Texture studies using neutron diffraction

Various aspects of the application of neutron scattering methods to texture studies are reviewed. The neutron method is compared with other methods of texture measurement and techniques of neutron diffraction registration of texture are discussed.Examples are presented of the use of neutron scattering for texture examination in materials having various grain sizes and degrees of structural inhomogeneity. It is also demonstrated that the information about texture can be used in the discussion of the deformation and recrystallization processes in metals.Neutron diffraction results are shown to be helpful in the examination of the influence of texture on the anisotropy of physical properties in materials. The possibility of neutron diffraction measurements of magnetic texture is reported. Finally the accuracy of texture measurements using the neutron method is discussed.On leave from Academy of Mining and Metallurgy, Cracow, Poland.     

用于驱动次临界堆的惯性约束聚变中子源与加速器中子源的分析比较

分析了用惯性约束聚变（ＩＣＦ）中子源和加速器（ＡＤ）中子源驱动一个热功率为百万千瓦级（ＭＷｔ）的次临界包层的可能性。给出了驱动不同次临界度包层所需的中子源强度及其相应的物理参数。比较了两种中子源系统的特点及可能实现的前景。     

A half century of radioisotope neutron sources in China

Near fifty years history of the development of radioisotope neutron sources in China is briefly reviewed. The structure design, preparing technology and production status of routine neutron sources including 210Po-Be source, 210Po mock fission source, 241Am-Be source, 238Pu-Be source, 252Cf spontaneous fission source and other special-shape neutron sources are summarized. In addition, the prospects of development on radioisotope neutron source in China are predicted from the needs of nuclear power construction, oil well-logging, neutron moisture gauges and neutron brachytherapy.     

Simulations of neutron deceleration in a multistage UCN turbine using a multilayer monochromator

A neutron turbine is a neutron decelerator with neutron reflectors on a rotor. The multistage neutron turbine using multilayer monochromators has three rotors to decelerate very cold neutrons to ultra-cold neutrons. Reflecting blades on the rotors are flat and the incident direction of neutrons is perpendicular to the mirror surface. The use of a multistage turbine makes the incident velocity to be about 150 m/s which is faster than the existing neutron turbines and the three rotors make the velocity change smaller in one stage than the Doppler shifter employing Bragg reflection. It simultaneously improves the neutron extraction efficiency from a cold neutron source and the neutron deceleration. The peak deceleration efficiency assuming unit reflectivity in this three-stage turbine is about 0.71 from 150 m/s to UCN, and that of the final stage is about 0.81 from 50 m/s to UCN.     

功能/结构一体化中子屏蔽材料的研究现状

随着反应堆设计技术的发展,功能/结构一体化屏蔽材料成为一种发展趋势,要求中子屏蔽材料不仅具备中子屏蔽功能,而且可以兼作结构材料。中子屏蔽材料采用一体化设计可大幅简化屏蔽结构,实现屏蔽结构的轻量化和小型化。简述了功能/结构一体化中子屏蔽材料的设计要求和常见的热中子吸收核素。重点阐述了硼钢和具备功能/结构一体化潜力的铝基碳化硼复合材料、含Gd不锈钢、B/Pb复合材料的研究现状及存在问题。最后指出了功能/结构一体化中子屏蔽材料的发展方向。     

Quasi-monoenergetic neutron reference fields in the energy range from thermal to 200 MeV

Well-characterised neutron fields are a prerequisite for the investigation of neutron detectors. Partly in collaboration with external partners, the PTB neutron metrology group makes available for other users neutron reference fields covering the full energy range from thermal to 200 MeV. The specification of the neutron fluence in these beams is traceable to primary standard cross sections.     

Storage of multiple cold neutron pulses with perfect crystals

New measurements with the cold neutron storage apparatus VESTA are reported which are based on confining neutrons between two perfect single-crystal plates by means of subsequent Bragg reflections. An important issue is the coupling of the incoming beam to the neutron storage cavity by altering the transmission probability through the perfect crystal plates. Two methods based on magnetic field gating are described. The new experiments on VESTA deal mainly with the simultaneous storage of multiple neutron pulses. Theoretical predictions related to the storage process have been verified and the possibility of neutron beam manipulation demonstrated. Simultaneous storage of up to 6 neutron pulses is reported which leads to a new conceptual quality in neutron storage experiments. Multiple neutron pulse storage will be of specific interest for measurements with longer storage periods owing to the related intensity enhancement. Several further development steps will be discussed.     

A highly adaptive detector system for high resolution neutron imaging

An optimized detector system that allows high-resolution neutron imaging with desired flexibility is described. The presented system can be adapted and integrated with standard CCD-based neutron detectors. Novel neutron scintillating materials with good photon discrimination and optical lens components are tested and optimized for high-resolution neutron tomographic purposes. The presented detector system provides variable field of view and can be used in combination with different techniques, including dark-field, energy-selective, and neutron spin polarized imaging.     

