Radioactivity

1. Radioactivity Ch 10

2. Radioactivity is the process in which an unstable atomic nucleus emits charged particles & energy

3. Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope

4. How is the Atom Unstable? The nuclear “glue” that holds the nucleus together sometimes isn’t strong enough. Over time the atom “drops” some of it’s subatomic particles …called radioactive decay!

5. New Way of WritingNuclides & Isotopes 3919 K ; 4019 K Superscript is the mass number Subscript is the atomic number 146C ; 126 C

6. Isotopes have the same number of p+, different number of no Another way to show an isotope is to have the mass number follow the name of the element (Carbon-14 or C-14)

7. Types of Nuclear Radiation Alpha 2.Beta 3. Gamma

8. Alpha Decay Alpha particle—a positively charged particle made up of two p+ & two no the least penetrating can be stopped by a sheet of paper

9. Alpha Decay An alpha particle looks like a helium atom (42He) mass reduces by 4 atomic# reduces by 2

10. Examples: 23892 U  20984 Po 

11. Beta Decay A beta particle is an e- emitted by an unstable nucleus can be stopped by a thin sheet of metal such as aluminum

12. Beta Decay A beta particle is written 0-1 e mass remains the same & the atomic # increases by one

13. Examples: 21482 Pb 21884 Po

14. Gamma decay • A gamma ray is a penetrating ray of energy emitted by an unstable nucleus • Gamma rays are energy waves that travel through space at the speed of light

15. Gamma decay atomic # and mass remain the same, but the energy of nucleus decreases Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

17. Thanks Cambridge Physics Outlet for amazing graphics!

18. STAR Questions U-238 loses 4 total subatomic particles, 2 being protons. What elements are formed? Thorium and Helium What type of decay has it undergone? Alpha decay What is the most penetrating decay? Gamma rays

19. Background radiation is nuclear radiation that occurs naturally in the environment (levels are low enough to be safe) Radioisotopes in the air, water, rocks, plants, & animals all contribute

20. Background Radiation

21. Cosmic rays (streams of charged particles) from outer space that collide with the Earth’s atmosphere also contribute • When nuclear radiation exceeds background levels, cells in your body can mutate

23. Detecting Radiation Devices used to detect radiation include Geiger counters & film badges

24. RATES OF NUCLEAR DECAY A half-life is the time required for one half of a sample of radioactive material to decay Unlike chemical reactions, nuclear decay rates are constant regardless of temperature, pressure or surface area

25. C-14 has a half life of 5730 years. What fraction of a sample will be remaining after 1 half life? After 2 half lives?

26. C-14 has a half life of 5730 years. If you have a sample of 50 grams. How much of the sample will be remaining after 1 half life? After 2 half lives?

27. Examples • Iodine-131 has a half-life of 8.07 days. What fraction of a sample of iodine-131 is left unchanged after 16.14 days?

28. Examples • The radioactive isotope Ni-63 has a half-life of 100 yrs. How much of a 10g sample remains after 300 yrs?

29. Examples • How long will it take a sample of Po-194 to decay to 1/8 of its original amount, if Po-194 has a half life of 0.7 seconds?

30. Examples • A sample of Cl-38 is observed to decay to 25% of its original amount in 74.4 min. What is the half-life of Cl-38?

31. RATES OF NUCLEAR DECAY Transmutation is the conversion of atoms of one element to atoms of another

32. Transuranium elements are elements with atomic numbers higher than 92 (Uranium) A quark is a subatomic particle theorized to be among the basic units of matter

33. FISSION AND FUSION Fission is the splitting of an atomic nucleus into two smaller parts Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus

34. Fission Advantages: is the lack of air pollution. Disadvantages: include the risk of exposure & radioactive waste Harris plant, near Raleigh Lake Harris

35. Fusion release huge amounts of energy occur in the sun and stars (plasma)

36. Fusion • We do not use fusion reactions for energy b/c of the extremely high temperatures needed to start the reaction & because the plasma would need to be contained.

37. Star Questions • The combining of two nuclei • Fusion • Alpha particle looks like the atom of which element? • Helium • This type of nuclear radiation is the most penetrating? • Gamma • Boron-10, what is the nuclide look like?

38. Fission A tremendous amount of energy is produced during a fission reaction

39. Fission A chain reaction is a chain of fission reactions triggered by neutrons released during the fission of a nucleus About 20% of the electricity in the US comes from fission reactions

44. Not in my backyard…

45. Temporary Storage (6 months - 5 years) Wet Storage Dry Storage

46. Then sealed and transported by way of trucks and trains for more permanent storage. Low-level wastes will stay above ground until they become “stable”.

47. If high-level, the wastes are stored deep underground, where they wait for hundreds to thousands of years to become “stable”.

48. RECYCLE • France and Pakistan reprocessing spent nuclear fuel • Call it MOX fuel (Mixed oxide) refers to a blend of plutonium and natural uranium, reprocessed uranium, or depleted uranium • The use of MOX does change the operating characteristics of a reactor, and the plant must be designed or adapted slightly to take it

50. THREE MILE ISLAND • Three Mile Island power station is near Harrisburg, Pennsylvania • In 1979 at Three Mile Island nuclear power plant a cooling malfunction caused part of the core to melt in the # 2 reactor. The TMI-2 reactor was destroyed. • Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents. • There were no injuries or adverse health effects from the Three Mile Island accident.