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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]

Current conduction and saturation mechanisms in ungated AlGaN/GaN/SiC transfer length method test structures with contact-to-contact distance L varying from 2 to 32 μm are investigated. Current-voltage (I-V) characteristics are measured in the pulsed and in the direct current (dc) regimes. The pulsed characteristics were evaluated for the pulse duration of 50 ns, and together with the dc ones show that the current saturation value depends on the contact distance and the current saturation occurs at an electrical field <150 kV/cm. This behavior contradicts the theoretical expectation valid for the ungated structures. An analysis of the I-V characteristics shows that the dc saturation current values are up to 5.5 times lower than those under the pulsed conditions for the same L. If the self-heating effect was supposed to be responsible for this observation, an unrealistic temperature rise would be required. This together with the observed ∼1 s long transition time into the steady state, which is several orders of magnitude longer than what one can expect for the thermal transient, excludes the dominant role of the thermal effects in the current saturation mechanism. A model of the current conduction and saturation mechanism is suggested where the charge injection from the contacts and charging of the AlGaN surface are responsible for a AlGaN/GaN channel depletion. Thus the saturation mechanism is similar to that occurring in gated structures. The model explains well the observed dependencies and is further validated by a transient interferometric mapping method. This thermooptical method operated under the pulsed conditions allows to evaluate the free carrier concentration profiles along the structure channel and to make the comparisons with the concentration below Ohmic contacts. A strong channel depletion effect has been observed for the structure with L=32 μm in comparison to the negligible surface depletion effect found in the L=2 μm structure. This is in full agreement with the suggested model of the current saturation mechanism and with the measured I-V characteristics. [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]

Discusses a study which determined the spatial magnetic correlation in nickel-manganese base amorphous alloys. Measurement of the nuclear and magnetic parts of the structure factor of the alloy; Discussion of pulsed neutron scattering; Effects of annealing on the compositional short-range order.

The structures of glassy 7LiX–KX–CsX–BaX2 (X=Cl, Br, and I) have been investigated by means of pulsed neutron diffraction experiment. The obtained total radial distribution functions were discussed with the help of the molecular dynamics simulation based on the Tosi–Fumi potential. The Li–X (X=Cl, Br, and I) distances in the three glasses are 2.37, 2.49, and 2.70 Å, respectively, which are 0.2–0.3 Å shorter than those in the rocksalt-type LiX crystals. For each system, it is found that the coordination number of the X- ions around the Li+ ions is about four when only the closely contacting X- ions are counted. Because of the 1:1 monovalent character of the present systems, the first coordination shell around the Li+ ions has the ill-defined outer extent, compared with the 4:2 and 2:1 charged systems such as SiO2 and ZnCl2. This causes the increase of the coordination number, from four to six, when all the near-neighbor X- ions are counted as the surrounding ions. [ABSTRACT FROM AUTHOR]

Structure factors S(Q) of deuterated polyethylene (PE) in the solid and liquid states have been measured at 20, 130, and 170 °C in a wide range of Q from 0.55 to 25 A-1 by means of pulsed neutron total scattering technique. Very local intrachain structure of the PE melt, such as C–D and C–C bond lengths and /_ CCC, /_ DCD, and /_ CCD bond angles, is determined from a high Q part of S(Q), and is compared with that of solid PE. Interchain structure of the melt is also discussed, assuming that the PE chains are built of small segments of five –CD2 – units like pearl necklaces and furthermore, that orientations between the segments are completely uncorrelated and chain connectivity is entirely ignored. The experimental S(Q) is reproduced reasonably well by this simple model with an effective diameter σ of the segments of 4.34 A and a packing fraction η of the segments of 0.28, which are consistent with the experimental number density of the PE melt. The different size of the segments like four or six –CD2 – units, however, gives poor results with the values of σ and η being inconsistent with the experimental number density. [ABSTRACT FROM AUTHOR]

The structure factor Sm(Q) of liquid benzene and naphthalene have been measured by means of pulsed neutron total scattering. Both intramolecular and intermolecular structures are discussed. The intermolecular structures are analyzed by taking account of orientational correlations introduced between the nearest neighbors and a packing of uncorrelated molecules. The experimental Sm(Q) and the radial distribution function of liquid benzene are reproduced reasonably well by introducing a perpendicular orientation just between the nearest neighbors. The analysis of liquid naphthalene suggests an orientation somewhat similar to that in liquid benzene. [ABSTRACT FROM AUTHOR]

Structure factor Sm(Q) of liquid phosphorous tribromide (PBr3) has been measured at room temperature by means of pulsed neutron total scattering technique. Characteristic features of the experimental Sm(Q) are analyzed in terms of preferred orientations introduced between the nearest neighbors as well as a packing of effectively uncorrelated molecules. The preferred orientation estimated in this analysis is such that a top (or a P atom) of pyramidal shape of each PBr3 molecule points in nearly the same direction. [ABSTRACT FROM AUTHOR]

Pulsed neutron diffraction measurements have been made on liquid 1,2-dichloroethane-d4 (DCE). The wide momentum-transfer range (∼0.3–50 Å-1) available has been used to further refine previously measured molecular structure parameters as well as to test the validity of the inelasticity corrections applied. A measurement using chlorine isotopes on a steady (reactor) source served to partially separate the chlorine–chlorine and the chlorine–carbon plus chlorine–deuterium correlations. The isotopic difference curves were then analyzed and the relevant features of the distribution of internal dihedral angles [P(τ)] obtained by adequate inversion of the experimental difference–functions. The intermolecular pair correlation function was then derived and both sets of functions (from pulsed and steady sources) are compared and tentatively assigned. [ABSTRACT FROM AUTHOR]

The methods of steady-state and pulsed millimeter-wave rotational spectroscopy were used to probe the vibrationally excited products, CS and SO produced in the laser photolysis of CS2 and SO2 at 193 nm. The time dependence of the vibrational populations was measured for CS up to v=8 and for SO up to v=5. For CS, a Boltzmann-like population distribution was found with a vibrational temperature of 5795 K corresponding to a vibrational energy of 9.8 kcal mol-1. In the case of SO, significant excitation was observed only for the states v=0, 1 and 2 with v=2 having the largest initial population. A small percentage of the SO molecules were found in v=5. The precursor gases were diluted in Ar to enhance the ratio of rotational to vibrational relaxation times. Because rotational transitions were probed, it was necessary to wait for rotational equilibrium to be established before making the measurements. As a result, the vibrational populations may have been partially relaxed at the time of measurement. In order to evaluate the extent of relaxation, a discussion of the various relaxation processes is given. [ABSTRACT FROM AUTHOR]

Presents a study that described some attempts to observe magnetic structure in various actinide materials. Utilization of the pulsed neutron powder diffraction technique; Capabilities of the technique; Application of the pulsed technique.

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]