One new pair of positive-parity chiral doublet bands have been identified in the odd-A nucleus Nd-135 which together with the previously reported negative-parity chiral doublet bands constitute a ...third case of multiple chiral doublet (M chi D) bands in the A approximate to 130 mass region. The properties of the M chi D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M chi D bands in Nd-135 represents an important milestone in supporting the existence of M chi D in nuclei.
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Spectroscopy of proton-rich Zr-79 Llewellyn, R. D. O.; Bentley, M. A.; Wadsworth, R. ...
Physics letters. B,
12/2020, Volume:
811
Journal Article
Peer reviewed
Open access
Energy differences between isobaric analogue states have been extracted for the A = 79, Zr-79/Y-79 mirror pair following their population via nucleon-knockout reactions from intermediate-energy ...rare-isotope beams. These are the heaviest nuclei where such measurements have been made to date. The deduced mirror energy differences (MED) are compared with predictions from a new density-functional based approach, incorporating isospin-breaking effects of both Coulomb and nuclear charge-symmetry breaking and configuration mixing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Performance of HPGe detectors in high magnetic fields Sanchez Lorente, A.; Achenbach, P.; Agnello, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2007, Volume:
573, Issue:
3
Journal Article
Peer reviewed
Open access
A new generation of high-resolution hypernuclear
γ
-spectroscopy experiments with high-purity germanium detectors (HPGe) are presently designed at the FINUDA spectrometer at DA
Φ
NE, the Frascati
φ
...-factory, and at
P
¯
ANDA, the
p
¯
p
hadron spectrometer at the future FAIR facility. Both, the FINUDA and
P
¯
ANDA
spectrometers are built around the target region covering a large solid angle. To maximise the detection efficiency the HPGe detectors have to be located near the target, and therefore they have to be operated in strong magnetic fields (
B
≈
1
T
). The performance of HPGe detectors in such an environment has not been well investigated so far. In the present work VEGA and EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN magnet at GSI. No significant degradation of the energy resolution was found, and a change in the rise time distribution of the pulses from preamplifiers was observed. A correlation between rise time and pulse height was observed and is used to correct the measured energy, recovering the energy resolution almost completely. Moreover, no problems in the electronics due to the magnetic field were observed.
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Several new bands have been identified in Ba-130, among which there is one with band-head spin 8(+). Its properties are in agreement with the Fermi-aligned nu h(11/2)(2)523circle times 9/2(-)514 ...Nilsson configuration. This is the first observation of a two-quasiparticle t-band in the A = 130 mass region. The t-band is fed by a dipole band involving two additional h(11/2) protons. The odd-spin partners of the proton and neutron S-bands and the ground-state band at high spins are also newly identified. The observed bands are discussed using several theoretical models, total Routhians surfaces (TRS), tilted axis cranking (TAC), particle rotor model (PRM) and projected shell model (PSM), which strongly suggest the coexistence of prolate and oblate shapes polarized by rotation aligned two-proton and two-neutron configurations, as well as prolate collective rotations around axes with different orientations. With the new results, 130 Ba presents one of the best and most complete sets of collective excitations that a gamma-soft nucleus can manifest at medium and high spins, revealing a diversity of shapes and rotations for the nuclei in the A = 130 mass region.
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The nature of two high-spin bands in Nd-136 built on the two-quasiparticle configuration pi h(11/2)(2), predicted by the triaxial projected shell model as good candidates of transverse wobbling ...bands, are investigated experimentally. The mixing ratio of one Lambda I = 1 transition connecting the one-phonon and the zero-phonon wobbling bands is established from a high-statistics JuroGam II gamma-ray spectroscopy experiment by using the combined angular correlation and linear polarization method. The resulting wobbling excitation energy and ratios of reduced electromagnetic transition probabilities are in good agreement with results of a new particle-rotor model which rigidly couples the total angular momentum of two quasiparticles to a triaxial core in an orthogonal geometry, confirming thus the transverse wobbling nature of the bands.
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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(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{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(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+}) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+}) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N≈90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
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Background: The Xe isotopic chain with four valence protons above the Z = 50 shell closure is an ideal laboratory for the study of the evolution of nuclear deformation. At the N = 82 shell closure, ...136Xe presents all characteristics of a doubly closed shell nucleus with a spherical shape. In the very neutron-deficient isotopes close to N = 50, the alpha-decay chain of Xe was investigated to probe the radioactive decay properties near the drip-line and the magicity of 100Sn. Additionally, the Xe isotopes present higher order symmetries in the nuclear deformation such as the octupole degree of freedom near N = 60 and N = 90 or O(6) symmetry in stable isotopes.Purpose: The relevance of the O(6) symmetry has been investigated by measuring the spectroscopic quadrupole moment of the first excited states in 124Xe. In the O(6) symmetry limit, the spectroscopic quadrupole moment of collective states is expected to be null.Method: A stable 124Xe beam with energies of 4.03A MeV and 4.11A MeV was used to bombard a natW target at the GANIL facility. Excited states were populated via the safe Coulomb excitation reaction. The collision of the heavy ions with a large Z at low energy make this reaction sensitive to the diagonal E2 matrix element of the excited states. The recoils were detected in the VAMOS++ magnetic spectrometer and the gamma rays in the AGATA tracking array. The least squares fitting code GOSIA was used for the analysis to extract both E2 and M1 transitional and E2 diagonal matrix elements.Results: The rotational ground state band was populated up to the 8+1 state as well as the 2+2 and 4+2 states. Using high precision spectroscopic data to constrain the GOSIA fit, the spectroscopic quadrupole moments of the 2+1 , 4+1 , and 6+1 states were determined for the first time. Conclusions: The spectroscopic quadrupole moments were found to be negative, large, and constant in the ground state band underlining the prolate axially deformed ground state band of 124Xe. The present experimental data confirm that the is broken in 124Xe.
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The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88Ru has been measured using the combination of the Advanced Gamma Tracking Array (AGATA)spectrometer, ...the NEDA, and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88 Ru were populated via the 54 Feð 36 Ar; 2nγÞ 88 Ru fusion-evaporationreaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to 88 Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N 1⁄4 Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
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Tilted precession bands in Nd 135 Lv, B. F.; Petrache, C. M.; Lawrie, E. A. ...
Physical review. C,
04/2021, Volume:
103, Issue:
4
Journal Article
Peer reviewed
Two new excited bands built on the πh11/2 configuration have been identified in Nd135 in addition to the known πh11/2 band. The energy spectra of the excited bands and the available electromagnetic ...transition probabilities are in good agreement with theoretical results obtained using quasiparticle-plus-triaxial-rotor model calculations. The properties of the bands identify them as tilted precession bands instead of wobbling bands. Our results give a new insight into the interpretation of the low-lying bands in odd-A mass nuclei, and can stimulate future studies to address the nuclear triaxiality.
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Monte Carlo simulations of one of the possible configurations of the imaging phase for the DEGAS spectrometer situated at the DESPEC/NUSTAR experiment have been performed. The geometry consists of ...the coupling of the high-resolution γ spectroscopy array, AGATA, with a high-resolution segmented planar detector utilized as an implantation detector in a compact configuration. The sensitivity and performance of the array in terms of efficiency and imaging capability is deduced.
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