The measurement of neutron cross sections for contrast-enhancing penetrant fluids

The purpose of this experiment was to evaluate penetrant fluids of high neutron cross section. These fluids are useful in neutron radiographic investigations for contrast enhancement Saturated solutions of the gadolinium salts and one chelate were formed by using one of several solvents, and the resulting fluid’s macroscopic neutron cross sections were measured experimentally. The results of this experiment provided a quantitative measure of the mean and standard deviation of the macroscopic neutron cross section for the penetrant fluids. Inaddition, a confidence interval was generated for each fluid. The measured neutron cross section for a control fluid was in close agreement with published values.     

The Measurement of Neutron Cross Sections for Contrast-Enhancing Penetrant Fluids

Abstract

The purpose of this experiment was to evaluate penetrant fluids of high neutron cross section. These fluids are useful in neutron radiographic investigations for contrast enhancement. Saturated solutions of the gadolinium salts and one chelate were formed by using one of several solvents, and the resulting fluid's macroscopic neutron cross sections were measured experimentally.

The results of this experiment provided a quantitative measure of the mean and standard deviation of the macroscopic neutron cross section for the penetrant fluids. In addition, a confidence interval was generated for each fluid. The measured neutron cross section for a control fluid was in close agreement with published values.     

Investigation of Metallic and Ceramic Materials by Small-Angle Neutron Scattering

Small-angle neutron scattering measurements on a double-crystal spectrometer with perfect monochromator and analyzer crystals were used to follow microstructural changes in the aluminum alloy VD-17, refractory alloy ZhS-6, and dispersion-hardened zirconia-based ceramics with yttria additions. The measurements were carried out by the Warren method, involving determination of the small-angle neutron attenuation coefficient. The experimentally determined total macroscopic small-angle scattering cross section is correlated with different parameters characterizing external influences on the material: the number of loading cycles, heat-treatment temperature, and fracture stress. The potential of the proposed approach for optimizing processing technologies is discussed.     

In-situ neutron radiography investigations of hydrogen diffusion and absorption in zirconium alloys

The fast and non-destructive character of neutron radiography provides the possibility of in-situ investigations of hydrogen uptake and diffusion in zirconium alloys. A special reaction furnace with neutron transparent windows was constructed. The method of quantitative hydrogen determination by neutron transmission measurements was calibrated for each experimental run. Additionally, oxygen is absorbed in the α-Zr phase and precipitated in the oxide layer. The calibration of the correlation between hydrogen and oxygen concentrations and total neutron cross-sections at room temperature and between 1123 and 1623 K are described.Results of in-situ neutron radiography investigations of hydrogen diffusion and absorption are presented in this paper. A linear dependence of the total macroscopic neutron cross section on the H/Zr atomic ratio as well as on the oxygen concentration was found. No significant temperature dependence of the total neutron cross-sections of hydrogen dissolved in β-Zr or oxygen dissolved in the α-Zr or precipitated in the oxide layer was found.     

Three-Dimensional Localization of Defects in Stay Cables Using Magnetic Flux Leakage Methods

The application of magnetic flux leakage (MFL) methods to the nondestructive evaluation (NDE) of metal parts has been known for several decades. The inspection of large-diameter cables (Ø 100 mm), such as bridge stay cables, is a new field of application for the MFL method. The large cross-section of the cables requires the generation of strong magnetic fields in order to obtain the induction fields necessary for an accurate inspection of the cables. A new device for the inspection of stay cables has been developed in order to meet the requirements given by the size of the cables. Measurements performed with the developed device on full-scale specimens in the laboratory and first calculations confirm the validity of the MFL approach to the inspection of bridge stay cables. The equipment was used satisfactorily in 2001 for the NDE inspection of the 68 locked coil stay cables (121 mm < Ø < 167 mm) of a bridge in Southeast Asia. For such cables, no exact localization within the cross section was performed. Thus far, an accurate indication of the position of the detected flaws along the length of the cables could be given. A qualitative statement about position and size of the flaws within the cross section of the cable could also be made. Given the large steel cross-section of the cables, no other nondestructive method to confirm the findings could be applied to assess the exact size and position of the detected flaws. The proposed analytical method presented in this paper makes it possible to increase the amount of information that can be extracted from the measured MFL data with regard to the exact location of the detected flaws within a cross section of a stay cable.     

