On the branching ratios of several pairs of He(II) lines

Branching ratios of He(II) lines have been measured for the principal levels 5–10. The observations have been made on an He plasma produced by a hollow cathode-arc discharge, having an electron density of 3×10¹⁹m^-3 and an electron temperature of 2×10⁵ K on the axis of the discharge.The observed branching ratios differ by about 30% from the ones following from theoretical transition probabilities, if the sublevels of the main levels were populated according to their statistical weights. The shape of the He(II) 4686Åemission line observed off the axis of the discharge using a Fabry-Pérot interferometer gave evidence of a non-statistical population distribution for the sublevels.     

Excitation of He+ in a hollow cathode arc discharge

Population densities of the excited He(II) levels i=4 to i=10 in hollow cathode arc discharge have been determined and compared with those calculated from a collisional-radiative model. In the experiment the electron temperature was about 2x10⁵K and the electron density about 3x10¹⁹ m^-3. The observed population densities agree within 50% with those calculated by Drawin and Emard, but differ by a factor 4–6 from the ones found by McWhirter and Hearn. The results of the present experiment suggest that near the threshold energies the cross sections for electronic excitation of He⁺ levels from the He⁺ ground state are half those expected from the calculations of Burgess. We conclude that Drawin and Emard's calculations should preferably be employed for the determination of the electron density and the electron temperature from observed population densities.     

He(I) and He(II) populations in the Nagoya TPD plasma machine

A collisional-radiative model is used to explain the He(I) population densities observed by Otsuka, Ikee and Ishii in their TPD plasma machine. It is shown that a plasma model, which is partially optically thick to He(II) Lyman radiation, can explain the experimentally observed He(II) population density at T_e=3.17 eV. The agreement between the experimental and calculated He(II) population densities observed by Otsuka and others is shown to be due to an error in their calculations.     

The electronic structure of dinuclear transition-metal complexes containing metal—metal interactions: II. He(I) and He(II) photoelectron spectra of hexacarbonyldi-irondisulfur and related complexes

The He(I) and He(II) photoelectron spectra of a series of Fe₂(CO)₆LL¹-type complexes (L = L¹ = S, (i-propyl)S; L,L¹ = t-but of an all-electron, ab initio SCF MO calculation on Fe₂(CO)₆S₂ and of extended CNDO calculations on related molecules. Assignments given ar He(I)/He(II) intensity differences, and on comparison with related molecules.The coordination of the bridging ligands to the metal centres and the nature of the metal—metal interactions are discussed.     

Measurement of Stark broadened profile of He(II) 4686A

Stark broadened profiles of the He(II) 4686A line were measured using a Z-pinch plasma as source. The electron density was determined from the halfwidth of the He(I) 3889 line and the temperature from the intensity ratio of the He(II) 4686 and the He(I) 3889 lines. The electron densities covered the range 0.5?2.3×10¹⁷ cm³ and the electron temperature was 4 eV. The plasma homogeneity was checked by varying the length of the column observed. The experimental profiles are in better agreement with the recent calculations of Greene than with the earlier calculations of Keeple.     

Spin assignment for the 1.89 MeV level in42Sc

The gamma decay mode and the spin value of the 1.89 MeV state of⁴²Sc were investigated by studying the⁴⁰Ca(³He,p γ)⁴²Sc reaction at 10.0 MeV energy of the incident³He beam. The analysis of thep-γ angular correlation of the 1.89 MeV ground state transition — using method II of Litherland and Ferguson — yields the spin assignmentJ=1 for this level.     

Elastic scattering of intermediate energy protons on4He and12C

The elastic angular distribution and polarization of ～1 GeV protons on⁴He and¹²C have been analysed using the recently proposed correlation expansion for the Glauber amplitude by retaining terms up to three-body density only. The calculations include Coulomb and spin effects. Using realistic form factors for target nuclei it is found that we need to consider only up to the second-order density term to provide a satisfactory explanation of both kinds of experimental data in the available momentum transfer region. The contribution of the three-body density term is only marginal except in⁴He differential cross-section in the cm angular range 45°<θ _cm<65°.     

