ΔT-window neutron spectrometer

A high resolution neutron spectrometer making use of a ΔT-window filter for the analyser and time-of-flight technique for analysing incident neutron energy has been designed. The spectrometer will provide a continuously variable energy resolution ΔE from 40-50μeV at ~ 5230μeV. The range of energy transfer allowed is -1450μeV to +2950μeV and the range of wavevector transferQ allowed is 0.82-3.06 Å-1. Depending on the resolution used, the counting rates are expected to vary from 28-60 × 103 counts/hr if one assumes 10% isotropic elastic scattering from the sample

Magnetic field dependence of critical current density in YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB>

We have measured the transport critical current densityJ cof sintered YBa2Cu3O7, in various applied fields up to 185 Oe at 77 K. We find a sharp decay ofJ cwith magnetic field. We show that this sharp decay is consistent with the low field hysteresis results of Groveret al. We argue that the observed field dependence is not caused by intragranular weak links

Neutron quasi-elastic scattering in materials research

The paper reviews the quasi-elastic neutron scattering activities at the Bhabha Atomic Research Centre and demonstrates how this technique gives information on rates and geometries of stochastic motions in liquids and solids

Multilayer growth facilities and studies at IUC-DAEF: a review

Recently developed thin film and multilayer structure deposition facilities at IUC-DAEF, Indore Centre are discussed in the present paper. Using these facilities a number of single layer as well as multilayer systems were deposited and studied using various characterization techniques. Studies on some of these multilayer systems, viz. Nb-C, Fe-Ni, Nb-Fe and single-layer films of Ag, FeN and SiO2 are also presented

Neutron spectrometry at Trombay

The paper briefly describes three spectrometers which were commissioned after ICNS-88 at Dhruva reactor. The development of PSDs for neutrons at Trombay is also discussed

A cold neutron source for the DHRUVA reactor: optimization calculations

It is possible to obtain an increase in the flux of cold neutrons emerging from a nuclear reactor by remoderating the neutrons in a cold moderator. This paper evaluates the optimum height for a cylindrical liquid methane moderator (110 K) for the flux conditions in the DHRUVA reactor. Remoderated spectra emerging from cylindrical liquid methane moderator are calculated using a Monte Carlo technique for the height of the cylinder varying from 5 to 25 mm. The gain in flux quickly builds up with increase in height and nearly saturates beyond 20 mm. The effective temperature of the emerging spectrum is about 130 K. This calculation has been used to decide upon the height of the cylindrical cold source. It is possible to obtain an increase in the flux of cold neutrons emerging from a nuclear reactor by remoderating the neutrons in a cold moderator. This paper evaluates the optimum height for a cylindrical liquid methane moderator (110 K) for the flux conditions in the DHRUVA reactor. Remoderated spectra emerging from cylindrical liquid methane moderator are calculated using a Monte Carlo technique for the height of the cylinder varying from 5 to 25 mm. The gain in flux quickly builds up with increase in height and nearly saturates beyond 20 mm. The effective temperature of the emerging spectrum is about 130 K. This calculation has been used to decide upon the height of the cylindrical cold source

Temperature effects on lattice vibrations in germanium

Frequencies of selected normal modes of germanium at temperature of 100&#176;K and (roughly) 700&#176;K were determined using neutron spectrometry. The results (Table 1) show that the frequencies at 700&#176;K are uniformly lower than those at 100&#176;K by 4.5 (&#177; 0.6)%. The various harmonic force constants thus appear to have a common specific dependence on the temperature, probably through a general "softening" of the electronic structure. No energy broadening of the neutron groups was observed; this may simply be an aspect of the smallness of the anharmonicity in germanium

The one-dimensional CH<SUB>3</SUB>-quantumrotator in solid 4-methyl-pyridine studied by inelastic neutron scattering

The phenomenon of tunneling through potential barriers, representing motions which are classically forbidden, has been studied for the case of rotational motion of a methyl group in solid 4-methyl-pyridine. A sixfold hindrance potential of 11&#177;3 meV is inferred from a comparison of the directly observed transitions between the three lowest levels and theoretical calculations

Dynamics of liquid CH<SUB>4</SUB> from cold-neutron scattering

The scattering of 4.1 &#197; neutrons by liquid CH<SUB>4</SUB> at 98&#176;K has been studied at several angles using a rotating-crystal spectrometer. The spectra at all angles show a broad inelastic hump associated primarily with the rotational motions and a quasi-elastic peak which is related to the translational motions. The width of the quasi-elastic peak follows the simple diffusion behavior over almost the entire range of present experiments, and leads to a value of 2.2&#215;10<SUP>&#8722;5</SUP> cm<SUP>2</SUP>/sec for the diffusion coefficient. A more detailed analysis suggests that the delay time in the onset of simple diffusion behavior is similar to that in argon. The data clearly show that if the translations are viewed in terms of the Langevin model, then it is not necessary to consider a wavelength-dependent damping factor such as has been recently proposed by Griffing. High-resolution data taken at 15&#176; scattering angle do not reveal any sharp inelastic peaks, which should be present if the rotations are free. From this it is concluded that the rotations are hindered in the liquid state, in accord with earlier spectroscopic work, but in disagreement with the neutron work of Hautecler and Stiller. Calculations based on a model in which the rotations are free and the translations follow the simple diffusion model show poor agreement with experiments. Consideration of a more realistic model for the translations, based on the results of the computer experiments of Nijboer and Rahman for argon, yields only a slight improvement. It is suggested that a proper treatment of the hindered rotations is necessary to obtain agreement with experiment

Investigation of hydrogenous materials using neutrons

Slow neutrons have proved to be a very powerful probe for examining materials in general and hydrogenous materials in particular. In this article we review various neutron scattering techniques which have been utilised to investigate different aspects of a variety of hydrogenous materials. Translationally as well as orientationally disordered materials, ferroelectrics, superconductors, metal-hydrogen systems, polymers and biological molecules have been chosen as illustrative examples