Development and validation of a forward 0.7--4 MeV quasi-monoenergetic neutron capability at the CN Van de Graaff of LNL

TL;DR

This paper details the development and validation of a neutron source capable of producing quasi-monoenergetic neutrons in the 0.7--4 MeV range at the CN Van de Graaff accelerator, including experimental validation and model comparisons.

Contribution

It introduces a validated method for generating and measuring forward quasi-monoenergetic neutrons at low energies, with comprehensive experimental and computational validation.

Findings

Transport models agree within 5% for neutron yield predictions.

Time-of-flight measurements confirm the neutron energy and timing structure.

The neutron source demonstrates practical usability for low-energy neutron studies.

Abstract

The CN Van de Graaff accelerator of INFN--LNL provides forward-angle quasi-monoenergetic neutrons in the 0.7--4 MeV range via the 7Li(p,n)7Be reaction on thin metallic lithium targets. This work describes the development and experimental validation of this forward neutron capability, combining comparisons of commonly used transport tools with time-of-flight (ToF) measurements. Neutron yields calculated with EPEN, FLUKA, MCNPX, and PINO are compared over the CN energy range in order to assess model-dependent variations relevant for fluence estimates. For zero incident-energy spread, a mutually consistent set of transport calculations agrees within 5% and is used as a practical reference for normalisation. The effect of incident-energy convolution on the predicted yields is examined. Time-of-flight measurements performed using a sub-nanosecond secondary pulsing system verify the timing structure and forward-angle kinematics of the quasi-monoenergetic neutron component at the detector position, with neutron arrival times consistent with the expected forward kinematics within the experimental resolution. Using measured proton currents and transport calculations based on this reference set, forward neutron fluences at the device position are estimated with an overall uncertainty of approximately 9%, including contributions from current integration, target thickness, and geometry. A short device irradiation, carried out in parallel with the ToF campaign, demonstrates measurable response under CN beam conditions and confirms the practical usability of the beam for low-MeV neutron studies. Together, these results establish the current operational performance of the CN 0{\deg} forward quasi-monoenergetic neutron capability in the 0.7--4 MeV range and identify the steps required toward routine calibrated operation.