Preliminary design of a Gd-NCT neutron beam based on compact D-T neutron source

Gadolinium has been recently proposed, as neutron capture agent in NCT (Neutron Capture Therapy), due to both the nuclide high neutron capture cross section, and the remarkable selective uptake inside tumour tissue that Gd-loaded compounds, can provide. When a neutron external source is supplied, different Gd nuclear reactions, and the generated Auger electrons in particular, cause a high local energy deposition, which results in a tumour cell inactivation. Preliminary micro- as well as macrodosimetric Monte Carlo computational investigations show that the tumour-to-healthy tissue biological damage ratio is in close relation to the neutron beam energy spectrum. The results points out that the optimum neutron spectrum, to be used for Gd-NCT, seems to lie in the 1 to 10 keV energy range. In order to 'tailor' such spectra, an original, accelerator-driven, neutron source and spectrum shaping assembly for hospital-based Gd-NCT are presented and preliminary results are reported.     

Magnetic moments of low-energy neutron resonances in 161Dy

A low-energy neutron beam and polarized ¹⁶¹Dy target at the Weapons Neutron Research Facility in Los Alamos have been used to determine magnetic moments of 7 neutron resonances. The ferromagnetic dyspromium metal was cooled by a ³He–⁴He dilution refrigerator to 35 mK. With a time-of-flight setup the total cross section was measured at temperatures of 4 K and 35 mK. The magnetic moments are derived from the shift of the resonance energy. Results obtained with a random orientation of the ferromagnetic domains agree well with a previous experiment. The target was also magnetized in a field of 6 T. In this case, the degree of nuclear polarization could be derived from the change of the resonance shape.     

Scattering and binding of rotons

The interaction of rotons is studied by a direct examination of their orbital dynamics. It is found that upon representing rotons as point dipoles in the superfluid, obeying the Landau dispersion relation, negative energy states occur, some of which are stable and some unstable. The binding energy and effective mass of these states are found, but are too large to agree with experiment. Improvements in the Hamiltonian are explored which recognize the actual dispersion curve as well as higher moments in the interaction. Both modifications lead to binding energy and effective mass in better agreement with experiment. Scattering is also examined, and one finds that a representative roton-roton cross section may be obtained in the dipole approximation, again using Landau dispersion. The scattering cross section is shown to be in satisfactory agreement with neutron linewidths in the roton-dominated region, as well as the roton contribution to the shear viscosity.     

A spectrometer for double-differential neutron-emission cross section measurements in the energy range 1.6 to 16 MeV

A neutron spectrometer for the measurement of double-differential neutron-emission cross sections has been set up.An electron linac (GELINA) is used as a pulsed white neutron source. The energy of the incident neutrons is determined by the time-of-flight method. The secondary neutron spectra are determined by unfolding the pulse-height distributions observed in eight NE213-scintillators surrounding the sample.The measured spectra are normalised to the shape of the incident neutron flux measured with a ²³⁵U-fission chamber, and afterwards converted to absolute cross sections using as standard the carbon differential elastic scattering cross section below 2 MeV.     

The Microscopic Dynamics of Liquid and Solid Parahydrogen

We have measured the almost-pure incoherent scattering function of liquid and solid parahydrogen, using inelastic neutron scattering. The experiment was carried out on TOSCA, a time-of-flight, inverse-geometry, crystal-analyser spectrometer, operating on the pulsed neutron source ISIS (UK). The measured double differential cross section gives a direct experimental access to the microscopic dynamics of condensed hydrogen. From the high energy region of the spectrum, where the Impulse Approximation for the center of mass motion applies, we have been able to extract the translational mean kinetic energy, which turns out to be density dependent. The density behaviors of the liquid and solid mean kinetic energy are slightly different. In the low energy region we used the Gaussian approximation to compare, in the liquid phase, the results of a novel quantum simulation calculation with the experimental data. Results are encouraging, but suggest further work, possibly beyond the Gaussian approximation.     

