Feasibility of Using the H(n,el) Cross Section Reference in a White Source Neutron Beam with the fissionTPC

The Neutron Induced Fission Fragment Tracking Experiment built the fissionTPC as an instrument to precisely measure fission cross section ratios. Past and current measurements in this detector have used actinide references of 235U(n,f) and 238U(n,f). Employing a more precise cross section reference, such as H(n,el), has the potential to further reduce the evaluated cross section uncertainty. The fissionTPC is unique as it can simultaneously detect both fission fragments and protons with the same device. We provide a quantitative description for a measurement method using a hydrogenous gas target and the proton recoil kinematics to reconstruct the incident neutron energy. This method enables the fissionTPC to operate in a white-source neutron beam like that at LANSCE-WNR. We show such a measurement is feasible in the energy range of 0.5–10 MeV, however the precision is limited by the method of energy reconstruction. Using a direct measurement of neutron time-of-flight for the recoil proton or a mono-energetic neutron source would provide a path to a sub-percent precision measurement.