The work presented in this dissertation used a variety of facilities and methods to make precise measurements of neutron reaction cross sections and γ-ray branching ratios important for the study of high energy density environments. While measurements related to thulium used commercially available detectors, others required the development of a new detection
system. A 4π gas proportional beta counter was designed and characterized specifically for the measurement of fission product branching ratios. Measurements of increasing precision were performed for 147 Nd and 95 Zr. The instrumentation and techniques developed in this dissertation have set the path for an ongoing series of fission product branching ratio measurements. With work towards refinements mentioned here, precision will continue to improve in the measurements and results of future studies with these devices.