Low Energy Dosimetry With Photon Counting Pixel Detectors Such as Medipix

Hybrid semiconductor photon counting pixel detectors like the Medipix detector have several advantages for an use in X-ray dosimetry. The noiseless photon counting principle allows to monitor low photon energies down to 3.5 keV. Due to the small pixel size (55 mum in case of Medipix2) dosimetry at very high dose rates is possible still processing each photon individually. The large amount of pixels in combination with the possible thickness of the sensor layer enables dosimetry at very low dose rates. A method has been developed to determine personal dose equivalents from the number of counts in energy deposition intervals measured with a semiconductor photon counting pixel detector, despite the strong influence of charge sharing effects among pixels. We tested the method experimentally by reconstructing the air kerma free in air for different qualities of X-radiation in the energy range below 150 keV with an accuracy better than 4%. We show that the response of a dosimeter based on a hybrid photon counting pixel detector can fulfill the IEC type testing requirements. The statistical precision is high due to the thickness and the large area of the sensor layer. We estimate that a dosimeter based on the Medipix detector will be able to cope with dose rates of more than approximately 57 Sv/h for mathdot Hp (0.07) or 19 Sv/h for mathdot Hp(10) . We outline the advantages and perspectives of using this kind of detector in a dosimeter in comparison to standard active personal dosimeters.