Neutron Detection Techniques Research Articles

Investigating neutron scattering in a Spherical Proportional Counter: A tabletop experiment

In this paper, we report on a tabletop experiment studying neutron scattering in a Spherical Proportional Counter using an Am-Be source. Systematic studies were carried out to investigate the effect of gas mixture, pressure, operating voltage, and sphere size on the drift time-rise time relationship of the signal in a spherical proportional counter. Our experimental results showed good agreement with MagBoltz-based simulations. These findings are a crucial step towards measuring the quenching factor in gases using a neutron beam for the New Experiments With Spheres-Gas (NEWS-G) experiment and has important implications for the development of neutron detection techniques and their potential applications in nuclear and particle physics.

Measurement of the Cosmic Ray Muon Component Using the Neutron Detection Technique at the Tien Shan Mountain Station

Measurement of the Cosmic Ray Muon Component Using the Neutron Detection Technique at the Tien Shan Mountain Station

High spatial resolution neutron detection technique based on Commercial Off-The-Shelf CMOS image sensors covered with NaGdF_4 nanoparticles

We present a position-sensitive neutron detection technique based on a Commercial Off-The-Shelf CMOS image sensor (CIS) covered with nanoparticles of sodium gadolinium fluoride (NaGdF4). The synthesis procedure and characterization of the NaGdF4 nanoparticles are detailed, as well as the deposition method of the conversion layers over the surface of the chips. We also present a manufacture method of test patterns made with neutron-absorbing materials. These patterns were designed to evaluate the performance of the proposed technique. Analyzing the obtained neutron images we conclude that the intrinsic spatial resolution of the developed method is better than (15±6) μm, this upper bound for the spatial resolution is comparable with that obtained with the best neutron position-sensitive detectors available nowadays.

Analysis of radiation emission from MYRRHA spent fuel and implications for non-destructive safeguards verification

The radionuclide composition of, and emitted radiation in, spent nuclear fuel from the future MYRRHA facility have been studied using depletion simulations to understand potential consequences for safeguards verification using non-destructive assay. The simulations show that both the gamma-ray and neutron emission rates in spent MYRRHA assemblies are lower than in spent PWR UO2 and MOX assemblies. In addition, gamma-ray emission rates from 134Cs and 154Eu are considerably lower, and the total neutron emission rate in MYRRHA fuel is much less sensitive to fuel burnup and cooling time. The main reason is that the fast neutron spectrum in MYRRHA affects the radionuclide production in the fuel. One result is that 244Cm, the main contributor to the neutron emission in spent light water reactor fuel, has a limited production in MYRRHA. Consequently, neutron-detection techniques could be used to more directly assay the plutonium content of spent MYRRHA fuel.

β -delayed neutron emission studies of I137,138 and Cs144,145 performed with trapped ions

A detailed study of the $\ensuremath{\beta}$-delayed neutron emission properties of $^{137,138}\mathrm{I}$ and $^{144,145}\mathrm{Cs}$ has been performed by confining ions in the Beta-decay Paul Trap. The daughter ions following $\ensuremath{\beta}$ decay emerge from the trapped-ion cloud with negligible scattering allowing reconstruction of the recoil-ion energy from the time of flight. From this information, the neutron-emission branching ratios and neutron-energy spectra were deduced. The results for the $^{137}\mathrm{I}$ and $^{144,145}\mathrm{Cs}$ decays are in agreement with previous results performed using direct neutron-detection techniques. In the case of $^{138}\mathrm{I}$, a branching ratio of 6.18(50)% is obtained, yielding a value consistent with the more recent results, which are a factor of two larger than measurements made prior to 1978.

Determination of phase space region for cross-check validation of the neutron detection in the BINA experiments

Deuteron breakup reactions are basic laboratories for testing nuclear force models. Recent improvements in the data analysis allow for direct identification of neutrons in the BINA detection setup. This opens up the opportunity to study new aspects of few-nucleon system dynamics like charge dependence of nuclear force or Coulomb interaction. In this paper we determine regions along the kinematical curves where differential cross section of deuteron-proton breakup reactions can be measured by the proton-neutron and proton-proton coincidences simultaneously. %In this paper we determine regions along the kinematical curves where differential cross section of $^1$H$(d,pp)n$ and $^1$H$(d,pn)p$ breakup reactions overlap. This is particularly useful for validation of the neutron detection technique.

