Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus 57120La63. The observed γ rays have been assigned based on coincidences with lanthanum X rays ...measured with the JUROGAM 3 array and with A=120 fusion-evaporation residues measured with the MARA separator. The observed γ rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity 4+ to the ground state and a πh11/2⊗νh11/2 configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the np interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of E2 transitions, giving credit to the np interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei.
Excited states in the Tz=0,−1 nuclei 62Ga and 62Ge were populated in direct reactions of relativistic radioactive ion beams at the RIBF. Coincident γ rays were measured with the DALI2+ array and ...uniquely assigned to the A=62 isobars. In addition, 62Ge was also studied independently at JYFL-ACCLAB using the 24Mg(40Ca,2n)62Ge fusion-evaporation reaction. The first excited T=1,Jπ=2+ states in 62Ga and 62Ge were identified at 979(1) and 965(1) keV, respectively, resolving discrepant interpretations in the literature. States beyond the first 2+ state in 62Ge were also identified for the first time in the present work. The results are compared with shell-model calculations in the fp model space. Mirror and triplet energy differences are analyzed in terms of individual charge-symmetry and charge-independence breaking contributions. The MED results confirm the shrinkage of the p-orbits' radii when they are occupied by at least one nucleon on average.
The jurogam 3 spectrometer Pakarinen, J.; Ojala, J.; Ruotsalainen, P. ...
The European physical journal. A, Hadrons and nuclei,
05/2020, Letnik:
56, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The
jurogam 3
spectrometer has been constructed for in-beam
γ
-ray spectroscopy experiments in the Accelerator Laboratory of the University of Jyväskylä, Finland.
jurogam 3
consists of ...germanium-detector modules in a compact geometry surrounding a target to measure
γ
rays emitted from radioactive nuclei.
jurogam 3
can be employed in conjunction with one of two recoil separators, the
mara
vacuum-mode separator or the
ritu
gas-filled separator, and other ancillary devices.
Prolate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A≈120 nuclei is reported for the first time. One of the four reported bands in 119Cs, built on a 11/2− ...state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled πh11/250511/2− configuration associated with oblate shape. Together with the decoupled πh11/25413/2− band built on the 11/2− prolate state at 110 keV, for which a half-life of T1/2=55(5)μs has been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A≈120 nuclei, a phenomenon predicted since long time, but not yet observed. Calculations using the particle-number conserving cranked shell model and two dimensional tilted axis cranking covariant density functional theory support and well reproduce the observed oblate and prolate coexisting low-energy states in 119Cs.
In-beam $$\gamma $$-ray spectroscopy of $$^{94}$$Ag Pereira-López, X.; Bentley, M. A.; Wadsworth, R. ...
The European physical journal. A, Hadrons and nuclei,
03/2023, Letnik:
59, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
A recoil-beta-tagging experiment has been performed to study the excited
$$T=0$$
T
=
0
and
$$T=1$$
T
=
1
states in the odd–odd
$$N=Z$$
N
=
Z
nucleus
$$^{94}$$
94
Ag, populated via the
...$$^{40}$$
40
Ca(
$$^{58}$$
58
Ni,1p3n)
$$^{94}$$
94
Ag reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt
$$\gamma $$
γ
rays emitted at the reaction target, a number of transitions between excited states in
$$^{94}$$
94
Ag have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived
$$T=1$$
T
=
1
ground state of
$$^{94}$$
94
Ag. The transitions are proposed to proceed within and between the sets of states with
$$T=0$$
T
=
0
and
$$T=1$$
T
=
1
. Possible correspondence between some of these transitions from analog states in
$$^{94}$$
94
Pd has been discussed, and shell-model calculations including multipole and monopole electromagnetic effects have been presented, in order to enable predictions of the decay patterns between the
$$T=0$$
T
=
0
and
$$T=1$$
T
=
1
states and to allow a theoretical set of Coulomb energy differences to be calculated for the
$$A = 94$$
A
=
94
$$T=1$$
T
=
1
analog states.
Candidate revolving chiral doublet bands in 119Cs Zheng, K. K.; Petrache, C. M.; Zhang, Z. H. ...
