B. Fogelberg

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.

Single-neutron states in Sn-133

The location of several single-neutron states in Sn-133 has been identified. The P-3/2, h(9/2), and f(5/2) states were found at 853.7, 1560.9, and 2004.6 keV, respectively, by measuring gamma rays in coincidence with delayed neutrons following the decay o

Efficiency and delay of the integrated target-ion source of OSIRIS

Abstract The new compact target and ion source system of the OSIRIS ISOL-facility at Studsvik has now been in use for about five years. The system is used for studies of short lived nuclei obtained through fission with reactor neutrons. The ion source can simply be switched between two modes of operation, one being (thermal) surface ionization and the other an electron impact induced plasma mode. The efficiency for most elements in the fission product region has been measured. The use of a substantial (gram quantity) amount of target material introduces a delay between a fission event and the subsequent ionization of the products. This delay in a U+C target has been analyzed for several elements. Some observations of nuclidic yields as a function of the target temperature are reported.

Decay Properties of 75-80Zn and Qβ-values of Neutron-Rich Zn and Ga Isotopes

The decays of strongly neutron rich isotopes of Zn have been studied with the primary aim of nuclear mass determinations. The work has also resulted in considerable information on the previously practically unknown level structure of 75,76,77,79,80Ga. Improved Qβ-values are obtained for 75,76,77,78Zn and 76,78,80Ga. The Qβ-values of 79,80Zn are reported for the first time. The experimental results are compared with predicted values of nuclear masses.

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.

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,

Enhanced and quenched B(E1) transition rates between parity doublet bands in 227Ra

Abstract The fast timing βγγ ( t ) method has been used to measure level lifetimes in the parity doublet bands in 227 Ra populated in the β − decay of 227 Fr. In particular T 1 2 = 254(9) ps , 236(30) ps , ⩽41 ps and 16(13) ps have been measured for the 3 2 − and 5 2 − members of the K π = 3 2 − band and for the 1 2 − and 3 2 − members of the K π = 1 2 − band, respectively. These results indicate surprisingly fast B (E1) rates in this octupole transitional nucleus with the average | D 0 | value of ⩾ 0.11 e ·fm for the K π = 1 2 − band and | D 0 |= 0.10 e ·fm for K π = 3 2 − band. The general enhancement (and occasional quenching) of E1 intra-doublet and some enhanced extra-doublet transitions in 227 Ra are interpreted within the quasiparticle-plus-phonon model with the inclusion of Coriolis coupling. Similar calculations, performed for 223 Ra, are found to be in good agreement with the experimental data.

Octupole correlations in 229Ra

Abstract The structure of 229 Ra has been studied in the β − decay of 229 Fr. Spins and parities have been determined from the conversion electron measurements, while half-lives for the 137.5, 142.7, 168.8, 213.0 and 479.0 keV levels have been measured in the ps and ns ranges via the fast timing βγγ ( t ) method. Our data confirm the previous results and enrich the knowledge of the structure of this nucleus by 25 new states and several strong transitions. Structural similarities are established between 229 Ra and its N = 141 isotone 231 Th. The experimental results are compared with the theoretical predictions of the quasiparticle-phonon model with inclusion of Coriolis coupling. The reduced transition probabilities, and especially the moderately fast B (E1) rate for the 137.5 keV transition connecting the band-heads of the K π = 5 2 ± parity doublet bands, reveal the presence of significant octupole correlations in 229 Ra.

Experimental masses at doubly magic nuclide 132Sn

The beta-decay energies have been measured for nuclides very far off the beta-stability line and close to double-magic 132Sn. The experiments have been performed at the improved OSIRIS-facility by using a Ge(HP)-detector. The mass values for fifteen nuclides of In, Sn, Sb and Te with mass numbers from the region of A = (132 ± 0, 1, 2) have been determined. The accuracy of the obtained data considerably exceeds the known one from literature. The proton-neutron effective interaction energies derived from mass values for the tin region are equal or very close to the ones for the lead region, if (l, j) and (l + 1, j + 1)-configurations for both protons and neutrons are compared. This result supports the idea of a universal shell model discription of different magic regions of heavy nuclides, which may allow to predict properties of yet unknown magic nuclides throughout the nuclidic chart.