3D Surface Radiation Dosimetry of a Nuclear-Chicago NH3 Neutron Howitzer

TL;DR

This study uses Monte Carlo simulations to assess neutron and gamma-ray dose rates on a Nuclear-Chicago NH3 neutron howitzer's surface, providing detailed spatial dose distribution data for safety evaluation.

Contribution

It presents a detailed Monte Carlo simulation analysis of surface dose rates on a neutron howitzer, including contributions from neutrons and gamma-rays, which is novel for this specific device.

Findings

Vertical and horizontal outlet dose rates are similar.

Maximum dose rates occur near the neutron source location.

Top surface periphery shows the highest dose rates.

Abstract

The tracking of radiation dose is a fundamental concept for the safe operation of nuclear instruments, and this concept is a multi-task challenge in the case of neutron sources since not only the neutron emissions from the main radioactive source but also the neutron capture gamma-rays as well as the gamma-rays from the inelastic neutron scattering make contribution to the total dose received by the facility personnel. The present study is devoted to the assessment of the equivalent dose rates on the surface of a Nuclear-Chicago NH3 neutron howitzer with a 5-Ci 239Pu-Be neutron source by means of Monte Carlo simulations. The 5-Ci 239Pu-Be neutron source is mounted within a vertical aluminum channel at the center of the neutron howitzer, and we use the axial symmetry of the aluminum drum filled with an ordinary paraffin without any potent neutron absorber such as boron or cadmium. We utilise the ICRP-21 flux-to-dose rate conversion factors and we track the neutron and photon equivalent dose rates on the lateral and top surfaces including the outlets of the vertical and horizontal irradiation channels by the aid of point detectors in the MCNP5 code. From the results over a number of sub-regions on the semi-cylindrical drum of the Nuclear-Chicago NH3 neutron howitzer, we show that the outlets of both the vertical and horizontal irradiation channels deliver approximately the same level of equivalent dose rates, and the maximum equivalent dose rates for neutrons and photons on the lateral surface are obtained at the spatial coordinates aligned with the location of the 5-Ci 239Pu-Be neutron source, whereas the periphery around the source channel on the top surface of the neutron howitzer constitutes the highest level of equivalent dose rates among the tracked locations.