First observation of excited states in the neutron deficientN=86isotones159Taand160W

Isomeric state in the doubly odd196At nucleus

An excited isomeric state has been identified in the 196At nucleus using the recoil decay tagging technique. This is the first identification of an excited state in this neutron-deficient odd-odd nucleus. Several tentative prompt γ-rays have also been correlated with 196At α-decay, although it has not been possible to assign them to specific energy levels in 196At. The mean lifetime of the isomeric state has been measured as τ = 11±2 µs. The new level is compared with similar low-lying states in neighbouring nuclei and is de-excited by an E2 γ-ray transition, the large hindrance of which is not expected.

Proton radioactivity of117La

A new more precise measurement of the ground-state proton decay of ${}^{117}\mathrm{La}$ is presented $[{E}_{p}=806(5) \mathrm{keV},$ ${t}_{1/2,p}=26(3)$ ms]. ${}^{117}\mathrm{La}$ was produced via the $p4n$ fusion-evaporation channel by bombarding a ${}^{64}\mathrm{Zn}$ target with 310 and 295 MeV ${}^{58}\mathrm{Ni}$ beams. The proton decay rate is consistent with emission from a prolate deformed ${3/2}^{+}$ or ${3/2}^{\ensuremath{-}}$ Nilsson state. No evidence is found for a previously reported proton decay from a high spin isomer in ${}^{117}\mathrm{La}.$ An upper limit for the production cross section for proton decay of ${}^{116}\mathrm{La}$ at a bombarding energy of 325 MeV was esta…

High-resolution γ-ray spectroscopy: a versatile tool for nuclear β-decay studies at TRIUMF-ISAC

High-resolution γ-ray spectroscopy is essential to fully exploit the unique, high-quality beams available at the next generation of radioactive ion beam facilities such as the TRIUMF isotope separator and accelerator (ISAC). The 8π spectrometer, which consists of 20 Compton-suppressed HPGe detectors, has recently been reconfigured for a vigorous research programme in weak interaction and nuclear structure physics. With the addition of a variety of ancillary detectors it has become the world's most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.

Proton radioactivity of 117La

A new more precise measurement of the ground-state proton decay of 117La is presented @Ep 5806(5) keV, t1/2,p526(3) ms#. 117La was produced via the p4n fusion-evaporation channel by bombarding a 64Zn target with 310 and 295 MeV 58Ni beams. The proton decay rate is consistent with emission from a prolate deformed 3/21 or 3/22 Nilsson state. No evidence is found for a previously reported proton decay from a high spin isomer in 117La. An upper limit for the production cross section for proton decay of 116La at a bombarding energy of 325 MeV was established. peerReviewed

First observation of excited states in the neutron deficient N = 86 isotones 159Ta and 160W

The γ decays of excited states in the neutron deficient nuclei 159 Ta and 160 W have been identified for the first time. The nuclei of interest were produced in reactions induced by beams of 58 Ni ions at energies of 286 MeV, 291 MeV, and 298 MeV bombarding a 106 Cd target. Prompt γ rays were recorded using the JUROSPHERE spectrometer and were tagged through the subsequent α decays of associated recoil ions measured in a position-sensitive silicon strip detector at the focal plane of the gas-filled separator RITU. Level schemes have been deduced and compared with similar structures observed in neighboring nuclei. peerReviewed

Probing structures of exotic heavy nuclei

The JYFL gas-filled recoil separator RITU, combined with Ge detector arrays, has successfully been employed in Recoil-Decay-Tagging (RDT) experiments in order to probe, for the first time, structures of several very neutron deficient heavy nuclei. In this contribution new data for light even-mass Hg, Pb and Po nuclei are shown and discussed. peerReviewed

Identification of theg92proton and neutron band crossing in theN=ZnucleusSr76

High-spin states in $^{76}\mathrm{Sr}$ have been studied using Gammasphere plus Microball detector arrays. The known yrast band has been extended beyond the first band crossing, which involves the simultaneous alignment of pairs of ${\mathrm{g}}_{\frac{9}{2}}$ protons and neutrons, to a tentative spin of $24\ensuremath{\hbar}$. The data are compared with the results of cranked relativistic mean-field (CRMF) and cranked relativistic Hartree-Bogoliubov (CRHB) calculations. The properties of the band, including the ${\mathrm{g}}_{\frac{9}{2}}$ proton/neutron band crossing frequency and moments of inertia, are found to be well reproduced by the CRHB calculations. Furthermore, the unpaired CRMF …

Gamma-spectroscopy of the 199At nucleus with the recoil filter detector

The neutron deficient 199At nucleus has been studied in the 175Lu+28Si reaction at Eb= 141 MeV. In order to select events of interest in the presence of the very strong background caused by fission, γ-rays have been detected in coincidence with recoiling evaporation residues. The excited states of 199At observed for the first time may indicate that this nucleus is deformed.

In-beam γ-ray spectroscopy of 190Po: First observation of a low-lying prolate band in Po isotopes

Gamma rays from excited states of 190Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated with a collective band which from spin 4 onwards resembles the prolate rotational bands known in the isotones 188Pb and 186Hg. This indicates that in 190Po the prolate configuration becomes yrast above I = 2. The experimental results are interpreted in a two-band mixing calculation and are in agreement with α-decay data and potential energy surface calculations.

First observation of excited states in $^{197}$At: the onset of deformation in neutron-deficient astatine nuclei

Excited states in the Z= 85 nucleus 197At have been identified for the first time using the recoil-decay-tagging (RDT) technique. The excitation energy of these states is found to be consistent with the systematics of neutron-deficient astatine nuclei and with theoretical calculations indicating that the nucleus may be deformed in its ground state.

Deformation of rotational structures inKr73andRb74: Probing the additivity principle at triaxial shapes

Lifetimes have been deduced in the intermediate/high-spin range for the three known rotational bands in $^{73}\mathrm{Kr}$ and the $T=0$ band in $^{74}\mathrm{Rb}$ using the residual Doppler shift method. This has enabled relative transition quadrupole moments to be studied for the first time in triaxial nuclei as a function of spin. The data suggest that the additivity principle for transition quadrupole moments is violated, a result that is in disagreement with predictions from cranked Nilsson-Strutinsky and cranked relativistic mean-field theory calculations. The reasons for the discrepancy are not understood but may indicate that important correlations are missing from the models.