M. Sandzelius

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.

The SAGE spectrometer: A tool for combined in-beam γ-ray and conversion electron spectroscopy

The SAGE spectrometer allows simultaneous in-beam γ-ray and internal conversion electron measurements, by combining a germanium detector array with a highly segmented silicon detector and an electron transport system. SAGE is coupled with the ritu gas-filled recoil separator and the great focal-plane spectrometer for recoil-decay tagging studies. Digital electronics are used both for the γ ray and the electron parts of the spectrometer. SAGE was commissioned in the Accelerator Laboratory of the University of Jyvaskyla in the beginning of 2010.

Spectroscopy of proton-rich 66^Se up to J^π = 6^+: isospin-breaking effect in the A = 66 isobaric triplet

Candidates for three excited states in the 66^Se have been identified using the recoil-{\beta} tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analogue states across the A = 66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f_7/2 shell. Shell-model calculations indicate a continued need for an additional isospin non-conserving interaction in addition to the Coulomb isotensor part as a function of mass.

Lessons learned with the SAGE spectrometer

The SAGE spectrometer combines a high-efficiency γ-ray detection system with an electron spectrometer. Some of the design features have been known to be problematic and surprises have come up during the early implementation of the spectrometer. Tests related to bismuth germanate Compton-suppression shields, electron detection efficiency and an improved cooling system are discussed in the paper.

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 ...

High-spin spectroscopy of 140Nd

The population of the high-spin states in Nd-140 was investigated using the reaction Zr-96(Ca-48,4n). The results from two experiments, one with the EUROBALL array and one with the JUROGAM II + RITU + GREAT setup employing the recoil decay tagging technique, have been combined to develop a very detailed level scheme for Nd-140. Twelve bands of quadrupole transitions and eleven bands of dipole transitions were identified and their connections to low-lying states were established. Calculations using the cranked Nilsson-Strutinsky and the tilted axis cranking models were used to interpret the observed structures. The overall good agreement between the experimental results and the calculations assuming a triaxial shape of the nucleus strongly support the existence of a stable triaxial shape at high spins in this mass region. (Less)

γ -ray linear polarization measurements and (g9/2) −3 neutron alignment in 91Ru

The authors would like to thank the operators of the GANIL cyclotrons for providing the 36Ar beam. We would also like to thank the EXOGAM Collaboration for use of the clover Ge detector array, the DIAMANT Collaboration for use of the charged particle detector system, and the European gamma-ray Spectroscopy Pool for use of the neutron detector system. We acknowledge funding support from the French-Polish LEA COPIGAL and the IN2P3-Polish laboratories COPIN Agreement No. 06-122, from the UK STFC, from the Swedish Research Council (Contracts No. 2007-4067 and No. 2008-5793), from the Goran Gustafsson Foundation, from the OTKA under Contract No. K100835, and from the Bolyai Janos Foundation. AG has been supported by the Generalitat Valenciana, Spain, under Grant No. PROMETEO/2010/101 and by MINECO, Spain, under Grants No. AIC-D-2011-0746 and No. FPA2011-29854. AJ acknowledge financial support from the Spanish Ministerio de Ciencia e Innovacion under Contract No. FPA2011-29854-C04. ZY acknowledges the support from the Chinese Academy of Sciences, China.