Gamma Detector Research Articles

A gamma and neutron phoswich read out with SiPM for SPRD

A gamma and neutron phoswich was developed for spectroscopic personal radiation detectors (SPRDs). It consisted of a Φ25 × 25 mm NaI(Tl) crystal for gamma detection and a Φ25 × 3 mm LiI(Eu) crystal for neutron detection. The phoswich was read out by 8 × 8 ch SiPM array (24 × 24 mm2). Radiations in NaI(Tl) and LiI(Eu) were discriminated by pulse shape, while gammas and neutrons in LiI(Eu) were separated by pulse amplitude. For the LiI(Eu), the gamma equivalent energy for thermal neutrons was measured as 3.6 ± 0.1 MeV, providing satisfactory gamma rejection. For NaI(Tl), the response of SiPM array was well linear in the energy range up to 1408 keV, at which a deviation less than 2% was measured. Digital pulse shape discrimination (PSD) was implemented with an 8-bit digitizer running at 50 MSPS sampling rate and offline analysis. The signal pulses from NaI(Tl) and LiI(Eu) showed significant difference in falling edge allowing effective PSD. The best figure of merit (FOM) was measured as 4.4 ± 0.2 with optimized parameters, providing excellent PSD performance. The energy resolutions for 661.6 keV gamma rays in NaI(Tl) and thermal neutrons in LiI(Eu) were measured as 7.0 ± 0.2% and 11.2 ± 0.2% respectively, with selected PSD threshold.

Configuration of gamma detectors in a neutron interrogation system for detection of explosives

This paper investigates the use of a suitable gamma detector array to increase the detectably of explosives in a prompt-gammas neutron activation analysis (PGNAA) system. Monte Carlo simulations (MCNP-4C) were used for analyzing the system. It was found that the system's performance is enhanced by the use of four detectors: three of the are located on the same side as the neutron source and the fourth on the opposite side. Signature-based radiation-scanning, with nine signatures for each detector, is also discussed.

HRTEM Analysis of Crystallographic Defects in CdZnTe Single Crystal

In recent years, CdZnTe has attracted much attention due to its superior electrical and structural properties for room-temperature operable gamma and x-ray detectors. However, CdZnTe (CZT) material has often suffered from crystallographic defects encountered during the growth and post-growth processes. The identification and structural characterization of these defects is crucial to synthesize defect-free CdZnTe single crystals. In this study, Cd0.95 Zn0.05 Te single crystals were grown using a three-zone vertical Bridgman system. The single crystallinity of the material was ensured by using x-ray diffraction measurements. High-resolution electron microscopy (HRTEM) was used to characterize the nano-scale defects on the CdZnTe matrix. The linear defects oriented along the ⟨211⟩ direction were examined by transmission electron microscopy (TEM) and the corresponding HRTEM image simulations were performed by using a quantitative scanning TEM simulation package.

Sub-3mm spatial resolution from a large monolithic LaBr3 (Ce) scintillator

Abstract A Compton camera prototype for ion beam range monitoring via prompt (< 1 ns) gamma detection in hadron therapy is being developed and characterized at the Medical Physics Department of LMU Munich. The system consists of a large (50x50x30 mm3) monolithic LaBr3(Ce) scintillation crystal as absorber component to detect the multi-MeV Compton scattered photons, together with a stack of 6 double-sided silicon strip detectors (DSSSD) acting as scatterer component. Key ingredient of the γ-source reconstruction is the determination of the γ-ray interaction position in the scintillator, which is read out by a 256-fold segmented multi-anode photomultiplier tube (PMT). From simulations an angular resolution of about 1.5o for the photon source reconstruction can be expected for the energy range around 3 – 5 MeV, provided that a spatial resolution of 3 mm can be reached in the absorbing scintillator [1]. Therefore, particular effort was dedicated to characterize this latter property as a function of the γ-ray energy. Intense, tightly collimated 137Cs and 60Co photon sources were used for 2D irradiation scans (step size 0.5 mm) as prerequisite for studying the performance of the “k-Nearest-Neighbors” algorithm developed at TU Delft [2] (together with its variant ”Categorical Average Pattern”, CAP) and extending its applicability into the energy range beyond the original 511 keV. In this paper we present our most recent interaction position analysis in the absorbing scintillator, leading to a considerably improved value for the spatial resolution: systematic studies were performed as a function of the k-NN parameters and the PMT segmentation. A trend of improving spatial resolution with increasing photon energy was confirmed, resulting in the realization of the presently optimum spatial resolution of 2.9(1) mm @1.3 MeV, thus reaching the design specifications of the Compton camera absorber. The specification goal was reached also for a reduced PMT segmentation of 8x8 anode segments (each with 6x6 mm2 active area), thus allowing to reduce the complexity of the signal processing while preserving the performance.

