Radioactivity and Nuclear Reactions

1. Radioactivity and Nuclear Reactions

2. Radioactivity • Protons and Neutrons are attracted to each other in the nucleus of an atom by the “strong force” • The total force between these particles depends on how far apart they are • Smaller nuclei have a stronger attraction to each other and are more stable • Larger nuclei are held together less tightly and the strong force may not be enough to keep the atom stable. • When the “strong force” is not enough to hold a nucleus together, the nucleus begins to decay and give ff matter and energy. • This is called radioactivity

3. Radioactive decay is the process by which the unstable nuclei lose mass and/or energy by emitting radiation. Eventually unstable nuclei achieve a more stable state when they are transformed into atoms of a different element.

4. All nuclei that contain more than 83 protons are radioactive • Almost all elements with more than 92 protons don’t exist naturally on Earth and are only produced in laboratories • These are called synthetic elements and decay soon after they are created due to being unstable

5. Radioactivity is all around you, even in your body • It cannot be detected by smell, sight, sound, taste, or touch • Radioactivity can be captured on photographic plates (x-rays)

6. Radioactivity Radioactivity was 1st discovered by Antoine Becquerel, when a photographic plate never exposed to Sunlight in his lab had become exposed. The only possible culprit was a nearby uranium salt sitting on the bench top.

7. Nuclear Decay • There are three types of nuclear radiation • Alpha • Beta • Gamma radiation Alpha and Beta are particles Gamma radiation behaves like a wave of light at a very high frequency

8. Transmutation is changing one element to another by nuclear decay • In Alpha decay, two protons and two neutrons are lost from the nucleus so the new element has an atomic number two less than that of the original element

9. Alpha Particles • Alpha Particles are the least penetrating form of radiation. They can be stopped by a piece of paper • Ex. Smoke detectors give off alpha particles that ionize the surrounding air. Smoke particles absorb the ions and electrons and break a circuit which causes the alarm to go off

10. Alpha Particle Emission (α) Uranium - 238 Thorium - 238 Alpha Particle (α)

11. Beta Particles • Beta particles are faster and more penetrating than alpha particles. They can pass through paper and are stopped by a sheet of aluminum foil

12. During Beta decay an electron is emitted from the atom and a new element is formed

13. BETA EMISSION Beta Particle Nitrogen - 14 Carbon - 14 A beta particle (a high energy electron, charge of -1) is generated in the nucleus as a neutron is converted into a proton.

14. Gamma Rays • The most penetrating form of radiation are gamma rays • Gamma rays carry energy • Thick blocks of lead and concrete are required to stop gamma rays

15. Gamma Emission (λ) Generally accompanies other radioactive radiation because it is the energy lost from settling within the nucleus after a change.

16. Penetrating Power of Radiation

17. Radioactive Half-Life Half-Life (t1/2) is the time required for half of the atoms of a radioisotope to emit radiation and to decay to products.

18. Half-Life Example It takes 4.5 X 109 years for one half of a sample of uranium-238 to decay to lead-206. Therefore, it would take another 4.5 X 109 years for one half of the remaining uranium to decay, et cetera, et cetera, et cetera. 1 half-life 100g 50g 2nd half-life 50g 25g 25g 3rd half-life 12.5g 4th half life 12.5g 6.25g

19. How many atoms of a 2.97g. sample of molybdenum-91 would remain after 62 min. if the half-life of molybdenum-91 is 15.49 min.? How many ½ lives is this? Answer = 0.19 g 4 half-lives

20. Types of Nuclear Reactions • There are two types of nuclear reactions • Fission – splitting the nucleus • Fusion – fusing or combining of nuclei

21. Nuclear Fission Fission is the breaking apart of a very heavy nucleus into parts.

22. Fusion is the combining of 2 small nuclei into 1 larger one. Fusion of hydrogen into helium occurs in the sun. Fusions reactions should produce much more energy than fission and use much more accessible fuels. However, currently many problems exist in fusion reactions such as the extremely high temperature needed for the reaction.

24. Radiation Detection Film badges are used to monitor the amount of radiation exposure people have received.

25. Geiger Counter Instrument that detects radiation by measuring current produced by gas particles ionized by radioactivity

26. Scintillation Counter Instrument that converts light to an electric signal for detecting radiation.

27. Uses for Nuclear Radiation Since the physical and chemical properties of radioisotopes of an element are the same as stable ones, many uses for radioactive nuclides are possible.

28. In medicine radioactive nuclides are used to destroy cancer cells and as tracers to tract substances through the body or identify cancer and other diseases. Cobalt - 60 Radioactive Tracer

29. In agriculture, radioactive nuclides are used as tracers in fertilizer to determine the effectiveness or to prolong shelf life of food by irradiating to destroy microorganisms.

30. In dating radioactive nuclides are used to determine the age of objects. Example: Carbon -14 is used to date organic materials.

31. In energy production, currently nuclear fission is used to create energy. Example: Comanche Peak nuclear power plant in Glen Rose produces energy that is used by TXU.

32. Nuclear Waste Nuclear fission produces radioactive wastes that must be contained and stored on-site (temporary) or disposed of (permanent).