Characterization of the Energy Spectrum at the Indiana University Nrep Neutron Source

The neutron source at the Indiana University Cyclotron Facility produces neutrons via proton bombardment of a natural beryllium (100% 9Be) target. This source has two beam lines: the LENS and the NREP. The energy spectrum of the neutrons produced on the NREP beam line has not yet been characterized. Through simulation using the GEANT and MCNP particle transport codes as well as neutron activation analysis experiments, an attempt was made to characterize the energy spectrum of the neutron production source. First, the neutron production spectrum of beryllium, simulated using GEANT, was compared with literature; there are significant deviations. Next, foils and wires of pure elements were irradiated in the neutron beam target area and the resulting gamma spectrum measured. This information was used in an unfolding code, SAND-II, to deconvolve the neutron energy spectrum observed at the target. A number of approximations were made to properly account for beam duty time and neutron production anisotropy. The resultants provide a better understanding of the spectrum, but continued work is needed to produce a useful spectrum for the users of the facility.