Measurements Of He Research Articles

Thermal conductivity of dilute 3He 4He mixtures near the superfluid transition

Thermal conductivity measurements of 4He and very dilute mixtures of 3He in 4He (7 × 10 −4 < X 3 < 1 × 10 −2) at saturated vapor pressures near the superfluid transition T λ ( X) are reported. The results for the mixtures in the normal phase are compared with recent predictions by Dohm, Folk and Bhattacharjee, and Onuki. In the superfluid phase the data extrapolated to T λ ( X) are compared with previous experiments and with predictions.

Proposal for measurement of 4He II condensate — A reply to recent criticisms

Recent criticisms of a method to measure the temperature-dependent condensate fraction in 4He II, proposed by the authors some time ago, are assessed and found to be insufficient to discredit our procedure.

Foil non-uniformity correction in straggling measurements by the backscattering technique

A method for the accurate measurement of 4He + energy straggling in a thin Au layer is described. The foil non-uniformity is taken into account through the mean thickness fluctuation which is measured with a 14N + ion beam.

Transition temperatures, entropies, internal energies, and heats of desorption of 4He films adsorbed on graphite from vapor pressure measurements

Vapor pressure measurements of 4He adsorbed on Grafoil for coverages x = 0.94 and 1.00 were made as a function of temperature in the temperature range of 5–10 K. The data are presented as plots of ln p vs. 1/T and from these dp/dT vs. T curves are presented. For both coverages there is an indication of a phase transition, which agrees with the conclusions from specific heat data on the same system obtained by other authors. Molar entropies and internal energies, as well as isosteric heats of adsorption, were obtained as a function of coverage, and from the data the contribution to the total specific heat of the adsorbed films due to desorption was found to be considerable.

Determination of tritium by mass spectrometric measurement of 3He

A new technique for analysis of environmental tritium is described. The method consists of mass-spectrometer measurements of 3He allowed to accumulate for suitable times in degassed samples of water sealed in containers made of Corning type-1720 glass. Twelve samplesfrom the Pacific Ocean were measured by this method and also β-particle counting at the University of Miami. Agreement between the two methods in satisfactory, although our results seem to be systematically higher than the Miami results by ∼ 2%. Mass-spectrometric measurements were also made of the tritium concentration in the 1961 NBS tritiated water standard. These gave a concentration 1.6(±0.6)%higher than that calculated from the stated NBS activity per gram using a half-life of 12.26 years, which was also used to correct for decay to August 1975. If a half-life of 12.51 years is used, the above discrepancy is eliminated. As part of this work, the 3He/ 4He ratio in atmospheric helium has been redetermined, and found to be 1.384 × 10 −6 (±0.4%), which is in good agreement with the value of 1.399 × 10 −6 (±0.9%) measured by Mamyrin, Anufriyev, Kamenskiy and Tolstikhin.

Fine-structure measurements of4He by zero-field quantum beats

The complete finestructure beat frequency patterns ofn 3 P states of4He I (n=3–7) are measured by observation of zero field quantum beats using the beam-foil technique. The results provide a new experimental value for the 73 P 2–73 P o separation, confirm the beat amplitude ratios to be in accord with theory and allow comparison with the results of other techniques.