The European physical journal. A, Hadrons and nuclei,
2022/3, Letnik:
58, Številka:
3
Journal Article
Recenzirano
Two rotational bands are identified in
119
Cs, one of which having very similar pattern to that of the strongly-coupled
π
g
9
/
2
404
9
/
2
+
band. The properties of the bands with similar patterns ...extracted from the experimental data are in agreement with a chiral interpretation. Tilted axis cranking covariant density functional theory with pairing correlations and particle-number conserving cranked shell model calculations are employed to determine the deformation and to investigate the band configurations, respectively. It results that the backbending is induced by the rotational alignment of two
h
11
/
2
protons, whose angular momenta reorient from the short to the intermediate axis, in a plane orthogonal to the angular momentum of the strongly-coupled
g
9
/
2
proton which keeps aligned along the long axis. The total spin points in 3D, inducing the breaking of the chiral symmetry. This is the first observation of candidate chiral bands built on a configuration with three protons, one in the strongly coupled
404
9
/
2
+
orbital which does not change orientation with increasing rotational frequency, and two in the
h
11
/
2
orbital which reorients to the rotation axis. The bands are observed in the transient backbending regime, showing that the chirality in nuclei is a general phenomenon, being robust and present not only in nuclei with nearly maximal triaxiality and pure configurations, but also in nuclei with moderate triaxiality and mixed configurations which gradually evolve from one to three-quasiparticle configurations, like in the backbending region.
Lifetime measurements in
178
Pt with excited states de-exciting through
γ
-ray transitions and internal electron conversions have been performed. Ionic charges were selected by the in-flight mass ...separator MARA and measured at the focal plane in coincidence with the
4
1
+
→
2
1
+
257
keV
γ
-ray transition detected using the JUROGAM 3 spectrometer. The resulting charge-state distributions were analysed using the differential decay curve method (DDCM) framework to obtain a lifetime value of 430(20) ps for the
2
1
+
state. This work builds on a method that combines the charge plunger technique with the DDCM analysis. As an alternative analysis, ions were selected in coincidence with the
178
Pt alpha decay (
E
alpha
=
5.458
(
5
)
MeV) at the focal plane. Lifetime information was obtained by fitting a two-state Bateman equation to the decay curve with the lifetime of individual states defined by a single quadrupole moment. This yielded a lifetime value of 430(50) ps for the
2
1
+
state, and 54(6) ps for the
4
1
+
state. An analysis method based around the Bateman equation will become especially important when using the charge plunger method for the cases where utilising coincidences between prompt
γ
rays and recoils is not feasible.
Low-spin positive-parity yrare states of 66154Dy88 were established using the 155Gd(3He,4n) reaction at a beam energy of Elab=37.5 MeV. The AFRODITE spectrometer array at iThemba LABS was used to ...record γγ coincidences and measure DCO ratios and polarisation asymmetries. The Kπ=2+γ band has been observed up to spin 13+ in the odd spins and to 12+ in the even spins. The staggering parameter S(I) of the γ band is compared to that found in other N = 88 isotones. Different behaviour of S(I) with increasing spin is observed for each of the isotones. We conjecture that the variation in S(I) is mainly due to mixing of the even-spin states with the same spin and parity states in neighbouring rotational bands. A second Kπ=2+ band has been established up to a spin of 12+ in the even spins. We suggest that this is a γ band based on the Jπ=0+ state at Ex=660.6 keV.
Reduced transition probabilities have been extracted between excited, yrast states in the N=Z+2 nucleus 94Pd. The transitions of interest were observed following decays of the Iπ=14+, Ex=2129-keV ...isomeric state, which was populated following the projectile fragmentation of a 124Xe primary beam at the GSI Helmholtzzentrum für Schwerionenforschung accelerator facility as part of FAIR Phase-0. Experimental information regarding the reduced E2 transition strengths for the decays of the yrast 8+ and 6+ states was determined following isomer-delayed Eγ1−Eγ2−△T2,1 coincidence method, using the LaBr3(Ce)-based FATIMA fast-timing coincidence gamma-ray array, which allowed direct determination of lifetimes of states in 94Pd using the Generalized Centroid Difference (GCD) method. The experimental value for the half-life of the yrast 8+ state of 755(106) ps results in a reduced transition probability of B(E2:8→+6+) = 205−25+34 e2 fm4, which enables a precise verification of shell-model calculations for this unique system, lying directly between the N=Z line and the N=50 neutron shell closure. The determined B(E2) value provides an insight into the purity of (g9/2)n configurations in competition with admixtures from excitations between the (lower) N=3pf and (higher) N=4gds orbitals for the first time. The results indicate weak collectivity expected for near-zero quadrupole deformation and an increasing importance of the T=0 proton-neutron interaction at N=48.
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