Total Detection Efficiency Research Articles

Radioxenon beta-gamma coincidence efficiency for a SAUNA detector by Geant4 simulation

A simulation for SAUNA II detector was carried out using the GEANT4 platform. The results demonstrated the accuracy of the simulation, which was well consistent with the experimental results. The simulation was used to calculate the coincidence detection efficiency of each radioxenon isotope, as well as to calculate the resolution for conversion electron peaks. Furthermore, using a 137Cs point source, the simulation was also utilized to perform the beta detector calibration procedure in two scenarios: first, the 137Cs was placed close to the middle of the plastic scintillator, and second, the 137Cs was placed outside the NaI(Tl) detector. The results showed that the spectrum in the first case is better; the source is closer to the plastic detector, leading to maximum Compton scattering. In the second case, a line in the spectrum disappears, so a high-intensity source is needed. Several methods exist to determine the coincidence detection efficiency of the detector. The recommended approach is to determine the total detection efficiency for different regions of interest. The simulation was also used to investigate the effect of replacing helium with nitrogen as a xenon-carrier gas, with the nitrogen resulting in a slight improvement in coincidence detection efficiencies and conversion electron resolution.

Development of a silicon-based thermal neutron detection system

Neutron detection systems are of increasing importance in applications from basic science to medical applications and reactors. 3He proportional counters remain the most popular choice for monitoring thermal neutrons with a detection efficiency of around 60%, however, due to 3He global shortages, a new generation of detection technologies will be required to meet the rising demand. As a result, extensive research is being conducted to investigate alternative methods of neutron detection. This work presents such a system and demonstrates its calibration and evaluation using an AmBe neutron source. The detection system involves silicon sensors coated by converter layers to make the detectors sensitive to thermal neutrons via neutron capture and measurement of the resulting secondary charged particles. The detection system is presented in two configurations, a single and a multi-layer configuration, where the latter is used to increase the total detection efficiency. In addition, the system is capable of determining coincident signals from a single neutron capture, a feature which allows background suppression and an increase in the purity of the neutron signal which is particularly useful in mixed radiation environments.

Detection of 238Pu at picogram quantities by laser resonance ionization mass spectrometry

Based on the laser resonance ionization mass spectrometry (LRIMS) developed in the laboratory, a preliminary method was established to determine Pu isotope ratios. A three-color-three-photon resonance ionization scheme was confirmed, and the laser wavelengths of each excitation/ionization step were λ1 = 586.654 nm, λ2 = 606.181 nm and λ3 = 642.722 nm. The selective ionization of 238Pu/238U was realized by testing the Pu and U mixed sample, a selectivity ratio of over 107 was obtained. More effective electrothermal atomization of Pu was implemented by loading graphene oxide solution on the Pu sample surface, and the total detection efficiency of ∼40 ng Pu sample was above 3 × 10−4, which was three orders of magnitude higher than the efficiency of the unloaded graphene oxide solution Pu sample. Results showed that the relative standard deviation of 238Pu/239Pu ratio was ∼0.20%, indicating that LRIMS could effectively avoid the isobaric interference of 238U faced by other commercial mass spectrometers such as TIMS and ICP-MS, and could achieve precise measurement of 238Pu/239Pu ratio.

Experimental validation of Monte Carlo NaI(Tl) detector efficiency responses with surrogate 137Cs environmental contamination source term

Radiological site remediation is a resource intensive process requiring extensive field sampling to demonstrate regulatory compliance. Specifically, the application of Monte Carlo (MC) simulations and automated hybrid radiation transport methods has garnered interest in streamlining the remediation process by simulating detector responses for a plurality of contaminated media, contamination depths and profiles, and source-detector orientations. In this study, experimental validation of gamma-ray detector efficiency responses was conducted for simulations of radiological site-specific and idealized external contamination conditions. Measurements were performed with a cylindrical 2′′ × 2″ sodium iodide thallium-doped (NaI(Tl)) scintillator detector suspended above a 217.8 kBq, 50 cm × 50 cm 137Cs contamination source located on the surface of or buried within environmental soil. New area correction factors (ACFs) and gamma shielding factors (GSFs) were also derived to modify the simulated idealized detector efficiency responses, accounting for reductions in source area and clean soil covering layers, respectively, that may be encountered when performing in-situ gamma spectrometry in the field. The study concluded that simulated total detection efficiency from energy deposition in the active volume of the detector crystal can be adopted for radionuclide screening purposes. Furthermore, pragmatic implementation of environmental surveying using gamma-spectrometry requires site-specific information.

