1. 3/2003 Rev 1 I.2.6 – slide 1 of 43 Session I.2.6 Part I Review of Fundamentals Module 2Basic Physics and Mathematics Used in Radiation Protection Modes of Radioactive Decay and Types of Radiation Session 6 Modes of Radioactive Decay and Types of Radiation IAEA Post Graduate Educational Course Radiation Protection and Safety of Radiation Sources

2. 3/2003 Rev 1 I.2.6 – slide 2 of 43 Introduction  Modes of radioactive decay and types of radiation emitted will be discussed  Students will learn about alpha, beta, and gamma decay; positron emission; differences between gamma rays and X- rays; orbital electron capture; and internal conversion

3. 3/2003 Rev 1 I.2.6 – slide 3 of 43 Content  Alpha, beta, and gamma decay  Decay spectra  Differences between gamma rays and X-rays  Positron emission  Orbital electron capture  Internal conversion

4. 3/2003 Rev 1 I.2.6 – slide 4 of 43 Overview  Modes of radioactive de and types of radiation emitted will be discussed

5. 3/2003 Rev 1 I.2.6 – slide 5 of 43 Radioactive Decay  Spontaneous changes in the nucleus of an unstable atom  Results in formation of new elements  Accompanied by a release of energy, either particulate or electromagnetic or both  Nuclear instability is related to whether the neutron to proton ratio is too high or too low

6. 3/2003 Rev 1 I.2.6 – slide 6 of 43 Alpha Emission  Emission of a highly energetic helium nucleus from the nucleus of a radioactive atom  Occurs when neutron to proton ratio is too low  Results in a decay product whose atomic number is 2 less than the parent and whose atomic mass is 4 less than the parent  Alpha particles are monoenergetic

7. 3/2003 Rev 1 I.2.6 – slide 7 of 43 Alpha particle charge +2 Alpha Particle Decay

8. 3/2003 Rev 1 I.2.6 – slide 8 of 43 Alpha Particle Decay

9. 3/2003 Rev 1 I.2.6 – slide 9 of 43 Alpha Decay Example 226 Ra decays by alpha emission When 226 Ra decays, the atomic mass decreases by 4 and the atomic number decreases by 2 The atomic number defines the element, so the element changes from radium to radon 226 Ra  222 Rn + 4 He 28688

10. 3/2003 Rev 1 I.2.6 – slide 10 of 43 Beta Emission  Emission of an electron from the nucleus of a radioactive atom ( n  p + + e -1 )  Occurs when neutron to proton ratio is too high (i.e., a surplus of neutrons)  Beta particles are emitted with a whole spectrum of energies (unlike alpha particles)

11. 3/2003 Rev 1 I.2.6 – slide 11 of 43 Beta particle charge -1 Beta Particle Decay

12. 3/2003 Rev 1 I.2.6 – slide 12 of 43 Beta Particle Decay

13. 3/2003 Rev 1 I.2.6 – slide 13 of 43 Beta Decay of 99 Mo

14. 3/2003 Rev 1 I.2.6 – slide 14 of 43 Beta Spectrum

15. 3/2003 Rev 1 I.2.6 – slide 15 of 43 Rule of Thumb Average energy of a beta spectrum is about one-third of its maximum energy or: E av = E max 1 3

16. 3/2003 Rev 1 I.2.6 – slide 16 of 43 Positron (Beta + ) Emission  Occurs when neutron to proton ratio is too low ( p +  n + e + )  Emits a positron (beta particle whose charge is positive)  Results in emission of 2 gamma rays (more on this later)

17. 3/2003 Rev 1 I.2.6 – slide 17 of 43 Positron (Beta + ) Emission

18. 3/2003 Rev 1 I.2.6 – slide 18 of 43 Positron Decay

19. 3/2003 Rev 1 I.2.6 – slide 19 of 43 Positron Decay

20. 3/2003 Rev 1 I.2.6 – slide 20 of 43 Positron Decay

21. 3/2003 Rev 1 I.2.6 – slide 21 of 43 Positron Annihilation

22. 3/2003 Rev 1 I.2.6 – slide 22 of 43 Orbital Electron Capture  Also called K Capture  Occurs when neutron to proton ratio is too low  Form of decay which competes with positron emission  One of the orbital electrons is captured by the nucleus: e -1 + p +1  n  Results in emission of characteristic X-rays