Elastic neutron scattering studies at 96 MeV for transmutation

Elastic neutron scattering from (12)C, (14)N, (16)O, (28)Si, (40)Ca, (56)Fe, (89)Y and (208)Pb has been studied at 96 MeV in the10-70 degrees interval, using the SCANDAL (SCAttered Nucleon Detection AssembLy) facility. The results for (12)C and (208)Pb have recently been published, while the data on the other nuclei are under analysis. The achieved energy resolution, 3.7 MeV, is about an order of magnitude better than for any previous experiment above 65 MeV incident energy. A novel method for normalisation of the absolute scale of the cross section has been used. The estimated normalisation uncertainty, 3%, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target. Elastic neutron scattering is of utmost importance for a vast number of applications. Besides its fundamental importance as a laboratory for tests of isospin dependence in the nucleon-nucleon, and nucleon-nucleus, interaction, knowledge of the optical potentials derived from elastic scattering come into play in virtually every application where a detailed understanding of nuclear processes is important. Applications for these measurements are dose effects due to fast neutrons, including fast neutron therapy, as well as nuclear waste incineration and single event upsets in electronics. The results at light nuclei of medical relevance ((12)C, (14)N and (16)O) are presented separately. In the present contribution, results on the heavier nuclei are presented, among which several are of relevance to shielding of fast neutrons.     

Evaluation of N50 neutron slab monitor detection efficiency with TRIPOLI-4.3 Monte Carlo code

Monte Carlo code TRIPOLI-4.3 has been used to evaluate the N50 neutron slab monitor detection efficiency benchmark organised by the non-destructive assay (NDA) working group of European Safeguards Research and Development Association (ESARDA). The lattice geometry of TRIPOLI-4.3 was applied to simplify the modelling of the N50 monitor, which consists of four 3He tubes embedded in a high-density polyethylene (HDPE) moderator. Using additional HDPE slabs and/or Cd sheets, 10 geometry configurations with different states of moderation were considered in this study. Two cross section libraries from ENDF/B-VI.4 and JEF2.2 and three representations of the 252Cf fission spectrum were investigated and the calculation experiment (C/E) ratios were discussed. The perturbation option was used in order to study the sensitivity to the HDPE density. The S(alpha,beta) thermal scattering in HDPE was also tested to quantify its impact on the N50 detection efficiency calculations.     

Evaluation of silicon neutron resonance parameters in the thermal to 1800 keV energy range

Because silicon is a major constituent of concrete and soil, neutron and gamma ray information on silicon is important for reactor shielding and criticality safety calculations. Therefore, much effort was put into the ENDF/B-VI evaluation for the three stable isotopes of silicon. The neutron capture cross section of natural silicon was recently measured at the Oak Ridge Electron Linear Accelerator (ORELA) in the energy range 1-700 keV. Using the ENDF/B-VI evaluation for initial values, a new evaluation of the resonance parameters was performed by adding the results of the ORELA capture measurements to the experimental database. The computer code SAMMY was used for the analysis of the experimental data; the new version of SAMMY allows accurate calculations of the self-shielding and multiple scattering effects in the capture measurements. The accuracy of the radiative capture widths of the resonances was improved by this analysis. Accurate values of the s-, p- and d-wave neutron strength functions were also obtained. Although the resonance capture component of the present evaluation is 2-3 times smaller than that in ENDF/B-VI, the total capture cross section is much larger, at least for energies >250 keV, because the direct capture component contributes values of the same order of magnitude as the resonance component. The direct component was not taken into account in the ENDF/B-VI evaluation and was calculated for the first time in the present evaluation.     

