Radioactivity

1. 1 Radioactivity Clip

2. 2 1 . Differentiate among alpha and beta particles and gamma radiation . 2 . Differentiate between fission and fusion . 3 . Explain the process half-life as related to radioactive decay . 4. Describe nuclear energy , its practical application as an alternative energy source , and its potential problems.

3. 3 Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process. After decaying, radioactive atoms “change” into other atoms Clip

4. Why does the atom do this? the nucleus of an atom attempts to become more stable In some instances, a new element is formed and in other cases, a new form of the original element, called an isotope, appears. this process of change is often referred to as the decay of atoms. The rate of Radioactive decay is described in half-lives. 4

5. Energy is released during radioactive decay 5

6. 6 Types of Nuclear Radiation • When an unstable nucleus decays, particles and energy are given off from the decaying nucleus. • α and β radiation is in the form of particles • γ radiation is in the form of waves-kind of like light but higher frequency

7. 7 Nuclear Decay 2 protons & 2 neutrons Neutron decays into a proton

8. Alpha particles consist of two protons and two neutrons, identical to the nucleus of a helium atom. A sheet of paper or a person’s surface layer of skin will stop them. Alpha particles are only considered hazardous to a person’s health if they are ingested or inhaled and thus come into contact with sensitive cells such as in the lungs, liver and bones. 8

9. 9

10. Beta particles are electrons emitted from the nuclei of many fission products. 10 • They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood. • They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough. • Unstable Neutron decays into a proton.

11. 11

12. Gamma rays are a form of electromagnetic radiation (like light, radio, and television) that come from the nucleus of a radioactive atom. Occurs when an unstable nucleus emits electromagnetic radiation. The radiation has no mass, and so its emission does not change the element. They penetrate matter easily and are best stopped by water or thick layers of lead or concrete. Gamma radiation is hazardous to people inside and outside of the body. • However, gamma radiation often accompanies alpha and beta emission, which do change the element's identity. • Gamma rays have the lowest ionizing power, but the highest penetrating power. 12

13. 13

14. Biological Effects of Radiation: • Ionizing radiation causes physical damage to cells and DNA. • Radiation can excite DNA and result in the destruction on the DNA backbone. • At high doses of radiation (10,000 - 15,000 rads), death occurs in a few hours because of neurological and cardiovascular breakdown (Central Nervous Syndrome). 14

15. 14 • Biological Effects of Radiation: • Medium doses, 500 - 1200 rads, causes death to occur in a few days because of the destruction of the gastrointestinal mucosa. • Lower doses, 250 - 500 rads, causes death to occur after several weeks due to damage of the blood forming organs (hematopoietic syndrome).

16. Radiation is used positively in a variety of ways 15 • Medicine • For example, radiation and radioactive tracers • are used to diagnose and treat medical problems. • A radioactive tracer is a radioactive isotope that is added to a substance so that the substance can be detected later. • Radioactive tracers are used to locate tumors, to study the functioning of a particular organ, or to monitor the flow of blood. • For example, radioactive iodine-131 is used to diagnose thyroid problems. • Radiation therapyused to treat cancer may involve the use of implanted radioactive isotopes such as gold-198 or iridium-192.

17. Industry • Manufacturers can also use radiation to check the thickness of metal containers by measuring the amount of radiation that passes through. • Small amounts of radioactive isotopes, like magnesium-28, can be introduced in a water source to determine the flow of underground water or to determine if an underground water system is leaking. • Radioactive isotopes are even used in smoke alarms. 16

18. 17 Generate electrical power Nuclear fission is used to generate electricity as an alternative energy source. Dating Even the age of fossils or rocks can be determined by using radioactive isotopes.

19. 18 Fission and Fusion Fission Fusion Splitting a nucleus Combining of two nuclei.

21. 19 • Nuclear power can come from the fission of uranium, plutonium or thorium or the fusion of hydrogen into helium. • Today it is almost all uranium. • The fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

22. Issues for Fission Power Plants • Need for a spent fuel disposal facility and a decommissioning plan • Use of large amounts of water for cooling purposes (if wet cooling towers are used) –thermal pollution • Biological impacts on the ocean due to thermal discharge (if seawater cooling is used) • Public safety concerns 20 Clip

23. 21 • FUSION • A fusion reaction occurs when nuclei of light elements, specifically hydrogen and its isotopes (deuterium, or "heavy water," and tritium), are forced together at extremely high temperatures and densities until they fuse into nuclei of heavier elements and release enormous amounts of energy. • If fusion is to yield net energy, the fuel must be heatedin the form of plasma (a highly ionized gas) to a very high temperature and the plasma must then be held together for a sufficiently long time such that the number of fusion reactions occurring releases more energy than was required to heat the fuel.

24. 22 Half Life is the amount of time it takes for half of the nuclei in a sample to decay Mass (kg)

26. 12C 14C mass number 13C • Carbon occurs naturally in three isotopes. • All of these atoms have the same number of protons but different numbers of neutrons. • The number of neutrons and protons determines the mass, so the masses are different. • 14C is radioactive.

27. 14C • Radioactive 14C acts chemically just like 12C, so it becomes incorporated into plants an animals. • When the animal/plant dies the 14C begins to decay into 14N at a know rate, so we can determine how long ago the organism died. • This is called Carbon Dating. • It’s only good for about 50,000 years.

28. The half life of 14C is 5,730 years. If a sample originally contained 100 g, how much would be left after 11,460 years? 26 50g 25g

30. Older Dating Methods • The isotopes 235U and 238U can be used to date objects billions of years old. • 235U has a half life of 704 million years. • 238U has a half life of 4.5 billion years. • Mainly used for rocks.

31. Geiger Counter • Used to measure radiation. • The more intense the radiation the more “clicks”.