Intrinsic Detection Efficiency Research Articles

Solid, structured composite neutron detectors with high dynamic range capability

Neutron detectors are essential across disciplines such as fundamental science, nuclear security, safeguards, and civilian applications. While 3He-filled gas proportional counters have long been revered for their efficacy in detecting thermal neutrons and praised for their efficiency, neutron/gamma discrimination, and stability, the scarcity of 3He has spurred a search for alternatives. Here, we explore a solid structured scintillating particle composite (SPC) consisting of 6Li-containing scintillating glass particles within an acrylic matrix as a neutron detector for high dynamic range applications. We show for the first time that an SPC neutron detector can boast an intrinsic detection efficiency of 0.261% for pure 252Cf fission neutrons and an overall neutron detection efficiency of (0.546 ± 0.003)% at the Neutron Free-in-Air facility while being able to function in an intense gamma-ray environment. We also show that the SPC neutron detector supports fast neutron capture times and enables a dual-readout scheme that extends the detector dynamic range to high incident neutron fluxes. A scalable fabrication process allows for tailoring the SPC detector properties to the requirements of specific applications. Good agreement is found between the experimental results taken with a National Institute of Standards and Technology traceable 252Cf source and the coupled MCNP6 and optical-ray-tracing simulations.

A comparison of the neutron detection efficiency and response characteristics of two pixelated PSD-capable organic scintillator detectors with different photo-detection readout methods

We characterize the performance of two pixelated neutron detectors: a PMT-based array that utilizes Anger logic for pixel identification and a SiPM-based array that employs individual pixel readout. The SiPM-based array offers improved performance over the previously developed PMT-based detector both in terms of uniformity and neutron detection efficiency. Each detector array uses PSD-capable plastic scintillator as a detection medium. We describe the calibration and neutron efficiency measurement of both detectors using a 137Cs source for energy calibration and a 252Cf source for calibration of the neutron response. We find that the intrinsic neutron detection efficiency of the SiPM-based array is (30.2 ± 0.9)%, which is almost twice that of the PMT-based array, which we measure to be (16.9 ± 0.1)%.

Characterization of a Fast Neutron Irradiation Facility Using a Stilbene Scintillation Detector

This paper describes the characterization of a fast neutron facility located at Legnaro National Laboratories’ Van de Graaff CN accelerator. The neutron flux is produced by the 9 Be( p , xn ) reactions, generated by a beryllium thick target bombarded with 5-MeV protons. An iterative unfolding algorithm combined with a pulse shape discrimination technique were used to obtain the energy distributions of the emitted neutrons at different angles and to compute the absolute neutron flux as a function of the proton current. With a proton current of 180 nA and a distance of 5 cm from the emission point, a maximum neutron flux of 2.6 × 10 6 cm−2 s−1 ( ± 15%) was obtained. The gamma-ray component made up around 32% of the total radiation field. The measurements were taken with a Stilbene scintillation detector, therefore a comprehensive study of the detector was also performed, including energy calibration, determination of the proton light output function, and intrinsic neutron detection efficiency. Based on the results and the capabilities of the Stilbene detector, it can be concluded that this detector is suitable for fast neutron flux characterization. It enables quick measurements and real-time monitoring of the neutron field.

Disorder enhanced relative intrinsic detection efficiency in NbTiN superconducting nanowire single photon detectors at high temperature

The intrinsic detection performance of superconducting nanowire single photon detectors (SNSPDs) is highly dependent on the superconducting properties of underlying thin films. This report outlines the enhancement of detection performance for single telecom wavelength photons in disordered NbTiN SNSPD at 4.2 K. By increasing the nitrogen content and deposition pressure, the NbTiN films show suppression in critical temperature and an increase in sheet resistance. Notably, the resulting SNSPDs display a broader saturation plateau at 2.2 K, leading to superior detection performance at 4.2 K. With the disordered 7-nm-thick NbTiN films, we fabricated SNSPDs with system detection efficiency up to 83% for 1550 nm photons at 4.2 K. Moreover, these devices also show saturated intrinsic detection efficiency for 2000 nm photons. With the features outlined, the devices can be integrated into the idle 4.2 K stage of the dilution refrigerator for applications in optical quantum information processing or utilize for detecting laser radar signals in airborne platforms.

