Temporal Imaging CeBr₃ Compton Camera: A New Concept for Nuclear Decommissioning and Nuclear Waste Management

Abstract

Abstract-During nuclear decommissioning or waste management operations, a camera that could make an image of the contamination field and identify and quantify the contaminants would be a great progress. Compton cameras have been proposed, but their limited efficiency for high energy gamma rays and their cost have severely limited their application. Our objective is to promote a Compton camera for the energy range (200 keV -2 MeV) that uses fast scintillating crystals and a new concept for locating scintillation event: Temporal Imaging.Temporal Imaging uses monolithic plates of fast scintillators and measures photons time of arrival distribution in order to locate each gamma ray with a high precision in space (X,Y,Z), time (T) and energy (E). This provides a native estimation of the depth of interaction (Z) of every detected gamma ray. This also allows a time correction for the propagation time of scintillation photons inside the crystal, therefore resulting in excellent time resolution. The high temporal resolution of the system makes it possible to veto quite efficiently background by using narrow time coincidence (< 300 ps). It is also possible to reconstruct the direction of propagation of the photons inside the detector using timing constraints. The sensitivity of our system is better than 1 nSv/h in a 60 s acquisition with a 22 Na source.

Influence of sub-nanosecond time of flight resolution for online range verification in proton therapy using the line-cone reconstruction in Compton imaging

“…In order to realistically study the effect of the temporal resolution of the Compton camera on the precision of the fall-off position retrieval, the BGO absorber was replaced by a 35 × 35 × 4 cm 3 block of CeBr 3 . The energy resolutions of the scatterer and absorber detectors were modelled using an inverse square root law (Etxebeste et al, 2020) based on the known resolutions of 1.1% FWHM at 1 MeV for Si (Fontana et al, 2020) and 6.9% FWHM at 511 keV for CeBr 3 (Iltis et al, 2018). The centre-to-centre distance between the last silicon plane detector and the CeBr 3 absorber was set to 15 cm.…”

“…Table 1: The resolutions assigned to the scatterer and absorber in the simulations. Values for the scatterer were obtained from Fontana et al (Fontana et al, 2020) and values for the CeBr 3 absorber were taken from the measurements by Iltis et al (Iltis et al, 2018). The spatial resolution of the detectors is assumed to be constant, whereas their energy resolutions are inversely proportional to √ E, where E is the photon energy.…”

“…The upper limit, 1.3 ns, was chosen from the measured temporal resolution of the BGO absorber of the CLaRyS Compton camera (Fontana et al, 2020) and the lower limit, 100 ps, was chosen based on the limits of existing technology for monolithic, large volume scintillators (Lecoq et al, 2020). The CeBr 3 absorber block of the Compton camera developed by Damavan Imaging (Rosières près Troyes, France) (Iltis et al, 2018) for the localisation of radioactive sources is reported to have a temporal resolution of about 100 ps RMS at 511 keV. Moreover, coincidence time resolution of 100 ps was achieved in coincidence measurements with proton beams, using diamond detectors for projectile time stamp and monolithic scintillators for prompt γ (Marcatili et al, 2020).…”

Development of a compact alpha and beta camera for dismantlement applications

“…As an alternative, several methods to perform measurements directly on-site have been investigated, most notably for long range radiation [4]. Many projects have developed cameras capable to image directly gamma (see for example [5,6,7]) or neutron radiation (see for example [8,9]). Thus, different industrial solutions are currently available commercially.…”

3-D Reconstruction Benchmark of a Compton Camera Against a Parallel-Hole Gamma Camera on Ideal Data

“…The Compton camera was proposed during 70's simultaneously for astronomical ( [1]) and nuclear medicine ( [2]) imaging applications. Several prototypes ([3], [4], [5], [6], [7]) have been built and exploited for the observation of cosmic γ sources, or for monitoring nuclear plants and waste with the development of hand-held γ-detectors boosted by the recent accident in Fukushima, Japan ( [8], [9], [10], [11], [12]). Although Compton cameras should have superior efficiency ( [13], [14], [15], [16], [17], [18], [19]), imaging of γ sources in nuclear medicine is still carried out with collimator-based gamma cameras.…”