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.本报告呈现了一套基于多普勒频移衰减法（DSAM）测量核态寿命τ的程序集。该算法基于对DSAM实验过程中发生的概率模型的分析。通过此分析，我们得以将理论线形计算表述为应用积分变换的过程，该变换将级联时间（从核创建至状态衰变所经过的时间）的概率密度转换为实验室参考系中（缩放后的）光子能量的概率密度。此积分变换的核心，即包含与核停止和光子检测过程相关的信息，与状态衰变过程无关，因此无需在每次尝试候选τ值时重新计算，从而实现了理论线形的快速计算。通过使用算法对连续随机变量进行适当选择的离散化近似，进一步提高了效率。这些代码被用于测量83Y（罗德里格斯等，2019）通常变形带的激发态寿命和侧馈时间，实验线形与最佳拟合理论线形之间表现出良好的吻合度。