I. Borchert

Elastic scattering of γ-rays from lead for energies from 0.145 to 1.33 MeV

Abstract Differential cross sections for elastic scattering of 889 and 1120 keV γ-rays from lead have been measured at angles ranging from 30° to 150°. These results and previously measured differential cross sections at 145, 279, 412, 662 and 1332 keV are compared with theoretical predictions taking into account Rayleigh scattering, nuclear Thomson scattering, and Delbruck scattering. The Rayleigh amplitudes of the K-shell were obtained from the theory of Brown et al., the amplitudes of the other shells from form factors calculated from relativistic HFS wave functions. Discrepancies are found at 145, 889, 1120 and 1332 keV while the experimental data at 279, 412 and 662 keV are in good agreement with the theory. A discussion of possible explanations and consequences is presented.

Der Zerfall des77Kr

Abstract77Kr (T1/2=1.2 h) was produced by bombarding76Se with 48 MeV-α-particles. After irradiation the radioactive77Kr gas was collected in glass ampoules filled with charcoal and cooled by liquid air. The decay of77Kr has been investigated using Ge(Li)-counters and a Ge(Li)-Ge(Li)-coincidence circuit. 27 γ-transitions, 13 of them unknown up to the present, have been found and their relative intensities have been determined. A level scheme for77Kr→77Br having 14 levels is proposed. This accounts for all the observed γ-transitions.

Delbrück scattering of 2.75 MeV photons by lead

Abstract The differential cross section for the elastic scattering of photons was measured for Pb at θ = 120° and E = 2.75 MeV yielding d σ/ d Ω = 34.7 ± 1.6 μ b / sr in agreement with d σ/ d Ω = 32.2 μ b / sr calculated using the Delbruck amplitudes of Papatzacos and Mork. Definite evidence for the real part of the Delbruck amplitude has been obtained for the first time.

The Z-dependence of the elastic scattering of γ-rays

Abstract The differential cross sections for elastic scattering of 662 keV and 279 keV γ-rays from Pb, Ta, Nd, Sn, Mo, and Zn have been measured at angles ranging from 45° to 135°. The results are compared with theoretical predictions taking into account Rayleigh scattering and nuclear Thomson scattering. The theoretical Rayleigh amplitudes are based on second order perturbation theory according to Brown et al . and on form factors calculated from relativistic HFS wave functions. A semi-empirical method of correcting the form factors is developed, valid for energies between 150 keV and 750 keV and charge numbers up to Z = 82. The average difference between calculated and measured differential cross sections was found to be 6%.

Der Zerfall des Zn63

The decay of the 38.4 min-Zn63 has been investigated using Ge(Li)-counters and a Ge(Li)-NaJ(Tl)-coincidence circuit. 43γ-transitions in the energy range from 364.5 keV to 3100.9 keV have been found and their relative intensities have been determined. A level scheme for Zn63→Cu63 having 24 levels is proposed. This accounts for all observedγ-transitions except one.

The perturbation of a γγ directional correlation of75As in gaseous H275Se sources

Using gaseous H275Se sources the γγ directional correlation of the 121.0–279.5 keV γγ cascade of75As was measured as a function of pressure. The attenuation coefficientG2 varied between 0.67 and 0.96 for pressures between 0.1 and 200 Torr. Since the perturbation of the directional correlation is caused by hyperfine interaction of the highly charged ion formed after electron capture, the pressure dependence may be understood as being mainly due to changes of the charge states during collisions with neutral molecules. A simple model is proposed yielding a reasonable fit to the experimental data.

Coulomb fragmentation in InI and InI3

The fragmentation of InI and InI3 initiated by electron capture in In114itm was studied by investigating the profile of the 558 keV γ line emitted by the Cd114 nuclei. The profile was deduced from measured cross sections for the resonant scattering of the 558 keV quanta in coincidence with the preceding 724 keV quanta. Predictions using a simple model for the fragmentation are in agreement with the experimental results for InI. The average energy of the fragments amounts to about 120 eV.

The influence of the chemical environment on the decay constant of90mNb

An influence of the chemical environment on the decay constant λ of the 2.38 keV isomeric transition of90mNb was investigated. The relative difference of the decay constants for Nb atoms in Zr metal and in a fluorine complex was determined to be ¦λcomplex-λZr¦/λzr<1.8·10−3. This result is discussed in view of other experimental results and on theoretical estimates.

Resonance behaviour of a perturbed gamma gamma directional correlation in a magnetic field

Using a gaseous H275Se source at low pressure the perturbed directional correlation of the 121–279 keVγγ cascade of75As was measured as a function of an external magnetic field. The anisotropy shows a pronounced resonance behaviour around zero field. This effect may be understood as being due to the hyperfine interaction of the nucleus with the electronic shell of the highly charged ion formed after electron capture. The charge distribution of the As ions was estimated and the spin distribution derived from it. Then a comparison with the theory of Leisi was possible giving a qualitative agreement between theory and experiment.

γγ-Richtungskorrelationsmessungen am79Br

Using gaseous and solid sources of79Kr the γγ directional correlations of the 208.6–397.6 keV-, 299.6–306.6 keV- and 389.1-217.1 keV γγ cascades of79Br were measured. The results allow the unambiguous assignment of spin and parity to the levels at 397.6 keV (1/2−) and 306.6 keV (1/2−). In addition, they confirm the assignment to the level at 217.1 keV (5/2−).