A mathematical approach to calculate the absolute total detection efficiency of a 4[formula omitted] NaI(Tl) sum spin spectrometer

The absolute total detection efficiency of a detector for gamma rays intensely depends on the solid angle subtended by the detector’s front surface at the gamma source. In the present work, we have developed, for the first time, a new mathematical formalism to calculate the solid angle subtended by an n-sided polygonal detector at the point source when the source is placed along the axis of the detector. The method is based on the subtraction of the solid angle in which gamma rays do not enter the detector from that of the circular cross-section. The solid angle formula, so derived, has been applied to calculate the absolute total detection efficiency of NaI(Tl) scintillation detectors of pentagonal and hexagonal cross-sections for monoenergetic gamma rays. These efficiencies are then used to calculate the absolute total detection efficiency of 4π sum-spin spectrometer for gamma rays up to energy 20 MeV. The spectrometer is an array of 32 conical NaI(Tl) detectors of pentagonal and hexagonal cross-sections. To validate the formalism developed, the theoretically calculated efficiencies are compared with those obtained from realistic GEANT4 simulations and experimental measurements considering 137Cs and 60Co gamma sources. The reasonably good agreement clearly validates the developed formalism.

Hybrid extractive scintillator resin for simultaneous concentration and detection of plutonium from aqueous solutions

A scoping study of a commercially available resin selective for aqueous plutonium (Pu), AnaLig® Pu-02, modified with scintillator was investigated as a scheme to simultaneously concentrate and detect Pu in aquatic matrices. The extractive scintillating resin was comprised of a silica base, functionalized for plutonium extraction, grafted with plastic scintillator of polyvinyl toluene (PVT) and 2-(1-naphthyl)-4-vinyl-5- phenyloxazole (vNPO) fluor. Scintillator was incorporated onto the AnaLig® Pu-02 resin in a two-step process of silanization followed by surface-polymerization. Successful modification was facilitated by grinding the resin beads prior to silanization to expose cleaved silica surface sites appropriate for scintillator grafting. The modified resin was subjected to initial characterization of batch uptake and radioluminosity measurements where a total detection efficiency of 32.5% was observed. The modified resin was then subjected to pH 1 simulants containing environmental relevant groundwater constituents of varying concentration. Concentrations of 0.001M Fe(III) interfered with Pu uptake, while concentrations of up to 0.01M Ca(II) and 0.001 mM concentration of natural uranium and thorium had minimal influence on plutonium uptake. A translucent column packed with the modified AnaLig® Pu-02 was placed in a commercial flow-cell radiation detector for real-time detection of plutonium; a total detection efficiency of 20.4% was achieved for on-line measurements. The modification of AnaLig® Pu-02 results in a minimum detection limit capable of meeting the EPA limit for gross alpha activity in drinking water given a sufficient counting time of 15 min and approximately 300 mL of solution volume.

Liquid argon characterization of the X-ARAPUCA with alpha particles, gamma rays and cosmic muons

The X-ARAPUCA device is the baseline choice for the photon detection system of the first far detector module of the DUNE experiment. We present the results of the first complete characterization of a small scale X-ARAPUCA prototype, which is a slice of a full DUNE module. Its total detection efficiency in liquid argon was measured with three different ionizing radiations: α particles, γ's and muons and resulted to be ∼2.2% when the active silicon photomultipliers were biased at +5.0 V of over voltage, corresponding to a Photon Detection Efficiency around 50% at room temperature. This value comfortably satisfies the requirements of the first DUNE far detector module (detection efficiency >2.0%) and allows to achieve an energy resolution comparable to the one achievable with the Time Projection Chambers for energies below 10 MeV, which is the region relevant for Supernova neutrino detection.

