Neutron Detectors

Detection of nuclear materials is critical in preventing traffic of illicit nuclear materials. Several methods that are based on detection of spontaneous or induced emission of fission neutron are considered. Efficient fast and thermal neutron detectors are generally required. For some applications these detectors must have fast response and should be deployed with large or small detection area. This work expands upon the basic concept of coating a p-n junction solar cell with a neutron detection layer that typically employs either 6 Li or 10 B. 10 B has a larger absorption cross section and results in higher detection efficiency. When an incident neutron interacts with 10 B, it releases an α-particle and a 7 Li ion; this α-particle excites electron-holepairs in the silicon p-n junction. This work investigated a variety of different silicon trench/pillar/hole geometries in combination with the 10 B filling or coating; thermal neutron detection efficiencies as high as 30% are projected. It utilizes trenches spaced as closely as 2 µm and 50 µm deep. Simulations predict that when these single layer detectors are bonded in a multiple layer configuration, efficiencies in the range of 90% could be achieved. Along with nuclear and electrical simulations, a highly controllable deep-reactive-ion-etching (DRIE) recipe is developed for trench/pillar/hole etching. The ability to create p-n junctions along those trenches is presented. Trenches and pillars as small as 2 µm by 2 µm are fabricated and p-n junctions are created along their surface. Smooth, uniform trenches are ready for trench refilling procedures.

A b s tra c t: Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like W IMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

Using Monte Carlo method features of 10 B+ZnS(Ag) neutron detector under real operational conditions has been calculated, this results were compared against measurements. This detector is a viable substitute for 3He detectors installed in custom borders to prevent the illicit traffic of special nuclear materials, SNM.

We are investigating different micro-and nanostructure approaches to neutron detection based on inorganic scintillators. Specifically, we have been assessing various neutron converter-scintillator configurations through simulations and experiments. One promising inorganic scintillator is ZnO due to its relatively high light yield , reasonable optical transparency in the visible region , and relatively low refractive index compared to other Zn-based crystals such as ZnS . Accurate optical data and rigid simulation tools are necessary to optimize the dimensions of the neutron converter/scintillator systems. Accurate optical data are necessary since the optical parameters of a material depend on a variety of factors, including but not limited to its morphology, crystal structure, surface quality (surface roughness), as well as the temperature at which it was manufactured. Therefore, literature data show significant discrepancy when it comes to the optical parameters for the material and it is important to accurately measure these quantities for the specific sample of interest. Neutron detection is a complex process that includes neutron transport, charged particle transport, and light transport in the active detection medium. Hence, a rigid simulation tool is required to handle all these different areas of physics with sufficient accuracy. In this work, Geant4 has been chosen to carry out the simulations of these processes. Geant4 (GEometry ANd Tracking) is a toolkit used in various applications including high energy physics, astrophysics, and radiation detection . The optical simulation capabilities of Geant4 have been validated by comparing the transmission and reflection data from UV-Vis spectroscopy to the Geant4 models for different Zn-based crystals. After validating the optical response of single crystals, simulation models were constructed to model more complex structures of ZnS-based alpha detection sheets (EJ-440) from Eljen Technology. Optical parameters validated with experimental results have been used in radiation simulation in Geant4. This study will serve as a basis for our ongoing effort to optimize and manufacture an efficient and compact fast neutron detection module with micro-and nano-structures.

An algorithm for the simulation of HLNC measurement data on a personal computer (PC) has been developed and is presented in this paper. This algorithm is based on a leakage multiplication factor --- fissile mass correlation (with three parameters) derived from about 100 sets of published experimental data. Using this algorithm, the simulated totals and reals (coincidence pair) count rates agreed with all measurement data to within 10%. Uncertainties in isotopics as well as the effects of possible contaminants --- fluorine or moisture --- have also been modelled, but are not discussed in detail in this condensed account. The algorithm has been tested successfully against additional data obtained in field measurements. PC software based on the simulation algorithm has been developed for training inspectors and familiarizing them with HLNC measurement data and with errors affecting HLNC measurements.

