Passive Reactor Monitoring with Crystal Damage Measurement

Project Overview

Nuclear reactors and materials are robust generators of particles, such as neutrons and neutrinos. The measurement of these particles can indicate important information including reactor components, power, and fuel burning history. These neutral particle interactions can cause damages in crystals, such as LiF and CaF2. The damage caused by neutral interactions may also differ from the damages caused by charged particles, such as electrons, providing intrinsic background rejection with crystal damages. The selectivity of neutral and charged interaction by crystal damage, can potentially enable a passive crystal detector for reactor monitoring. We aim to test the feasibility of crystal-damage-based neutron detection by comparing the selectivity of neutral and charged interactions among CaF2, LiF, MgF2, BaF2, and Al2O3. We also test the material's resistance against aging, UV exposure, and heat. The goal is to find the crystal that is most suited for a passive reactor monitoring detector.

In the experiment, three samples of each material were exposed to a strong 252Cf source for neutron irradiation, while one of each material was exposed to a 60Co for gamma irradiation. The samples before and after the irradiations are measured with fluorescence and Raman spectroscopies to identify the neutron (neutral interaction) and gamma (charged interaction) caused crystal damages. These measurements are essential in identifying the signature optical features of the crystal damages. After finding promising optical signature, confocal Raman microscopic image was taken at selected samples with aims to observe the crystal damages. As a result, LiF, MgF2, and Al2O3 showed Raman spectral change after neutron radiation. The Raman spectra and microscopic images of LiF and MgF2 changed with the respect to neutron radiation. These two material also indicated different spectral responses between neutron and gamma irradiation. We also showed that aging, heating, and UV exposure affects the Raman spectrum intensities of irradiated crystals.

Mission Impact

These results provide us with promising materials for further R&D of a passive neutron/neutrino detector with the aim of reactor monitoring for nuclear safeguard needs. The Lawrence Livermore National Laboratory (LLNL) team gained expertise in characterizing crystals through spectroscopy and microscopy. The potential application of crystal-damage-based radiation measurement in the future is an advance nuclear non-proliferation tool, as it requires minimum maintenance and facility support for a neutron/neutrino measurement, enable NNSA to create new ways of responding to national security challenges. This technology can also be applied in particle physics measurement, which initiates the development for a variety of particle detection technology for fundamental physics needs, such as neutrino physics study and dark matter detection.

Publications, Presentations, and Patents

Stuti Surani, Xianyi Zhang, "Characterizing radiation damage in inorganic scintillators" (Presentation, RED group meeting, Lawrence Livermore National Laboratory, Livermore, CA, Aug. 2023).

Stuti Surani, Xianyi Zhang, "PALEOCCENE - Using crystals to look through time" (Presentation, Summer Slam, Lawrence Livermore National Laboratory, Livermore, CA, July 2023).