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1.
ABSTRACT

A new high pressure cell for neutron diffraction experiments using nano-polycrystalline anvils is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to ~82?GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of Fe3O4 at ambient conditions using this cell and discuss the current limitation and future developments.  相似文献   

2.
Abstract

The crystal structure of Nd2CuO4 has been studied by neutron diffraction at pressure up to 5 Gpa. The volume compressibility value was determined as 5·6·10?3/Gpa. The decrease of positional parameter of neodymium at high pressure has been observed. This structural change is explained by pressure induced neodymium ions charge increase.  相似文献   

3.
Abstract

Time-of-flight method of neutron diffraction is applied for materials under high pressure and low temperature. Extra-scattering from the pressure cell is reduced by geometrical design and by shielding with boron-plastics. Temperature is controled by adjusting the supply of liquid nitrogen: Successive transformations with pressure are observed in heavy ice.  相似文献   

4.
Abstract

X-ray and neutron powder diffraction data obtained from samples contained within high pressure cells are generally of lower quality than data collected from samples at ambient conditions. The far smaller sample size as well as possible contamination of the pattern by the pressure cell means that Rietveld refinement techniques must be adapted to extract the maximum useful information from the data. These problems become paramount as larger structures at high pressure are attempted. Techniques such as “leBail extraction”, “soft restraints” and “rigid body refinement” will be discussed with application to analysis of high pressure neutron powder diffraction data.  相似文献   

5.
Abstract

The experiments which were carried out showed the possibility of using a titanium-zirconium high pressure cell for small angle neutron scattering. We report on some curves measured by SANS with the help of this setup to illustrate the capabilities of the method.  相似文献   

6.
Abstract

In connection with the IAEA-neutron seed irradiation Programme, a standard neutron irradiation facility has been constructed. The application of solid state track recorders for fast neutron spectra measurements inside this facility is discussed. Fissionable targets of 235U, 239Pu, 237Np, 238W and 232Th will be used, an approximative solution for the incident neutron spectrum will be obtained by a five-group method.  相似文献   

7.
Abstact: The kinetic energy spectrum and the polarization of the PSI neutron beam produced in the reaction 12C(p,n)X at 0° with 590 MeV polarized protons were investigated. A strong energy dependence of the neutron beam polarization is observed which was not expected at the time the neutron beam was built. Received: 3 April 1998  相似文献   

8.
Abstract

Neutron diffraction was until recently confined to pressures below ~ 3 GPa. This restricted range has limited the high-pressure structural information that is available for a wide range of phenomena for which neutron diffraction is the technique of choice. But now the recently-developed Paris-Edinburgh cell can achieve pressures up to ~ 30 GPa with a sample volume large enough to allow accurate structural studies with neutrons. After a period of development of the neutron scattering techniques needed to obtain the best possible results using the cell, a variety of successful structural studies have been performed. These illustrate the value of neutron diffraction in important areas such as locating hydrogen and other low-Z atoms in structures, the measurement of accurate structural pressure dependence and the examination of the changes in atomic thermal motion with pressure.  相似文献   

9.
Abstract

Crystallographic structure determinations of H2O and D2O ice VI single crystals were performed between 207 K and ambient temperautre at pressures of 0.9 GPa. A neutron pressure cell of the Marburg-type was used. Single crystals were grown in situ under optical control in the pressure cell. Details of the cell construction, especially the design of the sapphire anvils and zero-scattering gaskets, are described.  相似文献   

10.
ABSTRACT

A simple modified Bridgman design for large volume pressure anvils usable in the Paris-Edinburgh (PE) press has been demonstrated at Oak Ridge National Laboratory Spallation Neutron Source. The design shows advantages over the toroidal anvils typically used in the PE press, mainly rapid compression/decompression rates, complete absence of blow-outs upon drastic phase transitions, simplified cooling, high reliability, and relative low loads (~40 tons) corresponding to relatively high pressures (~20?GPa). It also shows advantages over existing large-volume diamond cells as sample volumes of ~2–3?mm3 can be easily and rapidly synthesized. The anvils thus allow sample sizes sufficient for in situ neutron diffraction as well as rapid synthesis of adequate amounts of new materials for ex situ analysis via total neutron scattering and neutron spectroscopy.  相似文献   

11.
Abstract

The change in electrical properties of TGS crystals due to induced defects created by fast neutron irradiation of two different energies (2 and 14 MeV) and different integrated neutron fluxes have been studied in the vicinity of phase transition. It is observed that the electrical conductivity increases with increase of neutron fluence up to 1.7 × 1010 n · cm?2 and the values of the relative change of electrical conductivity in case of 2 MeV are higher than that of 14 MeV neutrons at the same neutron fluence (φ)  相似文献   

12.
Abstract

Single crystal X-ray and neutron diffraction is essential for determining occupancies, positional as well as static and dynamic displacement parameters in crystalline matter by measuring Bragg, satellite or diffuse reflections. In our contribution a new low-temperature high pressure cell for neutron single crystal diffraction will be presented. It is designed to operate from a few K to ambient temperature in “orange” cryostats at pressures up to at least 3 GPa. We will present first neutron diffraction results obtained at E4/HMI Berlin and discuss the quality of the data and the significance of the results. A software package has been written (as a part of the PROMETHEUS system), which deals with the data reduction for both X-ray and neutron high pressure cell single crystal data. Likewise a data collection program has been developed for single crystal data collection on four-circle diffractometers using Merrill-Bassett cells. A series of single crystal experiments on H2O and D2O ice VI and KDP (KH2PO4) show that results of very high quality can be obtained routinely including even higher order terms in the atomic displacement parameters.  相似文献   