In homeland security, neutron detection is used to prevent the smuggling of Special Nuclear Materials in the fight against nuclear terrorism Thermal neutrons are normally detected with 3 He proportional counters surrounded by a polyethylene box However, due to the 3 He shortage in the radiation portal monitors reported in 2009, new procedures are being studied In this work, Monte Carlo methods (using the MCNP6 code) have been used to study the neutron detection features of a 10 B + ZnS(Ag) under real conditions inside a radiation portal monitor The performance of neutron detection was carried out for 252 Cf, HEU 235 U (enriched at 70% and 94%) and 239 Pu (enriched at 93%) under two different conditions, bare and shielded with lead and polyethylene To mimic an actual situation occurring at border areas, when a vehicle was passing through the detection zone, a sample of Special Nuclear Materials, SNM, sited inside a cargo vehicle mixed with scrap was simulated, and the radiation portal monitors contained 10 B + ZnS(Ag) neutron detectors The responses were calculated for four different neutron detectors, two real detectors (N-15 and N-48) and two prototype detectors (N-15 plus and N-48 plus), which are based on the N-15 and N-48 geometries with an improvement in the amount of 10 B and a higher polymethyl methacrylate, PMMA, thickness Measurements were reported for the actuals detectors, and the response was greater than 200 cm from a neutron source of 252 Cf in c/s-ng of 252 Cf An array of three N-15 or one array of N-48 are close to detect 2 5 c/s-ng of 252 Cf as required the Pacific Northwest National Laboratory, PNNL The PNNL is the laboratory that tests almost every alternative detector It requires that each detector must have an absolute efficiency greater than 2 5 c/s-ng of 252 Cf for such a 252 Cf source, located 200 cm perpendicular to the geometric midpoint of the neutron sensor, complementing the ANSI recommendations that the detector must be able to detect the pass of a neutron source of 252 Cf of 20,000 n/s at a distance of 200 cm, to be considered an attractive alternative for the 3 He neutron detectors The N-15 plus system reached more than 2 5 c/s-ng of 252 Cf Therefore, the 10 B + ZnS(Ag) detectors are an innovative and viable replacement for the 3 He detectors in the radiation portal monitor

A 6 LiF:ZnS(Ag) based technology has been developed as a replacement for He-3 detectors in Radiation Portal Monitors (RPMs). An early prototype having an active area of 1000cm 2 has been independently tested at the Pacific Northwest National Laboratory [1]. These tests reported a sensitivity comparable with that of a 1m long, 5cm diameter, 3 atmosphere He-3 proportional counter and an ability to operate with a full-field gamma-ray dose-rate of 100mR/h (2.58x10 -5 c/kg/h in air). Subsequent developments have included scaling the detector technology to provide both smaller (200 cm 2 ) and larger-area detectors (1131 and 1740 cm 2 ) and using multiple detectors in combination. For example, the sensitivity and gamma-ray rejection performance of a neutron detection module (NDM) intended for use in an RPM which included 4x1131 cm 2 detection elements, has been verified by the UK Health Protection Agency [2] as providing a sensitivity of between 4.05±1.10 counts per second per nano-gram of...

The aim of the work is to design and describe the methodology of determination of the spatial weighting function of ex-core detectors for the WWER-440 reactor type using Monte Carlo N-Particle Transport code MCNP-4C2, taking into account the different operational parameters such as power, burn-up, boric acid concentration and position of control assembly group No 6. The spatial weight function provides relationship between the spatial neutron flux density distribution or the fission density distribution in the reactor core and the detectors placed outside of the reactor core (ex-core detectors). The spatial weight function will be used for interpretation of reloads startup rod drop measurements, assessment of the ex-core detectors response at deep subcritical reactor stage and for other applications.

The aim of the work is to design and describe the methodology of determination of the spatial weighting function of ex-core detectors for the WWER-440 reactor type using Monte Carlo N-Particle Transport code MCNP-4C2, taking into account the different operational parameters such as power, burn-up, boric acid concentration and position of control assembly group No 6. The spatial weight function provides relationship between the spatial neutron flux density distribution or the fission density distribution in the reactor core and the detectors placed outside of the reactor core (ex-core detectors). The spatial weight function will be used for interpretation of reloads startup rod drop measurements, assessment of the ex-core detectors response at deep subcritical reactor stage and for other applications.

