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A novel pulsed neutron imaging technique based on the finite element method is used to reconstruct the residual strain within a polycrystalline material from Bragg edge strain images. This technique offers the possibility of a nondestructive analysis of strain fields with a high spatial resolution. The finite element approach used to reconstruct the strain uses the least square method constrained by the conditions of equilibrium. This inclusion of equilibrium makes the problem well-posed. The procedure is developed and verified by validating for a cantilevered beam problem. It is subsequently demonstrated by reconstructing the strain from experimental data for a ring-and-plug sample, measured at the spallation neutron source RADEN at J-PARC in Japan. The reconstruction is validated by comparison with conventional constant wavelength strain measurements on the KOWARI diffractometer at ANSTO in Australia. It is also shown that the addition of a Tikhonov regularisation scheme further improves the reconstruction. [ABSTRACT FROM AUTHOR]

To solve the problem of offshore oilfield development, based on the newly introduced pulsed neutron oxygen activation logging instrument, the application research of test design and interpretation method was carried out and applied to actual production. The structure, technical indicators and logging principles of pulsed neutron oxygen activation logging tools were introduced. The test design under different well conditions was studied, including general positive and negative injection, oil sleeve injection, single oil pipe configuration and multitubing configuration. A large amount of field test data was collected and analysed technically. A set of effective interpretation models was proposed. The corresponding interpretation software was developed. A set of test design methods and operating specifications for different well conditions were developed. Based on the conventional interpretation method, the peak selection, the double-tuber peak identification and the carbon dioxide flooding interpretation method were added. The results show that the test design and interpretation methods were applied well through a large number of field tests and production applications. Therefore, pulsed neutron oxygen activated injection profile logging technology is successfully applied in offshore oil fields. [ABSTRACT FROM AUTHOR]

A detector based on the plastic scintillator film with large-area photonic crystals has been designed and demonstrated for measuring pulsed neutron flux. Compared with the reference detector, the neutron sensitivity and the gamma sensitivity of the detector using the scintillator film with photonic crystals were enhanced by more than 20%, which is attributed to the improved light extraction efficiency and the controllable angular profile of scintillation light by the photonic crystal. The application of the photonic crystals is beneficial to the improvement of the signal-to-noise ratio of the detector in the calibration experiment, thus expanding the lower limit of the measurable neutron flux without sacrificing the ratio of the neutron sensitivity to the gamma sensitivity. This research indicates that photonic crystals play an important role in the fields where scintillation photons need to be extracted and collected as many as possible. [ABSTRACT FROM AUTHOR]

Abstract The High Resolution Fourier Diffractometer (HRFD) is a neutron time-of-flight spectrometer with a fast Fourier chopper and a correlation mode of data acquisition designed to study atomic and magnetic structures of crystalline materials with high resolution in reciprocal space. The HRFD was constructed in the early 1990s by a collaboration of JINR (Dubna), PNPI (Gatchina) and VTT (Espoo) and began operating routinely in 1994 at the IBR-2 pulsed reactor in Dubna. If correlation analysis is used, the HRFD Δ d / d resolution is determined by the maximum rotational speed of the Fourier chopper. For V max = 6000 rpm, "high-resolution" patterns are measured by backscattering detectors with Δ d / d ≈ 0.0015 despite a very short flight path (L ≈ 20 m) between chopper and sample. Switching to a regular TOF-mode (without Fourier chopper) makes HRFD one of the world's best high-intensity diffractometers, capable of measuring diffraction patterns in the range of ∼1 min and less. In this paper, the experience of using HRFD at IBR-2 is considered and a possible solution for some technical and methodical problems of Fourier diffractometry at a long-pulse neutron source recognized during its operation is discussed. New possibilities appearing after the recent substantial HRFD upgrade and further perspectives on the method are also presented. [ABSTRACT FROM AUTHOR]

Abstract Pulsed neutrons generated in a plasma focus device are used for the thermal neutron activation analysis (TNAA) of selected three elements having widely different half-lives varying from a few seconds to a few days [Dysprosium (Dy), Manganese (Mn) and Gold (Au)]. Neutron pulse having strength of (1.2 ± 0.3) × 10 9 neutrons/pulse with a pulse width of 46 ± 5 ns is produced by "MEPF-12" device operated at a filling gas (deuterium + 0.5% krypton) pressure of 3 mbar. The fast 2.45 MeV D–D neutrons are thermalized before irradiating the sample. The decay gammas from the radioisotopes 165mDy (T 1 / 2 = 1.26 min.), 56Mn (T 1 / 2 = 2.58 hrs.), and 198Au (T 1 / 2 = 2.69 days) produced via reactions, 164Dy(n , γ)165mDy, 55Mn(n , γ) 56Mn, and 197Au(n , γ) 198Au respectively are counted off-line in a lead shielded well type 76 × 76 mm 2 NaI(Tl) detector coupled to a calibrated 2048 channel analyzer. The values of half-lives evaluated from the measured decay gammas, 1.43 ± 0.3 min. , 2.56 ± 0.5 hrs. and 2.84 ± 0.6 days respectively for the radioisotopes of Dy, Mn and Au, are seen to be close to the values reported in literature. Highlights • Indigenous development and optimization of a plasma focus device "MEPF-12". • Observed maximum neutron yield of (1.2 ± 0.3) × 10 9 n/pulse into 4 π Sr using "MEPF-12". • Production of radioisotopes using pulse neutrons and their half-lives measurement. • Radioisotopes (165mDy, 56Mn, 198Au) having wide range of half-lives are produced. • Measured values of half-lives closely match with the reported literature values. [ABSTRACT FROM AUTHOR]