Development and performance of a 14-MeV neutron generator

An accelerator-based 14-MeV neutron generator for fusion neutronics studies has been developed in Fusion Neutronics Laboratory (FNL) at Institute for Plasma Research (IPR). The generator is initially designed to produce a neutron yield of 1010 n/s and operated for 1.1×109 n/s. It will be further upgraded to the neutron yield of 1012 n/s. The neutron generator consists of various components such as 2.45 GHz ECR ion source, 300 kV linear accelerator, beam diagnostic system, TMP based vacuum system, solid tritium target, and control system. Various direct and indirect neutron detection techniques are deployed to evaluate the performance of the neutron generator in terms of neutron emission. These techniques include foil activation, alpha particle diagnostic, and He-3 proportional counter. The reaction rates for the foil activation are estimated using the Monte Carlo technique. Results of all independent diagnostics are obtained and compared. The paper describes the experimental setup and neutron diagnostics. It also describes the performance of the 14-MeV neutron generator highlighting its stability under continuous operation.

Gaussian mixture models as automated particle classifiers for fast neutron detectors

AbstractPulse shape discrimination (PSD) is the task of classifying electronic pulse shapes for different particle types such as gamma rays and fast neutrons interacting in scintillators and read out by photo sensitive detectors. This field has been limited in its adoption of techniques found in the statistical learning community. Methods initially employed in the 1960s for analog electronic circuitry persist in the current PSD literature describing operations performed on digitized pulses, which are amenable to statistical rigor. Despite vast amounts of data collected at low energy levels, traditional PSD methods are unable to discriminate particles below a certain threshold. In this work, Gaussian mixture models (GMMs) are used as a clustering technique for fast neutron detection in the absence of labeled data. GMMs yield improvements spanning the energy spectrum in a desirably efficient, unsupervised fashion. An extension, the Dirichlet Process GMM, provides further flexibility and classification improvement.

Quantitative monitoring of CO2 sequestration using thermal neutron detection technique in heavy oil reservoirs

CO2 enhanced oil recovery (CO2-EOR) project is of significance for CO2 sequestration and heavy oil recovery. Quantitative monitoring of CO2 saturation (SCO2) is essential to recognizing and understanding the migration and distribution of CO2 injected into the geological formations. In this paper, based on the difference in the neutron moderation ability of CO2, water and heavy oil, thermal neutron detection technique is applied in heavy oil reservoirs to monitor CO2 sequestration. By Monte Carlo simulation, the responses of thermal neutron count ratio versus different porosities and CO2 saturation were studied. Then, a mathematical model of CO2 saturation versus thermal neutron count ratio and formation porosity was established to quantitatively calculate CO2 saturation. Besides, the effects of formation pressure and temperature, heavy oil density, lithology, and other factors on the method were studied. Results show that variations of formation pressure, formation temperature, and density of heavy oil have little impact on the CO2 saturation measurement. However, the change of formation lithology results in larger CO2 saturation errors and needs corrections. In addition, the method has a low discrimination between CO2 and CH4 gas, and the results are easily affected by the CH4 content. Finally, a simulated case demonstrates the application of the method. For the heavy-oil sandstone with different porosities, the method shows a perfect performance: the SCO2 errors are less than 1% for the high and low gas saturated formation. This research provides an effective strategy to monitor CO2 storage and residual oil saturation in CO2-EOR reservoirs.

Gamma background characterization on VESUVIO: before and after the moderator upgrade

The VESUVIO spectrometer at the ISIS pulsed neutron and muon source is a unique instrument which makes use of eV neutrons and inverted geometry, allowing deep inelastic neutron scattering experiments with high values of energy and wavevector transfers. The neutron detection techniques on the VESUVIO forward-scattering detector banks is based on (n,γ) conversion, therefore neutrons are indirectly detected and the signals produced by scattered neutrons, accordingly the photons, is recorded using gamma scintillators. The use of γ-sensitive detectors make γ-background one of the main limiting factors affecting the data quality and instrument sensitivity on VESUVIO. This work aims to assess how the sample-independent gamma background has changed after the recent upgrades to the water moderator viewed by the instrument, which resulted in a twofold increase of the thermal neutron flux. Here we show that the gamma background is mainly influenced by the thermal neutron flux and that the recent upgrade results in a fivefold increase in the gamma background in the photon energy range 300 keV-3 MeV. We point out the possibility of providing a thermal-neutron filter along the incident beam in order to suppress this background source.