Design of MICADO advanced passive and active neutron measurement system for radioactive waste drums

In the frame of the MICADO H2020 project, a passive and active neutron measurement system is being developed to estimate the nuclear material mass inside legacy waste drums of low and intermediate radioactivity levels. Monte-Carlo simulations have been performed to design a new modular and transportable neutron system, with the main objective to reach a good tradeoff between the performances in passive mode, i.e. neutron coincidence counting, and in active interrogation mode with the Differential Die-away Technique. Different designs are compared, which mainly differ in their moderation materials, graphite and polyethylene. This parametric study allowed us to define a prototype taking into account practical constraints in view of its final implementation in a wide range of in-situ locations and nuclear facilities. The total neutron detection efficiency of the prototype is 6.75%, as calculated for an empty drum, i.e. without waste matrix. The detection limit in terms of nuclear material equivalent mass have also been estimated based on assumptions for a homogeneous distribution of nuclear materials inside the drum, filled with four types of matrices covering the range of nuclear waste drums defined in the frame of the project. The most favorable matrix is made of stainless steel in passive mode and of polyethylene in active mode, with an apparent density of 0.7 g cm−3 and 0.1 g cm−3, respectively. The calculated mass detection limits are respectively 68 mg of 240Pu, 62 mg of 235U and 39 mg of 239Pu. The most penalizing matrix is made of polyethylene with an apparent density of 0.7 g cm−3, which leads to a mass detection limit of 519 mg of 240Pu in passive mode, and 564 mg of 235U or 349 mg of 239Pu in active mode. Measurement time is 30 min for both passive and active modes. Next steps will be a complete investigation of matrix effects based on intensive Monte-Carlo calculations and an experimental design to figure out the appropriate corrections. Experiments will also be conducted at CEA Cadarache Nuclear Measurement Laboratory with the construction and the assembly of the neutron system prototype, and the measurement of mock-up drums filled with different matrices.

Polarization resolving and imaging with a single-photon sensitive superconducting nanowire array.

Superconducting nanowire single-photon detectors (SNSPDs) have attracted remarkable interest for visible and near-infrared single-photon detection due to their outstanding performance. However, conventional SNSPDs are generally used as binary photon-counting detectors. Another important characteristic of light, i.e., polarization, which can provide additional information of the object, has not been resolved using the standalone SNSPD. In this work, we present a first prototype of the polarimeter based on a four-pixel superconducting nanowire array, capable of resolving the polarization state of linearly-polarized light at the single-photon level. The detector array design is based on a division of focal plane configuration in which the orientation of each nanowire division (pixel) is offset by 45°. Each single nanowire pixel operates as a combination of a photon detector and almost linear polarization filter, with an average polarization extinction ratio of ∼10. The total system detection efficiency of the array is ∼1% at a total dark count rate of 680 cps, with a timing jitter of 126 ps, when the detector array is free-space coupled and illuminated with 1550-nm photons. The mean errors of the measured angle of polarization and degree of linear polarization were about -3° and 0.12, respectively. Furthermore, we successfully demonstrated polarization imaging at low-light level using the proposed detector. Our results pave the way for the development of a single-photon sensitive, fast, and large-scale integrated polarization polarimeter or imager. Such detector may find promising application in photon-starved polarization resolving and imaging with high spatial and temporal resolution.

The MULTI spectrometer for measurement of β-decay process in exotic nuclei

The construction of the portable spectrometer, MULTI, is designed for the measurement of β-γ-neutron coincidences on beams of radioactive exotic nuclei. It will be used in measurements of the β-decay process of neutron-rich nuclei with large Qβ values accessible in radioactive beams facilities. The experimental technique includes the measurement of the ratios between gamma-ray emission and multi-neutron emission, following beta-decay of radioactive nuclei implanted into an active target. The construction of a gamma-ray spectrometer based on high-volume CeBr3+NaI(Tl) phoswich scintillation detectors is introduced. Results of the measurements of its fundamental characteristics – total detection efficiency, peak efficiency and Compton suppression effect with a 60Co source are presented. Design of the neutron counter array, consisting of 40 proportional counters filled with 3He gas, was optimized with Monte Carlo simulations. Results were validated with a 252Cf spectroscopic source, leading to expected detection efficiency of ∼35% for neutrons with energy < 1MeV. Further development plans are discussed.

