Citation:
J. Corder, M. Easley, C. Mathew, L. Wood, and C. Marianno “Analysis of incorporating Gamma Detectors in an in-line Neutron Well Counter for Nuclear Material Control and Accountability”, Symposium on Radiation Measurements and Applications (SORMA), 21-24 July 2025, Berkeley, California.
Abstract:
Neutron well counters are a common and reliable instrument for verifying the mass of special nuclear material. In addition to mass quantification, verifying the isotopic composition of a nuclear sample is useful in contributing to the nuclear material accounting process. For facilities that utilize neutron well counters in a fixed in-line configuration, such as glovebox line processes, design constraints underneath the gloveboxes make it difficult to include high-resolution gamma detectors, such as a germanium detector, near the well counter. This requires nuclear samples to be measured twice to in order perform gamma spectroscopy. In addition, if the nuclear sample were needed to be transported for a gamma measurement, this can introduce a dynamic background that can result in an invalid background subtraction and potentially provide incorrect information about the nuclear sample. This research integrates gamma detectors in a neutron well counter for performing identification and quantification measurements simultaneously to reduce the measurement time and improve the efficiency of the nuclear material accounting process.rnrnA traditional neutron well counter was modeled with the addition of various gamma detectors to replace certain 3He neutron detectors in a well counter. The gamma detectors of choice were cesium iodide, cadmium zinc telluride, and compact high-purity germanium detectors for their smaller size to fit in a detector channel and their variation of specifications. Simulations were run using the Monte Carlo N-Particle Transport (MCNP) code for its interface to design and optimize radiation detectors and the environment around them. A plutonium oxide source was modeled inside the well cavity to emulate a detector measurement, and tallies were used in MCNP to track the information about the sample. These simulations examined the comparison in measurement times between gammas and neutrons to achieve statistical accuracy, the ability to identify the sample, and sensitivity to background radiation. A comparison between the results from the different gamma detectors was performed to evaluate the overall performance of the detection system. The methodology behind these simulations provided insight on the effectiveness of introducing gamma detectors in a neutron well counter for nuclear material accounting.