Survivability of microstructure semiconductor neutron detectors (MSND) in a thermal neutron radiation environment

The performance of five representative microstructured semiconductor neutron detectors (MSND) were investigated after exposure to varying magnitudes of thermal neutrons fluences ranging from 107 cm−2 to 1012 n cm−2. The devices have 95% enriched microparticulate 6LiF granules backfilled in microscopic trenches within a Si pvn diode. Neutron interactions in the 6Li causes the emission of reaction products which ionize the trenched Si diode depletion regions. The average intrinsic thermal-neutron detection efficiency (ϵtn) of the five devices before irradiation measured as 24.09% ± 0.35% with an operating leakage current below 11 nA at a −3 V reverse bias condition. The observed threshold of performance deterioration was approximately 1010 n cm−2, resulting in an spectral shift in the reaction product spectrum to lower energy channels and a general increase in leakage current. Although damage was observed beyond a thermal-neutron fluence of 1010 n cm−2, the devices remained operable. Beyond a thermal-neutron fluence of 1012 n cm−2, the devices experienced severe damage and demonstrated poor detector performance. At the highest thermal neutron fluences tested, near 1012 n cm−2, the average ϵtn of the five devices decreased to 4.42% ± 0.10% with an average operating leakage current of 300 nA at a −3 V reverse bias condition. Performance degradation was attributed to reaction-product damage in the MSND pvn diode structure.

Enhancing SNSPDs detection efficiency via suspended SiO2 membrane

Superconducting nanowire single-photon detectors (SNSPDs) with high detection efficiency have played significant role in numerous applications for photon detection from visible light to mid-infrared band. However, it is still a challenge to easily promote the sensitivity of SNSPD without compromising its other performance. We report a method to improve the detection sensitivity of devices via suspended SiO2 membrane, and the intrinsic detection efficiency is significantly enhanced from 78% to 100% for a 1550 nm wavelength. The electro-thermal simulation and hotspot relaxation time measurement indicate that a suspended SiO2 membrane can significantly decrease the cooling efficiency between the hotspot and the substrate, and the relaxation time is enlarged twice than before. Meanwhile, we note that the proposed method does not affect other properties of devices, such as dark count rate, detection speed, and timing jitter. Because the thermal dissipation process can be controlled continuously (by varying the size of the suspended area), the proposed method may also help to obtain a deeper understanding of the thermal diffusion and detection process of SNSPDs.

Development of a multi-channel gamma-blind fast neutron detector based on wavelength shifting fibers embedded in a ZnS:Ag epoxy mixture

This paper presents a fast neutron detector based on elastic scattering with hydrogen, a silver-activated zinc sulfide scintillator to convert the recoil proton energy to light, and wavelength-shifting fibers (WLSFs) to collect the scintillation light. The detector uses silicon photomultipliers (SiPMs) to recognize individual scintillation photons and a digital filter algorithm based on single photon counting to find clusters of photons belonging to neutron events. The detector presented in this paper features four detection channels, arranged in a 2 × 2 square. The sensitive volume of each detection channel covers a ∼5mm by ∼5mm area from the frontal direction, is 3 cm long, and contains 49 WLSFs. The detector is versatile and performs well under different conditions. Its performance can be tuned to match different applications by simply changing some parameters of the digital filter algorithm. This is illustrated in this paper by extensive measurements in different environments. Using one set of parameters, the detector achieved a gamma-blindness of 10−8 with an intrinsic neutron detection efficiency of ∼1%. With another set of parameters and with lower requirements for gamma blindness, the intrinsic neutron detection efficiency was increased to ∼11%. Yet another set of parameters allows the detector to time incoming fast neutrons with an accuracy of ∼60ns. Additionally, the decay time of the scintillation light created by neutron events was measured, falling to 10% of its peak value in ∼10 μs. Finally, the detector was exposed to strong gamma radiation for a prolonged time to test its radiation resistance. The detection efficiency dropped about linearly with the accumulated gamma fluence, reaching a drop of 40% compared to the initial efficiency at a total gamma fluence of ∼2⋅1013 cm−2.