Thermal neutron detector based on COTS CMOS imagers and a conversion layer containing Gadolinium

In this work we will introduce a novel low cost position sensitive thermal neutron detection technique, based on a Commercial Off The Shelf CMOS image sensor covered with a Gadolinium containing conversion layer. The feasibility of the neutron detection technique implemented in this work has been experimentally demonstrated. A thermal neutron detection efficiency of 11.3% has been experimentally obtained with a conversion layer of 11.6 μm. It was experimentally verified that the thermal neutron detection efficiency of this technique is independent on the intensity of the incident thermal neutron flux, which was confirmed for conversion layers of different thicknesses. Based on the experimental results, a spatial resolution better than 25 μm is expected. This spatial resolution makes the proposed technique specially useful for neutron beam characterization, neutron beam dosimetry, high resolution neutron imaging, and several neutron scattering techniques.

Comparison and research on the GRAVEL and PRIP algorithms of neutron energy spectrum unfolding

Objective Neutron energy spectrum unfolding is a key technique for neutron detection. It is essentially an inversion problem. The GRAVEL algorithm has been widely used in this field, and the PRIP algorithm transforms neutron energy spectrum unfolding into a typical nonnegative linear complementarity problem and solves it by interior point algorithm for potential reduction.

Neutron assay in mixed radiation fields with a 6Li-loaded plastic scintillator

A novel technique for assay of thermal and fast neutrons in a 6Li-loaded plastic scintillator is presented. Existing capture-gated thermal neutron detection techniques were evaluated with the 6Li-loaded plastic scintillator studied in this work. Using simulations and experimental work, shortcomings in its performance were highlighted. As a result, it was proposed that by separating the combined fast and thermal neutron events from gamma events, using established pulse shape discrimination techniques, the thermal neutron events could then be assayed. Experiments were conducted at the National Physical Laboratory, Teddington, performing neutron assays with seven different neutron fields using the proposed technique. For each field, thermal and fast neutron content was estimated and were shown to corroborate with the seven synthesised fields.

The μTPC method: improving the position resolution of neutron detectors based on MPGDs

Due to the 3He crisis, alternatives to the standard neutron detection techniques are becoming urgent. In addition, the instruments of the European Spallation Source (ESS) require advances in the state of the art of neutron detection. The instruments need detectors with excellent neutron detection efficiency, high rate capabilities and unprecedented spatial resolution. The Macromolecular Crystallography instrument (NMX) requires a position resolution in the order of 200 μm over a wide angular range of incoming neutrons. Solid converters in combination with Micro Pattern Gaseous Detectors (MPGDs) are proposed to meet the new requirements. Charged particles rising from the neutron capture have usually ranges larger than several millimetres in gas. This is apparently in contrast with the requirements for the position resolution. In this paper, we present an analysis technique, new in the field of neutron detection, based on the Time Projection Chamber (TPC) concept. Using a standard Single-GEM with the cathode coated with 10B4C, we extract the neutron interaction point with a resolution of better than σ = 200 μm.

Development of a novel neutron detection technique by using a boron layer coating a Charge Coupled Device

This article describes the design features and the first test measurements obtained during the installation of a novel high resolution 2D neutron detection technique. The technique proposed in this work consists of a boron layer (enriched in 10B) placed on a scientific Charge Coupled Device (CCD). After the nuclear reaction 10B(n,α)7Li, the CCD detects the emitted charge particles thus obtaining information on the neutron absorption position. The above-mentioned ionizing particles, with energies in the range 0.5–5.5 MeV, produce a plasma effect in the CCD which is recorded as a circular spot. This characteristic circular shape, as well as the relationship observed between the spot diameter and the charge collected, is used for the event recognition, allowing the discrimination of undesirable gamma events. We present the first results recently obtained with this technique, which has the potential to perform neutron tomography investigations with a spatial resolution better than that previously achieved. Numerical simulations indicate that the spatial resolution of this technique will be about 15 μm, and the intrinsic detection efficiency for thermal neutrons will be about 3%. We compare the proposed technique with other neutron detection techniques and analyze its advantages and disadvantages.

HELNED: Helium-3-free low-cost neutron detectors

We developed a technique for thermal neutron detection not making use of 3 He, also suitable for online real time monitoring of CASTOR spent fuel containers. As a neutron converter we used 6 LiF, being the neutron capture cross section of 6 Li very well known and with only an alpha and a triton in the exit channel. We can deposit thin layers of converter onto several different substrates, to be placed on top of solid state detectors or scintillators capable of efficiently detecting the decay products.