A b s tra c t: Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like W IMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

In an effort to characterize the fast neutron radiation background, 16 EJ-309 liquid scintillator cells were installed in the Radiological Multi-sensor Analysis Platform (RadMAP) to collect data in the San Francisco Bay Area. Each fast neutron event was associated with specific weather metrics (pressure, temperature, absolute humidity) and GPS coordinates. The expected exponential dependence of the fast neutron count rate on atmospheric pressure was demonstrated and event rates were subsequently adjusted given the measured pressure at the time of detection. Pressure adjusted data was also used to investigate the influence of other environmental conditions on the neutron background rate. Using National Oceanic and Atmospheric Administration (NOAA) coastal area lidar data, an algorithm was implemented to approximate sky-view factors (the total fraction of visible sky) for points along RadMAPs route. Three areas analyzed in San Francisco, Downtown Oakland, and Berkeley all demonstrated a suppression in the background rate of over 50% for the range of sky-view factors measured. This effect, which is due to the shielding of cosmic-ray produced neutrons by surrounding buildings, was comparable to the pressure influence which yielded a 32% suppression in the count rate over the range of pressures measured.

A Bonner Sphere Spectrometer (BSS) is a widely used neutron spectrometer in the health physics and research arenas. It provides the means to measure neutron spectra over many orders of magnitude in energy with a single instrument, but has decreased response above 20-MeV. To increase the sensitivity of BSS at higher energies, a low cost, easily fabricated Bonner Sphere Extension (BSE) has been designed and constructed. The BSE extends the sensitivity of the BSS to higher energies and utilizes either an active (LiI(Eu) scintillator) or passive (gold foil activation) detector. Two factors which affect the uncertainties in unfolded neutron spectra are the energy dependence arising from the cross sections used to generate the response functions and the directional dependence of the measurement system. We assessed the energy dependence of the BSE by calculating the response functions using two different cross section libraries (ENDF B. VI and ACTL). These response functions were then used to unfold data measured with the BSE at the WNR facility at Los Alamos Neutron Science Center (LANSCE). The spectrum unfolded with the ENDF B.VI response functions was in better agreement with the LANSCE time of flight (TOF) spectrum. We evaluated the angular response of the BSE by unfolding data which were measured with the detector parallel, perpendicular, and at a 45 angle to the incident neutron beam using response functions computed in three directional orientations (parallel, perpendicular, and at a 45 angle). Directional dependence was found to be more significant for the passive detector, especially when used with small moderating spheres.

Borexino, a liquid scintillator detector at LNGS, is designed for the detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear reactors, and the Earth. The feeble nature of these signals requires a strong suppression of backgrounds below a few MeV. Very low intrinsic radiogenic contamination of all detector components needs to be accompanied by the efficient identification of muons and of muon-induced backgrounds. Muons produce unstable nuclei by spallation processes along their trajectory through the detector whose decays can mimic the expected signals; for isotopes with half-lives longer than a few seconds, the dead time induced by a muon-related veto becomes unacceptably long, unless its application can be restricted to a sub-volume along the muon track. Consequently, not only the identification of muons with very high efficiency but also a precise reconstruction of their tracks is of primary importance for the physics program of the experiment. The Borexino inner detector is surrounded by an outer water-Čerenkov detector that plays a fundamental role in accomplishing this task. The detector design principles and their implementation are described. The strategies adopted to identify muons are reviewed and their efficiency is evaluated. The overall muon veto efficiency is found to be 99.992 % or better. Adhoc track reconstruction algorithms developed are presented. Their performance is tested against muon events of known direction such as those from the CNGS neutrino beam, test tracks available from a dedicated External Muon Tracker and cosmic muons whose angular distribution reflects the local overburden profile. The achieved angular resolution is ∼3 •-5 • and the lateral resolution is ∼35-50 cm, depending on the impact parameter of the crossing muon. The methods implemented to efficiently tag cosmogenic neutrons are also presented.

