Lucian Mihailescu

Standoff 3D Gamma-Ray Imaging

We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ray sources distributed in the environment. Unlike standard 3D tomographic methods, this technique does not require the radioactive sources to be bounded within a predefined physical space. In the present implementation, the gamma-ray imaging system is based on two large planar HPGe double sided segmented detectors, which are used in a Compton camera configuration. A LIDAR system is used in conjunction with the gamma-ray imaging system to confine the gamma-ray image space to the interior of physical objects situated within the detection range of the gamma-ray imager. This approach results in superior image contrast and efficient image reconstruction. Results demonstrating the operating principle are reported.

First-generation hybrid compact Compton imager

At Lawrence Livermore National Laboratory, we are pursuing the development of a gamma-ray imaging system using the Compton effect. We have built our first generation hybrid Compton imaging system, and we have conducted initial calibration and image measurements using this system. In this paper, we present the details of the hybrid Compton imaging system and initial calibration and image measurements

Detector module development for the High Efficiency Multimode Imager

The High Efficiency Multimode Imager (HEMI) is an instrument currently under development for the purpose of detecting, locating, and spectroscopically characterizing gamma-ray emission sources at long-range standoff distances. The instrument design consists of multiple planes of relatively large-volume, good-energy-resolution detector modules configured for combined coded aperture and Compton scatter (multimode) gamma-ray imaging. The basic building block of HEMI is a detector module consisting of a CdZnTe coplanar-grid detector packaged along with its front-end and pulse-shaping electronics. We have developed a module that can be used to form close-packed arrays, has low dead mass, and is easily adjusted for optimum spectroscopic performance. In this paper, we provide an overview of HEMI and then detail the design, production, and testing of the detector modules.

First results of the High Efficiency Multi-mode Imager (HEMI)

The High Efficiency Multi-mode Imager (HEMI) is a combined Compton and coded mask imager designed to detect and image gamma rays from ~30 keV up to a few MeV. It consists of 1-cm3-size coplanar-grid CdZnTe detectors with an energy resolution of ~2 % FWHM at 662 keV. We present the simulation and data analysis pipeline for HEMI as well as first results from measurements with an eight-detector test setup in Compton mode (spectra, angular resolution, and reconstructed images) and comparisons with simulations.

Real-time radioactive source localization with a moving coded-aperture detector system at low count rates

We present a feasibility study of real-time radioactive source localization in which the effects of low count rates on source localizations with a moving coded-aperture detector system are addressed. The conventional crosscorrelation method with the installed binary mask was not reliable enough to filter out background noise at low count rates in this study. To improve the cross-correlation performance, we adopted a new binary mask design method for future work. Offline data processing to mimic on-line data processing was based on multi-CPUs and multi-GPUs (graphics processing units) parallel processing. We also show an iterative list-mode localization method using background-free simulated data.

MO-FG-CAMPUS-JeP1-01: Prompt Gamma Imaging with a Multi-Knife-Edge Slit Collimator: Evaluation for Use in Proton Beam Range Verification

PURPOSE To evaluate and characterize a multi-slit collimated imaging system for use in prompt gamma range verification of proton therapy. METHODS Acrylic (PMMA) targets were irradiated with a 50 MeV proton beam. With the collimator placed 13 cm from the beam axis, photons of energy from 2-7 MeV were measured. Image reconstruction provided 2-dimensional distribution of gamma rays. Estimated Bragg peak location was compared with 1-dimensional profiles of photon images. Shifts in Bragg peak were simulated by physically moving the targets in 1 mm increments. RESULTS The imaging system measured prompt gamma emissions resulting from a 50 MeV proton beam, at currents up to 2 nA, incident on a PMMA target. Overall system detection efficiency was approximately 2.6×10-5 gamma/proton. With delivery of 1×1011 protons, shifts of 1 mm in the target location were detected in 2D prompt gamma images and 1D profiles. With delivery of 1×108 protons, shifts of approximately 3 mm were detectable. CONCLUSION This work has characterized the performance of a prototype multi-slit collimated imaging system. The system can produce 2D images of prompt gamma distributions and detect shifts in Bragg peak location down to 1 mm. These results encourage further development and optimization of the system for clinical proton beam applications. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number: DENA0000979 through the Nuclear Science and Security Consortium.

Status of the High Efficiency Multimode Imager

The High Efficiency Multimode Imager (HEMI) is an instrument to detect, locate, and spectroscopically characterize radioactive sources with gamma-ray emissions at long-range standoff distances. HEMI consists of modular cubic-centimeter coplanar-grid CdZnTe detector elements configured in a two-plane array that allows for both Compton scattering and coded aperture imaging. Measurements and simulations have been performed using a variety of radioactive sources at different positions with respect to a prototype HEMI array in order to demonstrate the source identification and localization capabilities of the system. This paper will provide an overview of the HEMI instrument as well as present results from simulations and measurements using the completed detector array.

A Spherical Active Coded Aperture for

Gamma-ray imaging facilitates the efficient detection, characterization, and localization of compact radioactive sources in cluttered environments. Fieldable detector systems employing active planar coded apertures have demonstrated broad energy sensitivity via both coded aperture and Compton imaging modalities. However, planar configurations suffer from a limited field of view, especially in the coded aperture mode. To improve upon this limitation, we introduce a novel design by rearranging the detectors into an active coded spherical configuration, resulting in a

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Gamma-Ray Imaging

isotropic field of view for both coded aperture and Compton imaging. This paper focuses on the low-energy coded aperture modality and the optimization techniques used to determine the optimal number and configuration of 1-cm3 CdZnTe coplanar grid detectors on a 14-cm diameter sphere with 192 available detector locations.