Comparisons of Lightning Rates and Properties From the U.S. National Lightning Detection Network (NLDN) and GLD360 With GOES‐16 Geostationary Lightning Mapper and Advanced Baseline Imager Data

AbstractFlash‐level comparisons between the Geostationary Lightning Mapper (GLM; primarily from GOES‐16), the U.S. National Lightning Detection Network (NLDN), and the Global Lightning Dataset GLD360 have been done at quasi‐climatological scale and in smaller samples of both severe and nonsevere thunderstorms. A small sample of data from GOES‐17 has also been analyzed. These comparisons show that the total lightning detection efficiencies of the GLM instruments drop off within about 2,000 km of the edges of their fields of view, particularly over terrestrial areas. In severe storms, low detection efficiency by GLM is clearly associated with very high midaltitude reflectivity, consistent with the idea that large multiple scattering path lengths, together with absorption of the near‐infrared signals by water (in all of its phases), depresses the GLM detection efficiency. This effect appears to be coupled with additional factors, including time of day, flash energetics, and the incident angle at the GLM sensor. The “lightning jump,” the sought‐after signature of severe storms in lightning observations, tends to be poorly correlated between NLDN and GLM unless the storms are fairly isolated, not close to the edge of the GLM field of view, and have moderate midaltitude reflectivity.

Beta-ray imaging system with γ-ray coincidence for multiple-tracer imaging.

Beta-ray imaging systems are widely used for various biological objects to obtain a two-dimensional (2D) distribution of β-ray emitting radioisotopes. However, a conventional β-ray imaging system is unsuitable for multiple-tracer imaging, because the continuous energy distribution of β-rays complicates distinguishing among different tracers by energy information. Therefore, we developed a new type of β-ray imaging system, which is useful for multiple tracers by detecting coincidence γ-rays with β-rays, and evaluated its imaging performance. Our system is composed of position-sensitive β-ray and γ-ray detectors. The former is a 35×35×1-mm3 Ce-Doped((La, Gd)2 Si2 O7 ) (La-GPS) scintillation detector, which has a 300-µm pitch of pixels. The latter is a 43×43×16-mm3 bismuth germanium oxide (BGO) scintillation detector. Both detectors are mounted on a flexible frame and placed in a user-selectable position. We experimentally evaluated the performance of the β-ray detector and the γ-ray efficiencies of the γ-ray detector with different energies, positions, and distances. We also conducted point sources and phantom measurements with dual isotopes to evaluate the system performance of multiple-tracer imaging. For the β-ray detector, the β-ray detection efficiencies for 45 Ca (245-keV maximum energy) and 90 Sr/90 Y (545 and 2280-keV maximum energy) were 14.3% and 21.9%, respectively. The total γ-ray detection efficiency of the γ-ray detector for all γ-rays from 22 Na (511-keV annihilation γ-rays and a 1275-keV γ-ray) in the center position with a detector distance of 20mm was 17.5%. From a point-source measurement using 22 Na and 90 Sr/90 Y, we successfully extracted the position of a positron-γ emitter 22 Na. Furthermore, for a phantom experiment using 45 Ca and 18 F or 18 F and 22 Na, we successfully extracted the distribution of the second tracer using the annihilation γ-ray or de-excitation γ-ray coincidence. In all the imaging experiments, the event counts of the extracted images were consistent with the counts estimated by the measured γ-ray efficiencies. We successfully demonstrated the feasibility of our β-ray autoradiography system for imaging multiple isotopes. Since our system can identify not only a β-γ emitter but also a positron emitter using the coincidence detection of annihilation γ-rays, it is useful for PET tracers and various new applications that are otherwise impractical.

Development of a handheld thermal neutron detector (GAMBE) using stacked silicon sensors coated with 6LiF films

