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Depth of interaction and bias voltage dependence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.ORCID iD: 0000-0002-8325-5177
Diamond Light Source, Didcot, Oxfordshire OX11 0DE, United Kingdom.
University of Glasgow, Glasgow G12 8QQ, United Kingdom.
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2012 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, no 3, Art. no. C03002- p.Article in journal (Refereed) Published
Abstract [en]

High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20Όm pinhole to measure the detector spectral response in dependance on the depth of interaction. The sensor was a 1mm thick CdTe detector with a pixel pitch of 110Όm, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The beam was entering the sensor at an angle of ∌20 degrees to the surface and then passed through ∌25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-over-Threshold (ToT) mode were recorded showing each individual interaction. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the bottom part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

Place, publisher, year, edition, pages
2012. Vol. 7, no 3, Art. no. C03002- p.
Keyword [en]
Detector design and construction technologies and materials; X-ray detectors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-16738DOI: 10.1088/1748-0221/7/03/C03002ISI: 000304015300002Scopus ID: 2-s2.0-84858777567Local ID: STCOAI: oai:DiVA.org:miun-16738DiVA: diva2:545678
Available from: 2012-08-21 Created: 2012-08-17 Last updated: 2016-10-20Bibliographically approved
In thesis
1. Hybrid pixel detectors: Characterization and optimization
Open this publication in new window or tab >>Hybrid pixel detectors: Characterization and optimization
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2015. 209 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 228
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-26794 (URN)STC (Local ID)978-91-88025-37-1 (ISBN)STC (Archive number)STC (OAI)
Public defence
2015-09-08, 13:00
Supervisors
Available from: 2016-01-04 Created: 2016-01-04 Last updated: 2016-12-23Bibliographically approved

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Fröjdh, ErikFröjdh, ChristerNorlin, BörjeThungström, Göran
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