The impact of source-to-film distance on the accuracy of beta-ray surface density measurement

[Background] The beta-ray surface density measurement instrument is widely used for the online measurement of the surface density of electrode sheets in the coating process of lithium batteries. A significant measurement error was observed when the source-to-film distance (SFD) varied under fixed source-to-detector distance (SDD). [Purpose] This study aims to investigate and minimize the impact of SFD variations on the accuracy of beta-ray surface density measurements. [Methods]First, experimental tests were conducted using the beta-ray surface density measurement device with a fixed SDD to quantify the influence of SFD changes (4–8 mm) on copper film surface density measurements. Second, Geant4 Monte Carlo simulations were performed to model beta-ray scattering effects under three collimator configurations: detector-side single collimator, source-side single collimator, and dual collimators. Finally, the optimized source-side single collimator geometry was experimentally validated by reproducing SFD variations and recalculating measurement deviations. [Results]Initial experimental measurements revealed that 1 mm SFD variation caused a maximum measurement deviation of 13.3% in surface density values. Monte Carlo simulations demonstrated that the source-side single collimator configuration minimized scattering effects, showing the smallest mean absolute deviation among all three geometries tested. Experimental validation confirmed this improvement, with the maximum deviation decreasing from 13.3% to 3.5% after device optimization. [Conclusions]By adopting a source-side single collimator, the study achieved a 73.7% reduction in measurement error caused by SFD variations, providing a practical solution for enhancing online surface density measurement accuracy in lithium battery production.