Neutron Response Research Articles

Evaluation of Gas Reservoir of the Meghna Gas Field, Bangladesh Using Wireline Log Interpretation

The gas reservoir from the well Bakhrabad-09 of the Meghna Gas Field, Bangladesh was evaluated in this study in order to appraise the qualities of the reservoir based on quantitative analysis of petrophysical parameters. Among 24 permeable zones, two zones were gas-bearing and rests were water-bearing zones which identified in the study well. Relatively high resistivity, high SP log, low gamma ray log, very low neutron and low density log responses indicate hydrocarbon type might be gas-bearing zones than that of water-bearing zones. The shale volume of those zones ranged from average 21% to 22 % indicated that shaly sand dominating lithology and less affect the water saturation values in the gas reservoir. The average porosity of these zones ranged from 31% to 34 % which was within the limit for good hydrocarbon accumulation. Three saturation equations were used to evaluate the water saturation which was converted to gas saturation. The average gas saturation values of these zones were more than 60 % indicate high hydrocarbon accumulation. The average permeability of these zones ranged from 42.5 md to 50 md respectively which was within ranged for commercial gas accumulation. Average bulk volume of water ranged from 0.045 to 0.053 was shown that the reservoir consist of mainly fine to very fine grained sandstone and more or less at irreducible water state. It can be concluded that gas reservoir are good qualities for commercial hydrocarbon accumulation and production. erroneous values for water saturation and porosity in the presence of shale effect. The determinations of reservoir quality and formation evaluation processes are largely depend on quantitative evaluation of petrophysical analysis. Petrophysical analysis of gas reservoir of different gas field was carried out by Islam et al. (3-7) in Bengal Basin, Bangladesh. Rahman et al. (8) was carried out the analysis of reservoir sand of Titas-15 well using well log interpretation. In this regard, the study was focused on the gas reservoir evaluation in the well Bakhrabad-09 of Meghna Gas Field, Bangladesh using wireline log interpretation. The objective of the study is to identify the gas zones of reservoir using composite log responses and to determine petrophysical parameters of the gas reservoir of the Meghna Gas Field, Bangladesh. It is located in Bancharampur upzila under Brahmanbaria District some 40 km away of northern most east direction from capital city of Dhaka, Bangladesh. Meghna Gas Field was discovered by BAPEX in 1990 (9) (Figure 1).

Analysis of the ground level enhancement on 17 May 2012 using data from the global neutron monitor network

AbstractWe have analyzed the data of the world neutron monitor network for the first ground level enhancement of solar cycle 24, the ground level enhancement (GLE) on 17 May 2012. A newly computed neutron monitor yield function and an inverse method are applied to estimate the energy spectrum, anisotropy axis direction, and pitch angle distribution of the high‐energy solar particles in interplanetary space. The method includes the determination of the asymptotic viewing cones of neutron monitor stations through computations of trajectories of cosmic rays in a model magnetosphere. The cosmic ray particle trajectories are determined with the GEANT‐based MAGNETOCOSMICS code using Tsyganenko 1989 and International Geomagnetic Reference Field models. Subsequent calculation of the neutron monitor responses with the model function is carried out, that represents an initial guess of the inverse problem. Derivation of the solar energetic particle characteristics is fulfilled by fitting the data of the global neutron monitor network using the Levenberg‐Marquardt method over the nine‐dimensional parameter space. The pitch angle distribution and rigidity spectrum of high‐energy protons are obtained as function of time in the course of the GLE. The angular distribution appears quite complicated. It comprises a focused beam along the interplanetary magnetic field line from the Sun and a loss‐cone feature around the opposite direction, possibly indicative of the particle transport in interplanetary magnetic field structures associated with previous coronal mass ejections.

Evaluation of the neutron response of a criticality accident alarm system detector

A neutron irradiation experiment was performed to determine the neutron absorbed dose rate response of a criticality accident alarm system detector. For this purpose, the authors tailored a neutron field by the use of a 252 Cf neutron source and 50-mm-thick lead blocks, which removed unwanted gamma rays emitted from the source itself while allowing the neutrons to pass through. The evaluated neutron response of the detector was confirmed to be in reasonably good agreement with the prior computer-predicted response.