Development and calibration of a new gamma camera detector using large square Photomultiplier Tubes

Large area scintillation detectors applied in gamma cameras as well as Single Photon Computed Tomography (SPECT) systems, have a major role in in-vivo functional imaging. Most of the gamma detectors utilize hexagonal arrangement of Photomultiplier Tubes (PMTs). In this work we applied large square-shaped PMTs with row/column arrangement and positioning. The Use of large square PMTs reduces dead zones in the detector surface. However, the conventional center of gravity method for positioning may not introduce an acceptable result. Hence, the digital correlated signal enhancement (CSE) algorithm was optimized to obtain better linearity and spatial resolution in the developed detector. The performance of the developed detector was evaluated based on NEMA-NU1-2007 standard. The acquired images using this method showed acceptable uniformity and linearity comparing to three commercial gamma cameras. Also the intrinsic and extrinsic spatial resolutions with low-energy high-resolution (LEHR) collimator at 10 cm from surface of the detector were 3.7 mm and 7.5 mm, respectively. The energy resolution of the camera was measured 9.5%. The performance evaluation demonstrated that the developed detector maintains image quality with a reduced number of used PMTs relative to the detection area.

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is >1.5 carbon weight % (standard deviation ± 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

Estimation of neutron energy distributions from prompt gamma emissions

A technique of estimating the incident neutron energy distribution from emitted prompt gamma intensities from a system exposed to neutrons is presented. The emitted prompt gamma intensities or the measured photo peaks in a gamma detector are related to the incident neutron energy distribution through a convolution of the response of the system generating the prompt gammas to mono-energetic neutrons. Presently, the system studied is a cylinder of high density polyethylene (HDPE) placed inside another cylinder of borated HDPE (BHDPE) having an outer Pb-cover and exposed to neutrons. The emitted five prompt gamma peaks from hydrogen, boron, carbon and lead can be utilized to unfold the incident neutron energy distribution as an under-determined deconvolution problem. Such an under-determined set of equations are solved using the genetic algorithm based Monte Carlo de-convolution code GAMCD. Feasibility of the proposed technique is demonstrated theoretically using the Monte Carlo calculated response matrix and intensities of emitted prompt gammas from the Pb-covered BHDPE–HDPE system in the case of several incident neutron spectra spanning different energy ranges.

Lead foil wrapping of the plastic scintillators for the gamma ray detection: optical reflector or spectrum intensifier?

This paper studies the effect of lead wrapping on the response of the plastic scintillators as gamma detectors. Experimental tests and Geant4 simulations showed that lead wrapping cannot increase the gamma absorption efficiency of the detector but, as a reflector, it can improve the optical properties of the detector. The reflectivity of the lead foil as an optical reflector was determined equal to 66% using an experimental-simulation combined method. Based on the obtained results, the optical collection efficiency of the detector was also increased about 4% after employing the lead reflector.

Characterization of Large Volume CLYC Scintillators for Nuclear Security Applications

We report on our development of large volume Cs2LiYCl6 (CLYC) detectors for nuclear security applications. Three-inch diameter boules have been grown and 3-in right cylinders have been fabricated. Crystals containing either >95% 6Li or >99% 7Li have been grown for applications specific to thermal or fast neutron detection, respectively. We evaluated their gamma and neutron detection properties and the performance is as good as small size crystals. Gamma and neutron efficiencies were measured for large crystals and compared with smaller size crystals. With their excellent performance characteristics, and the ability to detect fast neutrons, CLYC detectors are excellent triple-mode scintillators for use in handheld and backpack instruments for nuclear security applications.

Large-Area, Low-Cost, High-Efficiency Neutron Detector for Vehicle-Mounted Operation