The MCNP input file of Example 3.1 describes a 13 × 13 fuel assembly in a cylindrical water tank. It shows the MCNP repeated structures lattice capability. The aim of the input file is to calculate the induced fission in the enriched and depleted uranium pins in the fuel assembly in the water tank when the starting source of neutrons is spontaneous fission.

The active Uranium Neutron Coincidence Collar-Light Water Reactor Fuel (UNCL) provides a means of non-destructively assaying the fissile linear density of fresh fuel assemblies containing low enriched uranium. Historically the generic calibration curves and correction factors were established experimentally on mock assemblies. This is time consuming, expensive and suffers from limitations owing to the limited inventory of pins and simplifications of the laboratory arrangements. At Los Alamos National Laboratory we operate a BWR UNCL-II in conjunction with a 6x6 array of 2.34wt% reference pins. The array is supported by grids held together by steel lifting rods, one at each corner. There is no wrapper. The rods are in interrogation zone. The absence of the wrapper and presence of the support rods constitute a perturbation that requires correction. We have prepared a detailed MCNPX model of the arrangement and computed the correction using the "FT8 CAP tally" correlated neutron capture tally. To establish confidence in our calculations we benchmarked the MCNPX simulations to a series of high precision measurements performed on the mock bundle but two fuel pins replaced by dummy Pb filled pins to change the fuel content and scattering contribution. Having validated the model we addressed how to construct improved corrections for the presence of Gd 2 0 3 burnable poison rods. Experimentally we used 8 poison pins to construct various configurations. These were also modeled to confirm MCNPX could accurately calculate the relative impact. The MCNPX model will be used to model a variety of enrichments and poison rod configurations covering the anticipated range and arrangement of modern fuel so that suitable correction factors could be estimated. Maintaining traceability to direct physical measurements is essential, but the benefits and flexibility of MCNPX modeling demonstrated in this work for deriving perturbation and poison rod configurations and by extension calibrations for different fuel types is clear.

We present a readout system for thermal neutron detection. Redesigning neutron detector electrical fields can speed time response without an increase in gamma sensitivity. Gamma distribution affects the neutron counting area as single events rather than pileup of very low amplitude pulses. Operation at negative bias can resolve humidity issue. New shaper design could improve dead time and capacitance tolerance over what is commercially available .

This paper describes the techniques that are available to calculate the performance of 3He alternative detectors using MCNPX. Calculations of the performance of safeguards detectors that use 3He have been successfully carried out for many years. In the case of coincidence or multiplicity counting, specific tallies have been implemented to calculate the Singles, Doubles and Triples counting rates. The implementation of the method was done in such a way that it equates every capture in some nuclide in the detection zone with the production of an electronic pulse from the detector. This is a very good approximation for 3He detectors and BF3 detectors. However it is not appropriate for detectors such as boron-lined proportional counters, in which the fraction of capture events leading to an electronic pulse above threshold is very dependent on the geometric arrangement, in particular the thickness and composition of the boron-containing layer. This paper gives calculations of the ideal pulse height distributions to be expected from different detector types and gives values for the probability, as a function of detector energy threshold, that a neutron capture reaction will cause an electronic pulse from the detector. This is termed the electronic efficiency. This electronic detection efficiency depends very little on the energy of the captured neutron, which in most practical cases are heavily weighted towards thermal energies. It does not depend on the position of the source neutron or moderation in the sample. For cases of interest to nuclear safeguards, measurement of uranium and plutonium in specially designed detectors, the spectrum of detected neutrons is fairly constant and thus the electronic detection efficiency becomes a detector constant. The paper discusses how the electronic detection efficiency needs to be included in the calculation of Singles, Doubles and Triples, and describes proposals to improve the tallying capability of MCNPX for such cases.

