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Dosimetry with the photon counting pixel detector Dosepix

Thilo Michel

Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg

Abstrakt:

The hybrid-pixel detector Dosepix has been developed for dosimetry in a collaboration of CERN and the Erlangen Centre for Astroparticle Physics. It comprises an ASIC, designed by CERN, with a 16x16 pixel matrix at a pitch of 220 micrometers that can be connected pixel-wise to a 300 micrometers thick silicon sensor layer. The sensor layer is segmented into 12 rows of 220 μm squares for large sensitive area, and 4 rows of 55 μm squares to cope with high dose rates. The pixel’s charge sensitive preamplifier is connected to an in-pixel discriminator which generates a digital pulse whose length corresponds to the deposited energy. This pulse length is measured internally in a digital manner as time-over-threshold (ToT) and processed further in the pixel. The corresponding energy channel to which a measured ToT belongs to is determined by the in-pixel energy binning state machine circuitry by sequentially comparing 16 stored digital energy thresholds with the measured ToT. Thus, each pixel is a 16-channel spectrometer. The 16 thresholds are defined individually for each pixel. The energy bin counts are read out column-wise. To avoid dead time due to the necessary read-out procedure, 15 of the 16 columns are ready to detect events at all times, except the column which is read out. In addition to the energy bin readout, the last recorded ToT in each pixel can be read out. An integrating operation mode was implemented to sum the ToTs of several events, imitating an integrating detector. Dosepix can also be operated in single-threshold counting mode with 8 bits of counter depth per pixel, allowing fast readout. Thus, this very compact detector (3.5 x 3.5 mm2) is very well adapted to dosimetry: dead-time free recording of events, no dependence on radiation pulse duration, capability to operate at very high dose rates and excellent sensitivity. 

In this talk, I will give an overview about the functionality and performance of the Dosepix detector, present our concept to measure personal dose equivalents with this detector, and show results on the performance to measure personal dose equivalents (deep and surface dose) in continuous and pulsed photon fields. The disturbing influence of electron irradiation will also be discussed.

Seminář se koná v úterý 10. března ve 14:00
v zasedací místnosti ÚTEF ČVUT, Praha 1, Husova 240/5.

Ing. Bartoloměj Biskup, Ph.D.
tajemník semináře
doc. Ing. Ivan Štekl, CSc.
ředitel ÚTEF
doc. Dr. André Sopczak
předseda NPS, ČS IEEE

IEEE logoNUCLEAR & PLASMA SCIENCES SOCIETY CHAPTER
IEEE Czechoslovakia section
http://www.ieee.cz/en/nps

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