Abstract Pendellösung interferometry is one of the technique for accurate determination of the structure factors of crystals. Observation method of Pendellösung fringes by using pulsed cold neutrons and the time-of-flight analysis were established. We measured the nuclear scattering length of silicon by the Pendellösung fringes with pulsed neutrons as (4. 125 ± 0. 003 (stat.) ± 0. 028 (syst.)). This indicates the applicability of Pendellösung interferometry at high-intensity pulsed neutron facilities for various precision measurements. [ABSTRACT FROM AUTHOR]

Abstract Tight gas reservoirs have been one of the most important field of gas exploration and development, and the dynamic monitoring of gas saturation is of great significance to the adjustment of oilfield development scheme. Pulsed neutron logging technology plays an important role in the evaluation of gas saturation in cased holes. The low porosity of tight gas reservoir presents a new challenge to the application of pulsed neutron logging technology. In order to further investigate the measurement information of pulsed neutron logs to improve the performance of gas saturation measurement, the Monte Carlo numerical simulation method is used to study the gas saturation responses of different parameters obtained by the pulsed neutron-gamma logging instrument with an extra gamma-ray detector added. The results show that the capture count ratio measured by the instrument is mainly affected by changes in the hydrogen index of the formation. The ratio of pure inelastic gamma rays is more sensitive to the variation of formation density. When the porosity of the reservoir is fixed, the gas layer has a low hydrogen index and low density relative to the water layer. By combining the response characteristics of the two ratios, a new gas saturation evaluation parameter (GSEP) is proposed to evaluate gas saturation. The new method displays a higher gas sensitivity compared with the conventional ratio method and macroscopic capture cross section (Sigma) method. In addition, the response characteristics of GSEP in different well logging environments are also studied. It displays GSEP is less affected by the variation of the formation water salinity and clay contents compared with the Sigma method. At last, field examples are presented to validate the effectiveness of the proposed method. Highlights • A method with pulsed neutron logs to evaluate gas saturation is proposed. • It has higher gas sensitivity compared with conventional ratio and Sigma method. • It is less affected by the variation of clay content and formation water salinity. • Field examples validated the performance of the method in evaluating gas saturation. [ABSTRACT FROM AUTHOR]

Pulsed-neutron well logs (PNLs) were acquired to monitor CO 2 storage associated with enhanced oil recovery. This work quantifies the precision of repeat PNLs using data from four wells and 15 repeat PNLs. Root-mean-square (RMS) precision for the repeat PNLs was less than 3%, indicating good agreement between the baseline and repeat PNLs. Evaluations of scaled relative difference (Scaled-D) showed variation in precision among individual wells and formations. Analysis of false-positive rates (FPRs) across the entire data set showed that a Scaled-D threshold in sandstone formations of approximately ±8% resulted in a 1% FPR. These Scaled-D precision thresholds were used to estimate the value of CO 2 saturation able to be confidently distinguished from baseline. The detection limit for CO 2 is lowest for high-porosity formations filled with saline water and is highest for low-porosity formations filled with fresh water. Thus, detection of vertical out-of-zone CO 2 migration using repeat PNLs is a function of instrument precision, petrophysical properties, and hydrology, all of which must be taken into account as part of the monitoring program. The results of this work provide insight into how PNLs may be included within monitoring plans to detect vertical out-of-zone CO 2 migration along a wellbore or instances of wellbore failure and provide a quantitative basis for establishing detection limits of repeat PNLs to distinguish change from baseline conditions. [ABSTRACT FROM AUTHOR]

In this work, the implicit Euler-Maruyama method is used to solve the stochastic point kinetics equations for different forms of reactivity: constant, linear and sinusoidal. A covariance matrix is proposed considering the one-speed diffusion theory of a nuclear reactor subject to the initial condition applying to the pulsed neutron methods. The results obtained with this method are more efficient in the calculation of neutron densities and delayed neutron precursors. It was possible to reduce the standard deviation with a very good precision for the expected values. [ABSTRACT FROM AUTHOR]

