Vol.:(0123456789) 1 3 Journal of Radioanalytical and Nuclear Chemistry https://doi.org/10.1007/s10967-019-06818-w Feasibility study of Compton imaging for PGAA H. Heather Chen‑Mayer 1  · Steven Brown 2  · Hao Yang 2 Received: 31 July 2019 © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2019 Abstract We are developing a one-sided tomographic method for imaging prompt gamma rays, without moving the source, sample, or detector, in a standard prompt gamma activation analysis setting. Dual-plane pixelated CdZnTe detectors developed from a commercial system with external timing synchronization electronics are used to measure prompt gamma rays that are scat- tered in the first plane and subsequently absorbed in the second plane. Tomographic images have been reconstructed from the 2.2 MeV gamma rays from H in 3 mm plastic balls using inter-plane events for the first time, demonstrating the feasibility of spatially resolving mm scale H features. Keywords Prompt gamma activation analysis (PGAA) · Compton imaging · Spatially resolved PGAA Introduction The current state of the art in spatially resolved PGAA is achieved by collimating either the incident neutron beam or the emitted gamma rays, requiring scanning of the sample or collimator [1]. In Compton imaging tomography, the gamma ray photons may be used to reconstruct 3D elemental distri- bution within a solid sample, without rotating the sample or the source-detector as in conventional transmission tomog- raphy. This approach has been developed as a proton beam range finder for proton beam cancer therapy in a clinical setting [2] and has recently been investigated for use in the neutron capture prompt gamma environment [3]. Employ- ing the principle of Compton Telescope, a Compton imag- ing spectrometer comprised of dual plane pixelated CdZnTe (CZT) detectors has been developed from the commercial H3D system 1 [4]. The external timing electronics generate a list of the coincident events between the two planes, and a list-mode Maximum-likelihood Expectation Maximization (MLEM) algorithm [5] is used to estimate the spatial dis- tribution of the origin of the prompt gamma ray emission. We report preliminary findings of imaging the H 2.2 MeV gamma ray peak in a standard cold neutron beam PGAA setting. Measurements have been performed to assess the feasibility of spatially resolving H features in plastic test samples in the mm scale, as well as the performance of multi-elemental imaging and quantification. Challenges such as limited dynamic range due to high prompt gamma back- ground are addressed. This study will aid detector design and reconstruction software development for PGAA of real samples in the future. Theory The principle of Compton imaging is simple and elegant (Fig. 1), and the implementation of which has seen success in looking for “hot” spot on a “cold” background, such as radi- oactive sources in normal ambient condition, thanks to the rapid development of the thick pixelated CdZnTe detectors and application-specific integrated circuit (ASIC) readout electronics [6, 7]. These detectors offer excellent 3D-posi- tion resolution for imaging (about 0.5 mm at 662 keV) and good energy resolution (1% FWHM at 662 keV) without the need for cryogenic cooling [8]. However, their imple- mentation in the PGAA environment where both source and background rates are relatively high is especially challeng- ing. We are interested in assessing the feasibility in spatially * H. Heather Chen-Mayer chen-mayer@nist.gov 1 National Institute of Standards and Technology, Gaithersburg, MD, USA 2 H3D Inc., Ann Arbor, MI, USA 1 Identification of certain commercial equipment in this paper is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the equipment identified is necessarily the best available for the pur- pose.