Gerfried J. Kumbartzki

Magnetic moments in the backbending region of 158Dy

Abstract Yrast levels in the backbending region of 158 Dy were Coulomb excited with a 4.7 MeV/u 208 Pb beam. Employing the transient field technique with a thin magnetized iron foil, the precessions of the angular correlations of decay γ-rays from levels up to spin I π = 16 + were measured. The results show a clear reduction of the g -factor for states in the backbending region relative to that of the low-spin levels, thus demonstrating that the backbending in 158 Dy is mainly caused by the alignment of i 13 2 neutrons. In a similar experiment, precession measurements on Coulomb excited low-spin levels of 164 Dy served to determine the static hyperfine field of Dy in Fe and the g -factor of the 6 + state in 164 Dy.

High-energy photofission of gold and uranium

Abstract Bremsstrahlung induced photofission of 197Au and 238U has been measured for energies Emaxγ = 0.8 to 2.2 GeV using catcher foil techniques. The mass distributions of the fission fragments of uranium were measured as a function of the maximum bremsstrahlung energy. The peak-to-valley and forward-backward ratios have been determined for 238U.

Magnetic moment measurements on Hg nuclei

Abstract Perturbed particle-γ angular correlations were measured for Coulomb-excited 198, 199, 200, 202, 204 Hg recoiling into helium and vacuum at v c = 0.010 . Relative g -factors of the first 2 + states of the even nuclei were obtained from the perturbation parameters and shown to be in disagreement with theoretical predictions and IMPAC measurements. Absolute g -factors were extracted by calibrating the ionic hyperfine field with the 158 keY 5 2 − state in 199 Hg. This field is discussed in the light of the general systematics for atoms in the range 60 ≦ Z ≦ 80. A lower limit was placed on the g -factor of the 208 keV state in 199 Hg. In a separate measurement using a radioactive source the lifetime of this state and the mixing ratio of the subsequent ground state transition were determined.

High-energy photonuclear reactions in vanadium and iron

Abstract Yields of photonuclear reactions in vanadium and iron were measured by the activation method at 1.5 GeV bremsstrahlung energy and analysed with an empirical spallation formula given by Rudstam. Yields of light nuclei (20 30. The energy dependence of the yields and the recoil energy of these nuclei investigated in a catcherfoil experiment deviate considerably from the general behaviour of spallation products. The yields of the photopion reactions 51 V (γ, π + ) 51 Ti and 51 V (γ, π − 2 n ) 49 Cr were measured in the energy range between 1.0 and 2.1 GeV.

The g-factor of the yrast 4+ state in 20Ne from transient-field precession measurements

Abstract Transient field precessions of the first excited 2 + and 4 + states in 20 Ne nuclei traversing polarized gadolinium have been measured. The deduced g -factor of the 4 + state, g = + 0.08(20), agrees with our earlier reported value of g = − 0.10(19) measured in iron by the same technique. The significant reduction in the value of the g- factor , g = − 0.01(14) , relative to that of the 2 + state, g = + 0.54(4), is incompatible with the pure T = 0 character expected for low-lying states in this self-conjugate nucleus. In addition, the lifetime of the 4 + state has been measured to be τ = 95(13) fs, in agreement with a previous measurement.

Search for a quadrupole component in the hyperfine interaction on recoil into vacuum

Abstract Time-differential perturbed γ-ray angular correlations have been measured with the plunger technique for fast Nd nuclei recoiling into vacuum. A clear trend of increasing quadrupole interaction with increasing nuclear quadrupole moment has been found. The hyperfine interaction on recoil into vacuum and recoil into gas is discussed in terms of stochastic models.

Photospallation of medium-heavy elements with bremsstrahlung of maximum energies between 0.8 and 2.1 GeV

Abstract Yields of spallation products after irradiation of the elements 27 Al, 51 V, 55 Mn, 56 Fe, 59 Co and 75 As with bremsstrahlung of maximum energies between 0.8 and 2.1 GeV have been measured by the activation method. For constant Z the yield as a function of the number of ejected particles is similar to that found for proton induced spallation. It is possible to reproduce the spallation data with an analytical formula, the parameters of which have been determined for various energies and mass numbers.

Einfluß der thermischen Behandlung auf die Ionenleitfähigkeit von KCl im Störleitungshereich

The ionic conductivity of Harshaw KCl-crystals has been measured in the extrinsic range using adc-method. For the steady state currentOhms law was obeyed up to 2000 V cm−1. The influence of the heating- and cooling-rates on the conductivity was extensively studied. It was concluded from the results that in the range 160–250 °C the carrier concentration changed with temperature according to a very slow, reversible process, which is tentatively interpreted as precipitation of impurities. If the same values for the conductivity at a given temperature were to be obtained in the heating stage as in the cooling stage, the sample had to be passed through this temperature range very slowly. The precipitation could be frozen in by rapid cooling from 250 °C. In this quenched state the increased conductivity was accompanied by an increased polarization.

Evidence for K-shell polarization of C-ions in ferromagnets via molecular-orbital promotion

Abstract Transient field precessions of the 12 C 4.43 MeV state in polarized Fe and Ni are found to scale with the polarized electron density of the hosts at υ ion = 4.1 υ 0 , but are comparable at υ ion = 2.1 υ 0 . The latter is attributed to direct K-shell polarization of carbon via molecular-orbital promotion.

Can projectiles traversing solids bind electrons at all velocities

Abstract PAC measurements on the 4.43 MeV 12 C(2 + ) state on recoil in magnetized iron at velocities υ ion = 0.058 c , 0.071 c yield integral nuclear precession angles of Φ = −0.18 (30), +0.17 (39) mrad respectively. Evidently, the high electron-spin-polarization transfer to the innermost carbon orbits implied by a previous measurement (υ ion = 0.03 c , Φ = +0.85 (14) mrad) is suppressed at higher ion velocities.