Lecture 3: Modes of Radioactive Decay Unit I—Physics of Nuclear Medicine From “Researchers Find Cancer in Ancient Egyptian Mummy.” The Cosmos News. Retrieved 27 Aug 2012 from http://www.cosmostv.org/2012/01/researchers-find-cancer-in-ancient.html

Lecture 3 Objectives Define radioactive and that term’s relation to decay Define the line of nuclear stability Name and describe the primary forms of radioactive decay. Diagram the schematics of the various radioactive decay processes. Explain the structure of the trilinear chart and how it relates to the nuclear families Describe the extra-nuclear release of characteristic X-rays and Auger electrons Define fluorescent yield

Clarifying terms Radioactive Decay Atomic nucleus in an unstable state Can happen regardless of proton-electron balance Decay A process of transformation and atomic nucleus undergoes in order to become more stable Decay may involve a nuclear having multiple transformations until it results in a stable nuclide Image from “Radioactivity.” Tutorvista.com. Available at http://chemistry.tutorvista.com/nuclear-chemistry/radioactivity.html accessed 10 Sep 2017. Parent: form of nucleus before it transforms (decays) Daughter: form of nucleus after it transforms Image from “Radioactivity.” nuceng.ca. Available at http://www.nuceng.ca/igna/radioactivity.htm . accessed 10 Sep 2017.

Line of Nuclear Stability Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-5, p 43.

Decay Schematics Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-11, p 49.

Decay Processes: Alpha Decay Recently has become relevant to nuclear medicine http://www.xofigo-us.com/index.php Tends to occur when Z ≥ 150 Helium nucleus (2 protons, 2 neutrons) with no electrons. + 2 charge (it immediately wants two negative charges, i.e. electrons) An electron stripper. Excites and steals electrons from surrounding atoms, thus creating ion pairs (a positive ion and a negative ion). One Alpha can produce hundreds of thousands of ion pairs— very, very bad for biochemistry.

Decay Processes: Alpha Decay Radium 223 T1/2 = 11.4 hrs α Radon 219 T1/2 = 4 sec α Polonium 215 T1/2 = 1.8 msec

Isobaric Decay Three types of decay in which the parent and daughter have the same number of nucleons (isobars) Beta minus (negatron, or β-) Beta plus (positron, β+) Electron capture (abbreviated EC)

Decay Processes: Beta Minus (negatron) Emission Used in nuclear medicine for therapies High Velocity, negatively charged electron emitted from a neutron-heavy nucleus Neutron  proton + beta + antineutrino + energy Energy=kinetic energy to beta + instantaneous gamma emission 1 MeV beta specific ionization: 45 ion pairs/cm (1 MeV Alpha specific ionization: 60,000 ion pairs/cm) But beta more penetrating than alpha n = p + β- + v + energy

Decay Processes: Beta Minus Emission Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-12, 2-13, p 49.

Decay Processes: Beta Plus (Positron) Emission P + N + + +  + 2  Annihilation Photon (Also results in the eventual emission of 2 X 511 keV annihilation photons at 180 if positron and negatron are at rest mass) Annihilation Photon Happens with proton-rich nuclei, or either decay will occur by electron capture (explanation to follow). M. Crosthwaite “Nuclear Medicine not Unclear Medicine”

Decay Processes: Beta Plus (Positron) Emission

Decay Processes: Electron Capture (EC) Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-15, p 50. http://commons.wikimedia.org/wiki/File:Electron_capture_NT.PNG

Line of Nuclear Stability Low N/P: EC Β+ High N/P: Β- Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-5, p 43.

Decay Processes: Gamma Emission Result of a nucleus in a higher energy state Energy needs to be released for the nucleus to return to a more stable lower energy state May result as part of alpha and beta decay, or from a metastable nucleus

Gamma Emissions with Other Decay Processes Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-16, p 50.

Decay Processes Isomeric Tranisition Energized state of a nucleus: metastable Transitions by releasing energy in the form of a gamma photon Parent & daughter have same atomic mass and number (isomers) Unlike I-131 and some beta emitters, the gamma emission is not instantaneous Not really a disintegration but a change in energy state of the nucleus. Prime example: Tc-99m  Tc-99

Decay Processes: Beta Decay to Isomeric Transition Decay Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-14, p 49.

Decay Processes: Gamma Decay Energy States of the Nucleus Like the electron shells, an atomic nucleus can have different energy states of specific energies. A nucleus of a certain type of atom will have specific “quantum”-like levels of energized states. It dissipates the energy by emitting electromagnetic radiation (gamma rays) at energies equivalent to the energized state. Paul Early, D. Bruce Sodee, Principles and Practice of Nuclear Medicine, 2nd Ed., (St. Louis: Mosby 1995), pg. 15.

Multiple Gamma Emissions Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Table 2-1, p 50.

Decay Processes: Internal Conversion Often accompanies isomeric transition

Trilinear Chart of Nuclides Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-6, p 44

(Mo-99 to Tc-99) Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig. 2-6, p 44

Extra Nuclear Release: (Energy States of Electrons) This picture from the Sodee text represents the electron energy states as different speed limits around the nucleus of an atom. In order for a car at 70 mph to go down to the 65 mph speed limit, it must lose a “quantum” of 5 mph. For electrons, this quantum is in the form of a specific wavelength of electromagnetic radiation. Paul Early, D. Bruce Sodee, Principles and Practice of Nuclear Medicine, 2nd Ed., (St. Louis: Mosby 1995), pg. 11.

Extra Nuclear Release: Characteristic X-rays Paul Christian, Donald Bernier, James Langan, Nuclear Medicine and Pet: Technology and Techniques, 5th Ed. (St. Louis: Mosby 2004) p 54. This figure shows what happens when an electron loses energy to move from the L shell to the K shell. Again Electromagnetic radiation is emitted, but it is of a higher energy (shorter wavelength/higher frequency) than visible light and is in the form of an X-ray photon. Such an emission is called a “characteristic X-ray” and its “character” is dependent upon and equal to the specific difference in energy states between the L and K shells of the atom.

Extra Nuclear Release: Auger Electrons Paul Christian & Kristen M. Waterstram-Rich, Nuclear Medicine and Pet/CT: Technology and Techniques, 6th Ed. (St. Louis: Mosby 2004), Fig 2-25, p 57.

Extra Nuclear Release: The Concept of Fluorescent Yield Ratio of emitted X-rays to total transistions

Next time: Mathematics of Decay and Units of Radioactivity