Dead time correction algorithms are being evaluated at Los Alamos National Laboratory (LANL) as part of a strategic R&D program to advance correlated neutron analysis. Such algorithms have an immediate impact on currently and soon to be deployed neutron detection systems. The Monte Carlo N-Particle eXtended radiation transport code (MCNPX) can be used to generate a pulse train file that can be post-processed by bespoke analysis software that includes the simulation of dead time effects. This simulation methodology is known as Monte Carlo pulse train generation. Further analysis of the simulated pulse trains with multiplicity shift register (MSR) algorithms can be used to study the dead time perturbed Singles, Doubles and Triples counting rates. MSR analysis is being included in the scope of work since many currently deployed counters cannot benefit from pulse trains acquired using list mode data acquisition, because they are constrained by hardware. In February 2006 the ESARDA non-destructive assay (NDA) working group published multiplicity benchmark (phases I and II) results in the ESARDA bulletin number 34. This benchmark compared the codes and analysis algorithms used for the simulation of neutron multiplicity counters. The basis for comparison was a series of neutron pulse trains generated by LANL using MCNPX. This paper will present the Monte Carlo pulse train methodology developed for this benchmark exercise and the simulation of dead time effects. The original benchmark simulations have been re-visited to explore the effects of dead time and extended in an attempt to validate dead time correction algorithms. The simulation work in this study accounted for the total dead time in the detection system, based on an extending (or paralyzable) model.

We present a readout system for thermal neutron detection. Redesigning neutron detector electrical fields can speed time response without an increase in gamma sensitivity. Gamma distribution affects the neutron counting area as single events rather than pileup of very low amplitude pulses. Operation at negative bias can resolve humidity issue. New shaper design could improve dead time and capacitance tolerance over what is commercially available .

Monte Carlo simulation is a powerful tool used to model neutron coincidence detectors for international safeguards. The simulation has typically sampled properties such as the fission neutron multiplicity, energy, and direction, from independent probability density functions. However, multiplicity counters detect event-based neutron correlations and thus more accurate fission event modeling is needed. To respond to this need, the Fission Reaction Event Yield Algorithm (FREYA) and the Cascading Gamma-ray Multiplicity with Fission (CGMF) models were added in the newest version of MCNP, MCNP6.2. The models simulate individual fission events conserving momentum, energy, and angular momentum such that correlated particles are emitted. The effects of the new models on simulations of safeguards neutron coincidence counters were studied and compared to standard MCNP simulations. The MCNPX-PoliMi model was also included in the comparison. The properties of fission neutrons from safeguards relevant isotopes were compared to literature references. Then a hypothetical simplified detector was modeled to isolate the effects of specific differences between models. Experimental measurements from previous work were modeled and agreements were compared. Finally, the probabilities of correlated events occurring in the experimental measurements were calculated with the different models. For example, the probability was calculated of detecting neutrons from both induced fission in uranium and spontaneous fission of Cf-252 in the same fission chain.

In neutron coincidence counting using the shift register autocorrelation technique, a predelay is inserted before the opening of the (R+A)-gate. Operationally the purpose of the predelay is to ensure that the (R+A)-and A-gates have matched effectiveness, otherwise a bias will result when the difference between the gates is used to calculate the accidentals corrected net reals coincidence rate. The necessity for the predelay was established experimentally in the early practical development and deployment of the coincidence counting method. The choice of predelay for a given detection system is usually made experimentally, but even today long standing traditional values (e.g., 4.5 µs)are often used. This, at least in part, reflects the fact that a deep understanding of why a finite predelay setting is needed and how to control the underlying influences has not been fully worked out. In this paper we attempt to gain some insight into the problem. One aspect we consider is the slowing down, thermalization, and diffusion of neutrons in the detector moderator. The other is the influence of deadtime and electronic transients. These may be classified as non-ideal detector behaviors because they are not included in the conventional model used to interpret measurement data. From improved understanding of the effect of deadtime and electronic transients on the predelay bias in neutron coincidence counting, the performance of both future and current coincidence counters may be improved.

