Detector Shielding Research Articles

Improvement of detector shield in PGNAA facility for boron concentration measurement

A radiation shield consists of borated polyethylene (7% wt of boron) and lead was used for the HPGe detector in Isfahan MNSR’s PGNAA facility in order to remove scattered neutrons and gamma rays, respectively. Therefore, the boron peak in gamma spectroscopy is related to both resources in the sample and in the shield, and it has caused a challenge in determination of boron concentration in the samples. In this research, various methods have been investigated to remove the effect of boron in the shield of the detector. For this purpose, Monte Carlo simulations of radiation transportation have been used. The results showed that by covering the detector shield using a cadmium sheet can greatly (99.32%) reduce the height of the boron peak in prompt gamma spectrum recorded in the detector that come from the shield. The experiments have been done to validate the results obtained from the simulations.

Study on gamma spectrum measurement of high-dose-rate radiation

Currently, spectrometers are almost used for spectrum measuring of low-dose-rate radiation. Therefore, the sensitive volume of the spectrometer detector is usually big, and the width of the nuclear pulse is often wide. The pulse throughput of the spectrometer does not have to be very high. However, if a nuclear accident or a nuclear burst occurs, the dose rate will be high. When we measure the spectrum of the radiation, pulses output from the spectrometer detector will pile up seriously. The current spectrometer cannot meet the needs of high-dose-rate radiation energy spectrum measurement. To solve the problem of spectrum measuring of high-dose-rate radiation, in this paper, a solution of measuring the gamma spectrum of high-dose-rate radiation is put forward, and many measures are taken, such as lessening the detector volume, detector shielding, narrowing down the nuclear pulse width, pulse anti-pileup, and increasing the pulse throughput of the multi-channel analyzer through FPGA parallel processing. Analysis design and experiment show that the gamma spectrum of high-dose-rate radiation can be measured through these measures.

MRI compatibility study of a prototype radiofrequency penetrable oval PET insert at 3T.

To perform an MRI compatibility study of an RF field-penetrable oval-shaped PET insert that implements an MRI built-in body RF coil both as a transmitter and a receiver. Twelve electrically floating RF shielded PET detector modules were used to construct the prototype oval PET insert with a major axis of 440mm, a minor axis of 350mm, and an axial length of 225mm. The electric floating of the PET detector modules was accomplished by isolating the cable shield from the detector shield using plastic tape. Studies were conducted on the transmit (B1) RF field, the image signal-to-noise ratio (SNR), and the RF pulse amplitude for a homogeneous cylindrical (diameter: 160mm and length: 260mm) phantom (NaCl + NiSO4 solution) in a 3T clinical MRI system (Verio, Siemens, Erlangen, Germany). The B1 maps for the oval insert were similar to the MRI-only field responses. Compared to the MRI-only values, SNR reductions of 51%, 45%, and 59% were seen, respectively, for the spin echo (SE), gradient echo (GE), and echo planar (EPI) images for the case of oval PET insert. Moreover, the required RF pulse amplitudes for the SE, GE, and EPI sequences were, respectively, 1.93, 1.85, and 1.36 times larger. However, a 30% reduction in the average RF reception sensitivity was observed for the oval insert. The prototype floating PET insert was a safety concern for the clinical MRI system, and this compatibility study provided clearance for developing a large body size floating PET insert for the existing MRI system. Because of the RF shield of the insert, relatively large RF powers compared to the MRI-only case were required. Because of this and also due to low RF sensitivity of the body coil, the SNRs reduced largely.

Research on instrument structure scheme for improving the sensitivity of wireline D-T source porosity logging