13.
The average stopping power of the recoiled nuclei generated by neutron elastic interactions with the Freon-12 drops in a superheated drop detector has been used to determine the maximum neutron energy of the 241Am–Be source. In an elastic interaction of neutrons with the Freon-12 liquid, the nuclei of 12C, 19F and 35Cl with different values of stopping power are scattered. The stopping power of these scattered nuclei corresponding to the energy transferred to them through the head-on collision was extracted from the SRIM code. The stopping power values were weighted by considering the neutron–nucleus elastic scattering cross section and the number of each nucleus in the Freon-12 molecule and the average stopping power was calculated from known neutron energy.The maximum energy of the 241Am–Be neutron source was estimated as 10.9 ± 3.0 MeV. The consistency between the determined energy and the other reported values confirms the validity of using the average stopping power in the superheated drop detectors. The average stopping power was also used to determine the threshold neutron energy as a function of external applied pressure at different temperatures. Knowing the threshold neutron energy as function of applied pressure, can be used in pressure scanning method for neutron spectrometry by superheated drop detectors.  相似文献   

14.
Ling Li  Hui Wu 《辐射效应与固体损伤》2013,168(11-12):1068-1074
Abstract

The operating durability of lithium-ion batteries is a principal problem in universe exploration or rescuing work in the nuclear radiation area. In the study, the neutron irradiation experiments were conducted on film-tin electrodes using the radiation dose of 1011, 1012, 1013 and 1014?n?cm?2, respectively. The results show that the particle size grows with the increasing radiation does by atomic force microscopy (AFM) and scanning electron microscope (SEM). In addition, the degressive trend of specific capacity of tin anodes after neutron radiations increases with the increasing radiation dose. The fade of electrochemical performances may be attributed to the increasing particle size and defects induced by neutron radiation.  相似文献   

15.
Abstract

This paper reports developments to enable neutron diffraction at simultaneous high temperatures and pressures using the Paris-Edinburgh cell. These include a new design of a cell assembly with internal heating. One of the novel features of our system is the use of neutron radiographic methods for measurement of temperature. Fully refinable neutron diffraction patterns obtained by time of flight technique with our apparatus are found to be of comparable quality to previous high-pressure studies at ambient temperatures. In this paper we describe the procedures for the generation and measurement of pressure and temperature and illustrate the quality of the data which can be obtained. The present system may be used on a routine basis for experiments up to 7 GPa and temperature approaching 2000 K. Current attempts are discussed for extending these measurements to a wider domain of pressures and temperatures.  相似文献   

16.
Abstract

High pressure neutron diffraction using the Paris-Edinburgh cell has attracted considerable interest ever since it has been shown that full structural data can be obtained at pressures up to 10 GPa. In this paper we will focus on the current state of this technique. Specifically, we report on new experimental possibilities concerning: i) access to “ultrahigh” pressures beyond 20 GPa, ii) experiments at variable temperatures down to 100 K, and iii) experiments on single crystals in inelastic neutron scattering. Current attempts to increase the pressure and temperature range are discussed.  相似文献   

17.
Abstract

The design of a titanium-zirconium clamped cylinder-piston type pressure cell for neutron diffraction investigations under hydrostatic pressure up to 10 kbars without supports is described. It is the first time that Freon-11 has been used as a hydrostatic pressure transmitting medium. The following results carried out at the room temperature are presented: the discovery of the transition from I to 111 phase in a LiKSO4 single crystal and the results of the investigation on the influence of pressure upon the structure of the YBaCuO HTSC obtained by means of the powder diffraction method.  相似文献   

18.
Abstract

The development of the Paris-Edinburgh cell has extended the pressure range for neutron diffraction by a full order of magnitude to 30 GPa. This advance has provided a wealth of new information on the high-pressure behaviour of ices such as water-ice, ammonia, methane and hydrogen sulphide. We have now put in place technique developments to permit loading of water-gas mixtures into the Paris-Edinburgh cell.  相似文献   

19.
The Fermi energy, pressure, internal energy, entropy, and heat capacity of completely degenerate relativistic electron gas are calculated by numerical methods. It is shown that the maximum admissible magnetic field on the order of 109 G in white dwarfs increases the pressure by a factor of 1.06 in the central region, where the electron concentration is ∼1033 cm−3, while the equilibrium radius increases by approximately a factor of 1.03, which obviously cannot be observed experimentally. A magnetic field of ∼108 G or lower has no effect on the pressure and other thermodynamic functions. It is also shown that the contribution of degenerate electron gas to the total pressure in neutron stars is negligible compared to that of neutron gas even in magnetic fields with a maximum induction ∼1017 G possible in neutron stars. The neutron beta-decay forbiddeness conditions in a superstrong magnetic field are formulated. It is assumed that small neutron stars have such magnetic fields and that pulsars with small periods are the most probable objects that can have super-strong magnetic fields.  相似文献   

20.
Abstract

The suitability of using 10B and 5LiF in contact with cellulose acetate butyrate (CAB) for the measurement of slow neutron densities has been investigated. The upper energy threshold of clear Diacel cellulose nitrate (CN) and of the CAB have also been measured. The CAB in good contact with thick 10B or 5LiF sources offers good promise for the detection of slow neutrons. For the actual CAB samples used, the CAB-10B combination had an efficiency of ~1.3 × 10?2 tracks per thermal neutron incident in a 2π solid angle. The corresponding number for the CAB6-Li combination is ~5.6 × 10?3 tracks per thermal neutron.  相似文献   

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