The influence of different hydraulics models in treatment of some physical processes in super-critical states of light water reactors accidents

This work presents the development and testing of some thermal hydraulic models designed to address the limitations of using the Homogeneous Equilibrium Model (HEM) in predicting and simulating the hydraulic response of the positive reactivity-initiated power excursion accidents in small light water reactors. The neutronic response of such accidents has been investigated based on the neutron diffusion method. Most of the power reactors have a code system to analyse such accidents. Unfortunately, the training and research of Budapest University of Technology (BME) has to build its own code system. In this sense, a number of different 3D space–time-dependent neutron diffusion models with thermal hydraulic feedback have been introduced, compared and tested together and with the point-kinetic REMEG model for this purpose. The results show that the fuel parameters are maintained below specified limits during the accident so that fuel failure and release of radioactivity will not occur.

Characterisation of OSL and OSLN droplets for dosimetry

In spite of considerable progress in neutron dosimetry, there is no dosemeter that is capable of measuring neutron doses independently of the neutron spectrum with good accuracy. Carbon-doped aluminium oxide (Al2O3:C) is a sensitive material for ionising radiation (beta-ray, X ray and electron) and has been used for applications in personal and medical dosimetry as an optically stimulated luminescence (OSL) dosemeter. Al2O3:C has a low sensitivity to neutron radiation; this prevents its application to neutron fields, representing a disadvantage of Al2O3:C-OSL when compared with LiF, which is used as a thermoluminescent detector. Recently an improvement for neutron dosimetry (Passmore and Kirr. Neutron response characterisation of an OSL neutron dosemeter. Radiat. Prot. Dosim. 2011; 144: 155-60) uses Al2O3:C coated with (6)Li2CO3 (OSLN),which gives the high-sensitive response as known for Al2O3:C with the advantage of being also sensitive to thermal neutrons. In this article, the authors compare small-size detectors (droplets) of Al2O3:C (OSL) and of Al2O3:C+(6)Li2CO3 (OSLN) and discuss the advantages and drawbacks of both materials, regarding size vs. response.

Coalbody structure classification method based on dual-lateral and RXO crossplot analysis

According to the positive correlation of coal ash content and natural gamma, using a new coal core reposition method, which is ordered by global and local extreme, coal samples from medium-thickness seam are reasonably located. Integrated the data of coal macrostructure characteristics, coal petrography analysis and coal gas production test, it studies the relationship between coalbody structure and amplitude variation of different well logging data, and the tectonic coal recognition method with well logging data in fresh-water mud invasion. The results show that: the anomalous response of natural gamma ray, neutron, density and apparent resistivity does not reflect the coalbody structure type. In fresh-water drilling mud invasion, using the crossplot technique of dual-lateral, RXO resistivity response and the coalbody structure can classify granulated coal accurately; the proposed method is of good practicability and high reliability.

The Effect of Atmospheric Water Vapor on Neutron Count in the Cosmic-Ray Soil Moisture Observing System

Abstract The cosmic-ray method for measuring soil moisture, used in the Cosmic-Ray Soil Moisture Observing System (COSMOS), relies on the exceptional ability of hydrogen to moderate fast neutrons. Sources of hydrogen near the ground, other than soil moisture, affect the neutron measurement and therefore must be quantified. This study investigates the effect of atmospheric water vapor on the cosmic-ray probe signal and evaluates the fast neutron response in realistic atmospheric conditions using the neutron transport code Monte Carlo N-Particle eXtended (MCNPX). The vertical height of influence of the sensor in the atmosphere varies between 412 and 265 m in dry and wet atmospheres, respectively. Model results show that atmospheric water vapor near the surface affects the neutron intensity signal by up to 12%, corresponding to soil moisture differences on the order of 0.10 m3 m−3. A simple correction is defined to identify the true signal associated with integrated soil moisture that rescales the measured neutron intensity to that which would have been observed in the atmospheric conditions prevailing on the day of sensor calibration. Use of this approach is investigated with in situ observations at two sites characterized by strong seasonality in water vapor where standard meteorological measurements are readily available.

