A.V. Ramayya

Rotation-aligned coupling and axial asymmetry in 189−195Au

Abstract Levels in 189, 191, 193Au have been studied by radioactive decay of isotopically separated 189, 191, 193Hg. The systematics of the levels are followed from 195Au to 189Au and show a remarkable insensitivity to neutron number. The h 1 1 2 bands are identified and provide a critical test of the model of a single-j nucleon subject to rotation-aligned coupling to an asymmetric core. Within the framework of the model the triaxial degree of freedom appears to be very stable.

The decay of 110mAg: Gamma-ray energy and intensity standardization

Abstract The energies and intensities of the transitions from the decay of 110mAg have been carefully measured with three different systems which use Ge(Li) detectors. The following energies in keV and intensities in parentheses were determined for standards: 446.77 ± 0.04 (3.5 ± 0.2), 620.22 ± 0.03 (2.9 ± 0.2), 657.71 ± 0.03 (100), 677.55 ± 0.03 (12.2 ± 0.7), 686.80 ± 0.03 (7.4 ± 0.6), 706.68 ± 0.04 (17.2 ± 07), 744.19 ± 0.04 (4.4 ± 0.4), 763.88 ± 0.04 (24.0 ± 0.8), 818.00 ± 0.04 (7.8 ± 0.3), 884.67 ± 0.04 (79.6 ± 2.0). 937.48 ± 0.04 (36.5 ± 1.1), 1384.22 ± 0.04 (27.7 ± 0.8) 1475.73 ± 0.04 (4.5 ± 0.2), 1504.90 ± 0.08 (14.8 ±0.4) and 1562.22 ± 0.06 (1.33 ± 0.06). All these transitions fit into the well-known decay scheme of 110mAg. Transitions previously reported at 566.0, 667.2, 753.0, 785.0 and 1443.0 keV were not observed, but weak new transitions at 626, 997 and 1334 keV were observed. Transitions of 434.00 ± 0.10, 614.37 ± 0.10 and 722.95 ± 0.08 keV were observed from the decay of 108mAg.

Mean life of the 854 keV 02+ state in 74Se and the coexistence model

Abstract The mean life of the first excited 0 2 + state in 74 Se, only 219 keV above the first excited 2 + state at 635 keV, was measured to be 1.2±0.2 nsec, with delayed coincidence techniques. The 0 2 + state was populated by the decay of 74 Br produced via the 60 Ni( 16 O, pn) 74 Br reaction. The extracted B (E2; 0 2 + → 20 1 + ) value is 14±2 s.p.u. which suggests that the 0 2 + state is collective. Application of a coexistence model in terms of spherical and deformed shapes is discussed for 74 Se.

Levels in 72Ge populated by 72Ga

Abstract The radioactive decay of 72 Ga has been investigated by means of Ge(Li) and Si(Li) detectors. The energies and intensities of 71 γ-rays have been determined from the γ-ray singles spectrum. Extensive γγ coincidence experiments were performed with two Ge(Li) detectors coupled to a two-parameter analyser. Internal conversion electron measurements were performed with a Si(Li) detector system. The electron-γ delayed coincidence experiments were carried out with an anthracene crystal and a 35 cm 3 Ge(Li) detector. These extensive coincidence relationships were used to identify the levels of 72 Ge populated by 72 Ga with excited states at 691.2, 834.02, 1463.88, 1728.24, 2064.80, 2402.0, 2463.74, 2514.65, 2583.5, 2754.1, 2943.45, 3035.41, 3094.7, 3324.92, 3341.68, 3439.3, 3455.2, 3566.0, 3678.1, 3707.1, 3758.6 and 3815.4 keV. The β − feedings and the log ƒt values were calculated from the relative γ-ray intensities.

