Gamma-ray imaging with a coaxial HPGe detector (original) (raw)

Gamma-ray Compton camera imaging with a segmented HPGe

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001

In this paper, we investigate our concept to develop a -ray Compton camera out of a single coaxial High Purity Germanium (HPGe) detector. The imaging properties of the HPGe can be realized by way of a segmented outer contact and digital pulse-shape analysis. Limiting factors in performance will be related to the intrinsic electron momentum in Ge and the noise in the preampli"er JFETs. In addition to discussing these issues, we will present experimental and theoretical imaging studies that we have done using an existing segmented HPGe: the GRETA prototype detector at LBNL.

Gamma-ray imaging with position-sensitive HPGe detectors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

Due to advances in manufacturing large and highly segmented HPGe detectors along with the availability of fast and high precision digital electronics it is now possible to build efficient and high-resolution Compton cameras. Two-dimensionally segmented semiconductor detectors along with pulse-shape analysis allow to obtain three-dimensional positions and energies of individual gamma-ray interactions. By employing gamma-ray tracking procedures it is possible to determine the scattering sequence in the detector and ultimately to deduce the incident direction of gamma rays without the use of a attenuating collimator. These advanced gamma-ray tracking based Compton cameras are able not only to image gamma-ray sources with higher sensitivity than collimator-based systems but can increase the sensitivity in finding gamma-ray sources over non-imaging detectors, particularly in complex radiation fields. We have implemented a Compton camera built of a single doubule-sided strip HPGe detector with a strip pitch size of 2mm. A three-dimensional position resolution of 0.5mm at 122keV by using simple pulse-shape analysis is achieved. We have implemented image reconstruction procedures for search scenarios, which are of interest for national security applications. In addition, we have developed reconstruction procedures to optimize image quality which potentially finds applications in other areas as well.

Response of AGATA Segmented HPGe Detectors to Gamma Rays up to 15.1 MeV

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

The response of AGATA segmented HPGe detectors to gamma rays in the energy range 2-15 MeV was 29 measured. The 15.1 MeV gamma rays were produced using the reaction d( 11 B,n ) 12 C at E beam = 19.1 MeV, 30 while gamma-rays between 2 to 9 MeV were produced using an Am-Be-Fe radioactive source. The energy 31 resolution and linearity were studied and the energy-to-pulse-height conversion resulted to be linear within 32 0.05%. Experimental interaction multiplicity distributions are discussed and compared with the results of 33 Geant4 simulations. It is shown that the application of gamma-ray tracking allows a suppression of 34 background radiation following neutron capture by Ge nuclei. Finally the Doppler correction for the 15.1 35 MeV gamma line, performed using the position information extracted with Pulse-shape Analysis, is 36 discussed. 37 38 39 65 Shape Algorithms [19-28]. The energy and direction of 66 the individual photons are extracted through dedicated 67 gamma-ray tracking algorithms [29-32]. It should be 68 remarked that the individual interaction points are 69 extracted with sub-segment precision, which 70 experimentally turns out to be better than a 3D 71 Gaussian with 5 mm FWHM in each direction (see for 72 instance [33-36]). In order to achieve this goal, 73 remarkable effort has been concentrated on the 74 characterization of highly-segmented HPGe detectors 75 [37-52]. 76 The possibility to improve the performances of a 77 gamma-ray spectrometer at high energies using 85 LaBr 3 :Ce scintillation detector. Lower panel: schematic 86 representation of the Am-Be-Fe source. 87 88 The gamma-ray spectrum acquired using the Am-Be-89 Fe source is displayed in Figure 2 and the gamma lines 90 used for the analysis are labeled according to the 91 reaction which originated them. These data allowed the 92 calibration of the detectors and a check of the linearity 93 and energy resolution of the AGATA detectors. The 94 average counting rate per crystal was 0.9 kHz for the 95 case of source measurement and 1.2 kHz for the in-96 beam test. 97 98 99 100 101 102 103 104

New Developments in HPGe Detectors for High Resolution Detection

Acta Physica Polonica B

High-Purity Germanium (HPGe) detectors continue to be a fundamental tool in nuclear gamma spectroscopy. The tracking of the gamma interactions inside the HPGe crystals is opening a new era in the use of these detectors for both basic science and applications, but they have also shown that new R&D is necessary for the production of even better and more reliable highly segmented detectors. In this work, we present recent results obtained in the framework of a multidisciplinary research program in HPGe detector technologies and we discuss the influence of these studies on the use of HPGe detectors.

