Quantitative assessment of the absorbed dose in cryodeposited noble-gas films under X-ray irradiation: Simulation vs. experiment

This work was aimed at quantitative determination of the absorbed doses under X-ray irradiation of cryogenic deposited films, particularly related to the matrix isolation experiment. The relative absorbed doses in the layers of solid noble gases of different thickness irradiated with an X-ray tube (46.6 kVp) in the specified cryostat geometry were calculated by Monte-Carlo simulation using a Geant4 code. In order to calibrate the obtained values, the relative absorbed dose in the ferrosulfate dosimeter irradiated in the same geometry was calculated in the same way. The effect of additional Al filter (420 mu m) on the photon spectrum and relative absorbed dose in noble gas layers and dosimetric system was simulated. The experimental verification was based on the monitoring of the radiation-induced decay rate of ethane molecules isolated in different solid noble gas matrices (Ar, Kr, and Xe, 1:1000) irradiated in the cryostat at 6 K. It was shown that the simulation reproduces well the experimentally observed effect of the filter on relative absorbed dose rate in both dosimetric system and the layers of different solid noble gases (80-180 mu m). Absolute absorbed dose rates were determined as a function of deposited layer thickness in different noble gases. The comparison of the simulation results with a crude estimation based on a single effective energy value is discussed.