The attenuation factor F responsible for the decay out of a superdeformed (SD) band is calculated with the help of a statistical model. This factor is given by 1/F = (1 + Gamma(down) / Gamma(S)). Here, Gamma(S) is the width for the collective E2 transition within the superdeformed band, and Gamma(down) is the spreading width which describes the mixing between a state in the SD band and the normally deformed (ND) states of equal spin. The attenuation factor F is independent of the statistical E1 decay widths Gamma(N) of the ND states provided that the Gamma(N) are much larger than both Gamma(down) and Gamma(S). This condition is generically met. Previously measured values of F are used to determine Gamma(down).
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