Evaluation of the next generation gamma imager
Résumé
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.
Mots clés
ALARA principle implementation
radiation exposure levels
next generation gamma imager evaluation
Gamma imaging
solid scintillation detector
instrumentation
nuclear instrumentation
radiation protection
radioactivity measurement
ionizing radiation
radioactivity
Detector
Camera
Apertures
Prototype
Image resolution
gamma-ray detection
gamma-rays
nuclear measurement solutions
radioactive hotspots
pixilated chip hybridization
CdTe substrate
background noise subtraction
gamma shielding
spatial radioactivity map
gamma-ray detection response
energy discrimination
parallax correction
Monte Carlo
simulation
MCNP code
coded mask aperture
CMOS pixilated readout chip
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