[en] We develop ab-initio coupled-cluster theory to describe resonant and weakly bound states along the neutron drip line. We compute the ground states of the helium chain ^3-10He within coupled-cluster theory in singles and doubles (CCSD) approximation. We employ a spherical Gamow-Hartree-Fock basis generated from the low-momentum N³LO nucleon-nucleon interaction. This basis treats bound, resonant, and continuum states on an equal footing, and is therefore optimal for the description of properties of drip line nuclei where continuum features play an essential role. Within this formalism, we present an ab-initio calculation of energies and decay widths of unstable nuclei starting from realistic interactions

[en] The principles of the helium dilution refrigerator are outlined. The lowest temperature attained with a continuously operated dilution refrigerator was about 10 mK, and 5 mK for a limited period when the supply of concentrated ³He to the mixing chamber was interrupted. (R.S.)

[en] The delayed annihilation time spectra (DATS) of antiprotonic helium atoms have been studied in isotopically pure low-temperature ³He and ⁴He gas at various densities. The DATS taken at 5.8 K and 400 mbar are very similar in shape except for (i) a small difference in the time scale and (ii) the presence of a distinct fast decay component in the case of ³He. The ratio of overall trapping times (mean lifetimes against annihilation), R=T_trap(⁴He)/T_trap(³He), has been determined to be 1.144 ± 0.009, which is in good agreement with a theoretical estimate yielding R=[M^*(bar p⁴He)/ M^*(bar p³He)]²=1.14, where M^* denotes the reduced mass of the bar pHe²⁺< enspace>system. The presence of a short-lived component with a lifetime of 0.154±0.007μs in the case of ³He suggests that the bar p³He⁺atom has a state of intermediate lifetime on the border between a metastable zone and an Auger-dominated short-lived zone. The fraction of antiprotons trapped in metastable states at 5.8 K and 400 mbar is lower by 22.2(4)% for ³He< enspace>than for ⁴He. All the data can be fitted fairly well with simple three-level and four-level cascade models. copyright 1996 The American Physical Society

[en] Short communication

[en] The typical helium property at a temperature lower than 2.17 K is a drop in viscosity. Superfluid helium features extra high thermal conductivity. Variations are given of the vapour pressure above liquid helium in a range of 0.01 to 1,000 torr with temperatures in a range of 0 to 3.5 K. The coefficient of heat transfer between the cryogenic liquid and the heat transfer surface grows from 300 to 15,000 Wm^-2K^-1. A single-phase flow may only be considered for the supercritical state helium. Helium density and thus also the intensity of cooling is significantly higher than for vapour of the same temperature under normal pressure. (J.B.)

[en] The authors carry out a comprehensive study of the binding of two helium atoms in unrestricted and, in particular, in restricted geometries in both two and three dimensions. Besides the well known binding of the ⁴He dimer in unrestricted geometry in two and three dimensions, the authors also find weakly bound states of the ³He-⁴He molecule and the ³He dimer in 2 dimensions. Furthermore, any combination of two ⁴He or ³He atoms can form a molecule if their motion is sufficiently confined. The calculations are carried out by numerically solving the Schroedinger equation as well as by constructing a suitable variational wave function

No abstract available

No abstract available

[en] The lifetime of long-lived antiprotonic helium atoms is mainly determined by Auger decay. The rate of this process is calculated for a number of states of the 3He p-bare and 4He p-bare systems

[en] The atomic and nuclear masses of ⁴He and ³He have been measured using doubly charged ions in a Penning trap connected to an electron beam ion source. Recent technical improvements allow mass determinations with uncertainties of a few parts in 10¹⁰. The obtained atomic masses are 4.002 603 256 8(13) u and 3.016 029 323 5(28) u respectively. These values deviate by as much as 5 standard deviations from the accepted values. (orig.)