Experimental study of stark broadening of nitrogen ion lines in a theta pinch plasma

We have studied the Stark broadening of the 3s-3p, 3p-3d and 3d-4f emission lines of the nitrogen II, III, and IV ions emitted from a hot plasma. The plasma was created by a 60 kJ, 60 kV single turn coil theta pinch, where the fill gas was 3 torr of (49%He+51%N₂). The plasma was diagnosed by measuring the Stark-broadened profile of the He(II) 4686 Å line and by taking shadowgrams of the plasma development. It was found that the ionization stage distribution and thus the electron density departed from that predicted by Saha-Boltzmann equilibrium relations. The analysis of the plasma parameters gave an electron density of 1.4 x 10¹⁸ cm^-3. The electron temperature was measured from the relative intensities of emission lines as well as from the line-to-continuum ratio and was found to be 5.0 eV. The line profiles have been fitted to Lorentzian profiles and the thus measure line widths are compared with earlier experimental data as well as with simple theoretical calculations. We find that our line widths are broader than earlier data taken at lower densities if we assume a linear scaling of the half width with the density. A simple Lorentzian profile fits in most cases quite well to the observed line profile. The simple calculations can predict the linewidths within 20% for the low lying levels of both the singly and doubly ionized nitrogen while the predictions are far too narrow for the higher lying levels from the multiply ionized atoms.     

Role of atomic inelastic collisions in a Cs-He steady state discharge

The population of various excited states and the electron temperature in a mixture of cesium vapor and helium have been measured spectroscopically in a stationary electrical discharge where helium atoms remain in their ground state. An equilibrium between the populations of highly excited cesium levels was observed to be characterized by a Boltzmann temperature equal to the gas temperature. It is concluded that the populations of these high levels are more influenced by Cs¹+He inelastic collisions than by Cs¹+e collisions when [He]/[e]?10⁶. The influence of the helium atoms has also been observed on the relation between electron temperature and electron density.     

Relative Production Rates of 6He, 9Be, 12C in Astrophysical Environments

We assume an environment of neutrons and ??-particles of given density and temperature where nuclear syntheses into ⁶He, ⁹Be, and ¹²C are possible. The resulting relative abundance as a function of density and temperature is investigated.     

Pairing energy of liquid 4He

The two-particle density matrix of a Bose system described by a Jastrow wave function displays off-diagonal long-range order associated with strong correlations between pairs of bosons with non-zero momenta ?q, -?q. In conjunction with the zero-momentum condensate, these correlations give rise to a finite contribution to the energy expectation value per particle, which is calculated for liquid ⁴He at two values of the density.     

Structure of the <Superscript>6</Superscript>He nucleus in the three-particle model

The properties of the ⁶He nucleus were investigated in a three-particle approximation (a alpha-particle cluster plus two neutrons) on the basis of the variational approach by using a Gaussian basis. For nn and nα interactions, potentials that make it possible to describe S-wave phase shifts for elastic scattering and, simultaneously, to reproduce faithfully the energy and the size of the ⁶He nucleus were proposed. Characteristic structural features of this nucleus that are manifested in the density distributions, elastic form factor, pair correlation functions, and momentum distributions of particles constituting the ⁶He nucleus in the three-particle model were revealed.     

On the verification of atomic data for <Emphasis Type="Italic">K</Emphasis><Subscript>α</Subscript> radiation spectra from the TEXTOR tokamak

High-resolution spectra from the Ar¹⁶⁺ and Ar¹⁵⁺ ions measured at the TEXTOR tokamak are used to verify atomic data necessary for simulation and diagnostics of a hot coronal plasma with an accuracy of about 5%. A self-consistent approach based on solving the inverse problem by the Bayesian iteration method in the framework of the proposed semiempirical “spectroscopic” model is used. The perturbation calculations of the atomic characteristics for [He] and [Li] argon ions by means of the ATOM and MZ codes require 10% correction of the ratios of the effective excitation rates for the intercombination line of the [He] ion and the group of dielectronic satellites corresponding to the 1s2p3l — 1s ²3l′ transitions in the [Li] ion to the resonance line of the [He] ion. The spectra calculated with this correction are in agreement with the measured spectra within the measurement accuracy ?10% in the wide ranges ～0.8–2.5 keV and ～10¹³–10¹⁴ cm^?3 of the central electron temperature and density, respectively. It is found that the central temperature value can be determined in the framework of the spectroscopic model with an accuracy of ～5%, and the abundances of the [Li] and [II] argon ions with respect to the [He] ions can be determined with an accuracy of ～20 and 50%, respectively. It has been shown that the use of the isothermal approximation when measuring the temperature from the ratio of the intensities of the dielectronic satellites to the resonance line can lead to a large error of ～20% in the presence of gradients typical for tokamak plasmas.     