Aircrew radiation dose estimates during recent solar particle events and the effect of particle anisotropy

A model was developed using a Monte-Carlo radiation transport code, MCNPX, to estimate the additional radiation exposure to aircrew members during solar particle events. The model transports an extrapolated particle spectrum based on satellite measurements through the atmosphere to aircraft altitudes. This code produces the estimated flux at a specific altitude where radiation dose conversion coefficients are applied to convert the particle flux into effective and ambient dose-equivalent rates. A cut-off rigidity model accounts for the shielding effects of the Earth's magnetic field. Comparisons were made between the model predictions and actual flight measurements taken with various types of instruments used to measure the mixed radiation field during ground level enhancements (GLEs) 60 and 65. An anisotropy analysis that uses neutron monitor responses and the pitch angle distribution of energetic solar particles was used to identify particle anisotropy for a solar event in December 2006. In anticipation of future commercial use, a computer code has been developed to implement the radiation dose assessment model for routine analysis.

Modelling of a self-sustained density wave oscillation and its neutronic response in a three-dimensional heterogeneous system

The main types of instabilities encountered in commercial Boiling Water Reactors (BWRs) are global and/or regional oscillations. In addition to those, pure Density Wave Oscillations (DWOs) have also been observed in some operating BWRs. These oscillations are particularly challenging from a modelling viewpoint because of the radially strongly localized character of the perturbation and of the corresponding neutronic response. In this paper, the features of a recently developed numerical tool, named CORE SIM, are taken advantage of. More specifically, this tool has the ability to estimate in the frequency domain the spatial and energy distribution of the stationary fluctuations of the neutron flux in any three-dimensional heterogeneous system. The perturbations should be directly defined in terms of fluctuations of the macroscopic cross-sections. In this study, the fluctuations in the macroscopic cross-sections are obtained by first modelling a boiling channel exhibiting a DWO with the US NRC RELAP5 code, and by thereafter converting the fluctuations of the coolant density along the channel into fluctuations of the macroscopic cross-sections using the Studsvik Scandpower CASMO-4E code. The RELAP5 and CASMO-4 models are representative of a typical BWR fuel assembly. The conditions modelled in RELAP5 were adjusted in order to obtain self-sustained DWOs. The axial distribution of the amplitude and phase of the fluctuations observed in the coolant density from the RELAP5 simulations are thus converted into fluctuations of the macroscopic cross-sections via CASMO-4E, and fed into a CORE SIM model representative of a heterogeneous BWR. The CORE SIM simulations in turn allow estimating the three-dimensional effects of a self-sustained DWO in a BWR core. More specifically, the axially dependent amplitude and phase of the variation of the coolant flow are properly accounted for, and the properties of the relative induced neutron fluctuations throughout the core are assessed.

Comparing hadronic models of GEANT4 for the neutron monitor response function

The NM64 neutron monitor is the most popular instrument that measures the number of highenergy particles impacting the Earth from space. A simulation of the NM64 neutron monitor response function with the GEANT4 toolkit is conducted, and the result is processed to compare low- and high-energy hadronic models provided by this Monte Carlo code. Results shows that the thermal interaction for hydrogen in polyethlene for neutron energies less than 4 eV has a great influence. G4NeutronHP and G4LEND models are compared for low-energy neutrons in this study. At energies from 20 MeV to 10 GeV, the Bertini Cascade and the Binary Cascade models are used and evaluated as applicable physics lists. At energies above 10 GeV, the FTFP and the QGSP physics models are applied to calculate the response function, and the results are a few percents higher than the FLUKA results found in the literature.

Modeling of a highly enriched 235U fission chamber for spent fuel assay

Fission chambers loaded with high enriched uranium are used for spent fuel measurements in the so-called Fork detector. The Fork detector is one of the work-horses used by safeguards inspectors for spent fuel measurements during verification activities in the framework of the Non-Proliferation and Euratom Treaties.Having an accurate and validated model of the measurement equipment is beneficial for the investigation of this type of applications. SCK•CEN is carrying out a significant effort to model the Fork detector with the MCNPX code. However, scarce information is known about the fission chambers.This work describes the impact of the design information of the fission chamber on the calculated detector sensitivity and, consequently, on the overall Fork detector response for neutrons, using Monte Carlo simulations.The heavy ions transport in the active layer of the fission chamber was also studied and the resulting fission product energy spectra were compared with the available experimental data.