We have developed a large-area, low-cost, high-efficiency neutron detector for vehicle-mounted operation. The detector, which has overall dimensions 12.7 cm $\times 91.4$ cm $\times 102$ cm (5” $\times 36$ ” $\times 40$ ”), a sensitive area equal to $0.85~\text {m}^{{\mathbf {2}}}$ (1320 in2), and weight of 110 kg (242 lbs), employs an array of 90 boron-coated straw (BCS) detectors. PTI has also developed electronics to minimize cost and space while providing low-noise signal conditioning for both neutron and gamma detection channels, as well as low energy Bluetooth communication with handheld devices. Extremely low power consumption allows continuous use for 225 hours (~10 days) using three AAA lithium-ion rechargeable batteries. We present radiological, mechanical, and environmental tests, collected from four full-scale prototypes. Outdoor neutron-counting tests with a moderated 252Cf source 2 m away from the center of the detector face showed an average detection rate of 5.5 cps/ng with a standard deviation of 0.09 cps/ng over the four individual detector measurements. Measurements showed a gamma rejection ratio of $1.0\times 10^{{\mathbf {-8}}}$ , and gamma absolute rejection ratio (GARRn) of 0.93. The prototypes were also operated successfully onboard a moving vehicle for high-speed tests and a long-range 1433-mile, two-day road trip from Houston, TX, USA, to Laurel, MD, USA. Using auxiliary DARPA SIGMA equipment, the GPS, timestamp, gamma and neutron data were transmitted over the cellular network with 10 Hz resolution to a server and real-time tracking website. Mechanical impact and electrostatic discharge testing produced no spurious counts in either the neutron or gamma channels. Ambient environmental temperature testing showed less than ± 1% response variation over the range from −30°C to +55°C.

A CZT-based blood counter for quantitative molecular imaging

BackgroundRobust quantitative analysis in positron emission tomography (PET) and in single-photon emission computed tomography (SPECT) typically requires the time-activity curve as an input function for the pharmacokinetic modeling of tracer uptake. For this purpose, a new automated tool for the determination of blood activity as a function of time is presented.The device, compact enough to be used on the patient bed, relies on a peristaltic pump for continuous blood withdrawal at user-defined rates. Gamma detection is based on a 20 × 20 × 15 mm3 cadmium zinc telluride (CZT) detector, read by custom-made electronics and a field-programmable gate array-based signal processing unit. A graphical user interface (GUI) allows users to select parameters and easily perform acquisitions.ResultsThis paper presents the overall design of the device as well as the results related to the detector performance in terms of stability, sensitivity and energy resolution. Results from a patient study are also reported. The device achieved a sensitivity of 7.1 cps/(kBq/mL) and a minimum detectable activity of 2.5 kBq/ml for 18F. The gamma counter also demonstrated an excellent stability with a deviation in count rates inferior to 0.05% over 6 h. An energy resolution of 8% was achieved at 662 keV.ConclusionsThe patient study was conclusive and demonstrated that the compact gamma blood counter developed has the sensitivity and the stability required to conduct quantitative molecular imaging studies in PET and SPECT.

Transparent Ultra-High-Loading Quantum Dot/Polymer Nanocomposite Monolith for Gamma Scintillation.

Spectroscopic gamma-photon detection has widespread applications for research, defense, and medical purposes. However, current commercial detectors are either prohibitively expensive for wide deployment or incapable of producing the characteristic gamma photopeak. Here we report the synthesis of transparent, ultra-high-loading (up to 60 wt %) CdxZn1-xS/ZnS core/shell quantum dot/polymer nanocomposite monoliths for gamma scintillation by in situ copolymerization of the partially methacrylate-functionalized quantum dots in a monomer solution. The efficient Förster resonance energy transfer of the high-atomic-number quantum dots to lower-band-gap organic dyes enables the extraction of quantum-dot-borne excitons for photon production, resolving the problem of severe light yield deterioration found in previous nanoparticle-loaded scintillators. As a result, the nanocomposite scintillator exhibited simultaneous improvements in both light yield (visible photons produced per MeV of gamma-photon energy) and gamma attenuation. With these enhancements, a 662 keV Cs-137 gamma photopeak with 9.8% resolution has been detected using a 60 wt % quantum-dot nanocomposite scintillator, demonstrating the potential of such a nanocomposite system in the development of high-performance low-cost spectroscopic gamma detectors.

Estimation of 222Rn exhalation rate and assessment of radiological risk from activity concentration of 226Ra, 232Th and 40K

The activity concentration of natural radionuclides and 222Rn (Radon) exhalation rate in soil samples were determined using NaI gamma detector and Scintillation based Smart Radon Monitor (SRM). Soil samples were collected from different geological formations of the same area. The concentration of three radionuclides (226Ra, 232Th and 40K) in the studied area has been varied from 25Bqkg−1 to 48Bqkg−1, 28Bqkg−1 to 47Bqkg−1 and 356Bqkg−1 to 598Bqkg−1 respectively. The average value of 226Ra (Radium) equivalent activity in soil samples of the studied area was 125Bqkg−1. The 226Ra equivalent activities of soil samples have been calculated to assess the radiation hazards arising due to the use of these soils in the construction of dwellings. The exhalation of 222Rn from the earth's crust and building material are the main source of 222Rn in indoor environment. The 222Rn exhalation rate in the studied area was varied from 16.9±0.5mBqKg−1h−1 to 38.2±0.9mBqKg−1h−1. A weak correlation was obtained between the 226Ra and 222Rn exhalation rate. The annual effective doses for different organs and radiation hazards have been also calculated in the studied area. The overall average annual effective dose in the studied is lower than the world recommended value of 1.0mSva−1.