Utilizing a D-T source to replace the chemical source is the development trend of nuclear logging technology. However, the wireline porosity logging with a D-T source has a lower sensitivity. To solve this problem, the key factors on the sensitivity of neutron porosity logging are analyzed. Combining the numerical simulation method, special structures such as neutron-source deceleration block and detector shielding sleeve are designed to improve the sensitivity of D-T source wireline porosity logging tool, and the detector-spacing selection of the improved instrument was discussed. Study indicates that the sensitivity of neutron porosity logging mainly depends on the fast-neutron deceleration length, the proportion of formation information in the detector count and the detector-spacing. In the instrument design, the tungsten neutron-source deceleration block is adopted to reduce the energy of neutrons emitted by source, thereby shortening the fast-neutron deceleration length and improving the logging sensitivity. Additionally, the detector shielding sleeve made of boron carbide can absorb thermal neutrons from the borehole to increase the proportion of formation information in the detector count, which can also effectively improve the sensitivity. Based on the above structure design, it was found that when the near detector-spacing was set at 30 cm and the far detector-spacing was set at about 70 cm, the performance of the instrument can reach the best. This study can provide theoretical guidance for the application of D-T source in the wireline porosity logging tool in the future.

Development of an integrated non-destructive analysis system, Active-N

ABSTRACT An integrated active neutron non-destructive analysis (NDA) system, Active-N, was developed to gain knowledge of active neutron NDA techniques that are applicable to measurements of nuclear materials in highly radioactive nuclear fuels. Active-N, equipped with a D-T neutron generator, combines three complementary active neutron NDA techniques: Differential Die-away Analysis (DDA), Prompt Gamma-ray Analysis (PGA), and Neutron Resonance Transmission Analysis (NRTA). In this paper, we provide an overview of Active-N and then demonstrate that the compact NRTA system in Active-N can quantify nuclear materials. Monte Carlo simulations were conducted to determine the design of the compact NRTA system including a moderator, flight tubes, and a detector shield. To investigate how accurately the compact NRTA system determines areal number densities in a sample, measurements were performed with a Pu pellet-type sample as well as metallic plate samples of In and Ag. The experimental areal number densities of 240Pu, 115In and 109Ag were consistent with those calculated for the individual nuclei. These results show that it is feasible to develop a compact NRTA system capable of determining the contents of nuclear materials in nuclear fuels.

Prompt gamma ray detection and imaging for boron neutron capture therapy using CdTe detector and novel detector shield - Monte Carlo study.

For boron neutron capture therapy (BNCT), the improvements in patient dosimetry will require information about the spatial variation of 10 B concentration in the tumor and critical organs. A non-invasive approach, based on the detection of prompt gamma (PG) rays from the BNC reaction, may be well-suited to obtain such information. The detectability of the BNC PG rays has been shown experimentally utilizing energy-resolving cadmium telluride (CdTe) detectors. However, the feasibility of this approach under the clinically relevant conditions of BNCT is currently unknown. The present work aimed to investigate the aforementioned feasibility by performing Monte Carlo (MC) simulations under the phantom irradiation geometry relevant to accelerator-based BNCT (a-BNCT). Especially, this investigation focused on demonstrating the enhanced detection of the BNC PG rays using a novel neutron shield for CdTe detectors. Upon demonstrating the efficacy of the proposed detector shield, the BNC PG ray-based quantitative imaging of clinically relevant concentrations of 10 B was also demonstrated. The Geant4 MC simulation toolkit was used to model the phantom irradiation by an epithermal neutron beam as well as the detection of the BNC PG rays from the phantom by CdTe detectors with and without the proposed gadolinium (Gd)-based detector shield. It was also used to model the BNC PG ray-based quantitative imaging of 10 B concentrations under a-BNCT scenarios. Each model included a 20cm-diameter/24cm-height cylindrical PMMA phantom containing 10 B inserts at various concentrations. Arrays of CdTe crystals of 5×5×1 mm3 each (up to 120 in the case of a ring detector) were modeled for acquiring the BNC PG ray signals and quantitative imaging. According to the MC simulations, thermalized neutrons from the phantom were found to reach the CdTe detector and captured by Cd and Te, resulting in the gamma ray background noise that directly interfered with the BNC PG ray signal. The proposed Gd-based detector shield was found to be highly effective in shielding thermal neutrons from the phantom, thereby reducing the unwanted gamma ray background noise. Owing to this shield, the detection of as low as seven parts-per-million (ppm) of 10 B within the phantom of clinically relevant size was possible using 20 billion incident neutron histories. Furthermore, quantitative imaging of 10 B distributed at low concentration (down to 50ppm) within the phantom was demonstrated using computed tomography (CT) simulations with 16 billion incident neutron histories per angular projection. The 10 B detection limit (7.5ppm) was also estimated using the reconstructed CT image. Both 10 B detection limits determined from this investigation are deemed clinically relevant for BNCT. The proposed Gd-based detector shield played an essential role for achieving the currently reported 10 B detection limits. Overall, the present MC simulation work demonstrated highly sensitive BNC PG ray detection and imaging under a-BNCT scenarios using CdTe detectors coupled with a novel detector shield.