The production of transuranium nuclides in pulsed neutron fluxes from thermonuclear explosions has been studied within the kinetic model of the astrophysical r-process taking into account the time dependence of external parameters and processes accompanying the beta decay of neutron-rich nuclei. Neutron fluxes depending on the time in the range of ~10-6 s have been simulated within the developed adiabatic binary model. The probabilities of beta-delayed processes have been calculated within the microscopic theory of finite Fermi systems. The yields of transuranium nuclides Y(A) have been calculated for three experimental thermonuclear explosions Mike (YM), Par (YP), and Barbel (YB) (United States). The rms deviations of the calculations from experimental data are 91, 33, and 29% for YM, YP, and YB, respectively. These deviations are much smaller than those for other known calculations and are comparable with the proposed exponential approximation ensuring rms deviations of 56, 86.8, and 60.2% for YM, YP, and YB, respectively. The even-odd anomaly in the observed yields of heavy nuclei is explained by the dominant effect of processes accompanying the beta decay of heavy neutron-rich isotopes. [ABSTRACT FROM AUTHOR]

Neutron imaging is a highly successful experimental technique ever since adequate neutron sources were available. In general, neutron imaging is performed with a wide wavelength spectrum for best flux conditions in transmission geometry. Neutrons provide outstanding features in the penetration of many structural materials, which often makes them more suited for bulk sample studies than other forms of radiation, often in particular as they are also highly sensitive to some light elements, especially Hydrogen. In contrast to neutron scattering applications, imaging resolves macroscopic structures, nowadays down to, in the best case, below 10 micrometre, directly in real space. However, since more than a decade there is a growing number of techniques and applications in neutron imaging that – supported by powerful neutron sources – are taking advantage of wavelength resolved measurements. In this review we summarize and discuss this outstanding development and how wavelength resolved transmission neutron imaging is successfully exploiting diffraction mechanisms to access crystal structure information in the Angstrom regime, which conventionally is probed in reciprocal space by diffraction techniques. In particular the combination of information gained in real space and on crystallographic length scales makes this neutron imaging technique a valuable tool for a wide range of new applications, while it also qualifies neutron imaging to fully profit from the new generation of powerful pulsed neutron sources. [ABSTRACT FROM AUTHOR]

Particle detectors operated in pulse mode are subjected to the dead-time effect. When the average of the detector counts is constant over time, correcting for the dead-time effect is simple and can be accomplished by analytical formulas. However, when the average of the detector counts changes over time it is more difficult to take into account the dead-time effect. When a subcritical nuclear assembly is driven by a pulsed neutron source, simple analytical formulas cannot be applied to the measured detector counts to correct for the dead-time effect because of the sharp change of the detector counts over time. This work addresses this issue by using the backward extrapolation method. The latter can be applied not only to a continuous (e.g. californium) external neutron source but also to a pulsed external neutron source (e.g. by a particle accelerator) driving a subcritical nuclear assembly. The backward extrapolation method allows to obtain from the measured detector counts both the dead-time value and the real detector counts. [ABSTRACT FROM AUTHOR]

A correlation measuring tool for an endogenous pulsed neutron source experiment is developed in this work. Paroxysmal pulses generated by a bursts of neutron chains are detected by a 10-kbit embedded shift register with a time resolution of 100 ns. The system is implemented on a single reprogrammable device making it a compact, cost-effective instrument, easily adaptable for any case study. The system was verified experimentally in the Esfahan heavy-water zero power reactor (EHWZPR). The results obtained by the measuring tool are validated by the Feynman-a experiment, and a good agreement is seen within the boundaries of statistical uncertainties. The theory of the methods is briefly initiated in the text. Also, the system structure is described, the experimental results and their uncertainties are discussed, and neutron statistics in EHWZPR is examined experimentally. [ABSTRACT FROM AUTHOR]

Since the mineral compositions can be obtained from the concentrations of the major elements in the formation, the accurate determination of the elemental concentration is very critical to the reservoir evaluation. However, it is always a challenge to accurately obtain the concentrations of major elements in the complex lithology or unconventional reservoirs (such as shale gas reservoirs) due to the complexity of lithology and the limitation of the current data processing method. The widely used weighted least squares (WLS) method, which is applied in the quantitative energy spectral processing for the pulsed neutron geochemical logging, suffers the absence of constraint condition of the solution variables and thus it is hardly to determine the elemental concentrations in a high precision and accuracy. In this paper, we introduced an active-set method (ASM) to improve the inversion accuracy after transforming the inversion problem into a quadratic programming problem with constraints. The ASM is capable of constraining the solution variables within reasonable boundary limits, and thus the high-precision elemental yields can be determined by the iterative processing. The conversion of elemental yields into elemental concentrations is accomplished via an oxide closure model and a pseudo-capture spectrum method. To verify the applicability, we numerically obtained the capture and inelastic spectra by the Monte Carlo simulation from three formation models with different porosities: simple formation, complex lithology formation, and unconventional formation models. Then the ASM and WLS methods are used to process both the capture and inelastic spectra in different models. The results comparison between the two methods shows that the elemental concentrations inverted by using the ASM are more accurate than those determined by using the WLS method. Finally, a field logging data set is processed by the ASM, and the results indicate the feasibility of the inversion result from the ASM from the pulsed neutron geochemical logging. [ABSTRACT FROM AUTHOR]

