1 AP Chemistry Lab Brockport High School NY USA β decay of 137 Cs and the half-life of Mr Keefer metastable 137 Ba by γ photon emission Introduction Radionuclides emit various particles and γ photons during their disintegration as a first order reaction. Alpha (α) and beta (β-) emitters decay at various rates as characterized by their decay constant, λ. The relationship between radioactive decay and the data collected in this lab is shown in the equation: N = N o e-λt where N o is the original activity, λ is the decay constant, and t is the elapsed time. Also, it is known that: T ½ = 0.693/ λ and λ = 0.693/ T ½ Using natural logarithms, we have: ln N- ln N o = -λt Hence, if we can measure the original and final activities of the radionuclide, we can calculate the half life and decay constant. In this lab, 137 Cs is the parent nuclide that emits a β particle and decays to metastable 137 Ba* and normal 137 Ba. The half life of this transition is approximately 30 years. However, the
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