Table of contents

Relativistic rigid motion, in the sense introduced by Born, is analyzed for the case of one-dimensional motion. A particular geometrical represenation is used. This representation is shown to bring out the essential features in a simple way. The discussion is illustrated by two examples.

Some recent articles on the Klein Paradox announce reflexion coefficients exceeding 100%. The origin of this result seems to be a widely disseminated misprint which is pointed out and rectified. In conclusion, a new approach to the problem - by means of Furry's interaction representation for an external field - is indicated.

The characterization of many-fermion wave functions as condensates of bosons built out of pairs of particles is further analyzed. It is emphasized that the properties of the many particle systems are extremely sensitive to small components in the structure of the boson. In particular a truncation of the boson to the dominant angular momentum components may lead to results that are qualitatively different from those obtained from the full wave function.

Transitions from the 2¹P₁ - and 2³P₁ -state to the ground state 1¹S₀ in helium-like sulphur ions have been measured with an accuracy of 4 × 10^-5. Energy calibration is described in detail and two reference wavelengths have been reevaluated. Substantial line-blending was observed, due to long-lived spectator electrons. The two transition energies were corrected for Doppler shift and compared with most refined theoretical calculations, including terms of order α⁴Z⁶ in the Breit operator and terms of order α⁵Z⁶ in the quantum-electrodynamical corrections. The experimental contributions to the ground-state QED shifts agree within its error (∼ 15%) with the theoretical values.

On the basis of spectral recordings in Lund (Sweden) the Nb V spectrum is thoroughly analysed, establishing nine new terms (14 levels) of the one-electron spectrum. Together with earlier work hereby confirmed, the following terms of this spectrum are now determined; n²D (n = 4-6), ²S (5-7), ²P (5-7), ²F (4-6) and ²G (5-7). Splitting of the ²G term could not be observed. Among the internally excited configurations 13 levels of 4p⁵4d5s and 11 of 4p⁵4d² are determined. The series limit is adopted to be 407 870 ± 50 cm^-1.

Pulsed atomic beams with flux densities above 10¹⁶ cm^-2 s^-1 have been produced in vacuum with high reproducibility by laser induced ablation from titanium and iron targets. The power of the TEA CO₂ laser was kept at a level where plasma production at the target surface was avoided: no ions were detectable. The beams were analysed by laser fluorescence. The high directionality of the beam, a discrepancy between velocity distribution and flux density as well as very low excitation temperatures of the fine structure levels of the ground state point to a non-thermal ejection process of the atoms and/or to impurity surface effects.

The E¹Σ⁺-X¹Σ⁺ band system in the isotopic molecules ⁷⁴Ge¹⁶O and ⁷⁴Ge¹⁸O is analyzed. The spectral region from 1800 Å to 2100 Å is studied and the vibrational numbering is determined from the isotopic shifts. For ⁷⁴Ge¹⁶O the following molecular constants of the E¹Σ⁺ state are determined: T_e = 46 041 cm^-1, ω_e = 533.9 cm^-1, ω_ex_e = 3.0 cm^-1, B_e = 0.3559 cm^-1, D_e = 0.46 × 10^-6 cm^-1, and r_e = 1.8978 Å.

The heat capacity of ³He adsorbed on thick films of solid neon preadsorbed on sintered copper has been measured for coverages from 1% of monolayer capacity to a complete monolayer with high resolution. The desorption heat capacity has a maximum at 7 K. At predesorption temperatures the heat capacity is linear and coverage dependent. The heat capacity of the lowest coverages has an anomalous behaviour below 0.7 K.

Applying the inhomogeneous hypernetted chain method we formulate the general impurity problem for a correlated Bose or Fermi fluid as a host. In the present paper we apply the method to an impurity in electron gas. From the Euler-Lagrange equation for the induced density one obtains the screening and cusp conditions. It turns out that these two conditions alone are sufficient to give accurate prediction for the positron annihilation in metals. We construct numerical solution for the Euler-Lagrange equation demanding the two conditions to be satisfied. The resulting energies compare well with existing field theoretical calculations for hydrogen and positronium impurities. The uniform limit approximation is used to derive an expression for the dielectric function. In the present theory the linear response to an external field is determined by one characteristic function which is calculable from the ground state quantities alone. Eliminating this function in favour of the dielectric function which is assumed to be known exactly we obtain an equation for the non linear density response which may have more general validity than the approximations made here suggest.

Linear response formalism within the density-functional scheme is applied in a calculation of core polarizabilities in simple metals. While the core polarizability changes relatively little (around 10%) from its free-ion value in the alkalis, Mg and Al, large increases are found for metals like Ga, Cd, In, and Sn with full d-shells. Low-frequency values for the dynamic polarizability are also obtained.

Proton NMR line widths and relaxation have been studied in powders of almost simple cubic NH₄ZnF₃ and NH₄MnF₃. The activation energy for NH₄⁺ reorientation is E_a/k_B = 650K above T_c = 115 K in NH₄ZnF₃ and E_a/k_B = 795 K below T_c, and probably about the same in NH₄MnF₃. The averaging of local fields because of rapid reorientation narrows the line and permits observation of critical relaxation near the antiferromagnetic T_N = 75.8 K in NH₄MnF₃. If T₁ ∝ (T - T_N)^ρ we find ρ in the range 0.1 to 0.3, compared to the expected ρ ≈ 0.33 for cubic Heisenberg antiferromagnets.

Corrections to Physica Scripta24, 601-608, 1981

Corrections to Physica Scripta24, 584-587, 1981

The 15th line on the left-hand column of p.587 should read:

However for cylindrically symmetric magnetoacoustic pump,...