AhKin: A modular and efficient code for the Doppler shift attenuation method
We present a set of programs for measuring lifetimes tau of nuclear states by the Doppler shift attenuation method (DSAM). The algorithms are based on the analysis of a probabilistic model of the processes occurring during a DSAM experiment. This analysis allows us to formulate the calculation of the theoretical lineshape as the application of an integral transform that converts the probability density of the cascade time (the time elapsed from nucleus creation to state decay) into the probability density of the (scaled) photon energy in the laboratory reference frame. The kernel of this integral transform, which encapsulates information related to the processes of nuclei stopping and photon detection, is independent of the state decay process, and hence needs not be recalculated on every trial of a candidate tau-value, allowing for fast computation of theoretical lineshapes. Further efficiency is gained by using algorithms that approximate continuous random variables by suitably chosen discrete ones. These codes were used to measure the lifetimes and sidefeeding times of the excited states of the normally deformed bands of 83Y (Rodríguez, et al. 2019) finding for all states good agreement between the experimental lineshape and the best-fitting theoretical one.