The active Uranium Neutron Coincidence Collar-Light Water Reactor Fuel (UNCL) provides a means of non-destructively assaying the fissile linear density of fresh fuel assemblies containing low enriched uranium. Historically the generic calibration curves and correction factors were established experimentally on mock assemblies. This is time consuming, expensive and suffers from limitations owing to the limited inventory of pins and simplifications of the laboratory arrangements. At Los Alamos National Laboratory we operate a BWR UNCL-II in conjunction with a 6x6 array of 2.34wt% reference pins. The array is supported by grids held together by steel lifting rods, one at each corner. There is no wrapper. The rods are in interrogation zone. The absence of the wrapper and presence of the support rods constitute a perturbation that requires correction. We have prepared a detailed MCNPX model of the arrangement and computed the correction using the "FT8 CAP tally" correlated neutron capture tally. To establish confidence in our calculations we benchmarked the MCNPX simulations to a series of high precision measurements performed on the mock bundle but two fuel pins replaced by dummy Pb filled pins to change the fuel content and scattering contribution. Having validated the model we addressed how to construct improved corrections for the presence of Gd 2 0 3 burnable poison rods. Experimentally we used 8 poison pins to construct various configurations. These were also modeled to confirm MCNPX could accurately calculate the relative impact. The MCNPX model will be used to model a variety of enrichments and poison rod configurations covering the anticipated range and arrangement of modern fuel so that suitable correction factors could be estimated. Maintaining traceability to direct physical measurements is essential, but the benefits and flexibility of MCNPX modeling demonstrated in this work for deriving perturbation and poison rod configurations and by extension calibrations for different fuel types is clear.

To address the urgent need to find a viable 3 He replacement technology, Los Alamos National Laboratory has developed an integrated test program for performance evaluation of 3 He replacement technologies with focus on safeguards specific parameters. In addition, a dedicated experimental setup was built to support the experimental activities. Current activity focuses on evaluation of 10 B lined proportional counters. This paper presents an overview of the test program as well as the first results from the GE/Reuter-Stokes 10 B lined system.

The Multi-Grid detector technology has evolved from the proof-of-principle and char- acterisation stages. Here we report on the performance of the Multi-Grid detector, the MG.CNCS prototype, which has been installed and tested at the Cold Neutron Chopper Spectrometer, CNCS at SNS. This has allowed a side-by-side comparison to the performance of 3He detectors on an operational instrument. The demonstrator has an active area of 0.2 m2. It is specifically tailored to the specifications of CNCS. The detector was installed in June 2016 and has operated since then, collecting neutron scattering data in parallel to the He-3 detectors of CNCS. In this paper, we present a comprehensive analysis of this data, in particular on instrument energy resolution, rate capability, background and relative efficiency. Stability, gamma-ray and fast neutron sensitivity have also been investigated. The effect of scattering in the detector components has been measured and provides input to comparison for Monte Carlo simulations. All data is presented in comparison to that measured by the 3He detectors simultaneously, showing that all features recorded by one detector are also recorded by the other. The energy resolution matches closely. We find that the Multi-Grid is able to match the data collected by 3He, and see an indication of a considerable advantage in the count rate capability. Based on these results, we are confident that the Multi-Grid detector will be capable of producing high quality scientific data on chopper spectrometers utilising the unprecedented neutron flux of the ESS.

The effects of thunderstorms (TS) on the electromagnetic and muon components of the cosmic ray secondary flux were studied during severe storms obtained in 2004, analyzing the variations of the counting rates shown in the upper and lower scintillators of the muon telescope installed in Mexico City and considering the data of storms report from the international airport of Mexico City.

We studied the effect of thunderstorms (TS) in the intensity variations of the electromagnetic (EM) and muon components of the Cosmic Rays during the year 2004. The results show variations of short period whose main periodicities are arranged in a distribution where the most important are the shortest. These may be associated to the electric fields of the TS. Significant long period variations were found too, these could be due to other processes linked to rainstorms. No systematic effect on the power of variations due to TS was found.

