F. Falk

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.

Reorientation precession measurements on 108, 110Pd and the quadrupole moments of their first 2+ states

Abstract The reorientation precession technique, REPREC, for measurements of quadrupole moments is described. The application of REPREC to the measurement of the static electric quadropole moments of the first excited 2 + states in 108, 110 Pd is presented. The possibility to measure the sign of the matrix product P 4 = M 02 M 22′ M 02′ M 22 is also discussed. Such measurements are presented for 108, 110 Pd. The results of these measurements are P 4 108 Pd and 110 Pd. For 108 Pd the quadrupole moment of the first excited 2 + state was found to be −0.66±0.18 e ·b and for 110 Pd, −0.72±0.14 e ·b. Intrinsic nuclear properties for 106−110 Pd are derived using the sum rules suggested by Kumar.

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.

Perturbations of the alpha-gamma angular correlation in the decay of 22688Ra

Abstract The gyromagnetic ratio for the first excited (2+) rotational state (185.7 keV, T 1 2 = 0.32 ns ) in 22286Rn has been obtained by the technique of perturbed α-γ angular correlations. The result gR = 0.45 ± 0.07 is somewhat larger than Z/A ≈ 0.39. The average internal magnetic field of radon atoms recoiling into nickel was found to be 15±3 kG and positive. The perturbations in different environments were studied by observing the coincidence rate in 180° between α and γ. In vacuum the perturbations were severe but could be decoupled in a parallel magnetic field. A number of solids were examined and the perturbations were in general small. In all measurements thin sources were used. The thickness of one typical source was deduced from the energy loss of α-particles.

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.

A search for after-effects of the 111In EC decay on the 111Cd γγ correlation

Abstract Three indium compounds: (i) In 2 O 3 , (ii) In 2 S 3 and (iii) In(C 9 H 7 NO) 3 (indiumhydroxyquinolate) were examined for evidence of after-effects on the 173–247 keV γγ correlation of the 111 In EC decay. The main experimental method was the application of a 23 kG decoupling magnetic field. The source temperature was also changed. No after-effects were found, although the correlation in case (iii) seems to be attenuated below the hard-core value. In the introduction after-effects and their detection are discussed at some length.

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.

Determination of HF fields of radon in ferromagnets

The α-γ angular correlation method has been applied to226Ra and224Ra decays to investigate the hyperfine fields of radon in iron, cobalt and nickel. A random, static quadrupole interaction combined with an aligned magnetic interaction was assumed in the analysis. Gadolinium has also been investigated as a ferromagnetic host, but the oxide layer proved to be too thick.

L/sub II/-ELECTRON-GAMMA CORRELATION IN

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.