Thorium and uranium trace ICP-MS analysis for AMoRE project

AMoRE (Advanced Mo-based Rare process Experiment) is an international collaboration searching for the neutrinoless double-beta decay of the 100Mo isotope with cryogenic detectors using molybdate (100MoO4)-based scintillation crystals. The process requires that the detector apparatus and its components, including bolometric crystals and thus initial materials used for the crystal growth, be extremely low in radioactive isotopes having decays that may generate background noise signals in the region of interest. The present study summarizes an ICP-MS assay program conducted for the AMoRE experiment. Firstly, the 100MoO3 powder, the main component of the crystals, was studied in the analysis. Before crystal synthesis, enriched 100MoO3 powder was purified at the Center for Underground Physics (CUP). To ensure its radio purity, a sample preparation technique with a UTEVA® resin was developed for Th and U analysis with ICP-MS. The recovery yield was over 90% for the extraction procedure, and the detection limits for Th and U were 2.3 and 1.0 ppt, respectively. To determine the most appropriate material for the detector frame and shielding, several types of high-purity Cu were measured: Cu-OFE (Aurubis and Mitsubishi Materials) and Cu–NOSV (Aurubis). Similarly, a solid-phase extraction was applied for Th and U analysis, and detection limits were calculated at 0.1 and 0.2 ppt, respectively. The 3M Vikuiti™ ESR film, the closest part to the crystal in the detector assembly, was used as a light reflector. Two types of Vikuiti film, a roll and a sheet, were checked for radiopurity via full decomposition using a microwave ashing system. The procedural Detection Limits were achieved at a level of about 1 ppt.

Comparative analysis of gamma ray spectrometers applied to Irati Formation, Paraná basin, São Paulo State, Brazil

This paper describes the use of gamma ray spectrometry in the study of rock samples from the Irati Formation, Paraná sedimentary basin, São Paulo State, Brazil. This technique allowed to measure the natural radiation emitted by 40K, as well the radionuclides belonging to the decay series of 238U (eU = 226Ra = 214Bi) and 232Th (eTh = 228Th = 208Tl) which occur in the analyzed samples. Four gamma ray spectrometers have been utilized for comparing the results obtained: a portable sodium iodide [NaI(Tl)] scintillation detector (Digidart), a handheld bismuth germanate oxide (BGO) detector and two bench NaI(Tl) crystals, differing in their geometry (Planar and Well types). This study involved the calibration of the spectrometers, except in the case of the BGO that is factory calibrated. Afterwards, gamma ray analysis was done for 122 rock samples colleted at Partecal Quarry located at Assistência District, Rio Claro city, which have been of interest for the oil and gas sector. For comparison purposes, the obtained datasets were subjected to different statistical tests, including the analysis of variance (ANOVA) that proved to be of great value for checking the differences of the mean concentration values of eU, eTh and K. The results pointed out several factors that affect the gamma ray analysis for the natural radioelements uranium, thorium, and potassium such as the samples size, shape and geometry, detector type, shielding and counting time. These factors are of difficult control in order to get reliable radiometric measurements by this technique.

Overview on the progress of the conceptual studies of a gamma ray spectrometer instrument for DEMO

