S. Törnkvist

Levels and transitions in 133Cs

Abstract The decay of 133 Ba to levels of 133 Cs has been studied. Energies of the transitions in 133 Cs have been determined from internal conversion spectra recorded in an iron-free, double-focussing spectrometer. From these data, precise level energies were obtained, 80.997±0.006 (ref. 1 )), 160±0.06, 384.09±0.20, and 437.26±0.16 keV. Intensities of conversion lines recorded in the double-focussing as well as in a lens spectrometer and of gamma transitions from Ge(Li) and NaI recordings are reported and used for ICC determinations. The following results were obtained: α K (384) = 0.017±0.004; α K (303) = 0.037±0.005 and α K (276) = 0.050±0.008. The following conversion coefficients were determined in separate coincidence experiments: α K (81) = 1.36±0.05, α K (80) = 1.36±0.10 and α K (161) = 0.39±0.13. Furthermore, the following directional correlation results are reported: A 2 (356 γ −81 γ ) = 0.037±0.005, A 4 (356 γ −81 γ ) =−0.002±0.006, A 2 (356K−81 γ ) = −0.064±0.064, A 2 (356 γ −81K) = −0.0081±0.0040, A 4 (356 γ −81K) = −0.0076±0.0080 and A 2 (53K−384 γ ) = 0.012±0.006. The EC decay energy to the 437 keV level is determined from the K/K+L+M… capture ratio to 49.0±0.7 keV. Using the experimental data and earlier results of lifetime measurements, we have calculated transition probabilities for most of the transitions. These are discussed and compared to predictions made by Kisslinger and Sorensen on the basis of their description of the levels in 133 Cs. The agreement is fairly good. Finally, the internal conversion process of the retarded l -forbidden Ml-transitions is discussed. No evidence for penetration effects is found.

A decoupling experiment on the α-γ correlation in Am243

The directional correlation betweenα particles from the decay of Am243 to the 75 keV level in Np239 and the deexciting 75 keVγ-rays has been studied. The recoiling atoms were allowed to escape into vacuum. This brings about a strong hfs interaction between the heavily ionized daughter atom and the nuclear magnetic moment, which has been shown earlier to result in an almost isotropic correlation pattern. By the application of a magnetic field along the direction of the emission of theα-particlesAsaro andSiegbahn showed that the correlation pattern could be restored to, or almost to, the theoretical value, depending on the theory chosen. This is interpreted as a decoupling of the Ms-interaction, where the degree of decoupling is dependent on the strength of the applied field. The highest field used in the earlier experiment was 12 kG.For this experiment a decoupling magnet giving 24 kG was constructed. Applying this magnetic field on three different sources gave a result (A2=−0.404±0.010) which confirms the so called quadrupole correction ofChasman andRasmussen to the theory ofBohr et al. of alpha decay of deformed nuclei.The decoupling magnet used in the experiment is described.

Internal conversion studies of transitions populating and depopulating the 161 keV level in 133Cs

Abstract Four transitions in 133 Cs have been studied by measurements of relative conversion electron intensities and electron-gamma directional correlations. The transitions studied, 276, 223, 161 and 80 keV respectively, all feed and de-excite the 161 keV level in 133 Cs. In addition the L-subshell ratios for the 81 keV transition have been measured and analysed. The 161 and 223 keV transitions show penetration effects in the internal conversion process. The penetration effects in the 223 keV transition are reported for the first time.

Nuclear spectroscopy of Ba133m

Abstract The decay of the 38.9 h isomer of Ba133 has been investigated. The energy of the d 3 2 → s 1 2 transition was determined by conversion electron measurements to 12.29±0.04 keV and the L subshell ratios of the same transition were found to be 100/9.6/3.1. The half-life of the 12.3 keV level was measured to 8.1±2.0 ns. The K conversion coefficient and the K/(L+M) ratio of the 276 keV h 11 2 → d 3 2 transition were measured with the result: αK(276) = 3.45±0.20 and K/(L+M) = 2.55 ± 0.10. The pairing plus quadrupole force model seems to explain the experimental data quite well.

A versatile electron-gamma correlation spectrometer

Abstract The construction of an electron-gamma directional correlation spectrometer is described. The electron momentum analysis is made by a lens spectrometer of a new type, allowing a resolution of 0.7%. The constructional details and the performance of the correlation set-up are described with emphasis on the electronic arrangements for automatic operation and for current supply and spectra recordings.

Internal conversion studies of the 114 keV transition in175Lu

Measurements of the conversion line intensities, the directional correlation and the conversion probability for the 114 keVM1+E2 transition in175Lu are reported. TheE2 admixture, determined from relativeK andL intensities, is (19.2±0.2)%. The theoreticalLI internal conversion coefficient is found to be about 8% too low relative theK,LII andLIII conversion coefficients.

Directional correlation measurements withLI andLII conversion electrons of the 31 ke V transition in195Pt

The (31L1−99γ) and (31LII−99γ) directional correlations have been measured in195Pt. The results give the mixing ratio for the 31 keV transition,δ+0.012±0.004.

LII-electron-gamma correlation in199Hg

The(50LII−158γ) directional correlation has been measured in199Hg. The result isA22=+0.038±0.024, which gives the mixing ratio for the 50keV transition,δ=+0.017±0.006. The accuracy of the method is discussed.

K, L and M electron directional correlations in 123Te

Abstract Directional correlations of the cascade in 123 Te involving K, L and M electrons from the 89 keV M4 transition have been measured in order to determine the δ (E2/M1) value for the 159 keV transition. The result agrees with that from older correlation measurements, but is in conflict with values derived from Coulomb excitation and lifetime measurements as well as from L subshell ratios.

Internal conversion studies of the 113 keV transition in 117Hf

Abstract The multipole mixing of the 113 keV transition in 177Hf has been studied by measuring the directional correlations involving K-LII and LIII electrons and by determining the K-conversion coefficient. All data are consistent giving δ = −3.1±0.6.