Optimization of a Linac-Based Neutron Source for Time-of-Flight Measurements

The conceptual design of a neutron source for time-of-flight (TOF) measurements with good energy resolution was presented in a previous paper, aiming at its implementation on a high energy electron Linac . There is a growing interest in nuclear data worldwide and the existing neutron sources are clearly insufficient. The distinguished feature of this source is the very small size of the neutron producing target, what reduces the uncertainty on the neutron pathlength and so helps improve resolution. This in turn allows one to reduce the neutron flightpath down to only 1 m, in order to keep the flux at an acceptable level for a given energy resolution. Hence a special design of the shielding used for background reduction is needed, if compared to other similar sources. The basic criterion used in designing the various components was the optimization of the TOF resolution, and consequent background reduction, which were done mainly by extensive simulations with the MCNP5 code. The optimization results of the main elements of this source (target, moderator, shielding, collimator) are reported on in this paper, suggesting the feasibility of a simple, cheap and flexible neutron facility with an energy resolution ≤5% to be implemented even on a low power but high energy electron Linac.