PhD Thesis Defense: Danielle Castley

Thursday, August 22, 2019, 8:30–10:30am

Jackson Conference Rm, Cummings Hall

“Computational and Experimental Comparison of Boron Carbide, Gadolinium Oxide, and Samarium Oxide as Additives for Neutron Shielding Materials”

Abstract

To overcome the thermal and weight constraints associated with existing neutron shielding designs, compounds containing isotopes with a high probability of absorbing slow, resonant, and intermediate neutrons were evaluated for use in neutron shielding. Monte Carlo N-Particle Software (MCNP) was first used to simulate neutron attenuation in different combinations of materials containing boron, gadolinium, and samarium. The MCNP model showed neutron attenuation was best in gadolinium and samarium containing samples but photon production was higher than in those containing boron. Boron carbide, samarium oxide, and gadolinium oxide were then experimentally incorporated in three base matrix materials; graphene, silicone elastomer, and concrete. The graphene-based materials introduced manufacturing challenges, but the elastomeric and concrete based neutron shielding materials were simple to manufacture and could withstand temperatures greater than 300oC with a density less than 2 g/cm3. To accommodate the secondary gamma released during neutron capture, multiple neutron absorbing compounds were included in the material. Another attempt to improve neutron attenuation properties was made by simulating the neutron absorbing nanoparticle size in polyethylene. It was computationally found that regardless of the nanoparticle type, boron carbide, gadolinium oxide, or samarium oxide, there was not an effect on the attenuation of fast neutrons, just thermal neutrons, at particle sizes less than 400 nm.

Since the density of the proposed elastomeric and concrete based materials varied between 0.95 and 2 g/cm3, a Figure of Merit comparing neutron stopping power and density was used to identify the best neutron shielding material for temperature and weight restricted applications. The lightweight concrete (0.95 g/cm3) with 13 wt% neutron absorber had the highest Figure of Merit of 0.060, more than double that of 5% borated polyethylene at 0.023. This work substantiates a claim that a combination of neutron absorbing compounds can achieve a high-temperature, lightweight neutron shielding material with neutron attenuation properties better than the state-of-the art is achievable.

Thesis Committee

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.