Response characterization for an EJ315 deuterated organic-liquid scintillation detector for neutron spectroscopy

Organic liquid scintillation detectors have shown promise as neutron detectors for characterizing special nuclear materials in various arms-control applications. Deuterated liquids, such as EJ315, are attractive for spectroscopy applications because the backward-peaked n–d scattering results in enhanced coupling between incident neutron energy and resulting pulse height. This will likely allow better spectrum unfolding. In this work, we present a measured neutron response matrix for a three-by-two-in. cylindrical EJ315 detector, and compare to the hydrogen-based liquid EJ309 in an otherwise identical assembly. We also present measured light-output relations for both detectors. A continuous-spectrum neutron source, obtained with the bombardment of 11B with 5.5-MeV deuterons at the tandem Van de Graaff accelerator at the University of Notre Dame, was used for the measurement. Detected neutrons were sorted via time of flight into 100-keV energy groups, over the energy range from 0.5 to 15MeV. The resulting response matrix represents a detailed characterization of pulse-height response to neutrons over that energy range. To the authors' knowledge, a measured response matrix and light-output relation for EJ315 have not been reported, and published characterizations of the similar NE230 are of less detail over this energy range. Matrix-condition analysis indicates an advantage for EJ315 over EJ309 in the number of independent parameters available in inversion procedures.

Neutron response of the LAMBDA spectrometer and neutron interaction length in BaF2

We report on the neutron response of the LAMBDA spectrometer developed earlier for high-energy γ-ray measurement. The energy dependent neutron detection efficiency of the spectrometer has been measured using the time-of-flight (TOF) technique and compared with that of an organic liquid scintillator based neutron detector (BC501A). The extracted efficiencies have also been compared with those obtained from Monte Carlo GEANT4 simulation. We have also measured the average interaction length of neutrons in the BaF2 crystal in a separate experiment, in order to determine the TOF energy resolution. Finally, the LAMBDA spectrometer has been tested in an in-beam-experiment by measuring neutron energy spectra in the 4He+93Nb reaction to extract nuclear level density parameters. Nuclear level density parameters obtained by the LAMBDA spectrometer were found to be consistent with those obtained by the BC501A neutron detector, indicating that the spectrometer can be efficiently used as a neutron detector to measure the nuclear level density parameter.

Thin Film Polymer Composite Scintillators for Thermal Neutron Detection

Thin film polystyrene composite scintillators containing LiF6 and organic fluors have been fabricated and tested as thermal neutron detectors. Varying fluorescence emission intensities for different compositions are interpreted in terms of the Beer-Lambert law and indicate that the sensitivity of fluorescent sensors can be improved by incorporating transparent particles with refractive index different than that of the polymer matrix. Compositions and thicknesses were varied to optimize the fluorescence and thermal neutron response and to reduce gamma-ray sensitivity. Neutron detection efficiency and neutron/gamma-ray discrimination are reported herein as functions of composition and thickness. Gamma-ray sensitivity is affected largely by changing thickness and unaffected by the amount of LiF6 in the film. The best neutron/gamma-ray discrimination characteristics are obtained for film thicknesses in the range 25–150 μm.

Neutron detection with LiCaAlF6 scintillator doped with 3d-transition metal ions

Abstract Capability of thermal neutron detection was examined for LiCaAlF 6 (LiCAF) scintillators doped with 3d-transition metal ions. Their radioluminescence spectra were measured with an 241-Am source to simulate 6 Li(n, α) 3 H reaction. The sufficiently intense radioluminescence was observed for the Mn, Co and Cu dopants, while only a weak one was observed for Ti, V, Fe and Ni. A Mn doped LiCAF crystal, which showed the highest radioluminescence intensity, was coupled with a Si avalanche photodiode for the examination of its neutron response. It was confirmed that the average current of the photodiode clearly increased under excitation with 13.5 meV neutron flux.

