A new experiment configuration was designed, developed and implemented to measure photoneutron yields using the Rensselaer Polytechnic Institute (RPI) electron linear accelerator (LINAC) at the RPI Gaerttner LINAC Center. The new experiment configuration includes a new target assembly that converts the LINAC electron beam into a high energy bremsstrahlung photon flux incident upon a sample material of interest. The photons excite nuclei in the sample of interest, which can subsequently emit neutrons (photoneutrons). The photoneutrons emitted in the direction of the detector system (90 degree orientation from the initial electron beam) travel through a series of collimated vacuum pipes before reaching a pair of proton-recoil (EJ-301) high energy neutron detectors. The signals generated by the neutron detectors are processed using a digital data acquisition system and subsequently analyzed to determine the energy-dependent photoneutron yield from the sample of interest.
The new experiment configuration was used to perform proof-of-concept experiments to measure the photoneutron yields from samples of tantalum and beryllium. The measured results were then compared against the results from Monte Carlo simulations of the detailed experiment configurations to perform preliminary assessments of evaluated photoneutron data libraries. For example, comparing the measured photoneutron spectrum from a tantalum sample with a Monte Carlo simulation using the ENDF/B-8.0 evaluation showed overall good agreement in the energy range from 0.5-20 MeV; however, differences observed in the range of 5-9 MeV warrant further investigation. Lessons learned and potential upgrades were identified and documented to support improving the photoneutron measurement capability for future experiments and allow more rigorous validation assessments of evaluated photoneutron data libraries.