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What do you think of radiation? 3 of 34 © Boardworks Ltd 2006

What is ‘radiation’? The term radiation (also known as nuclear radiation) refers to the particles or waves emitted by radioactive substances. Nuclear radiation comes from the nucleus of a radioactive atom. electron An atom has electrons orbiting the outside and a central nucleus, which is made up of protons and neutrons. proton neutron In a radioactive atom, the nucleus is unstable and so it emits particles or waves to form a more stable atom. This process is called radioactivity or radioactive decay. It is a natural and completely spontaneous process. 4 of 34 © Boardworks Ltd 2006

How can radiation be detected? Radiation is all around us – naturally occurring, and manmade sources, but it is invisible, so how do we actually know it’s there? The effects of radiation can be seen and so it can detected using instruments such as a Geiger-Müller tube. This is a device that can detect and measure radiation. Radioactivity can also be detected by the presence of photographic film, which darkens when struck by radiation. This effect led to the initial discovery of radioactivity more than one hundred years ago. 5 of 34 © Boardworks Ltd 2006

The discovery of radioactivity 6 of 34 © Boardworks Ltd 2006

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What is radioactive decay? 8 of 34 © Boardworks Ltd 2006

How do materials affect radiation? 9 of 34 © Boardworks Ltd 2006

How do magnetic fields affect radiation? 10 of 34 © Boardworks Ltd 2006

What is alpha (α) radiation? Description 2 neutrons, 2 protons Note: – An alpha particle is the same as a helium nucleus Electric charge +2 Relative atomic mass 4 Penetrating power Stopped by paper or a few centimetres of air Ionizing effect Strongly ionizing Effect of magnetic/ electric field Weakly deflected 11 of 34 © Boardworks Ltd 2006

What is beta (β) radiation? Description High energy electron Electric charge -1 Relative atomic mass 1/1860 Penetrating power Stopped by a few millimetres of aluminium Ionizing effect Weakly ionizing Effect of magnetic/ electric field Strongly deflected 12 of 34 © Boardworks Ltd 2006

Gamma ( ) radiation Description High energy electromagnetic radiation Electric charge 0 Relative atomic mass 0 Penetrating power Stopped by several centimetres of lead or several metres of concrete Ionizing effect Very weakly ionizing Effect of magnetic/ electric field Not deflected 13 of 34 © Boardworks Ltd 2006

Types of radiation and penetrating power 14 of 34 © Boardworks Ltd 2006

Types of radiation and range in air 15 of 34 © Boardworks Ltd 2006

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What is radiation used for? 17 of 34 © Boardworks Ltd 2006

How can radiation detect a fire? Smoke alarms contain a weak source of alpha radiation. The alpha particles ionize the air. If there is smoke present, it interacts with the ions produced by the alpha particles and ionization is reduced. smoke particle α This means that less current is flowing through the air, which causes the alarm to sound. 18 of 34 α © Boardworks Ltd 2006

How is radiation used in making paper? 19 of 34 © Boardworks Ltd 2006

How can radiation find leaks in pipes? 20 of 34 © Boardworks Ltd 2006

How can radiation detect cracks? Gamma rays can also be used to detect cracks after an object has been welded. Gamma rays are like X-rays. welded metal pipe welding flaws If a gamma source is placed on one side of the welded metal, and a photographic film on the other side, any flaws will show up on the film like an X-ray. photographic film 21 of 34 © Boardworks Ltd 2006

How is radiation used for sterilization? Gamma rays are used to kill bacteria, mould and insects in food. This can be done even after the food has been packaged. It can affect the taste, but supermarkets like it because it lengthens the shelf life. Gamma rays are also used to kill bacteria on medical equipment. It is particularly useful with plastic equipment that would be damaged by heat sterilization. 22 of 34 © Boardworks Ltd 2006

Uses of radiation – activity 23 of 34 © Boardworks Ltd 2006

Dangers of ionizing radiations 25 of 34 © Boardworks Ltd 2006

Dangers of ionizing radiations – activity 26 of 34 © Boardworks Ltd 2006

Radiation safety The three types of radiation differ in their effects and physical nature. All radioactive sources must be handled safely. The hazard symbol for radiation is shown below: As well as the normal laboratory safety rules you follow, are there any extra rules concerning radioactivity? 27 of 34 © Boardworks Ltd 2006

How are radioactive sources used safely? Radioactive materials could be very dangerous to handle if no safety precautions were taken. This is because people and their clothing could become contaminated. The safety precautions are: l keep exposure times as short as possible l monitor exposure with a film dose badge l label radioactive sources clearly l store radioactive sources in shielded containers l wear protective clothing l use tongs or a robotic arm to handle radioactive materials. 28 of 34 © Boardworks Ltd 2006

Background radiation is the radiation all around us. Most of the radioactivity you are exposed to is from natural sources. How many different sources of background radiation can you think of? 29 of 34 © Boardworks Ltd 2006

Calculating background radiation 30 of 34 © Boardworks Ltd 2006

Glossary l alpha radiation – Positively charged particles made up of two protons and two neutrons. l background radiation – Constant low-level radiation from food and environmental sources. l beta radiation – High-energy electrons emitted by some radioactive materials. l gamma radiation – Short-wavelength electromagnetic radiation emitted during radioactive decay. l Geiger-Müller tube – A device used to detect and measure radiation from radioactive materials. l ionizing radiation – High-energy radiation capable of ionizing substances through which it passes. l radioactivity – The spontaneous emission of radiation from the nucleus of an unstable atom. 32 of 34 © Boardworks Ltd 2006