1. It’s better to have a half-life than no life! Radioactive Decay Alpha, Beta, and Gamma Decay

4. The Atom The atom consists of two parts: 1. The nucleus which contains: 2. Orbiting electrons. protons neutrons

5. All matter is made up of elements (e.g. carbon, hydrogen, etc.). The smallest part of an element is called an atom . Atoms of different elements contain different numbers of protons . The mass of an atom is almost entirely due to the number of protons and neutrons . The Atom

6. X A Z Mass number Atomic number Element symbol = number of protons + number of neutrons = number of protons

7. A = number of protons + number of neutrons Z = number of protons A – Z = number of neutrons Number of neutrons = Mass Number – Atomic Number X A Z

8. There are many types of uranium: U 235 92 U 238 92 Number of neutrons Number of protons Z A Number of neutrons Number of protons Z A

9. There are many forms or “isotopes” of uranium: Isotopes of any particular element contain the same number of protons, but different numbers of neutrons. U 235 92 U 238 92 143 Number of neutrons 92 Number of protons 92 Z 235 A 146 Number of neutrons 92 Number of protons 92 Z 238 A

10. Most of the isotopes which occur naturally are stable . A few naturally occurring isotopes and all of the man-made isotopes are unstable . Unstable isotopes can become stable by releasing different types of particles. This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides .

12. An alpha particle is identical to a helium nucleus. It contains two protons and two neutrons. Alpha Decay

15. Example of Alpha Decay (Radium-226 to Radon, Half-life : 1,601 years) Ra 226 88 Rn 222 86 He 4 2

16. Alpha Decay (Radium-226 to Radon) X A Z Y A - 4 Z - 2 + He 4 2 Ra 226 88 Rn 222 86 + He 4 2

17. Alpha Decay (Radon-222 to Polonium, Half-life : 3.8 days) Rn 222 86 He 4 2 + Po 218 84 He 4 2 Rn 222 86 + Y A Z He 4 2

18. Alpha Decay (Uranium-234 to Thorium-230, Half-life : 246,000 years) He 4 2 U 234 92 + Th 230 90 He 4 2 X A Z + Th 230 90 He 4 2

19. Alpha Decay Thorium-230 to Radon-226, Half-Life : 75,380 years) Th 230 90 + Y A Z He 4 2 He 4 2 + Ra 226 88 He 4 2 Th 230 90

20. Alpha Decay Polonium-218 to Lead-214, Half-Life: 3.05 minutes) X A Z + Pb 214 82 He 4 2 He 4 2 + Pb 214 82 He 4 2 Po 218 84

22. Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton (+) and an electron (-).

23. Beta Decay As a result of beta decay, the nucleus has one less neutron , but one extra proton . The atomic number, Z, increases by 1 and the mass number, A, stays the same.

24. Beta Decay (Polonium-218 to Astatine, Half-Life: 3.1 Minutes) Po 218 84  0 -1 At 218 85

26. Beta Decay (Thorium-234 to Protactinium, Half-Life : 24 days) Th 234 90 Y A Z +  0 -1 Th 234 90 Pa 234 91 +  0 -1

27. Beta Decay (Thallium-210 to Lead-210, Half-Life : 1.3 minutes) X A Z Pb 210 82 +  0 -1 Tl 210 81 Pb 210 82 +  0 -1

28. Beta Decay (Bismuth-210 to Pollonium, Half-Life : 5.012 days) Bi 210 83 Y A Z +  0 -1 Bi 210 83 Po 210 84 +  0 -1

29. Beta Decay X A Z Bi 214 83 +  0 -1 Pb 214 82 Bi 214 83 +  0 -1

31. Gamma Decay Gamma rays are not charged particles like  and  particles. They are released with these particles . Gamma rays are electromagnetic radiation with high frequency. They have 10,000 times more energy than visible light. When atoms decay by emitting  or  particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10 -12 J).