The future DEMO tokamak will be equipped with a suite of diagnostics which will operate as sensors to monitor and control the position and operation parameters of DT plasmas. Among the suite of sensors, an integrated neutron and gamma-ray diagnostic system is also studied to verify its capability and performance in detecting possible DEMO plasma position variations and contribute to the feedback system in maintaining DEMO DT plasma in stable conditions. This work describes the progress of the conceptual study of the gamma-ray diagnostic for DEMO reactor performed during the first Work-Package contract 2015–2020. The reaction of interest for this Gamma-Ray Spectrometer Instrument (GRSI) consists of D(T, γ)5He with the emission of 16.63 MeV γ rays. Due to DEMO tokamak design constraints, the gamma and neutron diagnostics are integrated, both featuring multi-line of sight (camera type), viewing DEMO plasma radially with vertical (12) and horizontal (13) viewing lines to diagnose the γ and neutron emission from the DT plasma poloidal section. The GRSI design is based on the investigation of the reaction cross sections, on the calculations performed with GENESIS and MCNP simulation codes and on the physics and geometry constrains of the integrated instrument. GRSI features long collimators which diameters are constrained by the neutron flux at the neutron detectors of the Radial Neutron Camera (RNC) system placed in front, which are key to control DEMO DT plasma position. For these reasons, only few GRSI parameters can be independently selected to optimize its performance. Among these, the choice of the collimator diameters at the back side of the neutron detector box up to the GRSI detector, the use of LiH neutron attenuators in front of the GRSI detectors, the GRSI detector material and shielding. The GRSI detector is based on commercial LaBr3(Ce) inorganic scintillating crystal coupled with a photomultiplier tube or a silicon photomultiplier. They are designed to operate at high count rate although GRSI geometry constraints severely impact on this feature. The GRSI can also provide an independent assessment of DEMO DT fusion power and T burning.

Novel carbon nanotube-composite for electromagnetic shielding of radiation detectors: A step toward fully integrated positron emission tomography and magnetic resonance imaging systems

Carbon nanotubes (CNT) have shown promising properties, as a filler, for increasing the electrical conductivity of composites entering in the fabrication of high-frequency shielding materials. However, up to now, their features at low-frequency range have received little attention. In this study, composite layers based on pristine CNT and polydimethylsiloxane (PDMS) have been synthesized. Both multi-wall and single-wall CNTs were investigated to determine the specific electrical properties of the composite for eliminating the impact of low-frequency electromagnetic interferences in positron emission tomography/magnetic resonance imaging (PET/MRI) scanners. The CNT dispersibility was studied in various solvents. To fabricate a homogeneous composite, a hybrid method based on ultra-sonication and shear mixing of CNT mixtures was developed. The impedance measurements on thin layers confirmed that a well-processed composite provides the required conductivity (>103 S/cm) for electromagnetic interference shielding in the desired frequency range. Such composite layers achieved a shielding effectiveness of >68 dB in the MRI gradient range (10–100 kHz), and exceeded 80 dB in the MRI RF range (50–500 MHz). The results demonstrated that using these CNT-composite shielding layers, the artifacts due to the electromagnetic interferences of gradient and RF coils in the MRI environment can be avoided for PET imaging.

Time characterization of cosmic-ray induced events in HPGe detector by Monte Carlo simulations

Detailed studies of background events provide information necessary for the planning of active and passive shielding of the detector in all experiments, especially ones searching for rare nuclear events. An effective approach in understanding the contribution of cosmic rays to the background of the HPGe detector is the use of Monte Carlo simulations. In this study, the Monte Carlo simulations were performed in order to obtain the time spectrum of the events induced by cosmic-ray muons and neutrons in the materials in the vicinity of the detector system and the detector itself. In order to reject background events originating from environmental radionuclides (from 238U and 232Th series, 40K, etc.), a coincidence system based on a large-volume HPGe detector and plastic scintillation detector was developed and the same setup was constructed in simulations. The experimental spectrum was compared with the simulated one. The possibility to distinguish these events based on the time was presented and illustrated through the selection of several time intervals of the time spectrum obtained in the simulation and corresponding spectra.Furthermore, the contribution of the muon-induced neutrons and cosmic-ray neutron-induced events to the background spectrum of the large-volume HPGe detector was analyzed. It was found that neutrons produced in the interaction of cosmic-muons with detector shielding and the detector itself are relatively small contributors to the overall neutron-induced events (i.e. low-energy region up to 100 keV originating dominantly from recoils and gamma lines originating from inelastic neutron scattering) registered in coincidence spectrum of HPGe detector compared to the contribution of cosmic-neutron themselves. The share of neutron components in this low-energy region of the coincidence spectrum of the HPGe detector was estimated to be ≈88%. In experiments searching for hypothetical dark matter particles, expected signals are in this energy region, thus in this type of experiment, it is essential to perform rejection of events induced by neutron interaction, in order to avoid misidentification of registered signals.