Single photon detection performance of highly disordered NbTiN thin films

We experimentally investigated the detection performance of highly disordered based superconducting nanowire single photon detectors (SNSPDs). The dependence on the composition of the transition temperature for films show a dome-like behavior on the Nb content, with a maximal at and the films also combine relatively large sheet resistance and intermediate residual resistivity ratio. Moreover, 60-nm-wide and 7-nm-thick nanowires show a switching current as high as 14.5 μA, and saturated intrinsic detection efficiency with a plateau of more than 2 μA at 2.4 K. Finally, the corresponding SNSPDs on an alternative SiO2/Ta2O5 dielectric mirror showed a system detection efficiency of approximately 92% for 1550 nm photons, and the timing jitter is around 26 ps. Our results demonstrate that the highly disordered films are promising for fabricating SNSPDs for near- and middle-infrared single photons with high detection efficiency and low timing jitter.

High-resistivity niobium nitride films for saturated-efficiency SMSPDs at telecom wavelengths and beyond

Incorporating a micrometer scale strip as the sensitive element in superconducting single-photon detectors can lead to significant improvements in their speed, footprint, and fabrication yield. However, the current application of microstrips has resulted in a decline in the detectors' intrinsic detection efficiency. We address this issue through the utilization of niobium nitride films with high values of resistance per square. Notably, the films used in our study possess an important characteristic of retaining high critical temperature values, which enables the devices to operate in conventional closed-cycle cryostats.

Characterization of thermal neutron distribution of an Am–Be neutron source setup by CdZnTe detector

Owing to the developments in prompt gamma neutron activation analysis (PGNAA) and prompt gamma ray activation imaging (PGAI), it is necessary to develop an online thermal neutron distribution measurement method. The CdZnTe detector is considered as an alternative thermal neutron detector because of its high thermal neutron capture cross section. In this study, the thermal neutron field of an 241Am–Be neutron source was determined by CdZnTe detector. The intrinsic neutron detection efficiency of CdZnTe detector was calculated by using indium foil activation, and the value was 3.65%. Then the characteristics of neutron source were conducted with the calibrated CdZnTe detector. The thermal neutron fluxes in front of beam port were measured at several distances ranging from 0 cm up to 28 cm. Thermal neutron field at distances of 1 cm and 5 cm were also measured. The experimental data were then compared with Monte Carlo simulation. The results demonstrated that the simulated data agree well with experimental measurements.

Boron coated straw-based neutron multiplicity counter for neutron interrogation of TRISO fueled pebbles

Pebble bed reactors (PBRs) can improve the safety and economics of the nuclear energy production. PBRs rely on TRIstructural-ISOtropic (TRISO) fuel pebbles for enhanced fission product retention. Accurate characterization of individual fuel pebbles would enable the validation of computational models, efficient use of TRISO fuel, and improve fuel accountability. We have developed and tested a new neutron multiplicity counter (NMC) based on 192 boron coated straw (BCS) detectors optimized for 235U assay in TRISO fuel. The new design yielded a singles and doubles neutron detection efficiency of 4.71% and 0.174%, respectively, and a die-away time of 16.7 μs. The NMC has a low intrinsic gamma-ray detection efficiency of 8.71×10−8 at an exposure rate of 80.3 mR/h. In simulation, a high-efficiency version of the NMC encompassing 396 straws was able to estimate the 235U in a pebble with a relative uncertainty and error both below 2% in 100 s.