Boron-Coated Straw Detectors for Backpack Monitors

The limited inventory and minute natural abundance of 3He gas on Earth necessitate the adoption of new technologies for the detection of neutrons, especially in homeland security applications, where large volume deployments are required. We investigate the neutron detection efficiency of a backpack radiation detector based on an unmoderated array of boron-coated straws (BCS). A neutron module was configured that would be light and small enough to fit inside a regular-sized backpack. The module consisted of 36 tubes, arranged in two rows, for a total number of BCS detectors equal to 36 × 7=252. The overall dimensions of the neutron module were 3.18 cm × 26.7 cm × 38.1 cm, and its weight was 1.62 kg (3.57 lbs). The module was fitted immediately inside the back side of the backpack. The detectors are thus very close to the torso of the operator, which, together with a plastic scintillator for gamma detection, act as moderators for high-energy neutrons. In order to maintain a low weight, no other moderating material was installed inside the backpack. The weight of the pack containing both neutron and gamma detector panels, along with foam packing, electronics, and battery, was 5.36 kg (11.8 lbs). The compact dimensions of the design afforded use of a computer style backpack of minimal dimension providing significant additional operational advantages. The testing results indicate that, through use of high-density straw cluster detectors, the proposed design meets both neutron and gamma response government requirements for backpack monitors.

Measurements of Thermal Neutron Response in Cherenkov Glasses Designed for MeV Photon Detection

In order to obtain a meaningful gamma ray measurement in mixed neutron and high-energy photon environments, a quantitative understanding of neutron-induced backgrounds is crucial. Neutrons that can produce Cherenkov photons indirectly through (n, γ) activation reactions are found in radiation backgrounds in both passive and active-source search environments. The objectives of this research are to establish the properties and fabrication techniques for materials suitable for the production of photon-sensitive Cherenkov detectors (including low neutron sensitivity), or, for certain samples, to understand how the response to neutrons can be electronically discriminated from the signal caused by the interaction of MeV photons. Over a hundred glass samples have been fabricated, and radiation characterization results from selected samples are reported. The thermal neutron responses of these glasses were determined using neutron activation followed by time dependent radiation measurement and gamma ray spectroscopy. The results showed that the probability of thermal neutron capture, the thermal neutron activation time, the half-life of the activation products, the abundance of the target materials, and the magnitude of the energy of gamma and beta radiations that result from activation play significant roles in understanding the observed count rate due to Cherenkov radiation. Implications for Cherenkov detectors to be used for MeV photon detection are discussed.

Electrical Characteristics and Fast Neutron Response of Semi-Insulating Bulk Silicon Carbide

The electrical characteristics and fast neutron response of a High Temperature Chemical Vapour Deposition (HTCVD) grown semi-insulating bulk SiC wafer has been measured. Current-Voltage measurements demonstrated a low leakage current in the region of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12v</sup> A with a bulk resistivity of at least 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> Ω.cm. Alpha particle spectroscopy measurements demonstrated an electron charge collection efficiency of up to 90% with reasonable reproducibility of the acquired spectra. Evidence of (incident particle) rate dependent polarisation was seen following a constant applied bias combined with alpha irradiation over a period of time (order of tens of minutes). The ability of the wafer to detect fast neutrons was demonstrated and a comparison drawn with the MCNPX simulated response of a bulk SiC device. Comparing the MCNPX simulated response of a bulk SiC device to that of a silicon device suggests a superior ability to detect fast neutrons with an intrinsic efficiency 1.7 times that of silicon.

Characterization of a 6Li-loaded liquid organic scintillator for fast neutron spectrometry and thermal neutron detection

The characterization of a liquid scintillator incorporating an aqueous solution of enriched lithium chloride to produce a scintillator with 0.40% 6Li is presented, including the performance of the scintillator in terms of its optical properties and neutron response. The scintillator was incorporated into a fast neutron spectrometer, and the light output spectra from 2.5MeV, 14.1MeV, and 252Cf neutrons were measured using capture-gated coincidence techniques. The spectrometer was operated without coincidence to perform thermal neutron measurements. Possible improvements in spectrometer performance are discussed.

A compact stilbene crystal neutron spectrometer for EAST D-D plasma neutron diagnostics

A new compact stilbene crystal neutron spectrometer has been investigated and applied in the neutron emission spectroscopy on the EAST tokamak. A new components analysis method is presented to study the anisotropic light output in the stilbene crystal detector. A Geant4 code was developed to simulate the neutron responses in the spectrometer. Based on both the optimal light output function and the fitted pulse height resolution function, a reliable neutron response matrix was obtained by Geant4 simulations and validated by 2.5 MeV and 14 MeV neutron measurements at a 4.5 MV Van de Graaff accelerator. The spectrometer was used to diagnose the ion temperature in plasma discharges with lower hybrid wave injection and ion cyclotron resonance heating on the EAST tokamak.