Investigation of Active Background From Photofission in Depleted Uranium Using Cherenkov Detectors and Gamma Ray Time-of-Flight Analysis

Prompt gammas from induced fission could potentially be a valuable fission signature to use for detection of special nuclear materials like highly enriched uranium. Detectability requires an understanding of both signal and background, and the background from highly enriched uranium can be understood using depleted uranium as a surrogate. In order to study the prompt gamma active backgrounds from special nuclear materials induced through photofission, a combination of measurements using the Idaho Accelerator Center 44 MeV Electron Linear Accelerator and Monte Carlo N-Particle simulations were used. In this paper, we discuss the prompt, time-gated glass Cherenkov detector response to gamma emissions resulting from short pulse 6, 10, and 25 MeV bremsstrahlung beams incident on a depleted uranium target. Considering any threshold used with the Cherenkov detectors, the prompt gamma signal from depleted uranium is buried in the active background from the interrogating photon source. This paper describes the contributions to this prominent prompt active background observed in our measurements.