Thermal neutron detectors, which are based on semiconductor material such as silicon coated with neutron reactive material like 6LiF have been discussed for many decades. The performance of the thermal neutron detector system, GAMBE (GAMma Blind neutron Efficient), which is based on two silicon sensors in a sandwich configuration is investigated. This detector is able to achieve a total and a coincidence detection efficiency of 4% and ~1% respectively. The thermal neutron detection efficiency of the detector is enhanced by using a stacked detector configuration and high-density polyethylene (HDPE) sheets, as neutron moderators and reflectors. The GAMBE detector is positioned inside a box of HDPE with a lead window in the direction of the neutron flux for neutron moderation and a reduction of the effect of gamma-rays on the detector. The experimental layout was modeled in MCNP4C to investigate the contribution of HDPE to the thermal neutron flux (n/s/cm2). In this research a stack of 4 silicon semiconductor sensors with (2.6 ± 0.6) and (2.9 ± 0.6) mg/cm2 thick 6LiF film in a configuration of two sandwiches is shown to achieve a total and a coincidence detection efficiency of 27% and 4% respectively. This represents a significant improvement compared to a single detector. The effect of these stacked detectors for the development of a handheld thermal neutron detector, using 4 coated Si detectors is shown to have a 22% efficiency. This information is used to deduce the optimised design of the handheld detector. The results based on Geant4 and MCNP simulations indicate that the total detection efficiency of this portable detector with a stack of 7 sandwich detectors will increase up to 52% by using an optimal thickness of 6LiF of 3.95 mg/cm2 (≈17 μm).

Effects of surface recombination on the charge collection in h-BN neutron detectors

Hexagonal boron nitride (h-BN) epilayers have been recognized as a promising material for applications in solid-state neutron detectors. However, the highest detection efficiency of 58% attained so far for 1 mm2 detectors fabricated from 50 μm thick B-10 enriched h-BN films still falls short of the expected theoretical value of 64%. This is due to the less than perfect charge collection efficiency. In this work, we have fabricated and analyzed the photocurrent-voltage characteristics of 11 h-BN neutron detectors. The dependence of the charge collection efficiency (ηc) on the charge carrier mobility-lifetime (μτ) product of the bulk trapping parameter reveals that ηc is nearly perfect at a bias voltage of 200 V if we neglect the effects of surface recombination. Our results have clearly demonstrated that the surface recombination of charge carriers is the dominant factor that prevents a further enhancement in the charge collection efficiency in our current detectors. The surface recombination field ES (=s/μ), defined as the ratio of the surface recombination velocity (s) to the carrier mobility (μ) of holes, was found to have a linear relationship with that of electrons and has a magnitude of the order of 104 V/cm. The present study indicates that it is critical to reduce ES in h-BN in order to further push the charge collection and hence the total detection efficiency of h-BN neutron detectors to 100%.

GAMBE: Thermal neutron detection system based on a sandwich configuration of silicon semiconductor detector coupled with neutron reactive material

Silicon semiconductor detectors are used efficiently for neutron detection when coated with a suitable material. They detect secondary reaction products resulting from the interaction of thermal neutrons with a neutron sensitive material such as 6LiF. In the present work, the efficiency of the thermal neutron detector system, GAMBE, is discussed. This detector system based on two silicon sensors of 1 cm2 active area and a layer of 6LiF (1.5±0.6) mg/cm2 thick in a sandwich configuration. This arrangement achieves total and coincidence detection efficiency of (4.1±0.5)% and (0.9±0.3)% respectively. The coincidence method defines a true neutron hit by the simultaneous signal recorded by the two sensors facing the conversion film. This coincidence methodology is applied to enhance the rejection factor of fake hits due to high gamma background conditions up to 108 as discussed in previous work. Geant simulation indicates that total and coincidence detection efficiency up to 55% and 18% are possible using an advanced design of stacked detectors.

ARAPUCA light trap for large liquid argon time projection chambers

ARAPUCA is a totally innovative device for liquid argon scintillation light detection. It is composed of a passive light collector and of active devices. The active devices are standard SiPMs that operate at liquid argon temperature, while the passive collector is a photon trap that allows the collection of light with extremely high efficiency. The total detection efficiency of the device can be tuned by modifying the ratio between the area of the active components (SiPM) and that of the optical window. Few arrays of ARAPUCAs will be installed inside the prototype of the Deep Underground Neutrino Experiment - protoDUNE - and their performances will be compared with those of more standard solutions based on guiding bars. The results of the most recent tests of ARAPUCAs in a liquid argon environment, which led to the actual design for the protoDUNE, will be reported together with the proposal of a photon detection system for the Deep Underground Neutrino Experiment based on ARAPUCAs combined with dielectric mirror foils coated by wavelength-shifter.

