S.G. Malmskog

Properties of low-lying levels in the even platinum nuclei (182 ≦ A ≦ 192)

Abstract Decay properties of neutron-deficient even-mass Au isotopes obtained from the decay of on-line mass-separated Hg isotopes are presented. New information on energies, spins, parities and transition probabilities concerning low-lying states in even Pt isotopes are given. The experimental data are compared with the available theoretical predictions.

Possible deformed states in 115In and 117In

Levels and transitions in 115In and 117In have been studied from the beta decay of 2.3 d 115gCd and 2.5 h 117gCd. Using a Ge(Li) detector and a double focussing beta spectrometer, energies, intensities, conversion coefficients and multipolarities were obtained for the following transitions (energies in keV and multipolarities are given): 115In: 35.63 (97.0% M1 + 3.0% E2), 231.47 (E1), 260.80 (M1), 267, 336.23 (M4+< 5% E5), 492.14 (96% E1 + 4% M2), 527.70 (E1). 117In: 71.0, 89.80 (E2+< 20% M1), 273.32 (M1, E2), 315.27 (M4+<7% E2), 344.29 (E1), 434.12 (E1). Using the delayed coincidence technique, half-lives were measured for two levels in 115In and for three levels in 117In. Energies, spins, parities and half-lives are given for the following levels: 115In: 597.03, 32−; 828.39, 32+, 5.4 ns; 863.95, 12+ or 32+, 1.1 ns. 117In: 588.59, 32−; 0.20 ns; 659.56, 32+, 58.7 ns; 749.37, 12+ or 32+, 4.3 ns. Reduced transition probabilities are given for several transitions in both nuclei. The E2 transition rates between the two excited positive parity states in both nuclei were found to be about 100 s.p.u. indicating a possible deformation of these states. The energy spacing and transition rates between these states can be well accounted for within the Nilsson model assuming the states to form a K = 12+ rotational band. A deformation δ of about 0.20 is obtained for both nuclei.

Negative parity states in odd-mass Ir and au nuclei

Abstract The decays of 193 Os → 193 Ir , 191 Pt → 191 Ir , 189 Pt → 189 Ir and 193 Hg → 193 Au have been studied in γ-γ coincidences, internal conversion and electron-electron delayed coincidences. New levels with the following spin-parity assignments and half-lives are proposed: 193Ir: 299.45±0.09keV, I π = 7 2 − , T 1 2 = 0.19±0.03 ns ; 598.26±0.l5keV, I π = 3 2 − ; 740.46±0.15keV, I π = 5 2 − . 191Ir: 391.14±0.05 keV, I π = 7 2 − , T 1 2 = 0.24±0.02 ns ; 659.06±0.08 keV, I π = 3 2 − , T 1 2 ns . 189Ir: 615.70±0.08 keV, I π = 7 2 − , T 1 2 = 0.18±0.02 ns ; 1184.54±0.11 keV, I π = 5 2 − , T 1 2 ns . The 508 keV 7 2 − level in 193Au was found to have T 1 2 = 0.29±0.02 ns . In each nucleus these negative parity states and the 11 2 − isomeric state are strongly connected with E2 and Ml transitions and only weakly connected to the low-lying positive parity states. The B(E2) values are close to the values of B(E2; 2+ → 0+) in the neighbouring even nuclei. We propose these negative parity level systems to be associated with an essentially spherical shape of the nuclei in contrast to the low-lying positive parity states (including the ground state) of these nuclei, which in Ir are likely to be deformed states.

The level structure in 193Ir

Abstract The decay of 193 Os has been studied using Ge(Li) detectors and a 50 cmπ√2 spectrometer. Multipolarities and E2/M1 mixing ratios have been determined for 23 transitions. Half-life measurements applying the delayed coincidence technique have given the following mean lives: τ (138.97 keV level) = 108 ± 15 ps and τ (180.17 keV level) = 80 +11 −21 ps. The M1 and E2 transition probabilities obtained are discussed in terms of the core excitation model and the Nilsson model.

The low-energy level structure of 191Ir

Abstract The decay of 191 Pt to 191 Ir has been investigated using Ge(Li) detectors and a double focusing beta spectrometer. Thirty-five transitions were observed and most of them were placed in a level scheme. Special attention was given to the low energy level band structure. Several multipolarity mixing ratios were determined from L-subshell ratio measurements. Using the delayed coincidence technique the half-life of the 179.05 keV level was measured to 40±12 psec. The low-level decay properties are discussed in terms of the Nilsson model with the inclusion of Coriolis coupling.

