Q-value decay

When Er decreases toward threshold, at E = 0, the pole moves towards the negative imaginary axis and the value of A (f) increases, eventually making it comparable to Ap(f). In the limit Er = 0 the above decomposition is invalid, implying that the decay ceases to be exponential. This is known as small Q-value decay. For a theoretical analysis of this case and some examples, see Refs. [29, 30]. Small Q-value decay becomes noticeable when Q = Er - E < r/2. 

Q-values (decay energies for different decay modes) for beta minus (QP—), electron capture (Qe), alpha (Qa), and proton decay (Qp) are from Audi and Wapstra (1995). Systematic values are shown in square brackets. 

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