Prompt-gamma activation analysis (PGAA) measurements were carried out at the ISIS Spallation Neutron Source on two sets of functional commercial stainless steel orthodontic archwires, aiming at providing insights into the elemental and isotopic composition differences of two nominally equivalent archwires. The results were compared to those obtained from parallel cold neutron PGAA measurements on the same samples at the Budapest Neutron Centre in order to test the current status of PGAA at a pulsed neutron source and eventually to inform improvement in set-up and acquisition methods. In addition, time-resolved PGAA (T-PGAA) that combines PGAA and neutron time-of-flight methods was applied to the present set of samples, allowing the measurement of the neutron energy dependence of the PGAA spectra. The advantages of this technique were demonstrated to be that through incident neutron energy selection, spanning 0.07–67.94 eV, enhancement or decrease of specific gamma lines associated with isotopes of interest could be achieved. These were shown to reduce peak interference and to increase the signal-to-background ratio for certain species in order to facilitate accurate elemental identification. Suggestions for potential performance improvement for this evolving technique are proposed. [ABSTRACT FROM AUTHOR]

Accelerator-driven system experiments with spallation neutrons (100 MeV protons and Pb-Bi target) are carried out in the 235 U-fueled and Pb-Bi-zoned core at the Kyoto University Critical Assembly, under a subcritical state ranging between 1160 and 11,556 pcm. In these experiments, measurement of the prompt neutron decay constant and the subcriticality is conducted by the pulsed neutron source (PNS) method and the Feynman-α method with the use of optical fiber detectors. The experimental results successfully validate the prompt neutron decay constant and the subcriticality through the deduction of kinetic parameters by both the PNS and the α-fitting methods. The detector position dependency, neutron spectrum and subcriticality measurement methods still remain, however, in these experiments. For onward studies, the experimental benchmarks obtained from these experiments are expected to be involved in the numerical verification of subcriticality on-line monitoring, in the analysis of subcriticality uncertainty and in the deterministic approach to kinetic parameters. [ABSTRACT FROM AUTHOR]

A multistage generator of high-voltage pulses with a scroll geometry of spark switches, which is produced according to the Marx scheme, is presented. The device is designed for a small pulsed neutron source and makes it possible to obtain accelerating-voltage pulses with amplitudes of up to 450 kV at a stored energy of up to 50 J and a load current of up to 1.5 kA. [ABSTRACT FROM AUTHOR]

The results of a series of ground tests with a prototype of an active gamma-ray spectrometer based on a new generation of scintillation crystal (CeBr 3 ) are presented together with a consideration to its applicability to future Venus landing missions. We evaluated the instrument's capability to distinguish the subsurface elemental composition of primary rock forming elements such as O, Na, Mg, Al, Si, K and Fe. Our study uses heritage from previous ground and field tests and applies to the analysis of gamma lines from activation reaction products generated by a pulsed neutron generator. We have estimated that the expected accuracies achieved in this approach could be as high as 1–10% for the particular chemical element being studied. [ABSTRACT FROM AUTHOR]

The results of experimental studies of discharge generation regimes in ion sources of gas-filled neutron tubes are presented. The objects of investigation are neutron tubes developed at the Dukhov All-Russia Research Institute of Automatics (VNIIA) for portable pulsed neutron generators. The experiments showed that the conditions for igniting a discharge depend on the pulse-periodic powering system of the ion source and the conditions for heating the gas generator of the neutron tubes. The obtained data show that the efficiency and stability of gas-filled neutron tubes can be increased by optimizing the operating regimes of the powering systems and creating the appropriate ignition conditions for a discharge. [ABSTRACT FROM AUTHOR]

Pulsed neutron diffraction and synchrotron X-ray diffraction measurements were performed on Se 100- x Te x bulk glasses with x =10, 20, 30 and 40. The coordination numbers obtained from the diffraction results demonstrate that Se and Te atoms are twofold coordinated and the glass structure is formed by the chain network. The three-dimensional structure model for Se 60 Te 40 glass obtained by using reverse Monte Carlo modelling shows that the alternating arrangements of Se and Te atoms compose the major part of the chain clusters but several other fragments such as Se n chains and Te-Te dimers are also present in large numbers. The chain clusters have geometrically disordered forms and the interchain atomic order is different from those in the crystal structures of trigonal Se and trigonal Te. [ABSTRACT FROM AUTHOR]

