13 research outputs found
Spectroscopy in the transfermium region : probing rotational, non-yrast and isomeric structures in [sup 253, 254]No
Alpha-decay studies of the francium isotopes 198Fr and 199Fr nuclei
Very neutron deficient francium isotopes have been produced in fusion evaporation reactions using 60Ni ions
on 141Pr targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate
them from the scattered beam. The activities were implanted into a position sensitive silicon detector after
passing through a gas-counter system. The isotopes were identified using spatial and time correlations between
the implants and the decays. Two α-particle activities, with Eα = 7613(15) keV and T1/2 = (15+12
â5 ) ms and
Eα = 7684(15) keV and T1/2 = (16+13
â5 ) ms were identified in the new isotope 198Fr. In addition, the half-life and
α-particle energy of 199Fr were measured with improved precision. The measured decay properties deduced for 199Fr and 198Fr suggest that there is an onset of ground-state deformation at N = 112 in the Fr isotopes.peerReviewe
Gamma-ray and decay spectroscopy of 194,195,196At
Excited states of 195At have been studied by means of in-beam Îł -ray spectroscopy and the recoil-decay tagging
technique. A strongly coupled rotational band feeding the α-decaying 7/2â state via unobserved transitions was
identified. This band is presumably built on the oblate proton I Ï = 13/2+ state. Confirming earlier measurements,
α decays from the 1/2+ and 7/2â states were observed. Additionally, an E3 branch competing with the α decay
of the 7/2â state was inferred. Also α decays of the odd-odd isotopes 194,196At were examined.peerReviewe
High-spin states beyond the proton drip-line: Quasiparticle alignments in Cs-113
Excited states have been studied in the deformed proton emitter 113Cs. Gamma-ray transitions have been
unambiguously assigned to 113Cs by correlation with its characteristic proton decay, using the method
of recoil-decay tagging. Two previously identified rotational bands have been observed and extended to
tentative spins of 45/2 and 51/2 hÂŻ, with excitation energies over 8 MeV above the lowest state. These
are the highest angular momenta and excitation energies observed to date in any nucleus beyond the
proton drip-line. Transitions in the bands have been rearranged compared to previous work. A study
of aligned angular momenta, in comparison to the predictions of WoodsâSaxon cranking calculations, is
consistent with the most intense band being based on the Ï g7/2[422]3/2+ configuration, which would
contradict the earlier Ïh11/2 assignment, and with the second band being based on the Ïd5/2[420]1/2+
configuration. The data suggest that the band based upon the Ïh11/2 configuration is not observed.peerReviewe
Competing Decay Modes of a High-spin Isomer in the Proton-unbound Nucleus 158Ta
An isomeric state at high spin and excitation energy was recently observed
in the proton-unbound nucleus 158Ta. This state was observed to
decay by both α and γ decay modes. The large spin change required to decay
via γ-ray emission incurs a lifetime long enough for α decay to compete.
The α decay has an energy of 8644(11) keV, which is among the highest
observed in the region, a partial half-life of 440(70) ”s and changes the
spin by 11~. In this paper, additional evidence supporting the assignment
of this α decay to the high-spin isomer in 158Ta will be presented.peerReviewe
Multiparticle configurations of excited states in 155Lu
Excited states in the neutron-deficient N=84 nuclide 155Lu have been populated by using the 102Pd(58Ni,αp) reaction. The 155Lu nuclei were separated by using the gas-filled recoil ion transport unit (RITU) separator and implanted into the Si detectors of the gamma recoil electron alpha tagging (GREAT) spectrometer. Prompt Îł-ray emissions measured at the target position using the JUROGAM Ge detector array were assigned to 155Lu through correlations with α decays measured in GREAT. Structures feeding the (11/2â) and (25/2â)α-decaying states have been revised and extended. Shell-model calculations have been performed and are found to reproduce the excitation energies of several of the low-lying states observed to within an average of 71 keV. In particular, the seniority inversion of the 25/2â and 27/2â states is reproduced.peerReviewe
Blurring the Boundaries: Decays of Multiparticle Isomers at the Proton Drip Line
A multiparticle spin-trap isomer has been discovered in the proton-unbound nucleus 158
73Ta85. The isomer
mainly decays by Îł-ray emission with a half-life of 6.1Ă°1Ă ÎŒs. Analysis of the Îł-ray data shows that
the isomer lies 2668 keV above the known 9ĂŸ state and has a spin 10â higher and negative parity. This
19â isomer also has an 8644(11) keV, 1.4(2)% α-decay branch that populates the 9ĂŸ state in 154Lu.
No proton-decay branch from the isomer was identified, despite the isomer being unbound to proton
emission by 3261(14) keV. This remarkable stability against proton emission is compared with theoretical
predictions, and the implications for the extent of observable nuclides are considered.peerReviewe
Spectroscopy at the two-proton drip line: Excited states in 158W
Excited states have been identified in the heaviest known even-Z isotone 158W, which lies in a region of one-proton emitters and the two-proton drip line. The observation of γ-ray transitions feeding the ground state establishes the excitation energy of the yrast 6+ state confirming the spin-gap nature of the α-decaying 8+ isomer. The 8+ isomer is also expected to be unbound to two-proton emission but no evidence for this decay mode was observed. An upper limit for the two-proton decay branch has been deduced as 0.17% at the 90% confidence level. The possibility of observing two-proton emission from multiparticle isomers in nearby nuclides is considered.peerReviewe
Low-lying excited states in the neutron-deficient isotopes 163Os and 165Os
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 Îœf7/2 and
Îœh9/2 orbitals.peerReviewe
Evidence for prolate structure in light Pb isotopes from in-beam gamma-ray spectroscopy of 185Pb
For the first time, excited states in 185Pb have been observed in in-beam gamma-ray spectroscopic measurements using the recoil-decay tagging method. The resulting level scheme reveals a strongly coupled yrast band structure that originates from coupling of the i_13/2 quasineutron to a prolate deformed core. The band is also observed to de-excite via the spherical alpha-decaying 13/2+ isomeric state.status: publishe