Study on the radiofrequency transparency of electrically floating and ground PET inserts in a 3T clinical MRI system.

The positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system that implements the radiofrequency (RF) built-in body coil of the MRI system as a transmitter is designed to be RF-transparent, as the coil resides outside the RF-shielded PET ring. This approach reduces the design complexities (e.g., large PET ring diameter) related to implementing a transmit coil inside the PET ring. However, achieving the required field transmission into the imaging region of interest (ROI) becomes challenging because of the RF shield of the PET insert. In this study, a modularly RF-shielded PET insert is used to investigate the RF transparency considering two electrical configurations of the RF shield, namely the electrical floating and ground configurations. The purpose is to find the differences, advantages and disadvantages of these two configurations. Eight copper-shielded PET detector modules (intermodular gap: 3mm) were oriented cylindrically with an inner diameter of 234mm. Each PET module included four-layer Lutetium-yttrium oxyorthosilicate scintillation crystal blocks and front-end readout electronics. RF-shielded twisted-pair cables were used to connect the front-end electronics with the power sources and PET data acquisition systems located outside the MRI room. In the ground configuration, both the detector and cable shields were connected to the RF ground of the MRI system. In the floating configuration, only the RF shields of the PET modules were isolated from the RF ground. Experiments were conducted using two cylindrical homogeneous phantoms in a 3T clinical MRI system, in which the built-in body RF coil (a cylindrical volume coil of diameter 700mm and length 540mm) was implemented as a transceiver. For both PET configurations, the RF and MR imaging performances were lower than those for the MRI-only case, and the MRI system provided specific absorption ratio (SAR) values that were almost double. The RF homogeneity and field strength, and the signal-to-noise ratio (SNR) of the MR images were mostly higher for the floating PET configuration than they were for the ground PET configuration. However, for a shorter axial field-of-view (FOV) of 125mm, both configurations offered almost the same performance with high RF homogeneities (e.g., 76±10%). Moreover, for both PET configurations, 56±6% larger RF pulse amplitudes were required for MR imaging purposes. The increased power is mostly absorbed in the conductive shields in the form of shielding RF eddy currents; as a result, the SAR values only in the phantoms were estimated to be close to the MRI-only values. The floating PET configuration showed higher RF transparency under all experimental setups. For a relatively short axial FOV of 125mm, the ground configuration also performed well which indicated that an RF-penetrable PET insert with the conventional design (e.g., the ground configuration) might also become possible. However, some design modifications (e.g., a wider intermodular gap and using the RF receiver coil inside the PET insert) should improve the RF performance to the level of the MRI-only case.

Novel Carbon Nanotube-Composite for Electromagnetic Shielding of Radiation Detectors: A Step Toward Fully Integrated Positron Emission Tomography and Magnetic Resonance Imaging Systems

Novel Carbon Nanotube-Composite for Electromagnetic Shielding of Radiation Detectors: A Step Toward Fully Integrated Positron Emission Tomography and Magnetic Resonance Imaging Systems

Introducing the GammaPen: All-in-One Gamma Probe for Sentinel Lymph Node Biopsy

Purpose: Using an itra-operative gamma probe after injection of radiotracer during surgery helps the surgeon to identify the sentinel lymph node of regional metastasis through the detection of radiation. This work reports the design and specification of an integrated gamma probe (GammaPen), developed by our company. Materials and Methods: GammaPen is a compact and fully integrated gamma probe. The detector module consists of a thallium-activated Cesium Iodide (CsI (Tl)) scintillator, and a Silicon Photo Multiplier (SiPM), shielded using Tungsten housing. Probe sensitivity, spatial resolution and angular resolution in air and water, and side and back shielding effectiveness were measured to evaluate the performance of the probe based on NEMA NU3 standard. Results: The sensitivity of the probe in the air/water at distances of 10, 30, and 50 mm is 18784/176800, 3500/3050, and 1575/1104 cps/MBq. The spatial and angular resolutions in the air/scattering medium are 40/47 mm and 77/87 degrees at a 30 mm distance from the probe. The detector shielding effectiveness and leakage sensitivity are 99.91% and 0.09%, respectively. Conclusion: The results and surgeon experience in the operating room showed that GammaPen can be effectively used for sentinel lymph node localization.