We successfully derived the time-dependent flux of pulsed neutrons using a superconducting Nb-based current-biased kinetic inductance detector (CB-KID) with a 10 B conversion layer at Japan Proton Accelerator Research Complex. Our CB-KID is a meander line made of a 40-nm-thick Nb thin film with 1 − μ m line width, which is covered with a 150-nm-thick 10 B conversion layer. The detector works at a temperature below 4 K. The evaluated detection efficiency of the CB-KID in this experiment is 0.23 % at the neutron energy of 25.4 meV. The time-dependent flux spectra of pulsed neutrons thus obtained are in good agreement with the results obtained by the Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Background Neutron sources are increasingly employed in a wide range of research fields. For some specific purposes an alternative to existing large-scale neutron scattering facilities, can be offered by the new generation of portable neutron devices. Scope of review This review reports an overview for such recently available neutron generators mainly addressed to biophysics applications with specific reference to portable non-stationary neutron generators applied in Neutron Activation Analysis (NAA). Major conclusions The review reports a description of a typical portable neutron generator set-up addressed to biophysics applications. General significance New generation portable neutron devices, for some specific applications, can constitute an alternative to existing large-scale neutron scattering facilities. Deuterium-Deuterium pulsed neutron sources able to generate 2.5 MeV neutrons, with a neutron yield of 1.0 × 10 6 n/s, a pulse rate of 250 Hz to 20 kHz and a duty factor varying from 5% to 100%, when combined with solid-state photon detectors, show that this kind of compact devices allow rapid and user-friendly elemental analysis. "This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo". [ABSTRACT FROM AUTHOR]

The dense plasma focus (DPF) has long been considered a compact source for pulsed neutrons and has traditionally been optimized for the total neutron yield. In this paper, we describe the efforts to optimize the DPF for short-pulse applications by introducing a reentrant cathode at the end of the coaxial plasma gun. The resulting neutron pulse widths are reduced by an average of 21±9% from the traditional long-drift DPF design. Pulse widths and yields achieved from deuterium-tritium fusion at 2 MA are 61.8±30:7 ns FWHM and 1.8460:49 ± 1012 neutrons per shot. Simulations were conducted concurrently to elucidate the DPF operation and confirm the role of the reentrant cathode. A hybrid fluid-kinetic particle-in-cell modeling capability demonstrates correct sheath velocities, plasma instabilities, and fusion yield rates. Consistent with previous findings that the DPF is dominated by beam-target fusion from superthermal ions, we estimate that the thermonuclear contribution is at the 1% level. [ABSTRACT FROM AUTHOR]

China Spallation Neutron Source (CSNS) is the first high-performance pulsed neutron source in China, which will meet the increasing fundamental research and technique applications demands domestically and overseas. A new distributed data processing and analysis environment has been developed, which has generic functionalities for neutron scattering experiments. The environment consists of three parts, an object-oriented data processing framework adopting a data centered architecture, a communication and data caching system based on the C/S paradigm, and data analysis and visualization software providing the 2D/3D experimental data display. This environment will be widely applied in CSNS for live data processing. [ABSTRACT FROM AUTHOR]

We propose a basic formula and demonstration for a high-resolution quasi-elastic neutron scattering (QENS) by combining the time-of-flight (TOF) method with Modulation of Intensity by Zero Effort (MIEZE) type neutron spin echo spectroscopy. The MIEZE technique has the potential to develop a unique approach to study on slow dynamics of condensed matter; however, the energy resolution is limited owing to the hypersensitivity of the MIEZE signal contrast to the echo condition, which is strongly affected by the alignment of the instruments and the sample. The narrow allowance of the optimal alignment is a major obstacle to the wide use of this technique. Combining the TOF method with MIEZE (TOF-MIEZE), the hypersensitivity of MIEZE signals is significantly alleviated with a short pulsed beam. This robustness is very useful to optimize experimental alignments and enables accurate measurements of QENS. The experimental results demonstrate the characteristic of the TOF-MIEZE technique and are well described by the formula presented in this study. [ABSTRACT FROM AUTHOR]