Development of a TL detector for neutron measurement by CaSO4:Dy phosphors

Personal neutron dosimetry is quite a difficult area because a neutron is always accompanied with gamma radiation, which is required of a capability for mixed field dosimetry. CaSO4:Dy phosphor is known to have a very high sensitivity to gamma radiation, but the neutron capture cross section of the constituents of CaSO4:Dy are so small that the interactions between the thermal neutron and the phosphor are rare. One method to improve the neutron interaction is by introducing an impurity ion with a large thermal neutron captures cross section into the phosphor to act as a neutron target centre such as 6Li. In neutron-gamma mixed radiation fields, if two detectors for the 6Li-7Li compounds embedded CaSO4:Dy thermoluminescent (TL) pellets are used, a 6Li-compound embedded pellet can detect the neutron and gamma radiations together, and the other pellet can only detect the gamma radiation. Recently, the Korea Atomic Energy Research Institute (KAERI) has developed a new type of CaSO4:Dy TL materials embedded with phosphorous (KCT-300) to detect beta and gamma radiation with a very high sensitivity. This paper presents the development of CaSO4:Dy TL pellets embedded with 6Li compound for a thermal neutron measurement, and the detection method of the neutron and gamma dose in mixed fields with CaSO4:Dy TL pellets embedded with a 6Li compound (KCT-306) and CaSO4:Dy TL pellets embedded with a 7Li compound (KCT-307) is introduced. The net neutron sensitivity of CaSO4:Dy TL pellets embedded with 6Li compound developed in this study is about two times higher than that of the TLD-600 (Harshaw Chemical) dosemeter which is available commercially.     

Spin filters and supermirrors: a comparison study of two methods of high-precision neutron polarisation analysis

The precise knowledge of the neutron polarisation is needed in tests of the electroweak Standard Model using angular correlations in polarised neutron beta decay. We performed an experimental comparison study of two different methods of polarisation analysis of a cold neutron beam which are based on spin-dependent reflection, respectively, transmission. The compared devices are a supermirror analyser used in prior neutron decay studies and an opaque transmission spin filter of either polarised ³He or polarised protons. The results of the neutron polarisation measured with the supermirror analyser and with the spin filter coincided in three different experiments within 0.1–0.2%.     

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.     

Low-energy neutron spectrometer using position sensitive proportional counter—Feasibility study based on numerical analysis

There is no direct technique to measure a neutron energy spectrum, particularly in the lower energy region, because the reaction Q value for detection is much larger than the neutron energy to be measured. However, such techniques are becoming a necessity, for example, in medical applications such as boron neutron capture therapy. In this study, a new spectrometer to measure low-energy neutrons (from thermal to 100 eV) is investigated numerically. We propose a unique approach of estimating the neutron energy spectrum by analyzing the distribution of neutron detection depths in the detector using an exact relation between the neutron energy and nuclear reaction cross-section. The proposed spectrometer has been established to be feasible to manufacture. The conversion performance of the neutron detection depth distribution to the neutron energy spectrum has also been proven to be acceptable, with the unfolding process based on Bayes’ theorem, even though the detector response function is non-distinctive (without peaks or edges). The present spectrometer is now under development, and its practical performance will be reported as soon as the prototype detector is completed.     

Preliminary study of coded-source-based neutron imaging at the CPHS

A cold neutron radiography/tomography instrument is under construction at the Compact Pulsed Hadron Source (CPHS) at Tsinghua University, China. The neutron flux is so low that an acceptable neutron radiographic image requires a long exposure time in the single-hole imaging mode. The coded-source-based imaging technique is helpful to increase the utilization of neutron flux to reduce the exposure time without loss in spatial resolution and provides high signal-to-noise ratio (SNR) images. Here we report a preliminary study on the feasibility of coded-source-based technique applied to the cold neutron imaging with a low-brilliance neutron source at the CPHS. A proper coded aperture is designed to be used in the beamline instead of the single-hole aperture. Two image retrieval algorithms, the Wiener filter algorithm and the Richardson-Lucy algorithm, are evaluated by using analytical and Monte Carlo simulations. The simulation results reveal that the coded source imaging technique is suitable for the CPHS to partially solve the problem of low neutron flux.     