Study of the hydrothermal crystallization process of barium titanate by means of X-ray mass attenuation coefficient measurements at an energy of 59.54 keV

In this work, the X-ray mass attenuation coefficients of hydrothermally synthesized barium titanate (BaTiO3) samples were calculated with the purpose of determining the crystallization sequence of BaTiO3. Hydrothermally synthesized samples prepared at 100°C and 200°C, and reacted for varying reaction times between 15min up to 120h were studied. Attenuation coefficient measurements were done with a coaxial HPGe gamma detector (Ortec, GEM55P4-95) with a working range in the X-ray energy region. The samples were made into pellets and were exposed to 241Am radioisotopes at an energy of 59.54keV for 300s. Additionally, FT-Raman and XRD measurements were done to support the X-ray mass attenuation measurements. It was found that secondary barium titanate (BT) phases (BaTi2O5 and Ba2TiO4) were formed from the precursor material at the early stages of the hydrothermal reaction and that phase pure BaTiO3 was formed at longer reaction times. The sequence of barium titanate crystallization was determined as follows: BaTi2O5; BaTi2O5 and BaTiO3; BaTi2O5, Ba2TiO4 and BaTiO3: and phase pure BaTiO3.

Structure and symmetries of odd-odd triaxial nuclei

Rotational spectra of odd-odd Rh and Ag isotopes are investigated with the primary motivation to search for the spontaneous chiral symmetry breaking phenomenon in these nuclei. The experimental results obtained on the degenerate dipole bands of some of these isotopes using a large array of gamma detectors are discussed and studied using the triaxial projected shell (TPSM) approach. It is shown that, first of all, to reproduce the odd-even staggering of the known yrast bands of these nuclei, large triaxial deformation is needed. This large triaxial deformation also gives rise to doublet band structures in many of these studied nuclei. The observed doublet bands in these isotopes are shown to be reproduced reasonably well by the TPSM calculations. Further, the TPSM calculations for neutron-rich nuclei indicate that the ideal manifestation of the chirality can be realised in 106Rh and 112Ag , where the doublet bands have similar electromagnetic properties along with small differences in excitation energies.

Study of gamma detection capabilities of the REWARD mobile spectroscopic system

REWARD is a novel mobile spectroscopic radiation detector system for Homeland Security applications. The system integrates gamma and neutron detection equipped with wireless communication. A comprehensive simulation study on its gamma detection capabilities in different radioactive scenarios is presented in this work. The gamma detection unit consists of a precise energy resolution system based on two stacked (Cd,Zn)Te sensors working in coincidence sum mode. The volume of each of these CZT sensors is 1cm3. The investigated energy windows used to determine the detection capabilities of the detector correspond to the gamma emissions from 137Cs and 60Co radioactive sources (662keV and 1173/1333keV respectively). Monte Carlo and Technology Computer-Aided Design (TCAD) simulations are combined to determine its sensing capabilities for different radiation sources and estimate the limits of detection of the sensing unit as a function of source activity for several shielding materials.

Determination of coherent to Compton scattering differential cross section ratios of some inorganic materials with EDXRF

In this study, we aimed to determine coherent to Compton scattering differential cross section ratios of some inorganic materials (BaSO4, CaF2, Mg2SiO4, MgSO4, and ZnSO4(7H2O)) for several scattering angles (95°, 105°, 115°, 125°, and 135°). Coherent to Compton scattering differential cross section ratios were investigated experimentally by using an HPGe detector, which has a resolution of 199.6 eV at the 5.9 keV. The samples were excited with 59.54 keV gamma rays emitted from Am241 point source. The intensity ratios were corrected due to the photopeak efficiency of the gamma detector and absorption of photons in the target and air. It is observed that coherent to Compton scattering differential cross section ratios decrease with increasing scattering angle.

Study of bound states in 10Be by one neutron removal reactions of 11Be

The bound states of 10Be have been studied by removing single neutrons from 11Be nuclei. A 2.8 MeV u–1 beam of 11Be was produced at ISOLDE, CERN and directed on to both proton and deuteron targets inducing one-neutron removal reactions. Charged particles were detected to identify the two reaction channels (d, t) and (p, d), and the individual states in 10Be were identified by gamma detection. All bound states but one were populated and identified in the (d, t) reaction. The combination of REX-ISOLDE and MINIBALL allowed for a clean separation of the high-lying states in 10Be. This is the first time these states have been separated in a reaction experiment. Differential cross sections have been calculated for all the reaction channels and compared to DWBA calculations. Spectroscopic factors are derived and compared to values from the litterature. While the overall agreement between the spectrocopic factors is poor, the ratio between the ground state and the first excited state is in agreement with the previous measured ones. Furthermore, a significant population of the state is observed, which which may indicate the presence of multi-step processes at our beam energy.

