A simple system for measuring the transmittance curve of x-ray filters at low x-ray energies.

To prevent the x-ray detectors from the interference of optical photons, x-ray filters are widely used in x-ray space missions. As the flux of low energy x-rays would be significantly attenuated by the filters, it is important to derive the transmittance of the filters below 10 keV. In this paper, we present a simple experimental apparatus and data processing method to measure the transmittance curve of x-ray filters in the energy range from 1.6 to 10 keV. The measured spectra were further processed with Geant4 Monte Carlo simulation results and a direct demodulation algorithm. The obtained transmittance is in good accordance with the theoretical calculation and the synchrotron radiation test result, which proves that the proposed system with the algorithm is a reasonable way to characterize the x-ray transmittance performance of filters above 1.6 keV.