The results of characterization experiments carried out on a newly developed dense plasma focus device based intense pulsed neutron source with efficient and compact pulsed power system are reported. Its high current sealed pseudospark switch based low inductance capacitor bank with maximum stored energy of ~10 kJ is segregated into four modules of ~2.5 kJ each and it cumulatively delivers peak current in the range of 400 kA-600 kA (corresponding to charging voltage range of 14 kV-18 kV) in a quarter time period of ~2 μs. The neutron yield performance of this device has been optimized by discretely varying deuterium filling gas pressure in the range of 6 mbar-11 mbar at ~17 kV/550 kA discharge. At ~7 kJ/8.5 mbar operation, the average neutron yield has been measured to be in the order of ~4 × 109 neutrons/pulse which is the highest ever reported neutron yield from a plasma focus device with the same stored energy. The average forward to radial anisotropy in neutron yield is found to be ~2. The entire system is contained on a moveable trolley having dimensions 1.5 m × 1 m × 0.7 m and its operation and control (up to the distance of 25 m) are facilitated through optically isolated handheld remote console. The overall compactness of this system provides minimum proximity to small as well as large samples for irradiation. The major intended application objective of this high neutron yield dense plasma focus device development is to explore the feasibility of active neutron interrogation experiments by utilization of intense pulsed neutron sources. [ABSTRACT FROM AUTHOR]

Peking University Neutron Imaging Facility (PKUNIFTY) works on an accelerator–based neutron source with a repetition period of 10 ms and pulse duration of 0.4 ms, which has a rather low Cd ratio. To improve the effective Cd ratio and thus improve the detection capability of the facility, energy-filtering neutron imaging was realized with the intensified CCD camera and time-of-flight (TOF) method. Time structure of the pulsed neutron source was firstly simulated with Geant4, and the simulation result was evaluated with experiment. Both simulation and experiment results indicated that fast neutrons and epithermal neutrons were concentrated in the first 0.8 ms of each pulse period; meanwhile in the period of 0.8–2.0 ms only thermal neutrons existed. Based on this result, neutron images with and without energy filtering were acquired respectively, and it showed that detection capability of PKUNIFTY was improved with setting the exposure interval as 0.8–2.0 ms, especially for materials with strong moderating capability. [ABSTRACT FROM AUTHOR]

Crystalline mercury sulfide exists in two drastically different polymorphic forms in different domains of the P,T-diagram: red chain-like insulator α-HgS, stable below 344 °C, and black tetrahedral narrow-band semiconductor β-HgS, stable at higher temperatures. Using pulsed neutron and high-energy X-ray diffraction, we show that these two mercury bonding patterns are present simultaneously in mercury thioarsenate glasses HgS-As2S3. The population and interconnectivity of chain-like and tetrahedral dimorphous forms determine both the structural features and fundamental glass properties (thermal, electronic, etc.). DFT simulations of mercury species and RMC modeling of high-resolution diffraction data provide additional details on local Hg environment and connectivity implying the (HgS2/2)m oligomeric chains (1 ≤ m ≤ 6) are acting as a network former while the HgS4/4-related mixed agglomerated units behave as a modifier. [ABSTRACT FROM AUTHOR]

This paper considers the effect of pair production on the precision of D-T controllable neutron source density logging. Firstly, the principle of the traditional density logging and pulsed neutron density logging are analyzed and then gamma ray cross sections as a function of energy for various minerals are compared. In addition, the advantageous areas of Compton scattering and pair production interactions on high-energy gamma ray pulse height spectrum and the errors of a controllable source density measurement are studied using a Monte Carlo simulation method. The results indicate that density logging mainly utilizes the Compton scattering of gamma rays, while the attenuation of neutron induced gamma rays and the precision of neutron gamma density measurements are affected by pair production interactions, particularly in the gamma rays with energy higher than 2 MeV. By selecting 0.2−2 MeV energy range and performing proper lithology correction, the effect of pair production can be eliminated effectively and the density measurement error can be rendered close to the precision of chemical source density logging. [ABSTRACT FROM AUTHOR]

Hydrogen site positions and occupancy in the crystal structure of dense hydrous magnesium silicate (DHMS) phase E were determined for the first time by pulsed neutron powder diffraction. A fully deuterated pure phase E powder sample, which had space group $$R\overline{3} m$$ and lattice parameters of a = 2.97065(8) Å and c = 13.9033(4) Å, was synthesized at 15 GPa and 1100 °C. Through quantitative evaluation of refined structure parameters obtained with sufficient spatial resolution and very high signal-to-background ratio, we conclude that the O-D dipoles in the refined phase E structure are tilted by 24° from the direction normal to the layers of edge-shared MgO octahedra (octahedral layers). The tilted dipole structure of phase E is in remarkable contrast to that of brucite, Mg(OH), which has dipoles exactly normal to the octahedral layer. This contrast exists because the O-Si-O bonding unique in the phase E structure connects two adjacent octahedral layers and thereby reduces the interlayer O···O distance. This shrinkage of the interlayer distance induces the tilting of the O-D dipole and also generates unique O-D···O hydrogen bonding connecting all the layers in the phase E structure. [ABSTRACT FROM AUTHOR]

