Evaluation of gamma-ray transmission through rectangular collimator slits for application in nuclear fuel spectrometry

Gamma-ray spectrometry is widely applied in several science fields, and particular non-destructive gamma scanning emission tomography of irradiated nuclear fuel. Often, a collimator used the experimental setup, to selectively interrogate region interest For optimization instrument design, as well for planning measurement campaigns, predictive models transmitted gamma-ray intensity through are needed. Commonly, Monte Carlo radiation transport tools accurate prediction transport, however, long computation time requirements when low-efficiency setups present challenges. In this work, full-energy peak rectangular slit was examined. A uniform planar surface source emitting isotropically considered, rate photons reaching an ideal counter plane on opposite side evaluated by analytical integration. To find closed-form primitive function, some idealizations were required, thereby parametric obtained optical field view, dependent dimensions (length, height width) source-to-collimator distance. It shown that count detector independent collimator-to-source contributions from outside where expression cannot be found, instead fast numerical integration methods proposed. The results validated using code MCNP6.2. method, deviations larger, shorter collimator, with up 25% underestimation shortest examined 10 cm length. However, longer better observed agreement. This accuracy deemed sufficient design planning, often order magnitude not priori known. showed agreement within 3% all settings. planned use iterative routines Gamma Emission Tomography devices, spectra fuel inspections. An application proposed method demonstrated spectrum short cooling-time rod test Halden reactor.