High-sensitivity Compton imaging with position-sensitive Si and Ge detectors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007

We report on the development of high-sensitivity and compact Compton imaging systems built of large and position-sensitive Si(Li) and HPGe detectors. The primary goal of this effort is to provide improved capabilities in the passive detection of nuclear materials for homeland security. Our detectors are implemented in double-sided strip configuration, which-along with digital signal processingprovides energies and three-dimensional position information of individual g-ray interactions. g-Ray tracking algorithms then determine the scattering sequence of the g-ray, which in turn allows us-employing the Compton scattering formula-to reconstruct a cone of possible incident angles and ultimately an image. This Compton imaging concept enables large-field-of-view g-ray imaging without the use of a heavy collimator or aperture. The intrinsically high-energy resolution of the detectors used, the excellent position resolution we have demonstrated, both combined with the high efficiency of large-volume detectors is the basis for high Compton imaging sensitivity. These capabilities are being developed to identify and localize potential threat sources and to potentially increase the sensitivity in detecting weak sources out of the midst of natural, medical, or commercial sources. g-ray imaging provides a new degree of freedom to distinguish between spatial and temporal background fluctuations and compact threat sources. r

Position resolution studies with MSU 32-fold segmented HPGe detector

2001 Ieee Nuclear Science Symposium, Conference Records, Vols 1-4, 2002

We present position sensitivity measurements obtained with one of the 32−fold segmented HPGe detectors from Michigan State University. These measurements were performed with a collimated beam of 137 Cs gamma rays scattered by 90 degrees. This deposits 374 keV at a given location inside the crystal. A position resulution can be determined over many events by examining the digitally recorded pulse shapes on the 32 electrical contacts. If position resolution is adequate, gamma ray Compton camera imaging may be possible.

Portable high energy gamma ray imagers

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996

To satisfy the needs of high energy gamma ray imagers for industrial nuclear imaging applications, three high energy gamma cameras are presented. The RMD-Pinhole camera uses a lead pinhole collimator and a segmented BGO detector viewed by a 3 in. square position sensitive photomultiplier tube (PSPMT). This pinhole gamma camera displayed an energy resolution of 25.0% FWHM at the center of the camera at 662 keV and an angular resolution of 6.2" FWHM at 412 keV The fixed multiple hole collimated camera (FMCC), used a multiple hole collimator and a continuous slab of NaI(TI) detector viewed by the same PSPMT. The FMCC displayed an energy resolution of 12.4% FWHM at 662 keV at the center of the camera and an angular resolution of 6.0" FWHM at 412 keV. The rotating multiple hole collimated camera (RMCC) used a 180" antisymmetric rotation modulation collimator and CsI(T1) detectors coupled to PIN silicon photodiodes. The RMCC displayed an energy resolution of 7.1% FWHM at 662 keV and an angular resolution of 4.0" FWHM at 810 keV The performance of these imagers is discussed in this paper.

Development of gamma Ray Tracking Detectors

Acta Physica Polonica B, 2001

The next generation of 4 π arrays for high-precision γ -ray spectroscopy AGATA will consist of γ -ray tracking detectors. They represent high-fold segmented Ge detectors and a front-end electronics, based on digital signal processing techniques, which allows to extract energy, timing and spatial information on the interactions of a γ -ray in the Ge detector by pulse shape analysis of its signals. Utilizing the information on the positions of the interaction points and the energies released at each point the tracks of the γ -rays in a Ge shell can be reconstructed in three dimensions on the basis of the Compton-scattering formula.

Ultracompact Compton camera for innovative gamma-ray imaging

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018

A multipixel photon counter (MPPC) features excellent photon-counting capability as a radiation detector. In particular, a two-plane Compton camera consisting of Ce:GAGG scintillators coupled with MPPC arrays has significant application potential owing to its compact size and low weight. For example, the camera can be easily mounted on a commercial drone to identify radiation hot spots from the sky. In Fukushima, we demonstrated that a 137 Cs distribution within a 100 m diameter can be mapped correctly within a couple of tens of minutes. The advanced use of the Compton camera is also anticipated in the field of proton therapy. We evaluated an image of 511 keV annihilation gamma-rays emitted from a PMMA phantom irradiated by 200 MeV protons to mimic an in-beam monitor for proton therapy. Finally, we developed an ultracompact Compton camera (weight = 580 g), for 3-D multicolor molecular imaging. In order to demonstrate the performance capabilities of the device, 131 I (365 keV) , 85 SrCl 2 (514 keV), and 65 ZnCl 2 (1116 keV) were injected into a living mouse and the data were taken from 12 angles with a total acquisition time of 2 h. We confirmed that all tracers had accumulated on the target organs of the thyroid, bone, and liver, and that the obtained 3-D image was quantitatively correct with an accuracy of ±20%.