0000000000002602
AUTHOR
P.t. Greenlees
Spectroscopy of low-spin states in $^{157}\mathrm{Dy}$: Search for evidence of enhanced octupole correlations
Low-spin states of 157Dy have been studied using the JUROGAM II array, following the 155Gd ({\alpha}, 2n) reaction at a beam energy of 25 MeV. The level scheme of 157Dy has been expanded with four new bands. Rotational structures built on the [523]5/2- and [402]3/2+ neutron orbitals constitute new additions to the level scheme as do many of the inter- and intra-band transitions. This manuscript also reports the observation of cross I- to (I-1)- and I- to (I-1)+ E1 dipole transitions inter-linking structures built on the [523]5/2- (band 5) and [402]3/2+ (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s =…
Shape coexistence in $^{178}$Hg
Lifetime measurements of excited states in 178 Hg have been performed using the 103 Rh ( 78 Kr , p 2 n ) reaction at a beam energy of 354 MeV. The recoil-decay tagging (RDT) technique was applied to select the 178 Hg nuclei and associate the prompt γ rays with the correlated characteristic ground-state α decay. Lifetimes of the four lowest yrast states of 178 Hg have been determined using the recoil distance Doppler-shift (RDDS) method. The experimental data are compared to theoretical predictions with focus on shape coexistence. The results confirm the shift of the deformed prolate structures to higher lying states but also indicate their increasing deformation with decreasing neutron numb…
In-beam gamma-ray and electron spectroscopy of $^{249,251}$Md
The odd-Z Md251 nucleus was studied using combined γ-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the [521]1/2− configuration, another rotational structure has been identified using γ-γ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a [514]7/2− single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of ≃60% was well reproduced by simulating a set of unresolved ex…
Lifetime measurements of excited states in $^{162}$W and $^{164}$W and the evolution of collectivity in rare-earth nuclei
International audience; Lifetimes of the first excited 2+ states in the extremely neutron-deficient $^{162}$W and $^{164}$W nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data for the isotopic chains of hafnium, tungsten, and osmium, from the midshell region near the β-stability line towards the N=82 closed shell and the most neutron-deficient nuclides, are compared with predictions of nuclear deformations and 21+→0g.s.+ reduced transition strengths from different classes of state-of-the-art theoretical model calculations. The results reveal striking differences and deficiencies in the predictive power of current nuclear structure models.
Lifetime measurements of excited states in ¹⁶³W and the implications for the anomalous B(E2) ratios in transitional nuclei
This letter reports lifetime measurements of excited states in the odd-N nucleus $^{163}$W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2+→17/2+)/B(E2:17/2+→13/2+) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed.
New β-decaying state in 214Bi
A new β-decaying state in 214Bi has been identified at the ISOLDE Decay Station at the CERN-ISOLDE facility. A preferred Iπ = (8−) assignment was suggested for this state based on the β-decay feeding pattern to levels in 214Po and shell-model calculations. The half-life of the Iπ = (8−) state was deduced to be T1/2 = 9.39(10) min. The deexcitation of the levels populated in 214Po by the β decay of this state was investigated via γ -γ coincidences and a number of new levels and transitions was identified. Shell-model calculations for excited states in 214Bi and 214Po were performed using two different effective interactions: the H208 and the modified Kuo-Herling particle interaction. Both ca…
First candidates for $\gamma$ vibrational bands built on the $[505]11/{2}^{-}$ neutron orbital in odd-$A$ Dy isotopes
Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the 155Gd({\alpha},2n)157Dy and 148Nd(12C, 5n)155Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a K{\pi}= 2+ {\gamma} vibrational band, built on the [505]11/2- neutron orbital, in both odd-A 155, 157Dy isotopes. The coupling of the first excited K=0+ states or the so-called \b{eta} vibrational bands at 661 and 676 keV in 154Dy and 156Dy to the [505]11/2- orbital, to produce a K{\pi}=11/2- band, was not observed in both 155Dy and 157Dy, respectively. The implication of these findings on the interpretation of the f…
Evolution of deformation in neutron-rich Ba isotopes up to A=150
12 pags., 11 figs., 3 tabs. -- Open Access funded by Creative Commons Atribution Licence 4.0
Lifetime Measurements of Excited States in $^{172}$Pt and the Variation of Quadrupole Transition Strength with Angular Momentum
Lifetimes of the first excited 2 + and 4 + states in the extremely neutron-deficient nuclide 172 Pt have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B ( E 2 : 4 + 1 → 2 + 1 ) / B ( E 2 : 2 + 1 → 0 + gs ) = 0.55 ( 19 ) was found, similar to a handful of other such anomalous cases observed in the entire Segré chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N ≈ 90 – 94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B ( E 2 : 4 + 1 → …
Production cross section and decay study of $^{243}$Es and $^{249}$Md