A b s tra c t: Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like W IMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

Double pulsing in neutron coincidence counters is the result of a pulse processing chain-3 He proportional counter timing incompatibility known to nondestructive assay system designers. It is not currently widely acknowledged, or accounted for, in the user community. However, it is gaining attention as list mode data acquisition and analysis becomes more commonly used for system diagnostics, revealing features that have been overlooked by historic timing gate selection using traditional shift register data acquisition methods. Double pulsing increases the apparent number of measured neutron events from a source. Therefore, it may contribute to a falsely increased count rate if present at the operational high voltage used when assaying samples, even with set predelays. The authors have previously studied the effects of double pulsing, using list mode data acquisition and analysis on neutron pulse trains in three common neutron coincidence counting systems used in routine measurements for international safeguards: a Canberra Industries JCC-71 Neutron Coincidence Collar, a variant on the Canberra Industries JCC-51 Active Well Neutron Coincidence Counter (the Large Volume Active Well Neutron Coincidence Counter), and an AnTech Inc. N2071 Neutron Coincidence Collar. This non-ideal behavior was isolated to the Amptek A111 Charge Sensitive Preamplifier & Discriminator chip used in both the Canberra Industries and Antech systems. The double pulsing fraction was calculated in post-analysis for various high voltage settings in these A111-based systems, assuming no predelay settings. In this work, the authors expand upon this identification and analysis to make it more translatable between list mode data acquisition and analysis and shift register-based analysis. By investigating the double pulsing fractions in a JCC-71 Uranium Neutron Collar as a function of predelay settings, as well as describing and performing alternative tests and analyses to diagnose and quantify the double pulsing using shift register logic, this work hopes to complete the picture of double pulsing identification and analysis. ✩ This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Neutron coincidence counting is a well-established technique used for the nondestructive quantification of special nuclear material during international safeguards inspections. The neutron counters are commonly designed with an annular body, centered about an inner well or cavity into which a measurement item is placed, and the moderating annulus is populated with 3 He tubes connected to a varying number of preamplifiers. The Canberra Industries JAB-01 preamplifier/amplifier/discriminator board is employed within the company's neutron coincidence counters, built for use by the International Atomic Energy Agency. Non-ideal behavior of these boards was identified during a detector characterization, using list mode data acquisition, of a Canberra Industries JCC-71 Neutron Coincidence Collar implementing four JAB-01 boards. List mode data acquisition and analysis reveals features that have commonly been overlooked by historic timing gate selection while using shift register data acquisition methods, which are routinely adopted in international safeguards. It has been shown that double pulsing effects are not fully captured within the predelay setting; therefore, they may influence the response of the system within the standard operating regime. We set out to identify and correct for double pulsing in our post analysis of neutron pulse trains, while isolating this behavior to the relevant system. To understand and potentially address these concerns, the responses of two different JAB-01 board systems-the JCC-71 Neutron Coincidence Collar and a modified JCC-51 Active Well Neutron Coincidence Counter-are compared with the responses of an AnTech Inc. N2071 Neutron Coincidence Collar that also uses an amplifier built on the Amptek A111 Charge Sensitive Preamplifier & Discriminator chip, and a JCC-71 that employs custom preamplifiers designed at Oak Ridge National Laboratory. Contents ✩ Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Most radiation portal monitors (RPMs) use the max count rate (MCR) or the single interval test (SIT) methods for detecting the illicit transport of radioactive material. Point source detection using matched filtering for discriminating naturally occurring radioactive materials (NORM) from radioactive materials of concern was proposed in the literature for border crossing radiation portal monitoring. We show in this work that it is possible to increase the sensitivity of a radiation portal monitor by fusing the data produced by SIT with that produced by an improved version of the matched filtering technique.

Fast spectrum neutron-induced fission cross-section data for transuranic isotopes are of special demand from the nuclear data community. In particular highly accurate data are needed for the new generation IV nuclear applications. The aim is to obtain precise neutron-induced fission cross sections for 240 Pu and 242 Pu. To do so, accurate data on spontaneous fission half-lives must be available. Also, minimizing uncertainties in the detector efficiency is a key point. We studied both isotopes by means of a twin Frisch-grid ionization chamber with the goal of improving the present data on the neutron-induced fission cross section. For the two plutonium isotopes the high α-particle decay rates pose a particular problem to experiments due to piling-up events in the counting gas. Argon methane and methane were employed as counting gases, the latter showed considerable improvement in signal generation due to its higher drift velocity. The detection efficiency for both samples was determined, and improved spontaneous fission half-lives were obtained with very low statistical uncertainty (0.

