Wk7: Radioactivity
Thursday, November 12, 2020 6:04 PM
Abbreviations:
b/w = between
w/ = with
• Radioactivity = nuclear decay; aspects of nuclear decay include half-life and isotropic INC = increase
DEC = decrease
character of the emission.
• For example, 16O signifies an oxygen atom (Z = 8) with 16 - 8 = 8 neutrons.
• Isotopes: nuclei w/ the same # of protons but different # of neutrons.
• Radioactivity: phenomenon in which unstable nuclei (arrangement of protons/neutrons
in shells are poor) decay in other nuclei (radionuclides).
Sec 7.3.2: measures decay of cobalt into nickel via beta particle (e-) and antineutrino (𝜈):
60𝐶𝑜 →60 𝑁𝑖 + 𝑒− + 𝜈.
• 60Co has Z = 27, and thus the number of neutrons in its nucleus is A - Z = 33.
• Anti-neutrinos: particles w/ no charge, insignificant mass, and weakly interacts w/
normal matter. -> antineutrinos emitted are not detected.
• Why is it that low mass nuclei such as 16O are stable when the number of neutrons
equals the number of protons, but heavier nuclei need a larger number of neutrons than
protons to be stable? Hint: Consider the effect of the Coulomb force in the nucleus.
• 60Ni has Z = 28, and thus the number of neutrons in its nucleus is A - Z = 32. So the net
reaction in this decay is that one neutron in the original 60Co nucleus is changed into a
proton, the cobalt nucleus is transformed into nickel, and an electron is emitted to
conserve charge and a neutrino is emitted to conserve a quantity called lepton number.
○ The sum of the lepton number on both sides of the decay equation is 0, meaning
the net lepton number did not change as a result of the decay.
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