A. M. Bruce

94β -Decay Half-Lives of Neutron-Rich Cs55 to Ho67 : Experimental Feedback and Evaluation of the r -Process Rare-Earth Peak Formation

The β-decay half-lives of 94 neutron-rich nuclei ^{144-151}Cs, ^{146-154}Ba, ^{148-156}La, ^{150-158}Ce, ^{153-160}Pr, ^{156-162}Nd, ^{159-163}Pm, ^{160-166}Sm, ^{161-168}Eu, ^{165-170}Gd, ^{166-172}Tb, ^{169-173}Dy, ^{172-175}Ho, and two isomeric states ^{174m}Er, ^{172m}Dy were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of β-decay half-lives are observed at neutron-number N=97 for _{58}Ce, _{59}Pr, _{60}Nd, and _{62}Sm, and N=105 for _{63}Eu, _{64}Gd, _{65}Tb, and _{66}Dy. Features in the data mirror the interplay between pairing effects and microscopic structure. r-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system.

High-[ital K] structures in [sup 136]Sm

High-spin states have been studied in the very neutron deficient [ital N]=74 nucleus, [sup 136]Sm with the reaction [sup 107]Ag([sup 32]S,[ital p]2[ital n])[sup 136]Sm. Using time-correlated charged-particle--[gamma]--[gamma] spectroscopy, a rotational cascade built upon the [ital t][sub 1/2]=15 [mu]s, [ital K][sup [pi]]=8[sup [minus]] isomer has been identified. Although equivalent isomers are known in other [ital N]=74 isotones, this represents the only case where the associated band has been observed. The in-band decay properties of this structure are consistent with a 7/2[sup +][404][direct product]9/2[sup [minus]][514] two quasineutron assignment. A second high-[ital K] band, probably of a four-quasiparticle nature, is observed to feed into the [ital K][sup [pi]]=8[sup [minus]] band.

Gamma-Ray spectroscopy in the vicinity of Zr-108

F. Browne et al.; 4 pags.; 2 figs.; Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 31–September 7, 2014; PACS numbers: 21.10.Re, 21.10.Tg, 23.20.Js, 27.60.+j

GAMMA-RAY SPECTROSCOPY IN THE VICINITY OF 108 Zr

F. Browne et al.; 4 pags.; 2 figs.; Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 31–September 7, 2014; PACS numbers: 21.10.Re, 21.10.Tg, 23.20.Js, 27.60.+j

7Li-induced reactions for fast-timing with LaBr3:Ce detectors

7Li induced-reactions have been used with a 186W target to populate nuclei around A∼180-190 at the National Institute of Physics and Nuclear Engineering in Bucharest, Romania. An array of high-purity germanium (HPGe) and cerium-doped lanthanum bromide (LaBr3:Ce) detectors have been used to measure sub-nanosecond half-lives with fast-timing techniques. The yrast 2+ state in 190Os was measured to be t1/2 = 375(20)ps, in excellent agreement with the literature value. The previously unreported half-life of the 564-keV state in 189Ir has also been measured and a value of t1/2 = 540(100)ps ps obtained.

Heavy rotation – evolution of quadrupole collectivity centred at the neutron-rich doubly mid-shell nucleus 170Dy

In this contribution the low-excitation structural properties of the doubly mid-shell nucleus 170Dy are discussed, with a special empasis on the evolution of the ground state rotational band within the dysprosium isotopic chain. Recent results from an experiment with the EURICA setup at RIKEN are shown in the context of previous measurements at the PRISMA+CLARA as well as the PRISMA+AGATA setups at Laboratori Nazionali di Legnaro. A brief outlook on future planned measurements is also given.

Electromagnetic Transition Rate Measurements in the N=80 Isotone, 138Ce

A study of intrinsic state halflife measurements in the N=80 nucleus 138Ce has been made using the 130Te(12C,4n)138Ce fusion evaporation reaction at beam energy of 56 MeV. The fast-timing gamma-ray coincidence method was used with a mixed LaBr3(Ce)-HPGe array to establish the lifetimes of the yrast 6+ state at 2294 keV, the Iπ=5− state at 2218 keV, the Iπ=11+ state at 3943 keV and the 14+ state at that at 5312 keV, all of which are in the sub nanosecond regime. Reduced transition probabilities have been calculated for the electromagnetic decays from these states.

First results from the stopped RISING campaign at GSI: The mapping of isomeric decays in highly exotic nuclei

The first results from the Stopped Beam RISING experimental campaign performed at the GSI laboratory in Darmstadt, Germany, are presented. RISING (Rare ISotope INvestigations at GSI) constitutes a major new experimental program in European nuclear structure physics research aimed at using relativistic‐energy, projectile‐fragmentation reactions to study nuclei with exotic proton‐to‐neutron ratios. This paper introduces the physics aims of the Stopped RISING collaboration and presents some technical details and initial results from experiments using the RISING array to study decays from metastable nuclear states in both proton and neutron‐rich nuclei.

A K pi =8(-) isomer in 136Sm.

An isomer with a half-life of 15[plus minus]1 [mu]s has been observed in the [ital N]=74 nucleus [sup 136]Sm, populated following the reaction [sup 107]Ag([sup 32]S,[ital p]2[ital n])[sup 136]Sm. It is proposed to have a [ital K][sup [pi]]=8[sup [minus]] two quasineutron configuration. The isomer decays via a [Delta][ital K]=8, 466 keV [ital E]1 transition with a surprisingly low hindrance per degree of [ital K] forbiddenness, [ital f][sub [nu]]=25.

Collective And Single-particle Structures In The Neutron-rich Doubly Mid-shell Nucleus 170Dy

One of the most successful descriptions of the structure of atomic nuclei is the spherical shell model. It, however, becomes impractical when moving away from closed-shell nuclei. Instead, it is the interplay between the macroscopic shape degrees of freedom and the microscopic nature of the underlying single-particle structure in a deformed basis that determines the nuclear structure. Being the heaviest nucleus precisely in the middle of, known, closed proton and neutron shells,