Effect of Gd2O3 on the radiation shielding, physical, optical and luminescence behaviors of Gd2O3–La2O3–ZnO–B2O3–Dy2O3 glasses

The present work focuses on lead-free glasses, their shielding behavior, and other optical studies. The glass composition with xGd2O3+10La2O3+10ZnO+(79-x) B2O3+1Dy2O3, x = 0, 5, 10, 15, 20 mol% were prepared to the characterization on physical, absorption spectra, photo-, radioluminescence, and radiation shielding properties. In the experimental results, the density of Gd-1Dy glass samples increases with the increase of Gd3+ ions concentrations. The ten-strong peak in the 5Gd-1Dy glass of absorption spectra in UV–Vis–NIR regions. The white photoluminescence spectra base of Gd-1Dy glass samples can be generated under excitation at 351 nm makes the strongest emission of Dy3+ ions and excitation through energy transfer from Gd3+ in Gd-1Dy glass samples with 275 and 351 nm. This strong white emission of Dy3+ ions also strong in x-ray luminescence and performs the integral scintillation efficiency of 33% when compared with BGO crystal. The radiation shielding properties in the diagnostic medicine energies region are correlated, the values of glass samples better than commercial windows, bricks, and concrete. The HVL values of glass sample at 15 and 20 mol% of Gd2O3 has been found better than X-ray windows. The corollaries of Gd-1Dy glass samples can be a candidate for radiation detector and lead-free radiation shielding materials in future.

Monte Carlo simulation for the analysis of various solid samples using handheld X-ray fluorescence spectrometer and evaluation of the effect by environmental interferences

Handheld X-ray fluorescence (HH-XRF) has expanded its utilization areas according to recent technological developments. Most current applications, though, are still concentrated in traditional areas including mineral resource analysis and environmental regulation rather than forensic science for the purpose of investigating a nuclear security event involving nuclear material out of regulatory control. To apply HH-XRF to nuclear material analysis, it is necessary to first obtain calibration data using standard reference materials. Considering the difficulty in obtaining such standard reference materials as well as the high costs involved, one well-known alternative method is to use Monte Carlo simulation code. This study investigated the feasibility of employing Monte Carlo N-Particle transport 6 (MCNP6) simulation to provide calibration data through comparison with experimental measurements of pure solid samples of graphite, copper, SiO2, and UO2 using HH-XRF. The results showed that the MCNP6 simulation results were entirely consistent with the measurement spectra, except for environmental interferences stemming from interactions with the mechanical components below 10 keV which varied slightly according to sample type. To quantitatively evaluate the effect of these environmental interferences on the whole spectrum, the coefficient of determination (R2) was used. In the case of graphite, the effect of the environmental interferences was evaluated to be about 20% on the conformity of the measured and simulated results, while those for copper, SiO2, and UO2 were about 1%, 3%, and less than 1%, respectively. These results indicate that samples having elements with higher rates of photoelectric absorption followed by fluorescence compared to scattering tend to decrease the effect of the environmental interferences over the entire spectrum. The origin of the environmental interferences was estimated to be interference with the detector shield and/or X-ray tube collimator, which are particular design features of the device used. Their effect on contributing to the environmental interferences was evaluated by experiment for the detector shield and simulation for the X-ray tube collimator. As the detector shield was found to only contribute to a decrease in overall spectrum intensity, the major contributor to the environmental interferences was determined to be the collimator. It is believed that the results of this study will help to confirm that Monte Carlo simulation can properly provide calibration data for using HH-XRF on nuclear materials for which reference materials are hard to obtain.

The Simulated Characterization and Suitability of Semiconductor Detectors for Strontium 90 Assay in Groundwater.