THE USE OF FAST NEUTRON DETECTION FOR MATERIALS ACCOUNTABILITY

For many years at LLNL, we have been developing time-correlated neutron detection techniques and algorithms for applications such as Arms Control, Threat Detection and Nuclear Material Assay. Many of our techniques have been developed specifically for the relatively low efficiency (a few percent) inherent in man-portable systems. Historically, thermal neutron detectors (mainly 3 He ) were used, taking advantage of the high thermal neutron interaction cross-sections, but more recently we have been investigating the use of fast neutron detection with liquid scintillators, inorganic crystals, and in the near future, pulse-shape discriminating plastics that respond over 1000 times faster (nanoseconds versus tens of microseconds) than thermal neutron detectors. Fast neutron detection offers considerable advantages, since the inherent nanosecond production timescales of fission and neutron-induced fission are preserved and measured instead of being lost in the thermalization of thermal neutron detectors. We are now applying fast neutron technology to the safeguards regime in the form of high efficiency counters. Faster detector response times and sensitivity to neutron momentum show promise in measuring, differentiating, and assaying samples that have modest to very high count rates, as well as mixed neutron sources (e.g., Pu oxide or Mixed Cm and Pu ). Here we report on measured results with our existing liquid scintillator array and promote the design of a nuclear material assay system that incorporates fast neutron detection, including the surprising result that fast liquid scintillator becomes competitive and even surpasses the precision of 3 He counters measuring correlated pairs in modest (kg) samples of plutonium.

Novel Glass Ceramic Scintillator for Detection of Slow Neutrons in Well Logging Applications

One of the neutron detection techniques is based on the scintillation glasses enriched with the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li isotope. A limitation to increase the light yield (LY) in glass scintillators is imposed by the absence of long-range order in their atomic structure. As a result, the mean free path of excitons in glasses is very small and the delivery of electronic excitations to luminescent centers through the exciton migration has very low efficiency. The only way toward creating effective scintillation in glasses is to use direct excitation of the luminescent centers, which are dopants in the form of Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. However, the synthesis of the glasses heavily doped with cerium possesses significant technological challenge due to heterovalent properties of cerium. These limitations can be overcome by the impregnation of the glass matrix with scintillator nanocrystals with average size less than the emitted light wavelength. The controlled recrystallization of the glass enables control of the nanocrystal dimension and their distribution in the glass matrix. Details of the method are described in US patent application 13/242 839. By using this approach we have synthesized glass ceramic scintillation material obtained through partial crystallization of Ce-doped lithium-silica glass with the formation of the petalite nanocrystals in the glass matrix. Samples containing 16.5 at.% of lithium demonstrate bright radio-luminescence with maximum at 410 nm, fast scintillation with an average decay time constant of 70 ns, and LY up to 240% of LY of GS20 scintillation glass. LY of the obtained material is almost constant between 20° C and 70 °C and depends weakly on the temperature decreasing by ~30% with the temperature increase from 70 °C to 170 °C. Scintillation detectors based on this material can replace He3 neutron counters in many applications, including wireline and logging-while-drilling (LWD) “sourceless” neutron porosity measurement that requires the neutron detectors capable to operate at temperatures above 150 °C.

Study of 0+States at iThemba LABS

An initial series of experiments utilising the (3 He,n) reactions have been carried out at iThemba LABS. These are complimentary to transfer reactions such as (t,p) stripping or (p,t) pick-up reactions measurements using magnetic spectrometers. However, in the past, (3 He,n) measurements have suffered from ambiguities due to the low energy resolution inbuilt into the time-of-flight techniques used. By combining neutron detection techniques with the AFRODITE γ -ray array, it has been shown that very good energy resolutions can be achieved. This enables the relative strengths of two proton stripping to excited states, separated by only a few keV, to be accurately measured. This technique has been applied to first excited 02 + states and, in particular to those uniquely seen in double β -decay.

Superheated emulsions and track etch detectors for photoneutron measurements

This paper describes the criteria behind the selection of neutron detection techniques for photoneutron dosimetry as well as the methods adopted to obtain dosimetric readouts. The work was conducted within the framework of Working Group 9 (WG9 Radiation Protection Dosimetry in Medicine), coordinated by the European Radiation Dosimetry Group (EURADOS). WG9 research aims at estimating the risk of second cancer induction due to radiation therapy. Therefore, a comprehensive experimental programme was devised to measure doses received by non-target organs-at-risk (OAR) during radiation therapy. The techniques described in this work were selected and used for the neutron dosimetric assessment during in-phantom simulations of clinical prostate radiotherapy treatments, carried out in three European facilities. Non-conformal standard fields were used as a common reference between different facilities.Performing neutron measurements near linacs is a complex task, because of the intense pulsed photon primary field. Therefore, photon insensitive dosimeters such as superheated emulsions (SE) and solid state nuclear track detectors (SSNTD) were chosen. Their readout procedures were carefully assessed. Methods were developed to count the large number of tracks and bubbles in SE. These are described in detail in the present work, along with a brief introduction to the detector physics.