Spreading width of the IAS in even Pm isotopes measured via the ANd(3He,t)APm and ANd(3He,tp)A−1Nd reactions

Total and escape widths of IAS in even-A Pm isotopes have been measured via the ^ANd(³He, t)^APm and ^ANd(³He, t$\text{p}$)^A?1Nd reactions. Values for the spreading widths have been deduced and found to increase strongly with the excitation energy of the IAS through the chain of Pm isotopes. This behaviour, in contrast with the much smoother global increase with mass number, is attributed to a dependence on level density.     

Pressure effects of argon and helium on the first diffuse series doublet of singly ionized barium

The shift and broadening of the first diffuse series doublet of Ba II in emission was observed under various relative densities of Ar (20–107) and He (35–121) at 2500°K. By comparing the present data with those of the shift of the principal series doublet from a previous paper, it is suggested that argon pressure causes a downward displacement for 6p²P and 6d²D levels and an upward one for 5d²D and 7s²S levels, with respect to the ground state of Ba II.     

High density measurements of the Stark broadened profile of the He(II)4686 Å line

The Stark broadened profile of the He(II)4686 Å line has been scanned in the electron density range of 1–3 × 10¹⁸ cm^-3. The electron temperature, as determined from the line to continuum ratio, ranged from 9.4 to 19.9 eV. The plasma which emitted the He(II)4686 Å line was created in a 60-kJ theta pinch operated with a high fill pressure (3 and 5 torr) of pure helium. Electron densities were calculated from the half-half widths of the He(II)4686 Å line using two Stark broadening theories. These electron densities are compared with the electron densities determined from the absolute value of the continuum intensity and a total sweep up compressional model. The two theoretical models predict electron densities in good agreement with the electron densities from the absolute value of the continuum intensity.     

Sensitivity of reaction cross sections to halo nucleus density distributions

In order to clear up the sensitivity of the nucleus-nucleus reaction cross sections σ _R to the nuclear matter distributions in exotic halo nuclei, we have calculated the values of σ _R for scattering of ⁶He, ¹¹Li, and ¹⁹C nuclei on several nuclear targets at the energy of 0.8 GeV/nucleon. The calculations were performed in the “rigid target” approximation to the Glauber theory, different shapes of the nuclear density distributions in ⁶He, ¹¹Li, and ¹⁹C being assumed.     

Population densities and optical gain of VUV transitions of Cu II in Cu−He hollow cathode discharges

Population densities of excited Cu II-levels between 16 and 25 eV in Cu–He hollow cathode discharges were determined by emission spectroscopy. Population inversion was detected for several 6s-4p transitions. Investigation of the enhancement of Cu II vuv lines in He compared to Ne discharges showed that the excitation of the 6s levels by charge transfer is up to 100 times higher in He than in pure Ne discharges. Using the population densities and known transition probabilities, a single pass gain of 55% m^–1 at 780.8 nm and 1.2% m^–1 at 154.17 nm at a current density of 0.4 A cm^–2 was calculated.This paper is dedicated to Prof. Dr. H. Gobrecht on the occasion of his 75th birthday     

Trinucleon cluster structure at high-excitation energies in A=6 nuclei

Trinucleon molecular structures in ⁶He and ⁶Be were investigated by using the ⁶Li(⁷Li, ⁷Be)⁶He reaction at 455 MeV and ⁶Li(³He, t)⁶Be reaction at 450 MeV, respectively. Binary decays into t + t from a broad state at E _x =18.0±1.0 MeV in ⁶He and into ³He + ³He from one at E _x =18.0±1.2 MeV in ⁶Be, respectively, were observed by measuring trinucleon cluster decays in coincidence with reaction particles. The branching ratios for binary decay were estimated to be about 0.7 for ⁶He and ⁶Be. These large branching ratios show that a trinucleon cluster state exists as an isobaric partner around E _x =18 MeV in ⁶He and ⁶Be.