Measurement of absolute neutron yields and energy spectra using the RPI LINAC and assessment of evaluated photoneutron data for tantalum

Nuclear system design and analysis efforts commonly rely upon computer simulation of real or envisioned configurations. Such simulations typically rely on the information documented in nuclear data libraries to accurately predict the nuclear interactions occurring within the system. One such nuclear interaction is photoneutron production; that is, the emission of one or more neutrons from a nucleus following the absorption of a high energy photon and subsequent excitation. In order to validate the accuracy of existing photoneutron data libraries, it is necessary to compare simulations performed using the data libraries to measured results from nuclear systems. Accurately measured photoneutron nuclear data could also be used to assess the performance of theoretical models. Unfortunately, there are few examples of measured data results from photoneutron measurements of sufficient accuracy and documented with adequate detail to provide a means for such a validation. This work demonstrates the feasibility of performing experiments at the Rensselaer Polytechnic Institute Gaerttner Linear Accelerator Center to measure absolute photoneutron yields and energy spectra from materials of interest. A new experiment configuration (consisting of a new neutron producing target and supporting systems, and neutron detection system) was designed, developed and implemented. The new configuration was successfully used to perform a proof of concept experiment to measure the photoneutron yield from a tantalum sample. The measured results were then compared against a detailed simulation of the experiment configuration to assess the performance of the photoneutron data library. Lessons learned and potential upgrades have been identified and documented to support improving the photoneutron measurement capability for future experiments. The efforts described here represent the first steps toward establishing a photoneutron measurement capability of benchmark quality.