Fig. 1. Schematic diagram of the β-ray surface density measurement device (a) Detector structure, (b) Measurement device structure

Fig. 2. The measuredln(I/I0) results of Cu films with different SFD (color online)

Fig. 3. Measurement results of Cu film surface density at different SFD (color online) (a) Calculated surface densitytp from calibration curve, (b) Relative deviation between tp and the standard surface density tm

Fig. 4. Geant4 simulation results of Cu film surface density at different SFD (color online) (a) Calculated surface densitytp from calibration curve, (b) Relative deviation between tp and standard surface density tm

Fig. 5. Three types of collimator geometric models (a) Detector side single collimator, (b) Source side single collimator, (c) Dual collimators between the source and detector

Fig. 6. Mean absolute deviation between the calculated and standard Cu film surface densities under 1 mm SFD variation for three collimator geometries

Fig. 7. Measurement results of Cu film surface density at different SFD after device improvement (color online) (a) Calculated surface density tp from calibration curve, (b) Relative deviation between tp and standard surface density tm