Radioactivity: Principles and Applications (14 October)

1. Radioactivity: Principles and Applications (14 October) • Background • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of radioactivity and human health • Application of the principles of radioactivity

2. Take Home Message • Radioactivity is a natural process • Radioactivity is due to the instability of atoms, resulting in the spontaneous emission of subatomic particles and/or energy • Radioactivity has unique features including isotopes and radioactive decay • Human health issues of radioactivity are based on the ability of emissions to affect a cell’s biochemistry and metabolism • Radioactivity has been “harnessed” to provide a host of applications to enhance the quality of life • Radioactivity also has its liabilities associated with waste disposal and misuse

3. Radioactivity: Principles and Applications • Background • Isotopes • Stable • Unstable = radioactive • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of human radioactivity • Application of the atomic principles of radioactivity

4. Isotopes • Atoms have specific number of protons, neutrons and electrons 8 O 16 • If the number of protons is unchanged but the number of neutrons goes up or down, what happens to the properties of that element? 8 O 17

5. Isotopes Continued • Atoms of an element with same number of protons but different number of neutrons are isotopes • Key is the number of neutrons • Conventional notation ( AZX) • Not all elements have isotopes, but many do: • Hydrogen (common isotope: 11H; 31 H or tritium) • Nitrogen (common isotope: 714N; 157N) • Oxygen (common isotope: 816O; 188O) • Sulfur (common isotope: 1632S; 3316S

6. Isotopes of Hydrogen Hydrogen 11H Stable Deuterium 21H Stable Tritium 31H Unstable Proton Neutron

7. Stable versus Unstable Isotopes • Stable over time • Unstable: “transmutate by releasing mass and/or energy

8. Radioactivity: Principles and Applications • Background • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of human radioactivity • Application of the principles of radioactivity

9. Discovery of Radioactivity • Rutherford (as in the nucleus) and three forms of “transmutated” activity (“radioactivity”) • Alpha (a): nucleus of the helium atom (42He) • Beta (b): high energy electron • Gamma (g): electromagnetic radiation with very short wavelengths

11. Principal Early Observations • Atom exhibits “spontaneous” release of • mass (a or b) • energy (g) • Nucleus changes identity simpler atomic structure • 100% natural process • Spontaneous release of mass or energy is called radioactive decay

12. Radioactivity: Principles and Applications • Background • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of human radioactivity • Application of the principles of radioactivity

13. Natural/Background Radioactivity • Sources • Cosmic rays from outer space • Soils • Water • Building materials • Nuclear sources • Examples • Radon gas (Ra)

14. Radioactive Decay • Uranium – 238 23892U (92 protons; 238-92 (146) neutrons • Spontaneous release of an alpha (a) subatomic particle (helium nucleus or 42He) results in an atom with 90 protons and mass of 234 23490? or _____ (periodic table) • All isotopes of all elements with > 83 protons (Bismuth) are unstable and radioactively decay

15. Types of Decay • Alpha (a) • Release of 42He • Travel distance: easily stopped by sheet of paper (even air) • Eventually acquires electrons to yield normal He atom • Beta (b) • Release of high energy electron • Travel distance: 10 meters; 1 cm aluminum block • Eventually “finds” an atom needing an electron • Gamma (g) • Release of high energy electron • Travel distance: 100’s meters; 5 cm block lead brick • Eventually energy is absorbed by material

16. Penetration of Radiation

17. Radioactive Decay

18. Radioactive Decay • Rate of decay to a stable state (no more spontaneous decay) is specific for each isotope • Rate has unique terminology called half-life • Time for ½ (50%) of the nuclei to decay to the stable state is abbreviated t1/2 • Example: M&M’s

19. Radioactive Decay

20. Measurement of Radiation • Number of nuclear disintegrations per unit of time called a curi (Ci); 3.70 x 1010 nuclear disintegrations second-1 • Radiation at the site of absorption (living tissues) • Radiological dose in units called rem • Natural dose = 0.001 rem (1 millirem)/day • Lethal dose = 500 rem

21. Radioactivity: Principles and Applications • Background • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of radioactivity and human health • Application of the principles of radioactivity

22. Radioactivity: Human Health • Radioactivity in biological tissues results in atoms being ionized • Disrupts bonds • DNA as primary site of action • Fragments molecules and disrupts biochemistry • Sensitivity is greatest for actively growing cells and tissues • Blood • Bone marrow (Cesium-137) • Thyroid (I-131)

23. Radioactivity: Principles and Applications • Background • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of radioactivity and human health • Application of the principles of radioactivity

24. Application of Atomic Principles of Radioactivity • Radiation medicine and radiopharmaceuticals • Nuclear energy • Yucca Mountain, Nevada • Three Mile Island • Chernobyl • Dirty bomb

25. Chernobyl Reactor

26. Chernobyl

27. Yucca Mountain Waste Repository

28. A high speed electron emitted from a nucleus during radioactive decay is called a (an) _____. • Alpha • Beta • Gamma • All of the above

29. A sheet of paper will stop a (an) ____. • Alpha • Beta • Gamma • All of the above

30. Rate of radioactive decay is affected by changes in ______. • Temperature • Pressure • Sample size • Other radioactive materials nearby • None of the above

31. What is meant by background radiation? Is the dose of background radiation equivalent over the Earth’s surface?For you as an individual, what are the most common sources of natural/background radiation?

32. Why measure the duration of radioactivity in units of half life (t1/2) versus lifetime?

33. Beryllium-7 (74Be) is an unstable isotope of Beryllium (94Be). When the atom “transmutates”, the stable product that is formed is the element Lithium (73Li).What was emitted in the process of radioactive decay?Is 73Li stable or unstable?