Active dosimetry in pulsed photon fields using photon counting pixel detectors
Final Report Abstract
All in all we the project objectives were reached and we have clearly demonstrated the potential of Dosepix in the dosimetry of pulsed radiation fields. The prototype dosemeter showed excellent systematic accuracy and high sensitivity with low statistic uncertainties. The type testing requirements could be fulfilled by using 3 Dosepix detectors with different metal filters in front of them. By using one thin aluminum plate and hollow half-spheres made of tin and aluminum, we could achieve a broad range of angles of incidence with good systematic accuracy. We were able to modify the dose calculation method in a way (by using only the lowest energy channels to calculate the photon dose) such that the photon dose is only affected moderately by disturbing electron radiation. This method for suppression of the electron influence on the measured photon dose would fulfill the type testing. We were also able to demonstrate, that besides the personal dose equivalents Hp(0.07) and Hp(10), also the ambient dose quatity H*(10) and the fluence measuring quantity air-kerma can nicely be measured with our device and the weighting method for dose estimation. Here one can see the power of the 16 energy channels and the photon counting principle. Just by changing the conversion coefficients, various dose quantities can be reconstructed from one single measurement. Concerning high dose rates, we achieved a very large dynamic dose rate range for the small pixels up to several hundred Sv/h. The large pixels also performed better than expected: we achieved a range up to tens of Sv/h, depending on the spectrum. Thus, the pixel detector approach is the the right way to go for dosimetry in pulsed fields where dose rates can become high. Concerning the dependence on the pulse duration, we could experimentally prove that there is no such dependence of the measured dose values. This is due to the rolling shutter readout principle of the detector and the fact, that there is no readout dead-time in Dosepix. In addition to the work plan in the proposal of this project, we carried out measurements with extremely short pulses, like they appear with X-ray flash tubes or at the X-ray backlighter PHELIX. Here, we had to use artifical intelligence to reconstruct more or less correct doses due to pile-up of events during the shaping-time of the amplifier in the analog pixel electronics. The main problem for measurements at PHELIX is the mixture of the radiation field with electrons and photons combined with the very short exposure time. Nevertheless it seems that the pixel detector approach is valuable for building an electron/photon dosimeter/spectrometer to investigate the X-ray backlighter radiation field. There is currently no such device. Therefore, we will apply very soon for a further project to use the capabilities of Dosepix for spectroscopy and dosimetry in ultra-short fields such as at the X-ray backlighter PHELIX.
Publications
- (2021) ’Personal Dosimetry in Continuous Photon Radiation Fields With the Dosepix Detector’, IEEE Transactions on Nuclear Science, vol. 68 (5), 1129-1134
Haag, D., ..., Michel, T.
(See online at https://doi.org/10.1109/TNS.2021.3068832) - (2021) ’Personal Dosimetry in Pulsed Photon Fields with the Dosepix Detector’
Haag, D., ..., Michel, T.
