The results of more than 280 different experiments aimed at exploring the main features and performances of a newly developed gamma imager, called iPIX, are summarized in this paper. iPIX is designed to quickly localize radioactive sources while estimating the ambient dose equivalent rate at the measurement point. It integrates a 1 mm thick CdTe detector directly bump-bonded to a Timepix chip, a tungsten coded-aperture mask, and a mini RGB camera. It also represents a major technological breakthrough in terms of lightness, compactness, usability, response sensitivity, and angular resolution. As an example of its key strengths, an 241 Am source with a dose rate of only few nSv/h can be localized in less than one minute.

Towards the end of their life-cycle, nuclear facilities are generally associated with high levels of radiation exposure. The implementation of the ALARA principle requires limiting the radiation exposure of the operating people during the different tasks of maintenance, decontamination and decommissioning. CANBERRA's latest involvement in the provision of nuclear measurement solutions has led, in the framework of a technology transfer agreement with CEA LIST, to the development of a new generation gamma imager. The latter, which is designed for an accurate localization of radioactive hotspots, consists of a pixilated chip hybridized to a 1 mm thick CdTe substrate to record photon pulses and a coded mask aperture allowing for background noise subtraction by means of a procedure called mask/anti-mask, which greatly contributes to the reduced size and weight of the gamma imager as gamma shielding around the detector is less required. The spatial radioactivity map is automatically superimposed onto a pre-recorded photographic (visible) image of the scene of interest. In an effort to evaluate the performances of the new gamma imager, several experimental tests have been performed on a industrial prototype to investigate its detection response, including photon sensitivity and angular resolution, over a wide energy range (at least from 59 keV to 1330 keV). The impact of the background noise was also evaluated together with some future features like energy discrimination and parallax correction. This paper presents and discusses the main results obtained in the above experimental study. A comparison with Monte Carlo simulations using the MCNP code is provided as well.

Spatial localization of radioactive sources is currently a main issue interesting nuclear industry as well as homeland security applications and can be achieved using gamma cameras. For several years, CEA LIST has been designing a new system, called GAMPIX, with improved sensitivity, portability and ease of use. The main remaining limitation of this system is the lack of spectrometric information, preventing the identification of radioactive materials. This article describes the development of an imaging spectrometer based on the GAMPIX technology. Experimental tests have been carried out according to both spectrometric methods enabled by the pixelated Timepix chip used in the GAMPIX gamma camera. The first method is based on the size of the impacts produced by a gamma-ray energy deposition in the detection matrix. The second one uses the Time over Threshold (ToT) mode of the Timepix chip and deals with time spent by pulses generated by charge preamplifiers over a user-specified threshold. Both energy resolution and sensitivity studies demonstrated the superiority of the ToT approach which will consequently be further explored. Energy calibration, tests of different pixel sizes for the Timepix chip and use of the Medipix3 chip are future milestones to improve performances of the newly implemented imaging spectrometer

Spatial localization of radioactive sources is currently a main issue interesting nuclear industry as well as homeland security applications and can be achieved using gamma cameras. For several years, CEA LIST has been designing a new system, called GAMPIX, with improved sensitivity, portability and ease of use. The main remaining limitation of this system is the lack of spectrometric information, preventing the identification of radioactive materials. This article describes the development of an imaging spectrometer based on the GAMPIX technology. Experimental tests have been carried out according to both spectrometric methods enabled by the pixelated Timepix chip used in the GAMPIX gamma camera. The first method is based on the size of the impacts produced by a gamma-ray energy deposition in the detection matrix. The second one uses the Time over Threshold (ToT) mode of the Timepix chip and deals with time spent by pulses generated by charge preamplifiers over a user-specified threshold. Both energy resolution and sensitivity studies demonstrated the superiority of the ToT approach which will consequently be further explored. Energy calibration, tests of different pixel sizes for the Timepix chip and use of the Medipix3 chip are future milestones to improve performances of the newly implemented imaging spectrometer.

Imaging and spectroscopic performance studies of pixellated CdTe Timepix detector D Maneuski, V Astromskas, E Fröjdh et al. Characterization of a 2x3 Timepix assembly with a 500m thick silicon sensor M Zuber, T Koenig, E Hamann et al. TimepixCam: a fast optical imager with time-stamping M. Fisher-Levine and A. Nomerotski Depth of interaction and bias voltage depenence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays E Fröjdh, C Fröjdh, E N Gimenez et al. Investigation of charge collection in a CdTe-Timepix detector D Krapohl, C Fröjdh, E Fröjdh et al. X-ray absorption and charge transport in a pixellated CdTe detector with single photon processing readout E Fröjdh, B Norlin, G Thungström et al.