In the study of the odd-$Z$, even-$N$ nuclei $^{243}$Es and $^{249}$Md, performed at the University of Jyv\"askyl\"a, the fusion-evaporation reactions $^{197}$Au($^{48}$Ca,2$n$)$^{243}$Es and $^{203}$Tl($^{48}$Ca,2$n$)$^{249}$Md have been used for the first time. Fusion-evaporation residues were selected and detected using the RITU gas-filled separator coupled with the focal-plane spectrometer GREAT. For $^{243}$Es, the recoil decay correlation analysis yielded a half-life of $24 \pm 3$s, and a maximum production cross section of $37 \pm 10$ nb. In the same way, a half-life of $26 \pm 1$ s, an $\alpha$ branching ratio of 75 $\pm$ 5%, and a maximum production cross section of 300 $\pm$ 80 nb…
First β-decay spectroscopy of $^{135}$In and new $β$-decay branches of $^{134}$In
International audience; The $\beta$ decay of the neutron-rich $^{134}$In and $^{135}$In was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number $Z=50$ above the $N=82$ shell. The $\beta$-delayed $\gamma$-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three $\beta$-decay branches of $^{134}$In were established, two of which were observed for the first time. Population of neutron-unbound states decaying via $\gamma$ rays was identified in the two daughter nuclei of $^{134}$In, $^{134}$Sn and $^{133}$Sn, at…
A charge plunger device to measure the lifetimes of excited nuclear states where transitions are dominated by internal conversion
A charge plunger device has been commissioned based on the DPUNS plunger (Taylor et al., 2013) using the in-flight mass separator MARA at the University of Jyväskylä. The 152Sm(32S,4n)180Pt reaction was used to populate excited states in 180Pt. A lifetime measurement of the 21+ state was performed by applying the charge plunger technique, which relies on the detection of the charge state-distribution of recoils rather than the detection of the emitted γ rays. This state was a good candidate to test the charge plunger technique as it has a known lifetime and depopulates through a converted transition that competes strongly with γ-ray emission. The lifetime of the 21+ state was measured to be…
Recoil Isomer Tagging on Proton-Rich Odd–Odd N=77 Isotones 142Tb and 144Ho
The isomeric structure of the N=77 isotones 14265Tb and 14467Ho have been studied with the 92Mo(54Fe, xpn) fusion evaporation reaction at the University of Jyväskylä. The Jurospehere II germanium array was employed in conjunction with the RITU gas filled recoil separator. The feeding and decay of a 500(20) ns isomeric state in 144Ho has been established for the first time together with states built upon the known 15 μs isomer in 142Tb. The behavior of these new structures above the isomers suggest that they are low deformation configurations which display signs of triaxiality. peerReviewed
First Accurate Normalization of the beta-delayed alpha Decay of N-16 and Implications for the C-12(alpha,gamma)O-16 Astrophysical Reaction Rate
6 pags., 4 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0
Evidence against the wobbling nature of low-spin bands in 135Pr
International audience; The electromagnetic character of the ΔI=1 transitions connecting the 1- to 0-phonon and the 2- to 1-phonon wobbling bands should be dominated by an E2 component, due to the collective motion of the entire nuclear charge. In the present work it is shown, based on combined angular correlation and linear polarization measurements, that the mixing ratios of all analyzed connecting transitions between low-lying bands in 135Pr interpreted as 0-, 1-, and 2-phonon wobbling bands, have absolute values smaller than one. This indicates predominant M1 magnetic character, which is incompatible with the proposed wobbling nature. All experimental observables are instead in good agr…
Experimental observation of the M1 scissors mode in $^{254}No$
Physics letters / B 834, 137479 (2022). doi:10.1016/j.physletb.2022.137479
Normal and intruder configurations in $^{34}$Si populated in the $\beta^-$ decay of $^{34}$Mg and $^{34}$Al
The structure of Si34 was studied through γ spectroscopy separately in the β− decays of Mg34 and Al34 at the ISOLDE facility of CERN. Different configurations in Si34 were populated independently from the two recently identified β-decaying states in Al34 having spin-parity assignments Jπ=4− dominated by the normal configuration π(d5/2)−1⊗ν(f7/2) and Jπ=1+ by the intruder configuration π(d5/2)−1⊗ν(d3/2)−1(f7/2)2. The paper reports on spectroscopic properties of Si34 such as an extended level scheme, spin and parity assignments based on log(ft) values and γ-ray branching ratios, absolute β feeding intensities, and neutron emission probabilities. A total of 11 newly identified levels and 26 tr…
First -decay spectroscopy of and new -decay branches of
19 pags., 14 figs., 3 tabs.
Population of a low-spin positive-parity band from high-spin intruder states in Au: The two-state mixing effect
The extremely neutron-deficient isotopes $^{177,179}$Au were studied by means of in-beam γ-ray spectroscopy. Specific tagging techniques, α-decay tagging in $^{177}$Au and isomer tagging in $^{179}$Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in $^{177}$Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state.
Experimental study of 1/2(+) isomers in At-199,At-201
Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-alpha tagging techniques, a new isomeric 1/2(+) state [T-1/2 = 45(3) ms] in At-201 is identified, and an earlier reported corresponding state [T-1/2 = 273(9) ms] in At-199 is confirmed. The 1/2(+) state is suggested to originate from an intruder pi(s(1/2))(-1) configuration. In addition, nuclear structure of states below and above this 1/2(+) state are studied in both nuclei. The isomer decays through a cascade of an E3 transition followed by a mixed M1/E2 transition to the 9/2(-) ground state, and it is interpreted to be fed from nearly spherical 3/2(+) and 5/2(+) states originating f…