Improving Detection Efficiency of Silicon Carbide Neutron Detector Using Double Trench

In this article, we propose a double-trench-type silicon carbide (SiC) neutron detector and model it using the concept of a unit cell on the GEANT4 platform. When the low-level discriminator (LLD) value was fixed at 300 keV, the structural parameters of this double-trench-type SiC neutron detector were optimized to maximize the intrinsic detection efficiency. Compared with the single trench type, the double-trench-type SiC neutron detector can significantly improve the neutron intrinsic detection efficiency within a limited trench depth, which was especially suitable for the current technological status that SiC materials can only be used for shallow trench etching. Apart from optimizing the structural parameters, the energy deposition spectra in the SiC detector region by the generated secondary charged particles upon thermal neutron interaction in neutron conversion materials ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{10}}\text{B}$ </tex-math></inline-formula> and 6LiF) have also been estimated. It can be found that the double-trench-type SiC neutron detector counts significantly increased in the low-energy range, while the counts in the high-energy range are only slightly decreased. This is also the essential reason why the intrinsic detection efficiency of the double-trench-type SiC neutron detector was significantly improved compared to the single-trench-type SiC neutron detector.

Determination of absolute Np L x-ray emission intensities from 241Am decay using a metallic magnetic calorimeter

Photon emission intensities of radionuclides, i.e. the number of emitted photons per decay, are the single most important decay data when the photon spectrometry technique is employed in ionizing radiation metrology. However, their precise measurement is problematic because they are usually determined by photon spectrometry with spectrometers having a detection efficiency calibrated with x-ray and γ-ray emission intensities from other radionuclides. Therefore, these intensities are ultimately interdependent and correlated to some extent. A novel method was applied to determine the photon intensities of α-emitting radionuclides by measuring the ratio between the rate of photons in the full energy peaks and the rate of detected α-particles with the same detection set-up. Thus, there is no need to calibrate the detection efficiency and to standardize calibration sources by primary methods. The main condition to reach low uncertainties is to have a spectrometer with an intrinsic detection efficiency close to unity for the measured photons and α-particles. This condition was fulfilled by a metallic magnetic calorimeter (MMC) with an intrinsic efficiency of around 99% between 5 keV and 25 keV. In addition, the MMC provides an ultra-high energy resolution of 28 eV (full width at half maximum), facilitating the processing of the spectrum. The method was applied to determine L x-ray emission intensities from the decay of 241Am(α) → 237Np emitted between 11.9 keV and 22.4 keV. A total L x-ray emission intensity of 37.90 (12) per 100 disintegrations was obtained; the value agrees well with previous measurements and has a lower uncertainty. The uncertainties of the L x-ray groups Lα, Lηβ and Lγ were improved by a factor of two. Moreover, due to the high-energy resolution of 28 eV, a detailed set of 33 L x-ray emission intensities are provided.

Mid-infrared Nb4N3-based superconducting nanowire single photon detectors for wavelengths up to 10 µm.

Mid-infrared (MIR) single-photon detection is emerging as an important technology for various applications. Superconducting nanowire single photon detectors (SNSPDs) fabricated with superconducting films with energy gaps of a few meV are natural broadband single-photon detectors. Recently, extending SNSPDs' operation wavelengths into the MIR region is highly attractive. γ-Nb4N3 has a reduced N content and lower energy gap than the commonly used δ-NbN, making SNSPDs based on γ-Nb4N3 film more sensitive to low energy photons. We report on a Nb4N3-SNSPD based on 62-nm wide nanowire, with an optical absorption enhancement design and an optimized device package for efficient ZBLAN fiber coupling and dark count filtering. The developed device has a unity intrinsic detection efficiency (IDE) in the 1.5-4 µm wavelength region, and the device detection efficiency at 2.95 µm was measured to be 32.5%, with an uncertainty of 12.7%. Furthermore, we reduced the device geometry, and measured 3-10 µm photon response of a device based on 5-nm film and 42-nm nanowire, with an IDE of 95%, 81%, 40%, and 6% for 4.8, 6, 8, and 10 µm, respectively.

