O. Skilbreid

Inelastic scattering from even rare earth isotopes

Abstract The Coulomb excitation cross sections for the first excited state of 15 even-mass nuclei in the region of the rare earths have been determined from measurements on inelastically scattered protons and deuterons. From the cross sections, reduced E2-transition probabilities are obtained, in general in good agreement with those derived from the directly measured lifetimes of the nuclear states. The intrinsic quadrupole moments determined from the transition probabilities show, for each element, a regular variation with the mass number, but discontinuities occur when passing from one element to another. This behaviour appears to be correlated with the variation in the moment of inertia for the same nuclei. The individual intrinsic quadrupole moments of odd-mass nuclei in the same region often deviate from the moments of the neighbouring even isotopes, but on the average the quadrupole moments of odd-mass nuclei are almost the same as those for even nuclei.

INELASTIC SCATTERING FROM HAFNIUM AND WOLFRAM ISOTOPES

Abstract The reduced electric quadrupole transition probabilities and the excitation energies of the accessible low lying states in the stable isotopes of Hf and W (except the rare isotope W180) have been measured by Coulomb excitation. The measurements were performed on inelastically scattered protons and deuterons recorded in a heavy particle spectrograph. The results are discussed in terms of the rotational model. The measured transition probabilities are compared with those derived from lifetime measurements.

Inelastic scattering from separated lutecium isotopes

Abstract Lutecium targets of high isotopic purity have been prepared in an electromagnetic isotope separator. In order to obtain thin deposits of the target material on fragile backings, a method has been developed where the ions after the separation are strongly retarded by an electrical potential on the collector. Targets prepared in this way have been used to study the Coulomb excitation of the rare odd isotope Lu 176 and of the abundant isotope Lu 175 by observation of inelastically scattered protons and deuterons in a magnetic spectrometer. The measured excitation energies and transition probabilities in Lu 176 are in good agreement with the predictions of the rotational model if the ground state spin of this isotope is 7.

Levels in Ho162 and Dy162

Abstract An activity with half-life 11.8 min, representing the ground state of Ho 162 , has been isolated by a recoil method from the 68 min Ho 162 activity which belongs to an isomeric level about 90 keV above the ground state. A decay scheme for the Ho 162 levels is proposed, indicating the following levels in Ho 162 : ground state, ( K, I π ) = (1, 1 + ); 38.5 keV (1, 2 + ); 86.5 keV (1.3 + ); ≈ 90 keV (6, 6 − ). In Dy 162 the following levels are proposed: 81 keV (0, 2 + ); 266 keV (0, 4 + ); 549 keV (0, 6 + ); 1485 keV (5, 5 − ). Single-particle assignments in the Nilsson-Mottelson scheme can be proposed for the unpaired particles of the ground state and the 90 keV states of Ho 162 as well as of the 1485 keV level of Dy 162 , based on the abovespins and the fact that the K-capture transitions from Ho 162 are allowed unhindered.An activity with a half life of 11.8 min, representing the ground state of Ho/sup 1//sup 6//sup 2/, is isolated by a recoil method from the 68 min Ho/ sup 1//sup 6//sup 2/ activity, which belongs to an isomeric level about 90 kev above the ground state. A decay scheme for the Ho/sup 1//sup 6//sup 2/ levels is proposed, indicating the following levels in Ho/sup 1//sup 6//sup 2/: ground state, (K, I pi ) = (1, 1+); 38.5 kev (1, 2/sup +/); 86.5 kev (1.3/sup +/); approx equal 90 kev (6, 6/sup -/). In Dy/sup 1//sup 6//sup 2/ t he following levels are proposed: 81 kev (0, 2/sup +/); 266 kev (0, 4/sup +/); 549 kev (0, 6/ sup +/); 1485 kev (5, 5/sup -/). Single-particle assignments in the Nilsson- Mottelson scheme can be proposed for the unpaired particles of the ground state and the 90 kev states of Ho/sup 1//sup 6//sup 2/, and for the 1485 kev level of Dy/sup 1//sup 6//sup 2/, ba sed on the above spins and the fact that the K-capture transitions from Ho/sup 1//sup 6//sup 2/ are allowed unhindered. (auth)

The decay of 37.5 min 164mHo

Abstract It is shown that a 37.5−0.5+1.5 min activity of 164Ho belongs to a 139 keV state, whereas the ground state has a half-life of 29±2 min. The 139 keV level has probably spin 6− and decays through the 3+, 2+ and 1+ members of the K = 1+ ground state rotational band by transitions of 45.9 keV (E3), 56.1 keV (M1) and 37.0 keV (M1). This decay scheme is analogous to that of the 68 min 162Ho state at 106 keV. The log ft values for the β−-branches from the 164Ho ground state to the 0+ and 2+ states of the 164Er ground state rotational band are 5.5±0.2 and 5.8±0.2, whereas log ft ≤ 4.8 for the transition to the 164Dy ground state. Based on these allowed unhindered β− and electron capture transitions single-particle assignments can be made for the isomeric state as well as for the ground state of 164Ho. The difference in ft values for the transitions to the two even daughter nuclei is interpreted as an indication of individual behaviour of the single particles in the pair scattering process.