This document is a safety analysis of a novel neutron detection technology developed by Sandia National Laboratories. This technology is comprised of devices with tiny channels containing high pressure 3 He. These devices are further integrated into large scale neutron sensors. Modeling and preliminary device testing indicates that the time required to detect the

Radioactive material is widely used in energy, medicine, and industry [1]. But if it gets into the wrong hands it can cause serious harm. Illicit trafficking or smuggling of nuclear or other radioactive materials including special nuclear material (SNM, plutonium, and certain types of uranium) is an existing problem all over the world. A compact radiation imaging system capable of detecting, localizing, and characterizing SNM would be helpful, in which the detection of SNM that emits neutrons and gamma rays is implemented in one device. Hence, both gamma spectroscopy and neutron detection can be influenced by the presence of each other’s sources. Neutrons interact with environmental materials and produce gamma or X-ray by a reaction of (n, n'), which affects the main spectrum of gamma detector. The effects of neutrons on a traditional scintillator, such as NaI(Tl), are also described in [2], where new energy lines are added to gamma-ray spectrum due to the neutron interacts with...

In the frame of the European Commission funded integrated project CHANDA (solving CHAllenges in Nuclear DAta) the importance of nuclear target preparation for the accurateness and reliability of experimental nuclear data is set in a dedicated work package (WP3). The global aim of WP3 is the development of a network for nuclear target preparation and characterization, enabling to coordinate the target production corresponding to the experimental requirements. Therefore, a set of tasks within the work package needs to be followed. Primarily, an inventory of target related facilities and radioisotope providers was created. In the next step a priority list of target requests was made in agreement with the target user considering the technical specification, the scheduled experiments and the availability of the target laboratories. A set of target requests has been assigned to the Target Preparation laboratory of the European Commission-Joint Research Centre-Directorate G (EC-JRC.G.2) in Geel, Belgium. This contribution gives an overview of the nuclear targets that are produced within the CHANDA project. The equipment and techniques available for the preparation and characterization of uranium, plutonium and neptunium layers with an areal density ranging from 60 to 205 µg cm −2 will be emphasized.

The availability of 3 He in recent years is becoming restricted with an order of magnitude price increase for this material. Alternatives to the use of 3 He for the detection of thermal neutrons are under investigation. One of the most challenging applications for 3 He alternatives is in neutron multiplicity counters that provide rapid assay of samples which contain an unknown amount of plutonium in a potentially unknown configuration. With appropriate detector design that has minimal gamma-ray sensitivity and a high detection efficiency even for triple coincidence events, the neutron single, double, and triple coincidence events can be used to extract information of three unknown parameters such as the 240 Pu-effective mass, the sample self-multiplication, and the (α,n) rate. This project is aimed at determining if commercially available 3 He alternatives can satisfy this challenging application. Using MCNP modeling the best alternative is based upon LiF/ZnS neutron-scintillator sheets and wavelength shifting plastic for light pipes. A four-panel demonstrator module has been constructed, tested, and compared with detailed modeling results. However, to attain that high-level of performance two primary design challenges must be address. They include building a fast electronics system and robust neutron/gamma-ray discrimination based on pulse shape analysis at high rates. A review of the current effort and the most recent findings will be presented.

A b s tra c t: Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like W IMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

Multiple types of high quality neutron detectors are proposed for the first phase of the China Spallation Neutron Source (CSNS), which will be commissioned in 2018. Considering the shortage of 3 He supply, a detector module composed of 49 boron-coated straws (BCS) was developed by Proportional Technologies Inc. (PTI). Each straw has a length of 1000 mm and a diameter of 7.5 mm. Seven straws are tightly packed in a tube, and seven tubes are organized in a row to form a detector module. The charge division method is used for longitudinal positioning. A specific readout system was utilized to output the signal and simultaneously encode each straw. The performance of this detector module was studied using a moderated 252 Cf source at the Institute of High Energy Physics (IHEP). The signal amplitude spectrum indicates its n-gamma discrimination capability. Despite the complex readout method, a longitudinal resolution of 6.1±0.5 mm was obtained. The three-dimensional positioning ability qualifies this BCS detector module as a promising neutron scattering spectrometer detector.