Sarazin, FredericMiller, Eric D.2022-07-192022-07-192021https://hdl.handle.net/11124/14261Includes bibliographical references.2021 Fall.Doppler Shift Attenuation Methods (DSAM) are capable of determining very short lifetimes of excited states (from femtoseconds to picoseconds). Given the evolution of DSAM experiments and computational tools available to nuclear physicists, it is surprising that no standard implementation exists for simulating DSAM in Geant4 (G4), despite being a widely-used simulation framework and often considered the golden standard for simulating nuclear and high energy physics. This document demonstrated an implementation of DSAM in G4. The key additions to G4 were an improved representation of the Breit-Wigner width of unbound states, accurate in-flight radioactive decay, and precise control over the kinetic energy loss per simulation step. This implementation of DSAM is built for the use of an upcoming experiment investigating the nuclear structure and decay scheme of \atom{11}{}{Li}{}{}. Validation of the DSAM implementation used data from a previous iteration of the experiment with earlier generation detectors. The simplest line-shape in the measured data was used to verify that the new method can backcalculate the same details of the decay scheme as previous studies. When using the same energy loss data as earlier works, the additions to G4 recovered the half-life of the $0^+_2$ state of \atom{10}{}{Be}{}{} to be 991 fs, well within statistical error of the value published in \cite{mattoon2009}: 983 $\pm 27$(stat.) $^{+200}_{-120}$(syst.) fs. Using G4 for simulating DSAM allows easy access to several pre-existing energy loss models. The results of DSAM are very sensitive to the energy loss model used in the simulation. This document investigated the systematic error due to the range of energy losses and stopping powers predicted by various models. For the $0^+_2$ state of \atom{10}{}{Be}{}{}, the predicted half-life ranged from 981 fs to over 1500 fs depending on the employed energy loss model. This range of values is greater than the suggested systematic error reported 983 $^{+200}_{-120}$(syst.) fs in \cite{mattoon2009}.born digitalmasters thesesengCopyright of the original work is retained by the author.Doppler broadeningGeant4halo nucleiText2022-07-18