Particles