Energy levels of 166Er excited in the decay of 166Tm

Abstract The electron capture decay 166 Tm → 166 Er has been investigated in a six-gap β-ray spectrometer and with Ge(Li) γ-ray detectors. Conversion lines, single γ-ray spectra and e-γ coincidence relations have been extensively studied. The results with respect to the ground-state band and the gamma-vibrational band of 166Er are in good agreement with those of earlier investigations. Above the gamma-vibrational band, ten levels are definitely established, having the following energies (in keV), spin values and parities: 1460, (2)−; 1516, 3−; 1574, (4)−; 1920, 3−; 1941, (2 or 3)+; 1980, (2, 3 or 4)+; 2004, (4−?); 2135, 3+; 2162, 3+ and 2218, (1,2, or 3)−. Further three levels are suggested at 1530, 2023 and 2293 keV. The 1590 keV and 1687 keV (5−) levels found in other investigations are probably also populated in the decay of 166Tm. The decay scheme accounts for 70 of the 90 γ-transitions observed in the present work. The structure of the levels of 166Er is discussed in terms of current nuclear models. In particular, the 1460 keV level is interpreted as an octupole-vibrational K = 2− state, with the associated rotational band having parameters A = 9.5 keV and B = −10 eV. Evidence for a complicated structure of the 2135 keV 3+ state is presented.

The decay of 152Tb

Abstract The conversion electron spectrum, electron-gamma and β + -gamma coincidence spectra are investigated, and the gamma-ray spectrum is studied in two Ge(Li) semiconductor spectrometers. A decay scheme 152 Tb → 152 Gd is suggested, including many new levels among which two 0 + states at 1484.0 and 2720.7 keV. Relative intensities at 0.2 : 0.3 : 1 are found for positon branches from 152 Tb to the 615.6 keV (0 + ), 344.4 keV (2 + ) and to the ground state of 152 Gd. Spin 1 − is ascribed to the ground state of 152 Tb. Spin assignments are being made for the following excited levels: 755.6 keV 4 + , 1109.8 keV 2 + , 1123.8 keV 3 − , 1606.1 keV 2 + , 1643.9 keV 1 − , 1862.3 keV 2 + and 1942.5 keV 2 + .

Decay scheme of Tb152

Abstract The decay scheme Tb152→ Gd152 has been investigated with sources prepared in an isotope separator. In addition to obtaining γ-ray and conversion electron spectra, γ-γ and e-γ coincidence measurements were carried out. A disintegration scheme has been established that includes all transitions in Gd152 reported in earlier Eu152 β-decay studies. In addition, four new transitions which establish two excited levels in Gd152 were observed. One of these is a 0+ state at 1047 keV and the other, at 929 keV, has probably spin 2+. The 0+ state decays with two monopole transitions to lower 0+ states, and the transition from the 929 keV level to the 344 keV first excited level, seems to contain a considerable E0 admixture. The two new levels are tentatively interpreted as members of a three-phonon quintet.

High-energy spectra of 12 y 152Eu

Abstract An electromagnetically isotope-separated source of 152 Eu (10 −4 per cent 154 Eu impurity) has been investigated in a six-gap, beta spectrometer and with a Ge(Li) detector. The log ft value of the beta transition 152 Eu(ground state) → 152 Gd(ground state) is given a lower limit; log ft > 16.8. Some new conversion lines and the corresponding gamma lines were measured. The following transition energies (in keV) and multipolarities were found: 1252, E2; 1459, E1; 1528, E1; 1606, (E2); 1645, E2 and 1765, E2.

A measurement of β− and EC branching ratios in the decay of 8.15-h Ta180 and a search for the β− decay of Hf180m

The decay of the 8.15-hr Ta/sup 180/ isomer is studied, and it is found that the BETA /sup -/EC branching ratio is 0.15 plus or minus 0.02, the ratio of BETA - branching to the 0+ and 2+ levels in W/sup 180/ is 3.00 plus or minus 0.45, the ratio of EC branching to the 0+ and 2+ levels in Hf/sup 180/ is 2.20 plus or minus 0.33, and E/sub BETA -/ (max) is 710 plus or minus 15 kev for decay to the W/sup 180/ ground state. The observed branching ratios are within experlmental error of the theoretical branching ratios, assuming K = 1 for the Ta/ sup 180/ isomer. A lower limit is set on the intensity of a BETA /sup -/ group depopulating the 5.5-hr Hf/sup 180m/. An interpretation of the intrinslc structure of the Ta/sup 180/ isomers is discussed. (auth)