The decay of 187Pt: Comparison of the levels of 187Ir with those of heavier odd mass iridium isotopes

Abstract The decay scheme of 2.35 h 187 Pt has been investigated using isotopically separated samples produced by the ISOLDE facility at CERN. A total of 20 excited levels in 187 Ir have been established. For many of these levels, spin, parity and absolute probabilities of depopulating transitions have been determined. The results indicate that the 187 Ir nucleus can be described in terms of a single particle Nilsson model including Coriolis coupling between bands ( 3 2 + [402], 1 2 + [400] ).

Levels and transition rates in 199Au

Abstract The decay of 199 Pt to 199 Au (T 1 2 = 30.8 min ) has been investigated using a Ge(Li) detector and a double focussing beta spectrometer. 34 transitions were found and multipolarities were assigned for 11 of these, including a 55.15 keV M2+(0.9±0.5)%E3 isometric transition. Using these data together with the results of γ-γ and β-γ coincidence measurements, a decay scheme containing 9 excited levels and 25 transitions was constructed and spin and parity assignments were made. Using the delayed coincidence technique half-lives were determined for 3 levels and upper limits were obtained for 5 additional levels. The following levels were found: 77.21±0.03 keV ( 1 2 + , 1.1±0.1 ns ); 316.98±0.10 ( 5 2 + , ps ); 323.57±0.09 keV (( 1 2 ), 3 2 + , 35±20 ps ); 493.59±0.10 keV ( 7 2 + , ps ); 542.82±0.07 keV ( 5 2 + , ps ); 548.65±0.09 keV ( 11 2 − ); 734.44±0.11 keV ( 7 2 − , 0.36±0.04 ns ); 791.47±0.15 keV ( 3 2 + , 5 2 + , ps ); and 967.98±0.20 keV ( 3 2 (+) , 5 2 (+) , ps ) . The decay properties of the lowest excited positive parity levels are discussed in terms of de-Shalits core excitation model.

E2 and M1 transition probabilities in 193Au and 195Au

High-resolution conversion electron- and γ-ray spectroscopy has been made on the transitions depopulating the three lowest excited states in 193Au and 195Au. The half-lives of these levels have been measured with the delayed coincidence method. The multipole assignments are for the transitions in 193Au: 38.22 keV M1+(17.7 ± 1.0) % E2, 219.75 keV E2, 257.97 keV M1+(21 ± 7)% E2 and for 195Au: 61.44 keV M1+(16.6 ± 1.0) % E2, 180.32 keV M1 + < 3% E2, 200.38 keV E2, 261.74 keVM1+(21.5 ± 4.0) % E2. The obtained half-lives are for 193Au: 38.22 keV level (3.81 ± 0.18) ns, 224.84 keV level < 0.03 ns, 257.97 keV level (45 ± 20) ps and for 195Au: 61.44 keV level (3.0 ± 0.2)ns, 241.72 keV level < 0.03 ns, 261.79 keV level (54 ± 10) ps. A systematic compilation of absolute E2 and M1 transition rates in odd-mass Au nuclei is given and compared to the predictions of the pairing-plus-quadrupole force model and the core-excitation model.

Transition probabilities in 189Os

Abstract The level structure of 189 OS has been studied from the decay of 189 Ir (13.3 d) produced in proton spallation at CERN and mass separated in the ISOLDE on-line facility. Theγ-ray spectrum has been recorded both with a high-resolution Si(Li) detector and Ge(Li) detectors. Three previously unreported transitions were observed defining a new level at 438.5 keV. Special attention was given to the low-energy level band structure. Several multipolarity mixing ratios were deduced from measured L-subshell ratios which, together with measured level half-lives, gave absolute transition probabilities. The low-level decay properties are discussed in terms of the Nilsson model with the inclusion of Coriolis coupling.

E2 and M1 transition probabilities in odd-mass Hg nuclei

Abstract L- and M-subshell ratios have been measured for the 39.45 keV transition in 193Hg and the 37.13 and 16.2 keV transitions in 193Hg yielding 0.38±0.12,