Possibility study of the partial neutron calibration for neutron flux monitors in torus devices

The absolute calibration of the detection efficiency for the total neutron yield in the whole plasma is one of the most important issues in the neutron diagnostics such as a neutron flux monitor (NFM). The possibility of a partial neutron calibration is investigated based on the in-situ neutron calibration data of the Large Helical Device (LHD), JT-60U, and other tokamaks. In the case of NFM using a 235U fission chamber located outside of the vacuum vessel on the equatorial plane, more than 90% of the detector counts are contributed by neutrons in the toroidal angle range of −60° to +60°. The detection efficiency for the neutron source located at one toroidal position on the magnetic axis (called point efficiency) decreased exponentially with the absolute toroidal angle of the neutron source. We found that a partial calibration in the toroidal angle range of −60° to +60° combined with exponential extrapolations to -180° and +180°can estimate total detection efficiency within 5% uncertainty. In the case of point efficiency measurement at the limited number of the toroidal locations, the total detection efficiency for the whole plasma can be estimated within 4% uncertainty with the assistance of the MCNP simulation.

Optimization of 6LiF:ZnS(Ag) scintillator light yield using GEANT4

A new cold neutron detector has been developed at the NIST Center for Neutron Research (NCNR) for the CANDoR (Chromatic Analysis Neutron Diffractometer or Reflectometer) project. Geometric and performance constraints dictate that this detector be exceptionally thin (∼ 2 mm). For this reason, the design of the detector consists of a 6LiF:ZnS(Ag) scintillator with embedded wavelength shifting (WLS) fibers. We used the GEANT4 package to simulate neutron capture and light transport in the detector to optimize the composition and arrangement of materials to satisfy the competing requirements of high neutron capture probability and light production and transport. In the process, we have developed a method for predicting light collection and total neutron detection efficiency for different detector configurations.The simulation was performed by adjusting crucial parameters such as the scintillator stoichiometry, light yield, component grain size, WLS fiber geometry, and reflectors at the outside edges of the scintillator volume. Three different detector configurations were fabricated and their test results were correlated with the simulations. Through this correlation we have managed to find a common photon threshold for the different detector configurations which was then used to simulate and predict the efficiencies for many other detector configurations. New detectors that have been fabricated based on simulation results yielding the desired sensitivity of 90% for 3.27 meV (5 Å) cold neutrons.The simulation has proven to be a useful tool by dramatically reducing the development period and the required number of detector prototypes. It can be used to test new designs with different thicknesses and different target neutron energies.

ARAPUCA a new device for liquid argon scintillation light detection

We present a totally innovative device for the detection of liquid argon scintillation light, that has been named ARAPUCA (Argon R&D Advanced Program at UniCAmp). It is composed of a passive light collector and of active devices. The latters are standard SiPMs that operate at liquid argon temperature, while the passive collector is based on a new technology, never explored in this field before. It is a photon trap, that allows to collect light with extremely high efficiency. The total detection efficiency of the device can be tuned by modifying the ratio between the area of the active devices (SiPM) and the area of the optical window. For example, it will allow to reach a detection efficiency at the level of 1% on a surface of 50 × 50 cm2 with an active coverage of 2 × 2 cm2 (two/three large area SiPM). It is also a cheap device, since the major part of its cost is represented by the active devices. For these reason this appears to be the ideal device for scintillation light detection in large Time Projection Chambers. With appropriate modifications it can be used also in next generation Dark Matter detectors.

He stripping for AMS of 236U and other actinides using a 3 MV tandem accelerator

Interest in the long-lived radioisotope 236U (t1/2=23.4 million years) has significantly increased recently, due to the emergence of environmental and earth science applications. Presently, only a few (AMS) accelerator mass spectrometry instruments are suited for this measurement. One major limitation is the relatively low total detection efficiency (on the order of 10−4), which is partly caused by a low stripping yield of the positive ion charge state selected after the tandem accelerator. It has been shown that high yield can be achieved using helium as stripper gas for uranium ion energies below 0.35MeV. Here we investigate the potential of He stripping of U at the 3-MV tandem accelerator VERA. Phenomenological charge state distributions for U and Th are presented for terminal voltages from 1.0 to 1.7MV. These terminal voltages provide better background rejection than possible below 1MeV, and are suited to the widely used 1–3MV workhorses of many accelerator mass spectrometry laboratories. The methods can be applied to other actinides also.