等横截面无限声学水域的连分式公式

基于比例边界有限元法连分式理论,提出了等横截面无限声学水域的连分式公式,推导了高频连分式公式与双渐近连分式公式,比较了连分式公式与动态质量矩阵模拟等截面无限水域的计算效率,发现前者效率优于后者。利用该公式分析了等截面无限声学水域在顺河向激励下的瞬态响应。数值模拟结果表明高频连分式公式的稳定性与收敛性有待改进,而双渐近连分式则具有更好的稳定性和收敛性,能正确模拟等截面无限水域。     

Conceptual Design for SuperCDMS SNOLAB

Beyond the present dark matter direct detection experiment at the Soudan underground laboratory, the SuperCDMS Collaboration is engaged in R&D activities for a 100-kg scale germanium dark matter experiment nominally sited at SNOLAB (2070 m overburden of rock). The expected sensitivity after 3 years of running is 3×10^?46?cm² for the spin-independent cross section, an order of magnitude improvement over present exclusion limits for WIMP masses ～80?GeV/c². At this depth, and appropriate design of shielding and cryostat, neutron backgrounds will be negligible. The baseline design is an expanded version of CDMS II with Ge substrates (100×33?mm discs) instrumented with the iZIP phonon sensor layout to achieve the electron surface-event rejection power required.     

轻金属材料在核反应堆中的应用

元素周期表中与氢同族或相近的轻金属元素（Li、Be、Na、Mg、Al）及其合金具有中子吸收截面小,感应放射能小等核学性能优点,可做为核裂变、聚变反应堆中包壳、慢化剂、中子源、冷却剂、氚增殖等部件材料,本文对这些轻金属材料在核领域中的应用进行概述。     

基于Geant4模拟中子输运过程及建立中子监测模型

通过研究Geant4程序的中子输运模型与反应截面库,构建热中子至20 MeV中子的输运过程,为验证Geant4中子输运过程的正确性,通过建立中子监测模型,再根据监测模型设计试验装置,最后将试验装置放入中子参考辐射场中进行测试验证.模拟与实验结果表明:试验装置在241Am-Be中子源和252Cf源中子参考辐射场中测试结果最大误差为2.5％.     

A cargo inspection system based on pulsed fast neutron analysis (PFNA)

A cargo inspection system based on pulsed fast neutron analysis (PFNA) is to be used at a border crossing to detect explosives and contraband hidden in trucks and cargo containers. Neutrons are produced by the interaction of deuterons in a deuterium target mounted on a moveable scan arm. The collimated pulsed fast neutron beam is used to determine the location and composition of objects in a cargo container. The neutrons produce secondary gamma rays that are characteristic of the object's elemental composition. The cargo inspection system building consists of an accelerator room and an inspection tunnel. The accelerator room is shielded and houses the injector, accelerator and the neutron production gas target. The inspection tunnel is partially shielded. The truck or container to be inspected will be moved through the inspection tunnel by a conveyor system. The facility and radiation source terms considered in the shielding design are described.     

Measurement of neutron inelastic scattering cross sections for 52Cr from threshold up to 18 MeV

The powerful white neutron spectrum from Gelina is used for the investigation of gamma ray production cross sections in the reaction 52Cr(n,n'gamma)52Cr. The gamma rays from the inelastic process are detected with two large volume HPGe detectors placed at 110 degrees and 150 degrees with respect to the beam direction. The neutron flux has been measured with a 235U fission chamber. For the main transitions the inelastic cross section is given with an incident neutron energy resolution ranging from 1.12 keV at 1 MeV to 35.7 keV at 10 MeV, the overall statistical error being <5%. Based on the known 52Cr level scheme, the level and total inelastic cross sections have been obtained up to 3.77 MeV excitation energy. Progress on the implementation of a new acquisition system based on a fast digitiser is presented in this paper.     

A Monte Carlo simulation of monoenergetic neutrons traversing rectangular and spherical polyethylene moderators

A Monte Carlo-based simulation of the transport of a series of monoenergetic neutron sources through first a rectangular block of 0.93 g cm(-3) density polyethylene and secondly through a sphere made of the same substance is presented here. In both instances, the neutron fields are monitored at closely spread intervals through the moderator mass, producing a lot of data in the process. To reduce the amount of data presented, a figure of merit is created by estimating the cross section for each discrete neutron energy and by applying this to the number of neutrons present of each energy giving an arbitrary response figure. This work was undertaken in order to aid the design and development of a novel neutron spectrometer.