betabeta-delayed fission of isomers in 188Bi^188Bi

status: publishe

Laser-assisted decay spectroscopy for the ground states of 180,182Au^180,182Au

status: publishe

Hyperfine anomaly in gold and magnetic moments of Ipi=11/2−I^pi=11/2^- gold isomers

status: publishe

Laser-assisted decay spectroscopy and mass spectrometry of 178Au^178Au

A comprehensive study of the isotope 178Au has been made at the CERN-ISOLDE facility, using resonance laser ionization. Two long-lived states in 178Au were identified—a low-spin ground state and a high-spin isomer—each of which were produced as pure beams. Using the ISOLTRAP precision Penning trap, the excitation energy of the isomeric state in 178Au was determined to be E∗=189(14)keV. The α-decay fine structure patterns of the two states were studied using the Windmill decay station, providing information on the low-lying states in the daughter nucleus 174Ir. Nuclear spin assignments of I(178Aug)=(2,3) and I(178Aum)=(7,8) are made based on the observed β-decay feeding and hyperfine structure intensity patterns. These spin assignments are used for fitting the hyperfine structures of the two states from which values for the magnetic dipole moments are extracted. The extracted moments are compared with calculations using additivity relations to establish the most probable configurations for 178Aug,m

Identification of a 6.6 microsecond isomeric state in 175Ir

An experiment has been performed to study excited states in the neutron-deficient nucleus 175Ir via the use of the JUROGAM II high-purity germanium detector array and the RITU gas-filled separator at JYFL, Jyväskylä. By using isomer tagging, an isomeric state with a half-life of 6.58(15) μs has been observed in 175Ir for the first time. It has been established that the isomer decays via a 45.2 (E1)–26.1 (M1) keV cascade to new states below the previously reported ground state in 175Ir with Iπ = (5/2−). We now reassign this (5/2−) state to the isomeric state discovered in this study.peerReviewe

Laser-assisted nuclear decay spectroscopy of 176,177,179Au

A study of the laser-ionized and mass-separated neutron-deficient isotopes Au-176,Au-177,Au-179 was performed using the Resonance Ionization Laser Ion Source and the Windmill detection setup at ISOLDE, CERN. New and improved data on complex fine-structure alpha decays of the three isotopes were deduced, providing insight into the low-lying levels in the daughter nuclei Ir-172,Ir-173,Ir-175. New information on the properties of beta-decay daughter products Pt-177,Pt-179 was also obtained. From the first in-source laser spectroscopy measurements of the hyperfine structure in the atomic 267.6-nm transition of Au-176, the nuclear magnetic moments for both high- and low-spin alpha-decaying states were deduced. Together with the values determined from the additivity relations, they were used to propose the most probable spins and configurations for both states. The a-decay branching ratios were determined as b(alpha)(Au-176(1s)) = 58(5)% and b(alpha)(Au-176(hs)) = 29 (5)%

First observation of a shape isomer and a low-lying strongly-coupled prolate band in neutron-deficient semi-magic 187Pb

Prompt and delayed γ-ray spectroscopy of the neutron-deficient, semi-magic isotope 187Pb has been performed using the recoil-decay and isomer-decay tagging techniques at the Argonne Gas-Filled Analyzer. A new 5.15(15)-μs isomeric state at only 308 keV above the spherical 3/2− ground state is identified and classified as a shape isomer. A strongly-coupled band is observed on top of the isomer, which is nearly identical to the one built on the prolate 7/2−[514] Nilsson state in the isotone 185Hg. Based on this similarity and on the result of the potential-energy surface calculations, the new isomer in 187Pb is proposed to originate from the same configuration. The retarded character of the 308-keV (7/2−)→3/2gs− transition with a deduced B(E2)=5.6(2)×10−4 W.u. can be well explained by the significant difference between the prolate parent and spherical daughter configurations, leading to the shape isomerism. The excitation energy of the isomer is surprisingly low, being roughly half of the excitation energies of the known 0+ intruder bandheads in the neighboring 186,188Pb isotopes. The combined results of the present work and the previous α-decay and laser spectroscopy studies present evidence for triple shape coexistence at low energy in the negative-parity configurations of 187Pb, which is well reproduced by the potential-energy surface calculations

Change in structure between the I = 1/2 states in 181Tl and 177,179Au

The first accurate measurements of the α-decay branching ratio and half-life of the Iπ=1/2+ ground state in 181Tl have been made, along with the first determination of the magnetic moments and I=1/2 spin assignments of the ground states in 177,179Au. The results are discussed within the complementary systematics of the reduced α-decay widths and nuclear g factors of low-lying, Iπ=1/2+ states in the neutron-deficient lead region. The findings shed light on the unexpected hindrance of the 1/2+→1/2+, 181Tl→g177Aug α decay, which is explained by a mixing of π3s1/2 and π2d3/2 configurations in 177Aug, whilst 181Tlg remains a near-pure π3s1/2. This conclusion is inferred from the g factor of 177Aug which has an intermediate value between those of π3s1/2 and π2d3/2 states. A similar mixed configuration is proposed for the Iπ=1/2+ ground state of 179Au. This mixing may provide evidence for triaxial shapes in the ground states in these nuclei

Calculation of gamma-ray spectroscopy of pg9/2 + isomers in 69,71,73,75,77,79 as nuclei

We have calculated binding energy, reduced transition probabilities and deformation parameter in 69,71,73,75,77,79 As nuclei. The energies of projectile-like fragments and Q-value in 76Ge (635 MeV) + 198Pt reactions are also calculated. The theoretical calculations of projectile like fragments (PLFs) energies are compared with the experimental values. The systematic energies for 9/2+ 5/2- de-excitation of + those nuclei indicate maximum deformation at N=42. The decrease in excitation level of the 9/2 state 69 79 from As to As provides some evidence for decreasing quadruple “softness” towards the closed neutron shell at N = 40. We have reported single and coincidence ?-ray spectroscopy of 79As by deep- inelastic collision 76Ge (635 MeV) + 198Pt. The systematic isomeric level and reduced transition probabilities of 69,71,73,75,77,79As nuclei have been investigated

Deformation versus Sphericity in the Ground States of the Lightest Gold Isotopes

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