Development of an energy and efficiency calibration method for stilbene scintillators

A method for calibrating the energy scale and detection efficiency of stilbene scintillators is presented herein. This method can be used to quantitatively analyze the Compton continuum of gamma-ray spectra obtained using such scintillators. First, channel–energy calibration was conducted by fitting a semiempirical equation for the Compton continuum to the acquired energy spectrum and a new method to evaluate the intrinsic detection efficiency, called intrinsic Compton efficiency, of stilbene scintillators was proposed. The validity of this method was verified by changing experimental conditions such as the number of sources being measured simultaneously and the detector–source distance. According to the energy calibration, the standard error for the estimated Compton edge position was ±1.56 keV. The comparison of the intrinsic Compton efficiencies calculated from the single- and two-source spectra showed that the mean absolute difference and the mean absolute percentage difference are 0.031 %p and 0.557%, respectively, demonstrating reasonable accuracy of this method. The feasibility of the method was confirmed for an energy range of 0.5–1.5 MeV, showing that stilbene scintillators can be used to quantitatively analyze gamma rays in mixed-radiation fields.

Double photon coincidence crosstalk reduction method for multi-nuclide Compton imaging

Compton imaging based on Compton scattering kinematics has the potential to visualize multi-nuclides by discriminating the total energy of Compton scattering and photoelectric absorption events. This feature enables us to perform multi-tracer imaging that reflects different functional information in nuclear medicine, resulting in a definitive diagnosis and being useful for biological and medical research. One of the challenges with multi-nuclide imaging is the crosstalk artifacts caused by scattered photons of higher energy gamma-rays. In this study, we investigated the potential benefits of the double photon coincidence detection as a drastic crosstalk reduction method. Coincidence detection of successive gamma-rays can differentiate nuclides and reduce the background caused by other nuclides' gamma-rays because some nuclides emit two or more gamma-rays in rapid succession. In this study, we focused on the coincidence detection of a Compton event and a photoelectric absorption event, and we showed simultaneous double photon emitter imaging of 111In and 177Lu with a ring-type Compton imaging system. The artifacts caused by other nuclides' gamma-rays were reduced by extracting Compton events coincident with photoelectric absorption events. The coincidence Compton images demonstrated a signal-to-background ratio improvement of 1.1–1.7 times over the one of no-coincidence Compton images, despite a drop in intrinsic detection efficiency of the order of 10-2. This strategy of directly reducing crosstalk will be useful in other combinations imaging such as of 111In (or 177Lu) and a positron emission tomography nuclide.

Neutron detection efficiency of the Neutron dEtector with Xn Tracking (NEXT)

An efficient neutron detection system with good energy resolution is required to correctly characterize decays of neutron-rich nuclei where β-delayed neutron emission is a dominant decay mode. The Neutron dEtector with Xn Tracking (NEXT) has been designed to measure β-delayed neutron emitters. By segmenting the detector along the neutron flight path, NEXT reduces the associated uncertainties in neutron time-of-flight measurements, improving energy resolution while maintaining detection efficiency. Detector prototypes are comprised of optically separated segments of a neutron-gamma discriminating plastic scintillator coupled to position-sensitive photomultiplier tubes. The first performance studies of this detector showed that high intrinsic neutron detection efficiency could be achieved while retaining good energy resolution. The results from the efficiency measurements using neutrons from direct reactions are presented.

Gamma-blindness & neutron detection efficiency assessments with centrifugally tensioned metastable fluid detectors in low-scatter environment