The decay of 194Au to the levels of 194Pt

Abstract The γ-rays emitted in the decay of 194Au have been investigated by means of Ge(Li) detec tors. The energies and intensities of 93 γ-rays have been determined from the γ-ray singles spectrum. Two-parameter γ-γ coincidence experiments, with two Ge(Li) detectors, have been performed. The coincidence relations were used by the authors to construct a level scheme for 194Pt, consisting of 36 excited states. The ambiguities previously reported in the locations of several transitions have been removed, and several transitions have been placed in new positions. New levels at 1229.3, 1373.6, 2134.2, 2158.0, 2184.8 and 2287.3 keV have been postulated and five previously reported levels have been removed from the scheme. K-conversion coefficients, calculated from the γ-ray intensities of this work and the K-conversion electron intensities of Bergman and Backstrom, were used to determine the multipolarities of the transitions and the spin and parity assignments of the levels. Four levels are proposed as possible members of the quintet of three-phonon states.

The decay of 151Gd to the levels of 151Eu

Abstract The γ-rays of 151 Eu have been investigated with a 35 cm 3 Ge(Li) detector coupled to a 4096-channel analyser. Gamma rays of the following energies and intensities (in parenthesis) were found to decay with the half-life of 151 Gd: 106.51±0.06(1.29), 110.53±0.11(0.12), 153.57±0.06(100), 174.65±0.06(48.3), 196.46±0.09(0.45), 239.00±0.14(2.31), 243.22± 0.06(89.9), 260.39±0.09(0.84), 286.00±0.09(1.35), 307.43±0.09(16.5), 328.23±0.09(1.32), 332.13±0.12(0.17) and 353.51±0.09(2.04). Using the energy sum rules and coincidence relationships the levels at 21.54, 196.21, 196.46, 243.22, 260.44, 306.99, 307.47, 349.76 and 353.56 keV are proposed for 151 Eu. A decay scheme consistent with our results is presented. The present studies support the previously proposed collective states.

The UNISOR ISOL data acquisition system

Abstract The data collection system of the on-line separator at Oak Ridge (UNISOR) is described including an overview of the operation and a discussion of some new techniques. Tape transport and computer based data acquisition systems have been developed which allow several experiments to be performed simultaneously on a given mass chain and also enable experiments to be changed quickly. To make efficient use of the cyclotron beam time, methods have been developed for quickly extracting short-lived side masses from the separator. Also described are an on-line scanning Gerholm lens spectrometer, a multiple time analysis system and an angular correlation station for the tape transport.

Decay of 74As

Abstract Gamma-ray spectrum and γ-γ directional correlation measurements were performed with Ge(Li) and NaIGe(Li) detector arrangements on the decay of 74As. Eleven transitions from 595.7 to 2198.4 keV were observed and fitted into levels at 595.7±0.1, 1204.3±0.1, 1463.2±1.0, 1482.6±0.5, 1697.3±1.0, and 2198.2±0.5 keV in 74 Ge and 634.8±0.1 keV in 74 Se . Directional correlation measurements were performed on the 608-596 keV 2-2-0 cascade and on the 887-596 keV cascade. In the first case, A2 = −0.24±0.04, A4 = 0.30±0.05. These data yielded a (7−6+3)% M1 admixture for the 608 keV transition. For the latter correlation, values of A2 = 0.6±0.2 and A4 = 1.3±0.2 were found. These values are compatible only with the 0-2-0 cascade and thus the level at 1482.6 keV has spin zero. Percent feedings and log ft values were calculated for decays to 74Ge and 74Se.

Decay characteristics of two 3-t- states in 86Sr

Abstract The two lowest 3 − states in 86 Sr exhibit very different decay properties. The lower state, 3 1 − , decays predominantly to the 2 2 + state whereas the 3 2 − state decays preferentially to the 2 1 + state. The data suggest that B (E3:3 1 − → 0) is significantly larger than B (E3:3 2 − → 0) so that the 3 1 − state probably arises from octupole vibrations of the nucleus.

Magnetic properties of 166Er and the collective model

Abstract The E2/M1 admixtures for nine γ-ground band transitions in 166 Er were measured. Mixing ratios, δ(E2/M1), were calculated based on a general treatment of magnetic properties in the framework of the collective model. The agreement with the experimental values is generally good.