[en] An extensive interlaboratory comparison was conducted on high temperature superconductor (HTS) critical-current measurements. This study was part of an international cooperative effort through the Versailles Project on Advanced Materials and Standards (VAMAS). The study involved six US laboratories that are recognized leaders in the field of HTS. This paper includes the complete results from this comparison of critical-current measurements on Ag-sheathed Bi₂Sr₂Ca₂Cu₃O_10-x (2223) tapes. The effects of sample characteristics, specimen mounting, measurement technique, and specimen damage were studied. The future development of a standard HTS measurement method is also discussed. Most of the evolution of this emerging technology has occurred in improvement of the performance of the conductors. The successful completion of this interlaboratory comparison is an important milestone in the evolution of HTS technology and marks a level of maturity that the technology has reached

[en] The Cold Neutron Depth Profiling (CNDP) instrument at the NIST Cold Neutron Research Facility (CNRF) is now operational. The neutron beam originates from a 16 L D₂O ice cold source and passes through a filter of 135mm of single crystal sapphire. The neutron energy spectrum may be described by a 65 K Maxwellian distribution. The sample chamber configuration allows for remote controlled scanning of 150 x 150 mm sample areas including the varying of both sample and detector angle. The improved sensitivity over the current thermal depth profiling instrument has permitted the first nondestructive measurements of ¹⁷O profiles. This paper describes the CNDP instrument, illustrates the neutron depth profiling (NDP) technique with examples, and gives a separate bibliography of NDP publications

[en] The rate coefficients are calculated for trap loss due to excited state formation during s-wave collisions of two atoms in a light field in a cold atomic gas near conditions for formation of a Bose-Einstein condensate. Blue detuning from the allowed atomic resonance transition causes excitation of a repulsive molecular potential, whereas red detuning causes excitation when the light is tuned near a bound vibrational energy level of an attractive molecular potential. In either case, when the light intensity is low and the detuning is large compared to the natural linewidth of the atomic transition, the rate coefficient for the collisional los rate is proportional to a molecular Franck-Condon factor. A simple reflection approximation formula is derived which permits the rate coefficient to be given analytically in either case. The analytic reflection approximation formula, as well as a simple phase-amplitude formula for the intermediate range wavefunction, give excellent agreement with the results of numerical quantum mechanical calculations. The trap loss rates due to binary collisions are comparable to or exceed those due to atomic recoil heating for a wide range of detunings to the blue of atomic resonance and near the peaks of photoassociation resonances for the case of red detuning

[en] Two types of ultra high energy resolution neutron scattering instruments, the backscattering spectrometer and the spin echo spectrometer, are described. Examples of the types of research which can be done with these instruments are given and plans for a cold neutron backscattering spectrometer which will be built in the NIST Cold Neutron Research Facility (CNRF) are discussed. It is hoped that this information will be of use to researchers considering neutron scattering experiments at NIST

[en] PVT relations in liquid and solid T₂ near the melting curve were measured over 20.5 K--22.1 K and 0 MPa--7 MPa (0 bar--70 bar) with a cell that used diaphragms for pressure and volume variation and measurement. Because of ortho-para self conversion, the melting pressure Pm and the liquid molar volume V_im increased with time. The rates were consistent with a second order reaction similar to that for c the J = odd concentration: dc/dt = -k₁c² + k₂c(1-c), where k₁ = 6 - 9 x 10^-2h^-1. By extrapolation, the ortho and para forms differed by ΔP_m ∼ 6 bar and ΔV_im ∼ 0.5%. Measurements of the volume change on melting and the thermal expansion and compressibility for liquid T₂ were consistent with those for H₂ and D₂. Impurities such as H₂, HT, DT, and ³He were removed by a technique using an adsorption column of cold activated alumina. Correction for ³He growth during an experiment were adequate except near the triple point

[en] The observation of galactic γ lines following the decay of radioactive nuclei provides a direct link between nuclear physics experiments in earth-based laboratories and astrophysical observations with space-based observatories. Two examples are presented to illustrate this interplay: the measurement of the lifetime of ⁴⁴Ti to allow an improved determination of the ⁴⁴Ti mass of the supernova remnant Cassiopeia A from the observed γ ray activity and the measurements of excited states in ²⁴Si to determine the reaction rate of ²³Al(p,γ)²⁴Si which might be important for a reduced production of ²²Na in novae

[en] The Cold Neutron Research Facility (CNRF) at the National Institute of Standards and Technology (NIST) Research Reactor (NBSR) is now coming on line, with the first seven experimental stations operational, and more stations scheduled to be installed during 1992. The present article provides an introduction to the facility, and to other articles in the current issue that give more details on some of the research opportunities that the facility will bring to NIST

[en] As part of an international ²²²Rn measurement intercomparison conducted at Bermuda in October 1991, NIST provided standardized sample additions of known, but undisclosed (blind) ²²²Rn concentrations that could be related to US national standards. The standardized sample additions were obtained with a calibrated ²²⁶Ra source and a specially-designed manifold used to obtain well-known dilution factors from simultaneous flow-rate measurements. The additions were introduced over sampling periods of several hours (typically 4 h) into a common streamline on a sampling tower used by the participating laboratories for their measurements. The standardized ²²²Rn activity concentrations for the intercomparison ranged from approximately 2.5 Bq · m^-3 to 35 Bq · m^-3 (of which the lower end of this range approached concentration levels for ambient Bermudian air) and had overall uncertainties, approximating a 3 standard deviation uncertainty interval, of about 6% to 13%. This paper describes the calibration and methodology for the standardized sample additions

[en] The authors discuss various properties of the ground state of a Bose-condensed dilute gas confined by an external potential. They devote particular attention to the role played by the interaction in determining the kinetic energy of the system and the aspect ratio of the velocity distribution. The structure of the wave function near the classical turning point is discussed and the drawback of the Thomas-Fermi approximation is explicitly pointed out. They consider also states with quantized vorticity and calculate the critical angular velocity for the production of vortices. The presence of vortex states is found to increase the stability of the condensate in the case of attractive interactions

[en] Crystal-GRID measurements have been performed with ZnS single crystals. For the first time, an asymmetric Crystal-GRID line shape could be observed. The preliminary data evaluation indicates that the reported lifetime of the 3221 keV level in ³³S is too short. A value of about 60 fs has been found. Due to this long lifetime the line shape is much less structured than calculated with the reported lifetime