This paper examines the potential deployment of a 10 mm × 10 mm × 1 mm cadmium telluride detector for strontium-90 measurement in groundwater boreholes at nuclear decommissioning sites. Geant4 simulation was used to model the deployment of the detector in a borehole monitoring contaminated groundwater. It was found that the detector was sensitive to strontium-90, yttrium-90, caesium-137, and potassium-40 decay, some of the significant beta emitters found at Sellafield. However, the device showed no sensitivity to carbon-14 decay, due to the inability of the weak beta emission to penetrate both the groundwater and the detector shielding. The limit of detection for such a sensor when looking at solely strontium-90 decay was calculated as 323 BqL after a 1-h measurement and 66 BqL after a 24-h measurement. A gallium-arsenide (GaAs) sensor with twice the surface area, but 0.3% of the thickness was modelled for comparison. Using this sensor, sensitivity was increased, such that the limit of detection for strontium-90 was 91 BqL after 1 h and 18 BqL after 24 h. However, this sensor sacrifices the potential to identify the present radionuclides by their end-point energy. Additionally, the feasibility of using flexible detectors based on solar cell designs to maximise the surface area of detectors has been modelled.

Development and characterization of an all-in-one gamma probe with auto-peak detection for sentinel lymph node biopsy based on NEMA NU3-2004 standard

BackgroundA gamma probe is a handheld device used for intraoperative interventions following interstitial injection of a radiotracer to locate regional lymph nodes through the external detection of radiation. This work reports on the design and performance evaluation of a novel fully integrated gamma probe (GammaPen), recently developed by our group.Materials and methodsGammaPen is an all-in-one pocket gamma probe with low weight and adequate dimensions, consisting of a detector, a control unit and output all together. The detector module consists of a cylindrical Thallium-activated Cesium Iodide [CsI (Tl)] crystal optically coupled to a Silicon photomultiplier (SiPM), shielded using Tungsten housing on side and back faces. The electronics of the probe consists of two small boards to handle signal processing and analog peak detection tasks. A number of parameters, including probe sensitivity in air/water, spatial resolution in air/water, angular resolution in air/water, and side and back shielding effectiveness, were measured to evaluate the performance of the probe based on NEMA NU3-2004 standards.ResultsThe sensitivity of the probe in air at distances of 10, 30, and 50 mm is 18784, 3500, and 1575 cps/MBq. The sensitivity in scattering medium was also measured at distances of 10, 30, and 50 mm as 17,680, 3050, and 1104 cps/MBq. The spatial and angular resolutions in scattering medium were 47 mm and 87 degree at 30 mm distance from the probe, while they were 40 mm and 77 degree in air. The detector shielding effectiveness and leakage sensitivity are 99.91% and 0.09%, respectively.ConclusionThe performance characterization showed that GammaPen can be used effectively for sentinel lymph node localization. The probe was successfully used in several surgical interventions by an experienced surgeon confirming its suitability in a clinical setting.

Main results of the DAMPE space detector after 4 years in orbit

The DArk Matter Particle Explorer (DAMPE) is a high-performance space particle detector launched in orbit in 2015 by a collaboration of Chinese, Italian and Swiss scientific institutions, coordinated by the Chinese Academy of Sciences. It consists of a high-resolution segmented BGO electromagnetic calorimeter with a depth of 32 radiation lengths, a silicon-tungsten tracker-converter with an angular resolution below [Formula: see text], an anti-coincidence shield and ion detector, and a neutron detector. The detector characteristics and performance, and the latest observations of cosmic electrons up to 5 TeV, protons and nuclei up to 100 TeV and gamma-rays up to 10 TeV are presented.

SENSEI: Direct-Detection Results on sub-GeV Dark Matter from a New Skipper CCD.

We present the first direct-detection search for sub-GeV dark matter using a new ∼2-gram high-resistivity Skipper CCD from a dedicated fabrication batch that was optimized for dark matter searches. Using 24days of data acquired in the MINOS cavern at the Fermi National Accelerator Laboratory, we measure the lowest rates in silicon detectors of events containing one, two, three, or four electrons, and achieve world-leading sensitivity for a large range of sub-GeV dark matter masses. Data taken with different thicknesses of the detector shield suggest a correlation between the rate of high-energy tracks and the rate of single-electron events previously classified as "dark current." We detail key characteristics of the new Skipper CCDs, which augur well for the planned construction of the ∼100-gram SENSEI experiment at SNOLAB.