1. A philosopher places a grain of rice on the first square of a chess board, two on the next, four on the next and so on. How many go on the last (sixty-fourth square)?

2. A farmer has a warehouse with two million corn cobs in it. Every day he sells exactly half of his remaining stock. How long until he sells it all?

3. Definitions Isotope: A nucleus that has the same number of protons but a different number of neutrons Decay: Emission of an α, β or γ Activity: Number of decays each second Count rate: Number of α, β or γ detected by a Geiger counter every second

4. Typical half-lives http://www.colorado.edu/physics/2000/isotop es/radioactive_decay3.html Radon gas: 3.8 days Iodine: 8 days Uranium-235: 704 million years Carbon-14: 5,730 years Nitrogen-16: 7 seconds.

7. Radioactive Tracers P1b 6.4 What are radioactive tracers?

8. Radioactive atoms behave chemically exactly like their non-radioactive equivalents. This means that they can be used to watch movements of chemicals through the body. Doctors use radioactive iodine to look at how well the kidneys are working.

9. First the patient is injected with a small amount of chemical containing radioactive iodine. Most of the injection is not radioactive.

10. Doctors use special radiation cameras to detect the radioactive iodine getting into the kidneys. The cameras can measure the radioactive iodine present.  UCL

11. These images show what happens to the radioactive tracers. Look at the way the concentration changes as the kidneys clear it from the blood.

16. What is happening here? Time since tracer injected into blood (mins) Radiation detected (counts per second) Left kidney Right kidney Blood 70 60 50 40 30 20 10 0 10 20

17. Time since tracer injected into blood (mins) Radiation detected (counts per second) Left kidney Right kidney Blood 70 60 50 40 30 20 10 0 10 20 As the kidney filters the chemical out you can see the concentration in the blood falling. The chemical is passing into the kidneys here. The level rises. As the kidney filters the chemical out you can see the concentration falling.

18. What is happening here? Time since tracer injected into blood (mins) Radiation detected (counts per second) 70 60 50 40 30 20 10 0 10 20 Left kidney Right kidney Blood

19. Time since tracer injected into blood (mins) Radiation detected (counts per second) 70 60 50 40 30 20 10 0 10 20 Left kidney Right kidney Blood The right kidney is collecting iodine but is not passing it out properly. Its concentration stays high. The left kidney is working well, and filters out the chemical. You can see the concentration falling in the left kidney.

20. Gamma rays are used to kill bacteria, mould and insects in food. Gamma rays are also used to kill bacteria on medical equipment. How is radiation used for sterilisation? 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. It is particularly useful with plastic equipment that would be damaged by heat sterilization.

21. How can radiation find leaks in pipes?

22. How can radiation detect cracks? Gamma rays can also be used to detect cracks after an object has been welded. 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. Gamma rays are like X-rays. welded metal pipe photographic film welding flaws

23. Smoke alarms contain a weak source of alpha radiation. Smoke detectors The alpha particles pass across a small gap and are detected. If there is smoke present, it absorbs the alpha particles and detection is reduced. This causes the alarm to sound.

24. How is radiation used in making paper?