A. Kerek

Two-proton and proton-neutron states in the doubly closed shell 50132Sb81Sn82 region

Abstract Two states in 134 Sb with half-lives of 0.85 ± 0.10 sec and 10.3 ± 0.5 sec have been observed. The two states are ascribed the configurations (π g 7 2 , ν f 7 2 ) with spin assignments 0 − and 7 − , respectively. In the decay of the 10.3 sec (7 − ) state two excited 6 + states in 134 Te at 1691.3 and 2397.6 keV are populated. The lower 6 + state decays by a stretched E2 cascade via a 4 + state at 1576.1 keV and a 2 + state at 1279.1 keV to the ground state. The observed states of 134 Sb and 134 Te are compared to theoretical predictions using a δ-force interaction.

High-spin states and evidence for particle-core coupling in the N = 83 isotones: 143Nd, 145Sm and 147Gd

Abstract The level structure of the 143Nd, 145Sm and 147Gd nuclei has been studied using the 142 Ce (α, 3 n γ) 143 Nd , 144 Nd (α, 3 n γ) 145 Sm and 144Sm(α, nγ)147Gd reactions. Singles γ-ray, γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured at various bombarding energies. Gamma transitions between excited states with spin values up to 25 2 + have been observed in all the nuclei investigated. The lifetime and angular distribution measurements performed confirm the recently proposed reassignment of some low-lying high-spin states in the N = 83 isotones considered as 13 2 + excitations. The observed level structure in these N = 83 nuclei can be explained if the extra neutron outside the N = 82 closed shell is coupled to doubly even core excitations. The coupling of the neutron single particle excitations (mainly in the 2f 7 2 , 1h 9 2 and li 13 2 orbitals) to the lowest 2+ and 3− vibrations of the core is calculated within the framework of an intermediate coupling model. The results obtained in these calculations are in good agreement with the experimental data. The energies of the three-particle states, being the results of the coupling of the 2f 7 2 or the 1i 13 2 extra neutron to two-proton excitations in the core, are nicely reproduced in the calculations, when empirical values of the two-body interaction matrix elements are used.

Beta decay studies in the vicinity of 13250Sn82: Excited states in 13051Sb, 13052Te and 13252Te

Abstract Using the OSIRIS on-line isotope separator facility, the decays of 130 Sn and 130, 132 Sb have been studied. On the basis of singles γ and γ-γ coincidence Ge(Li) spectra and conversion electron Si(Li) measurements, level schemes for 130 Sb, 130 Te and 132 Te have been constructed. The corresponding half-lives have been measured using multiscaling technique. The 3.8 min ground state of 130 Sn populates only positive parity states in the πν −3 nucleus 130 Sb: the energetically lowest 5 + state with the (π1 g 7 2 , ν2 d 3 2 ) configuration assignment; the T 1 2 = 3.6 ± 0.3 ns 4 + state at 70.0 keV; the 2 + state at 262.5 keV; the (0, 1) + state at 697.2 keV; the 3 + state at 813.1 keV and the 1 + state at 1042.3 keV excitation energy. A 1.7 min isomeric state in 130 Sn, with the tentative spin assignment (7 − ), populates several odd parity levels in 130 Sb. These arise from the (π1 g 7 2 , ν1 h 11 2 -1 ) and/or (π2 d 5 2 , ν1 h 11 2 -1 ) configurations and are located 84.7 keV (6 − ), 144.9 keV (7 − ), 688.5 keV and 1044.0 keV above the 40 min 8 − β- decaying state. No transitions between odd and even parity states have been observed. The most important excited states in 130 Te found in the β − decay of the 6.6 min 130 Sb 5 + state are: 839.4 keV, 2 + ; 1632.8 keV, 4 + ; 1815.1 keV, 6 + ; 2100.8 keV, 5 − . Levels in the π 2 ν −2 nucleus 132 Te were observed in the β − decays of the 2.8 min 132 Sb (4 + ) and the 4.2 min 132 Sb (8 − ) states. Unique spin and parity assignments have been given to the following states: 973.9 keV, 2 + ; 1670.7 keV, 4 + ; 1774.1 keV, 6 + ; 1924.7 keV, 7 − ; 2053.0 keV, 5 − .

The first excited state in the doubly-closed-shell nucleus 132Sn populated in the 0.12 s β−-decay of 132In

Abstract A 0.12 ± 0.02 s beta activity assigned to the decay of 132 In and populating an excited state at 4041 ± 2 keV in the doubly-closed-shell nucleus 50 132 Sn 82 has been observed. This state is tentatively assigned to arise from the 3 − octupole vibration.

The Life-time Measurements of Some High-spin States in the 138,139Ce and 141,142Nd Nuclei

A search for high-spin isomeric states in the 138,139Ce anc 141,142Nd nuclei has been made using (α, xn) reactions and the intrinsic pulsing of the 225-cm Stockholm cyclotron. In 138Ce, besides the known 7- isomeric state at 2 128.8 keV, another one at 3 538.5 keV, 10+, with T1/2 = (78 ± 5) ns has been found. In 139Ce a new isomeric state at 2 631.5 keV, 19/2-, with T1/2 = (70 ± 5) ns has been identified. Also in 141Nd a high-spin isomeric level exists probably at 3 104.9 keV with T1/2 = (26 ± 5) ns. In 142Nd the level at 3 453.0 keV, with spin I = 6, shows a half-life T1/2 = (1.3 ± 0.1) ns while that at 4 718.5 keV, I = 8, decays with a half-life of about 0.8 ns. The time distributions in 142Nd show that the 3 242.9 keV, I = 7, or the 3 456.2 keV, I = 8, level is also delayed and decays with T1/2 = (1.6 ± 0.1) ns. The deduced transition probabilities are compared to theoretical predictions.

Structure of the levels in the doubly magic nucleus 50132Sn82

Abstract Delayed γ − γ coincidence measurements give a half-life of the 4415 keV state in 132 Sn of 2.1 ± 0.3 ns. The K conversion coefficients of the 299 keV and 374 keV transitions correspond to M1/E2 multipolarity. The levels excited in 132 Sn very likely form a 4 + , 6 + , 8 + sequence above the first excited 2 + level.

Excited states in the two-neutron-hole nucleus 13050sn80 observed in the 0.53 sec β− decay of 130In

Abstract By studying high-energy β − particles the 0.53±0.05 sec decay of 130 49 In 81 and excited states in the two-neutron-hole nucleus 130 50 Sn 80 have been observed. These states have been given the tentative assignments 2 + (1217 keV), 4 + (1992 keV) and 5 − (2119 keV).

HIGH-SPIN STATES IN THE SINGLE-CLOSED-SHELL NUCLEUS 142Nd

Abstract The excited states of 142 60 Nd 82 have been studied using the 140 Ce(α, 2nγ) 142 Nd and 142 Ce(α, 4γ) 142 Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even- Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in 142 Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons.

High-spin states in 14460Nd84 observed in the (α, 2nγ) reaction

Abstract Excited states of 144 60 Nd 84 have been studied using the 142 Ce (α,2 n γ) 144 Nd reaction. Singles γ-ray, γ-γ coincidence spectra, angular and time distributions of γ-rays with respect to the beam bursts have been measured. Excited states up to 4.986 MeV with spin values up to 13 were populated. The majority of the observed states with spin values up to 12 can be interpreted as two-quasiparticle states. Several of the highest-spin levels can also be explained quantitatively as four-quasiparticle states. No isomeric states with a half-life longer than 1 ns have been found.