A range of tests and associated analyses were performed in a state-of-art low scatter environment to demonstrate and validate the performance of the (Medium) Centrifugally Tensioned Metastable Fluid Detector (MCTMFD) for gamma blind detection of fast and epithermal neutrons for a variety of configurations, using Cf-252 and Am-Li isotope neutron sources. All measurements were performed in the Low Scatter Room (LSR) of Radiological Exposures & Metrology Laboratory at Pacific Northwest National Laboratory (PNNL). Experiments were performed to evaluate intrinsic neutron detection efficiency, ɛint n, the intrinsic gamma-neutron detection efficiency, ɛintγn, and the gamma absolute rejection ratio for neutrons (GARRn) as a function of tensioned metastable state negative pressure, Pneg, varying from 2.5 bar towards 9 bar. The specific embodiment of the MCTMFD utilized for the experiments at PNNL included a 16 cm 3 sensitive volume configured for either fast neutron detection using Decafluoropentane (DFP) as the detection medium, or fast and thermal neutron detection (using DFP with a chemical mixture composed of natural boron). Experiments were performed with Cf-252 neutron sources ranging in intensity from 1 × 104 n/s to 3.45 × 105 n/s, an Am-Li neutron source with intensity of 2.5 × 104 n/s, used in both a bare configuration and in combination with a 30 cm OD moderating sphere of D2O, with and without a 0.5 mm Cd shell, and intense Cs-137 and Co-60 gamma sources offering dose rates ranging from 27 mR/h to 53 R/h. It was found that the MCTMFDs remained gamma-blind (ɛintγn < 10−11) even under 53 R/h gamma background; the associated intrinsic fast neutron detection efficiency (ɛint n) varied from ∼0.2% for Pneg ∼2.5 bar, ∼10% for Pneg ∼5.5 bar and, ∼30% for Pneg ∼9 bar for a Cf-252 fission spectrum. In comparison, for the softer (Am-Li) spectrum, the ɛint n varied from ∼1% for Pneg ∼5.5 bar and approached the ɛint n values for Pneg states above 7 bar. The same MCTMFD when using a borated detection fluid with 20% B-10, offered a ×10–20 improvement in ɛint n for Pneg states ranging from 4.5–5 bar, for detecting epithermal neutrons from the Am-Li source (placed within a 30 cm OD, D2O moderator with and without a 0.5 mm Cd shield).

The microdosimetric one-hit detector model for calculating the relative efficiency of the alanine pellet dosimeter in low energy X-ray beams

The alanine pellet dosimeter is a widely used reference dosimeter in both medical and industrial dosimetry across a wide range of beam qualities. A challenge when using alanine in low energy X-ray beams is its strong energy dependence; a significant decline is observed in the alanine response per dose-to-water relative to irradiations in a cobalt-60 reference field. This decrease is caused by the physical difference in alanine to water dose ratios combined with a radiochemical decrease in the intrinsic detector efficiency but is difficult to characterize mainly due to experimental uncertainties.Here we have applied a microdosimetric one-hit detector model to characterize the intrinsic detector efficiency of the alanine pellet dosimeter in low energy X-ray beams. Microdosimetric distributions were estimated from track structure calculations using the Geant4-DNA Monte Carlo software, where literature data was used to determine free model parameters.The model was applied to two sets of X-ray spectra with low (40 kV to 170 kV) and medium (100 kV to 300 kV) tube potential, covering a wide range of beam qualities. A relative detector efficiency of 0.937 was obtained for the low energy set with variations between −1.0% and 1.5%, whereas the efficiency varied between approximately 0.925 and 0.985 for the medium energy set, with a strong correlation to the half-value layer of the beam.It is concluded, that the half-value layer of an X-ray beam is not sufficient characterization to uniquely determine the relative efficiency of an alanine pellet dosimeter. However, the variation in relative efficiency with respect to the half-value layer is small.

Performance evaluation of a beta-spectrometer comprising a plastic scintillator and multi-wire chamber using a coincidence method

This paper describes an experimental setup developed to measure the beta-ray energy spectrum as well as a Geant4 simulation study conducted to characterize the properties of a beta-spectrometer. The beta-spectrometer comprises a multi-wire chamber to generate signals to indicate the incidence of beta rays and a plastic scintillation detector to measure its energy. The coincidence method of the detector signals was used to remove high gamma-ray interference. To evaluate the performance of the developed spectrometer, the energy spectra were measured with the radionuclide sources (137Cs and 207Bi) emitting internal conversion electrons and gamma rays. The gamma-ray interference removal rate of the spectrometer using the coincidence method was 99.12 ± 0.09%. To reconstruct the beta spectrum from the measured spectrum, Monte Carlo simulations using the Geant4 toolkit were performed to calculate the coefficient related to the effect of gamma rays. The obtained spectrum confirmed that the energy resolution and intrinsic internal conversion peak detection efficiency of the beta-spectrometer were 10.2% at 1 MeV and 91.6%, respectively.