The development of elemental analysis at the ISIS pulsed neutron and muon facility, STFC Rutherford Appleton Laboratory, UK, is described. Presented are recent results from the calibration of the new setup and this shows the technique can be a powerful tool in determining the composition of materials in bulk, not just at the surface. Moreover, this technique is non-destructive and should be sensitive to all elements (perhaps with the exception of H and He). [ABSTRACT FROM AUTHOR]

Source output stability is important for accurate measurement in prompt gamma neutron activation. This is especially true when measuring low-concentration elements such as in vivo nitrogen (~2.5 % of body weight). We evaluated the stability of the compact DT neutron generator within an in vivo nitrogen measurement system. Review of gamma event/time patterns and data from an auxiliary detector showed significant variations among repeated phantom runs. Neutron generator instability had a significant effect on measurement precision. The neutron generator used in our system must be monitored for output consistency. Adjustments must be made to measurement results to correct for generator instability. [ABSTRACT FROM AUTHOR]

Research on transients is one of the main focuses in the field of accelerator driven subcritical reactor (ADSR). But inducing the transients by accelerator is inconvenient and costly. Simulating transients by sealed-tube neutron generator, through improving the driver of Penning ion source and modulating trigger signals of pulsed neutron, is a fast, accurate, reliable and low-cost method. This method has been used in simulating transients on the physics test platform of ADSR in China Institute of Atomic Energy (CIAE). And this method also can be applied in PGNAA. [ABSTRACT FROM AUTHOR]

A new method for improving REM counter performance in Pulsed Neutron Fields (PNFs) has been developed. This method uses an analysis of the build-up of space charge in the counter to compensate for an underestimation of Ambient Dose Equivalent (H*(10)) in intense pulsed fields. It was applied to three sets of experimental data acquired using the LUPIN-II REM counter device, which is designed for use in PNFs. The data was acquired using the cyclotron at Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), at the HiRadMat facility at CERN and at the ‘Elettra Sincrotrone Trieste’ (ELETTRA), Italy. A comparison of the data with and without this compensation method is used to highlight its effectiveness. The LUPIN-II performance, which has already been shown to be able to cope with fields of up to hundreds of nSv/burst, is improved by at least one order of magnitude, with further potential for improvement. [ABSTRACT FROM AUTHOR]

Accurate determination of the proppant placement and propped fracture height are important for evaluating and optimizing stimulation strategies. A technology using non-radioactive proppant and a pulsed neutron gamma energy spectra logging tool to determine the placement and height of propped fractures is proposed. Gd 2 O 3 was incorporated into ceramic proppant and a Monte Carlo method was utilized to build the logging tools and formation models. Characteristic responses of the recorded information of different logging tools to fracture widths, proppant concentrations and influencing factors were studied. The results show that Gd capture gamma rays can be used to evaluate propped fractures and it has higher sensitivity to the change of fracture width and traceable proppant content compared with the exiting non-radioactive proppant evaluation techniques and only an after-fracture measurement is needed for the new method; The changes in gas saturation and borehole size have a great impact on determining propped fractures when compensated neutron and pulsed neutron capture tool are used. A field example is presented to validate the application of the new technique. [ABSTRACT FROM AUTHOR]

A neutron spectrometer based on a single EJ299-33 plastic scintillator (5~\cm diameter\times 5~\cm) is described. A digital implementation of pulse shape discrimination is used to separate events associated with neutrons from those associated with gamma-rays. Measurements made using a ns-pulsed neutron beam are used to produce response functions of the detector for neutrons over the energy range 10 – 100 MeV. These lineshapes are used to test the capability of the spectrometer to produce neutron energy spectra, via the unfolding of pulse height spectra, for use in neutron fields having any type of time structure. The results are compared with those from a similar spectrometer constructed from EJ301 liquid scintillator. [ABSTRACT FROM PUBLISHER]

An annular shape silver lined proportional counter is developed to measure pulsed neutron radiation. The detector has 314 mm overall length and 235 mm overall diameter. The central cavity of 150 mm diameter and 200 mm length is used for placing the neutron source. Because of annular shape the detector covers >3 π solid angle of the source. The detector has all welded construction. The detector is developed in two halves for easy mounting and demounting. Each half is an independent detector. Both the halves together give single neutron pulse calibration constant of 4.5×10 4 neutrons/shot count. The detector operates in proportional mode which gives enhanced working conditions in terms of dead time and operating range compared to Geiger Muller based neutron detectors. [ABSTRACT FROM AUTHOR]

