Research on the Impact of Cosmic Ray Induced Neutron Background Based on Nuclear Safeguards Equipment

Abstract

Neutron detection technology is one of the most commonly used techniques for nondestructive analysis of nuclear materials in nuclear safeguards and verification. During the neutron detection measurement of nuclear materials, high-energy cosmic rays will react with high atomic number substances in the outer layer of the detecting equipment, producing a significant number of secondary neutrons. These neutrons, after being moderated in the polyethylene layer, further interact with 3He tubes in the equipment, leading to an increase in the neutron counts and contributing to the background interference, which affects the detection limits and accuracy of nuclear material measurements. Based on the neutron background measurement experiments with typical neutron detection equipment, this paper begins with a preliminary demonstration of the interference effect of cosmic rays on the neutron counts of nuclear safeguards equipment. Monte Carlo method is used to qualitatively study the neutron yields of different energies of high-energy muons interacting with materials with different atomic numbers such as lead, bismuth and iron. In order to further quantify the relationship between the mass of the shielding materials and the neutron background counts produced by the cosmic ray reaction, this paper conducts a series of comparative experiments of the neutron background counts produced by the three shielding materials most commonly used in nuclear safeguards equipment: lead, iron, aluminum, and corrects the measurements based on the spatial efficiency of the device. The results show that, for the shielded nuclear safeguard neutron measurement equipment, higher-energy muons can generate more neutrons, and higher atomic number materials like lead shielding can produce larger neutron counts compared to iron and aluminum. After spatial efficiency corrections, a linear relationship between the mass of shielding materials and neutron counts was established. This linear relationship has been verified to be applicable to other types of neutron detection devices as well, and can be further used for estimating background counts in other neutron detection systems.