Measuring and Simulating Neutron Capture γ-Ray Spectra using the RPI γ-Ray Multiplicity Detector

¹ Gaerttner LINAC Center, Rensselaer Polytechnic Institute, Troy, NY 12180
² Naval Nuclear Laboratory, P.O. Box 1072, Schenectady, NY 12301

^* e-mail: cookk4@rpi.edu

Published online: 25 June 2025

Abstract

Accurate modeling of neutron induced capture γ-ray production is essential for many applications such as reactor and shielding calculations, understanding γ-ray heating in critical systems, and non-proliferation efforts. To determine the accuracy of nuclear data evaluations and simulation tools used to transport capture γ-cascades, the 16-segment γ-ray multiplicity NaI(T1) detector at the Rensselaer Polytechnic Institute Gaerttner Linear Accelerator Center has been upgraded to measure neutron capture γ-ray spectra and multiplicity as a function of energy. Several samples including Fe, Mn, Co, Ta, and ^235,238U have been measured using the time-of-flight method for incident neutrons in the low-energy region from 0.01 – 100 eV. A new method has been developed to model the event-by-event capture γ-ray cascade energy deposition in the detector array using DICEBOX and a modified version of MCNP-6.2. The method has been validated using ²²Na and ⁶⁰Co coincidence sources and the well-studied thermal ⁵⁶Fe(n,γ) γ-ray intensities. Additional measured samples will be used for further validation and analysis. The new modeling capabilities coupled with measured γ-ray spectra can be used to test transport codes and nuclear data evaluations of neutron capture γ-rays used to simulate experimental results.