We demonstrate for the first time the viability of a three-dimensional (3D) elemental imaging technique based on Neutron Resonance Transmission Imaging (NRTI), which is a neutron technique based on the presence of a resonance structure in the neutron-induced reaction cross sections. These resonances allow the identification of elements and isotopes within an object in a non-destructive manner. A dedicated set-up on the INES (Italian Neutron Experimental Station) beamline of the ISIS spallation neutron source was employed for the experiments. An early mediaeval disc fibula from the Hungarian National Museum in Budapest was used for our demonstration. The methodology and analysis procedures are described and the results obtained from the reconstruction of the 3D NRTI elemental image of the ancient object are compared with the results obtained from other neutron-based 3D imaging techniques. [ABSTRACT FROM AUTHOR]

This article introduces a development of pulsed neutron uranium logging instrument. By analyzing the temporal distribution of epithermal neutrons generated from the thermal fission of 235U, we propose a new method with a uranium-bearing index to calculate the uranium content in the formation. An instrument employing a D-T neutron generator and two epithermal neutron detectors has been developed. The logging response is studied using Monte Carlo simulation and experiments in calibration wells. The simulation and experimental results show that the uranium-bearing index is linearly correlated with the uranium content, and the porosity and thermal neutron lifetime of the formation can be acquired simultaneously. [ABSTRACT FROM AUTHOR]

An explosive detection system based on the pulsed fast thermal neutron analysis (PFTNA) is developed. The 14 MeV D-T pulsed neutron generator, console, bismuth germanate (BGO) detector, main amplifier, gate circuit and 4096 multichannel analyzer (MCA) are applied in this system. The neutron collimator and shielding device are also designed to reduce the unnecessary external interference and improve the detection efficiency. Using the system, the explosive mimic (urea) is detected and identified by calculating the ratio of hydrogen atoms to oxygen atoms (H/O). The influence of detection conditions, such as detection distance and sample mass, to the experimental results is investigated. It shows that, when the high voltage of main amplifier is 755 V, the count rate is 4000 n/s, the sample is placed as close as possible to the bottom of the neutron generator, and the sample mass is more than 800 g, the sample can be distinguished well by comparing the H/O ratio. It is confirmed that the explosives can be detected by the detection system, which provides a new method for detecting explosives. [ABSTRACT FROM AUTHOR]

This study presents the methodology to calculate the Rossi-α distribution for a subcritical assembly driven by an external pulsed neutron source through MCNP6 computer simulations. The Rossi-α distribution is obtained from the signal (e.g., 3 He(n,p) reactions) of a neutron detector placed in one experimental channel of the subcritical assembly. The detector signal is obtained from MCNP6 computer simulations modeling a single pulse of the external neutron source. The MCNP6 output data for a single pulse of the external neutron source must be processed to take into account the effect of delayed neutrons born in all previous source pulses. The calculation of the Rossi-α distribution from a pulsed neutron source is time consuming because of the huge amount of processed data. Consequently, the algorithms introduced in this work use parallel computing platforms, e.g., CUDA or MPI, to reduce the computing time. [ABSTRACT FROM AUTHOR]

To realize neutron energy resolved three-dimensional (3D) imaging in the resonance neutron energy region, a camera system coupled with a high sensitivity and high frame-rate gating image-intensifier was developed. The resonance absorption 3D imaging was successfully demonstrated at the pulsed neutron source of the Japan Proton Accelerator Research Complex (J-PARC). The camera system allowed us to obtain a time-of-flight (TOF) image of 2352 (W)×1726 (H) pixels resolved into a narrow energy range. 3D images with enhanced contrast at corresponding resonance energy regions for cylindrical Au, Ta, and In samples were reconstructed by convolution filtered back-projection (FBP) and maximum likelihood expectation maximization (MLEM) methods. The spatial resolution in the depth direction was evaluated experimentally to be approximately 1 mm. Our results show that the system could have applications in industrial fields. [ABSTRACT FROM AUTHOR]

According to the rules of nuclear safety, the measurements of the subcriticality of reactors should be carried out in the process of performing nuclear hazardous operations. An advanced technique of shooting source of neutrons is proposed to meet this requirement. As such a source, a pulsed neutron source (PNS) is used. In order to realize this technique, it is recommended to enable a PNS with a frequency of 1-20 Hz. The PNS is stopped after achieving a steady-state (on average) number of neutrons in the reactor volume. The change in the number of neutrons in the reactor volume is measured in time with an interval of discreteness of ∼0.1 s. The results of these measurements with the application of a system of point-kinetics equations are used in order to calculate the sought subcriticality. The basic idea of the proposed technique used to measure the subcriticality is elaborated in a series of experiments on the Kvant assembly. The conditions which should be implemented in order to obtain a positive result of measurements are formulated. A block diagram of the basic version of the experimental setup is presented, whose main element is a pulsed neutron generator. [ABSTRACT FROM AUTHOR]