Application of gamma imaging techniques for the characterisation of position sensitive gamma detectors

A device to characterize position-sensitive germanium detectors has been implemented at GSI. The main component of this so called scanning table is a gamma camera that is capable of producing online 2D images of the scanned detector by means of a PET technique. To calibrate the gamma camera Compton imaging is employed. The 2D data can be processed further offline to obtain depth information. Of main interest is the response of the scanned detector in terms of the digitized pulse shapes from the preamplifier. This is an important input for pulse-shape analysis algorithms as they are in use for gamma tracking arrays in gamma spectroscopy. To validate the scanning table, a comparison of its results with a second scanning table implemented at the IPHC Strasbourg is envisaged. For this purpose a pixelated germanium detector has been scanned.

Abstract P2-01-02: The predictive value of sentinel node biopsy (SNB) in early breast cancer after neo-adjuvant chemotherapy (NACT): A prospective study

Abstract Background SNB has replaced axillary lymph node dissection (ALND) in those patients (pts) with clinically node negative axilla. This has reduced the morbidity, in particular lymphedema considerable. SLN after NACT is feasible but not accurate in clinically node positive (cN1-3) pts (false negative rate around 10%). Therefore, continuous efforts have to been made in randomized prospective studies to improve the detetion rate of SNB in order to avoid the morbidity of ALND. The purpose of this study is to determine the negative predictive value of the sentinel node in breast cancer after NACT. Method A single institution prospective study regarding the negative predictive value of the sentinel node in breast cancer after NACT was conducted in the Multidisciplinary Breast Clinic of the Antwerp University Hospital from 29/03/2010 untill 12-2015 (Study number: B30020108368). Inclusion criteria for study participation were: breast cancer, age above 18 years, female, tumor stages T2-T4 N0-3 or T1N1-N3. All pts were staged by a mammography, ultrasound of the axilla, MRI of the breast, 18F-fluoro-2-deoxy-glucose(18F-FDG) positron emission tomography (PET-CT) scan and bone scintigraphy. They received NACT consisting of 12 cycles of Paclitaxel or 4 cycles of Docetaxel followed by dose dense doxorubicin or epirubicin/cyclofosfamide or vice versa as a standard initial treatment. After 6 weeks a 18F-FDG PET-CT scan was performed for early tumor response evaluation. At the day of operation, all the pts had a preoperative injecting with a 99mTC-labelled nanocolloid in the peri-areolar region. A gamma detector was used to localize the SLN(s). All SLN(s) were removed and a complete ALND was performed. Results A total of 150 pts were enrolled in our study of which 129 were eligible for analysis. 53 pts had a positive SLN of which 32 have a positive axillary lymph nodes (ALN) (PPV 60%); 76 pts has a negative SLN of which 6 had a positive ALN (NPV 92%). The sensitivity is 84% and the specificity 76% with a false omission rate (FOR) of 8%. 45 pts had an initial clinical N0 (cN0 is defined as clinical negative and no suspect lymph nodes on ultrasound, on MRI breast and 18F-FDG-PET CT scan). 45 pts had negative SLN, with no ALN and 2 pts had a positive SNL of which 1 pts had axillary involvement (NPV 100%). The FOR of cN1: 5%, cN2: 37%, cN3 33%. A total of 22 pts out of 84 pts (26%) of which 15/49 cN1 (30%), 6/23 (26%) cN2, 1/12 (8%)have after 6 weeks of chemotherapy, 18F-FDG normalization on 18F-FDG PET-CT scan. A total of 17 pts had a negative SLN and ALN. The FOR was 0% Conclusion SNB after NACT in case of cN0 is very reliable with high NPV and low FOR. In case of 18F-FDG-PET CT normalization after 6 weeks of chemotherapy and a negative SLN, no ALND has to be performed. Citation Format: Huizing M, Najim O, Dockx Y, Huyghe I, Van den Wyngaert T, van Goethem M, Verslegers I, Papadimitriou K, Altintas S, Baldewijns M, Trinh B, van Dam P, Tjalma W. The predictive value of sentinel node biopsy (SNB) in early breast cancer after neo-adjuvant chemotherapy (NACT): A prospective study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-01-02.