lab9_radioactive_decay

lab9_radioactive_decay - PHY 252 Lab 9: Radioactive decay...

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PHY 252 Lab 9: Radioactive decay Fall 2009 1 Introduction In this experiment we will measure the half-life of an excited state of the 137 Ba nucleus. Samples are prepared from a radioactive isotope of 137 Cs. This isotope has too many neutrons to be stable; it decays by β -decay into 137 Ba * . This daughter nucleus is produced in an excited state, indicated by the asterisk (*). The excited state successively decays into the ground state of 137 Ba with a half-life of the excited state of 2.6 min. The decay of the excited state is detected by measuring the emitted γ -rays of 0.66 MeV. This energy corresponds exactly to the energy difference between the excited state in 137 Ba * and the ground state. Figure 1: The 137 Cs decay chain. The γ -ray emission rate is R ( t ) = - dN ( t ) /dt , where N ( t ) is the number of 137 Ba * nuclei present at time t . The emission rate is proportional to N ( t ) : dN ( t ) dt = - λN ( t ) , (1) where λ is defined as the decay constant. Integration of Eq. 1 leads to N ( t ) = N 0 exp[ - λt ] , (2) 1
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lab9_radioactive_decay - PHY 252 Lab 9: Radioactive decay...

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