23. 3/2003 Rev 1 I.2.6 – slide 23 of 43 Orbital Electron Capture

24. 3/2003 Rev 1 I.2.6 – slide 24 of 43 Orbital Electron Capture

25. 3/2003 Rev 1 I.2.6 – slide 25 of 43 radiation path ejected electron +1 ionized atomIonization

26. 3/2003 Rev 1 I.2.6 – slide 26 of 43 characteristic X-rays X-Ray Production electronejected electron fills vacancy

27. 3/2003 Rev 1 I.2.6 – slide 27 of 43 Electromagnetic Spectrum X- and  -rays Infra-redUltra-violet Visible Increase in wavelength : decrease in frequency and energy

28. 3/2003 Rev 1 I.2.6 – slide 28 of 43 Gamma Ray Emission  Monoenergetic radiations emitted from nucleus of an excited atom following radioactive decay  Rid nucleus of excess energy  Have characteristic energies which can be used to identify the radionuclide  Excited forms of radionuclides often referred to as “metastable”, e.g., 99m Tc. Also called “isomers”

29. 3/2003 Rev 1 I.2.6 – slide 29 of 43 Gamma Radiation Gamma Ray Emission

30. 3/2003 Rev 1 I.2.6 – slide 30 of 43 Gamma Ray Emission

31. 3/2003 Rev 1 I.2.6 – slide 31 of 43 Photon Emission DifferenceBetween X-Rays and Gamma Rays

32. 3/2003 Rev 1 I.2.6 – slide 32 of 43 Internal Conversion  Alternative process by which the excited nucleus of a gamma emitting isotope rids itself of excitation energy  The nucleus emits a gamma ray which interacts with an orbital electron, ejecting the electron from the atom  Characteristic X-rays are emitted as outer orbital electrons fill the vacancies left by the conversion electrons

33. 3/2003 Rev 1 I.2.6 – slide 33 of 43 Internal Conversion  These characteristic X-rays can themselves be absorbed by orbital electrons, ejecting them.  These ejected electrons are called Auger electrons and have very little kinetic energy

34. 3/2003 Rev 1 I.2.6 – slide 34 of 43 Internal Conversion

35. 3/2003 Rev 1 I.2.6 – slide 35 of 43 Internal Conversion Electron emitted about 10% Internal Conversion 137 Cs Emits Betas 0.946 x 0.898 = 0.85 Gamma Ray emitted during 85% of 137 Cs transitions

36. 3/2003 Rev 1 I.2.6 – slide 36 of 43 Summary of Radioactive Decay Mechanisms DecayModeCharacteristics of Parent Radionuclide Change in Atomic Number (Z) Change in Atomic Mass Comments Alpha Neutron Poor -2-4 Alphas Monoenergetic Beta Neutron Rich +10 Beta Energy Spectrum Positron Neutron Poor 0 Positron Energy Spectrum ElectronCapture Neutron Poor 0 K-Capture; Characteristic X-rays Emitted GammaExcited Energy State NoneNone Gammas Monoenergetic Internal Conversion Excited Energy State NoneNone Ejects Orbital Electrons; characteristic X-rays and Auger electrons emitted

37. 3/2003 Rev 1 I.2.6 – slide 37 of 43 Summary  Modes of radioactive decay were discussed (including alpha, beta, gamma, positron emission, orbital electron capture, and internal conversion)  X-ray production and the differences between gamma rays and X-rays were described

38. 3/2003 Rev 1 I.2.6 – slide 38 of 43 Where to Get More Information  Cember, H., Johnson, T. E., Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2008)  Martin, A., Harbison, S. A., Beach, K., Cole, P., An Introduction to Radiation Protection, 6 th Edition, Hodder Arnold, London (2012)  Jelley, N. A., Fundamentals of Nuclear Physics, Cambridge University Press, Cambridge (1990)  Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8 th Edition, 1999 update), Wiley, New York (1999)