Detection and Location of Gamma-Ray Sources with a Modulating Coded Mask (original) (raw)
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Large detectors can give better background characterization and can detect radiation sources at larger standoff distances. Small detectors, on the other hand, are less expensive, can often get closer to source materials, and can access places large detectors cannot (e.g. indoor environments). We systematically quantify the impact of detector size and number on source detection in area search applications. We analyze theoretical upper bounds on source detectability and establish first order approximations thereof. We demonstrate that these approximations give good comparisons of different choices of sensor size and number for practical source detection algorithms using semi-synthetic data. Our results indicate that multiple small detectors, in conjunction, can offer superior overall operational utility compared to a single large detector. Finally, we identify differences in detector response and likelihood of a close approach as key determinants of the relative utility of small sensors.
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Communications Faculty of Sciences University of Ankara. Series A2-A3: physics, engineerigng physics, electronic engineering and astronomy, 2021
This study shows the design, implementation, and test results of a lowcost portable radiation-detector system relies on a directionally designed multi detector probe that works in Geiger-Müller counting mode with a single chip solution. The proposed system can perform the functions of detecting the ionizing radiation source, counting gamma and showing the direction and angle of the gamma source relative to the position of the device. The radiation direction finding (RDF) system consists of a radiation probe and electronic sections that are mounted in a metal box. The probe has a has a cast housing made of lead material and it has 8 directional slots for placing the optically isolated PIN diode arrays where each array consists of 4 parallelly connected BPW 34 PIN model diode. The lead housing also blocks incident rays from unintended directions and provides a directional sensing for PIN diodes. The metal box contains 8 low noise amplifiers and pulse shaping detector boards that are assigned to each channel of PIN diode arrays, a signal inverter board, a step-up high voltage board, a 12 V battery and a parallel processing FPGA board with an embedded VHDL software that can process all 8 channels simultaneously and execute the direction estimation algorithm. The system also has an adjustable detector bias voltage and the applied voltage can be displayed on a seven-segment display located in front of the unit so that different models of PIN diodes can be used and tested with different bias voltage levels. It also has a HMI touch screen unit and user interface for displaying the Cpm or Cps values of each channel; a 360-degree scale showing the direction of the source with its pointer and an indicator showing the direction of the source numerically in degrees. The system works as a gamma detector and the source direction can also be detected within ±45° interval. The success of system within this interval is 99.22%. The detector was tested with low to high energy gamma sources (241 Am, 9.761 μCi, 59.54 keV, 137 Cs 661, 3.7 MBq, keV and 60 Co, μCi, 1173 and 1332 keV) and showed good sensitivity performance level in gamma ray detection. The major 94 B. ÇUHADAROĞLU, H.G. İLK outcome of this study and the major contribution of this work to the literature is therefore is the design and production details of a hand-held detector and source direction locator prototype; which is a light, portable and compact system.
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IEEE Transactions on Signal Processing, 2010
There are many systems for counting photons such as gamma-rays emitted from radioactive sources. Many of these systems are also position-sensitive, which means that the system provides directional information about recorded events. This paper investigates whether or not the additional information provided by position-sensitive capability improves the performance of detecting a point-source in background. We analyze the asymptotic performance of the generalized likelihood ratio test (GLRT) and a test based on the maximum-likelihood (ML) estimate of the source intensity for systems with and without position-sensitive capability. When the background intensity is known and detector sensitivity is spatially uniform, we prove that position-sensitive capability increases the area under the receiver operating characteristic curve (AUC). For cases when detector sensitivity is nonuniform or background intensity is unknown, we provide numerical results to illustrate the effect of the parameters on detection performance.
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A position sensitive detector for 9 MeV gamma rays has been developed as part of a contraband detection system for airports. The system images contraband, such as explosives or drugs, in a geometry similar to medical x-ray computed tomography. A point source of gamma rays shines through an unknown object. Transmission projections of the areal density of detected gamma rays are reconstructed into a 3D image, which shows the presence of concealed contraband inside the object. The image quality depends critically on the spatial resolution of the gamma ray detector. The existing detector is a modi ed version of ones developed by CTI for medical PET imaging with 0.511 MeV gamma rays. An initial prototype detector was characterized by exposing it to 9 MeV gamma rays from a 252 Cf + Ni source. Projection images of a simple phantom object show that the detector is capable of faithful imaging at 9 MeV.
Source-search sensitivity of a large-area, coded-aperture, gamma-ray imager
IEEE Transactions on Nuclear Science, 2000
We have recently completed a large-area, codedaperture, gamma-ray imager for use in searching for radiation sources. The instrument was constructed to verify that weak point sources can be detected at considerable distances if one uses imaging to overcome fluctuations in the natural background. The instrument uses a rank-19, one-dimensional coded aperture to cast shadow patterns onto a 0.57 m 2 NaI(Tl) detector composed of 57 individual cubes each 10 cm on a side. These are arranged in a 19 x 3 array. The mask is composed of four-centimeter thick, onemeter high, 10-cm wide lead blocks. The instrument is mounted in the back of a small truck from which images are obtained as one drives through a region. Results of first measurements obtained with the system are presented.
Determination of absolute detection efficiencies for detectors of interest in homeland security
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007
The absolute total and absolute peak detection efficiencies of gamma ray detector materials NaI:Tl, CdZnTe, HPGe, HPXe, LaBr 3 :Ce and LaCl 3 :Ce were simulated and compared to that of polyvinyltoluene (PVT). The dimensions of the PVT detector were 188.82 cm  60.96 cm  5.08 cm, which is a typical size for a single-panel portal monitor. The absolute total and peak detection efficiencies for these detector materials for the point, line and spherical source geometries of 60 Co (1332 keV), 137 Cs (662 keV) and 241 Am (59.5 keV) were simulated at various source-to-detector distances using the Monte Carlo N-Particle software (MCNP5-V1.30). The comparison of the absolute total detection efficiencies for a point, line and spherical source geometry of 60 Co and 137 Cs at different source-to-detector distance showed that the absolute detection efficiency for PVT is higher relative to the other detectors of typical dimensions for that material. However, the absolute peak detection efficiency of some of these detectors are higher relative to PVT, for example the absolute peak detection efficiency of NaI:Tl (7.62 cm diameter  7.62 cm long), HPGe (7.62 cm diameter  7.62 cm long), HPXe (11.43 cm diameter  60.96 cm long), and LaCl 3 :Ce (5.08 cm diameter  5.08 cm long) are all greater than that of a 188.82 cm  60.96 cm  5.08 cm PVT detector for 60 Co and 137 Cs for all geometries studied. The absolute total and absolute peak detection efficiencies of a right circular cylinder of NaI:Tl with various diameters and thicknesses were determined for a point source. The effect of changing the solid angle on the NaI:Tl detectors showed that with increasing solid angle and detector thickness, the absolute efficiency increases. This work establishes a common basis for differentiating detector materials for passive portal monitoring of gamma ray radiation. r