M. Nyman

Discovery of 157 W and 161 Os

The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target. The 161Os α-decay energy and half-life were 6890±12 keV and 640±60 μs. The daughter 157W nuclei β-decayed with a half-life of 275±40 ms, populating both low-lying α-decaying states in 157Ta, which is consistent with a 7/2− ground state in 157W. Fine structure observed in the α decay of 161Os places the lowest excited state in 157W with Iπ =9/2− at 318±30 keV. The branching ratio of 5.5+3.1 −2.2% indicates that 161Os also has a 7/2− ground state. Shell-model calculations analysing the effects of monopole shifts and a tensor force on the relative energies of 2f7/2 and 1h9/2 neutron states in N=83 isotones are presented.

Discovery of 157W and 161Os

The nuclides 157W and 161Os have been discovered in reactions of 58Ni ion beams with a 106Cd target. The 161Os α-decay energy and half-life were 6890±12 keV and 640±60 μs. The daughter 157W nuclei β-decayed with a half-life of 275±40 ms, populating both low-lying α-decaying states in 157Ta, which is consistent with a 7/2− ground state in 157W. Fine structure observed in the α decay of 161Os places the lowest excited state in 157W with Iπ =9/2− at 318±30 keV. The branching ratio of 5.5+3.1 −2.2% indicates that 161Os also has a 7/2− ground state. Shell-model calculations analysing the effects of monopole shifts and a tensor force on the relative energies of 2f7/2 and 1h9/2 neutron states in N=83 isotones are presented.

Coulomb shifts and shape changes in the mass 70 region

The technique of recoil {beta} tagging has been developed which allows prompt {gamma} decays in nuclei from excited states to be correlated with electrons from their subsequent short-lived {beta} decay. This technique is ideal for studying nuclei very far from stability and improves in sensitivity for very short-lived decays and for high decay Q-values. The method has allowed excited states in {sup 78}Y to be observed for the first time, as well as an extension in the knowledge of T=1 states in {sup 74}Rb. From this new information it has been possible to compare Coulomb energy differences (CED) between T=1 states in {sup 70}Br/{sup 70}Se, {sup 74}Rb/{sup 74}Kr, and {sup 78}Y/{sup 78}Sr. The A=70 CED exhibit an anomalous behavior which is inconsistent with all other known CED. This behavior may be accounted for qualitatively in terms of small variations in the Coulomb energy arising from shape changes.

In-beam and decay spectroscopy of very neutron deficient iridium nuclei

Iridium nuclei at and beyond the proton drip line have been studied via fusion evaporation reactions. A reaction of 92Mo(78Kr, p2n) at a beam energy of 360 MeV and target thickness 500 µg cm−2 was employed to study 167,167mIr. A reaction of 112Sn(58Ni, p2n) at a beam energy of 266 MeV and target thickness 500 µg cm−2 was used to study 169,169mIr. The experiments were performed at the University of Jyvaskyla utilizing the RITU separator in conjunction with the focal plane GREAT spectrometer and the JUROGAM Ge array at the target position. Excited states feeding both the ground state and isomeric state in 169Ir, excited states feeding the ground state of 167Ir and the ground state alpha decay of 165Re have been observed for the first time along with excited states feeding 167mIr. Experimental spectroscopic factors and reduced widths have been obtained for the proton and alpha decay of these nuclei.

Shape coexistence at the proton drip-line: First identification of excited states in Pb180

Excited states in the extremely neutron-deficient nucleus {sup 180}Pb have been identified for the first time using the JUROGAM II array in conjunction with the RITU recoil separator at the Accelerator Laboratory of the University of Jyvaeskylae. This study lies at the limit of what is presently achievable with in-beam spectroscopy, with an estimated cross section of only 10 nb for the {sup 92}Mo({sup 90}Zr,2n){sup 180}Pb reaction. A continuation of the trend observed in {sup 182}Pb and {sup 184}Pb is seen, where the prolate minimum continues to rise beyond the N=104 midshell with respect to the spherical ground state. Beyond-mean-field calculations are in reasonable correspondence with the trends deduced from experiment.

Spectroscopic factor and proton formation probability for the d3/2 proton emitter 151mLu

Abstract The quenching of the experimental spectroscopic factor for proton emission from the short-lived d 3 / 2 isomeric state in 151mLu was a long-standing problem. In the present work, proton emission from this isomer has been reinvestigated in an experiment at the Accelerator Laboratory of the University of Jyvaskyla. The proton-decay energy and half-life of this isomer were measured to be 1295(5) keV and 15.4(8) μs, respectively, in agreement with another recent study. These new experimental data can resolve the discrepancy in the spectroscopic factor calculated using the spherical WKB approximation. Using the R-matrix approach it is found that the proton formation probability indicates no significant hindrance for the proton decay of 151mLu.

Comparison of gamma-ray coincidence and low-background gamma-ray singles spectrometry.

Aerosol samples have been studied under different background conditions using gamma-ray coincidence and low-background gamma-ray singles spectrometric techniques with High-Purity Germanium detectors. Conventional low-background gamma-ray singles counting is a competitive technique when compared to the gamma-gamma coincidence approach in elevated background conditions. However, measurement of gamma-gamma coincidences can clearly make the identification of different nuclides more reliable and efficient than using singles spectrometry alone. The optimum solution would be a low-background counting station capable of both singles and gamma-gamma coincidence spectrometry.

Isomer spectroscopy in No-254

Isomeric states in No-254 were investigated using a calorimetric method. Two different isomers were found with half-lives of T-1/2 = 266 +/- 2 ms and T-1/2 = 184 +/- 3 mu s, respectively. The domin ...

Low-lying excited states in the neutron-deficient isotopes Os-163 and Os-165

Excited states in the neutron-deficient isotopes 163Os and 165Os were identified using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. The 163Os and 165Os nuclei were populated via the 106Cd(60Ni,3n) and 92Mo(78Kr,2p3n) reactions at bombarding energies of 270 MeV and 357 MeV, respectively. Gamma-ray emissions from these nuclei have been established unambiguously using the recoil-decay tagging technique and a coincidence analysis has allowed level schemes to be established. These results suggest that the yrast states are based upon negative-parity configurations originating from the νf7/2 and νh9/2 orbitals.

Identification of gamma rays from Au-172 and alpha decays of Au-172, Ir-168, and Re-164

The low-lying structures of the extremely neutron-deficient nuclei 106Te, 107Te, 110Xe, 170Ir and 172Au have been investigated experimentally. Prompt gamma rays emitted in fusion-evaporation reactions were detected by the Jurogam HPGe array. The gamma rays were assigned to specific reaction channels using the recoil-decay tagging technique provided by the gas-filled separator RITU and the GREAT focal-plane spectrometer. The experimental set-up and the technique used to extract the information from the experimental data are described in detail. Results were interpreted in terms of the nuclear shell model and Total Routhian Surface calculations. In addition, decay studies on 170Ir, 172Au and 164Re led to the discovery of new alpha-decay branches in these nuclei.