Neutron detection by measuring capture gammas in a calorimetric approach

The neutron capture detector (NCD) is introduced as a novel detection scheme for thermal and epithermal neutrons that could provide large-area neutron counters by using common detector materials and proven technologies. The NCD is based on the fact that neutron captures are usually followed by prompt gamma cascades, where the sum energy of the gammas equals to the total excitation energy of typically 6-9 MeV. This large sum energy is measured in a calorimetric approach and taken as the signature of a neutron capture event. An NCD consists of a neutron converter, comprising of constituents with large elemental neutron capture cross-section like cadmium or gadolinium, which is embedded in common scintillator material. The scintillator must be large and dense enough to absorb with reasonable probability a portion of the sum energy that exceeds the energy of gammas emitted by common (natural, medical, industrial) radiation sources. An energy window, advantageously complemented with a multiplicity filter, then discriminates neutron capture signals against background. The paper presents experimental results obtained at the cold-neutron beam of the BER II research reactor, Helmholtz-Zentrum Berlin, and at other neutron sources with a prototype NCD, consisting of four BGO crystals with embedded cadmium sheets, and with a benchmark configuration consisting of two separate NaI(Tl) detectors. The detector responses are in excellent agreement with predictions of a simulation model developed for optimizing NCD configurations. NCDs could be deployed as neutron detectors in radiation portal monitors (RPMs). Advanced modular scintillation detector systems could even combine neutron and gamma sensitivity with excellent background suppression at minimum overall expense.     

Normalization of a collimated 14.7 MeV neutron source in a neutron spectrometry system for benchmark experiments

In the present study a method used to normalize a collimated 14.7 MeV neutron beam is introduced. It combined a measurement of the fast neutron scalar flux passing through the collimator, using a copper foil activation, with a neutron transport calculation of the foil activation per unit source neutron, carried out by the discrete-ordinates transport code DOT 4.2. The geometry of the collimated neutron beam is composed of a D-T neutron source positioned 30 cm in front of a 6 cm diameter collimator, through a 120 cm thick paraffin wall. The neutron flux emitted from the D-T source was counted by an NE-213 scintillator, simultaneously with the irradiation of the copper foil. Thus, the determination of the normalization factor of the D-T source is used for an absolute flux calibration of the NE-213 scintillator.The major contributions to the uncertainty in the determination of the normalization factor, and their origins, are discussed.     

核防护用水泥基中子屏蔽材料的研究进展

不同能量的中子有不同的工程屏蔽方法,水泥基中子屏蔽材料具有重要应用价值.本文首先从中子防护的角度简要介绍了中子屏蔽原理,其次从快中子减速、慢中子吸收两个方面总结概括了水泥基中子屏蔽材料的研究现状,分析了水泥基中子屏蔽材料存在的不足:功能单一、耐久性、施工性及环境友好等问题,并指出了下一步研究方向:提高核防护水泥混凝土综...     

Initial neutronic target station studies for the national spallation neutron source (NSNS)

Results found during initial NSNS target station neutronic design efforts are reported including the success of comparing neutron sources at 1 eV and moderator performance normalized to 1 eV. The usefulness of an analytic form is demonstrated. The angular dependence of the neutron current from a moderator face is presented together with the changes in neutron current with variation of moderator width, poison plate location and moderator material. The formation of an equilibrium state at low neutron energy is also discussed.     

Ten years of personal neutron dosimetry with albedo dosemeters in The Netherlands

Since 1987, the dosimetry service of the Netherlands Energy Research Foundation (ECN) has been certified by the Dutch government to perform personal dosimetry, using thermoluminescence dosemeters (TLDs). Performing neutron personal dosimetry requires a rather large investment in readers, TLDs and personnel to operate the service. About 800 persons are subjected to routine neutron monitoring in The Netherlands and their annual neutron doses are a relatively small fraction (less than 10%) of the annual Hp(10). In general, the measured neutron dose values are low (on average 93% of the users receive an annual neutron dose <0.2 mSv). The collective annual (neutron) dose has tended to decrease since 1992, but incidentally high doses have been observed. Leaving these incidents out, the average collective annual neutron doses for the different users of neutron sources are about the same.     

Gamma dose measurement in a water phantom irradiated with the BNCT facility at THOR.

It has been proposed that a LiF thermoluminescence dosemeter (TLD) is used as a gamma dosemeter in a water phantom irradiated with the BNCT facility at THOR. Based on the TLD neutron sensitivity and neutron fluxes in the water phantom, which were simulated by the MCNP code, TLD-700 was chosen as a gamma dosemeter in this report. For the correction of the neutron influence on TLD-700, the thermal neutron sensitivity to TLD-700 was investigated with MCNP simulation and the thermal neutron flux was measured with gold foils using the cadmium difference technique. The correction to the neutron influence on the TLD was established on the TLD thermal neutron sensitivity. the thermal neutron flux, and the conversion factor from energy deposition in the TLD to the TLD response. By comparing the experimental data with the thermal neutron influence correction, these data are in very good agreement with the MCNP predictions.     

A simple facility to measure the scalar neutron spectrum in an assembly

An inexpensive, simple and safe facility was constructed to measure the neutron spectrum in an assembly, by setting a neutron source outside the assembly. A normalization technique for the neutron spectrum and error analyses are mentioned. The error of the calculated spectrometer efficiency is cancelled at the final spectrum normalization. The error caused by the present method is within acceptable levels.