Abstract
A computational assessment of the variation in terrestrial neutron and photon background due to extraterrestrial sources is presented. The motivation of this assessment is to evaluate the practicality of developing a tool or database to estimate background in real time (or near real time) during an experimental measurement or to even predict the background for future measurements. The extraterrestrial source focused on during this assessment is the naturally occurring galactic cosmic rays. MCNP6 was used to perform the computational assessment. However, the galactic cosmic ray source available in MCNP6 was not used. Rather models developed and maintain by NASA were used to generate the galactic cosmic ray sources. The largest variation in both neutron and photon background was found to be caused by perturbations in elevation on Earth’s surface, which can be as large as an order of magnitude. All other perturbations produced background variations on the order of a factor of three or less. The most interesting finding was that about 80% and 50% of terrestrial background neutrons and photons, respectively, are generated by particle interactions of extraterrestrial sources and their progeny in Earth’s surface and other naturally occurring and man-made objects surrounding a detector. This assessment shows that it will be very difficult to estimate the terrestrial background due to extraterrestrial sources without a very good understanding of a detector’s surroundings. Therefore, estimating or predicting background during a measurement environment like a mobile random search will be nearly impossible.
