Excited-State Half-Lives in Cd 130 and the Isospin Dependence of Effective Charges
Not Available
Jungclaus, A.↗
Engineering topics
Nowacki, F.
Publications and source records attributed to Nowacki, F..
An alternative viewpoint on the nuclear structure towards 100 Sn: Lifetime measurements in 105 Sn
This work aims at presenting an alternative approach to the long standing problem of the B(E2) values in Sn isotopes in the vicinity of the N=Z double-magic nucleus 100 Sn, until now predominantly measured with relativistic and intermediate-energy Coulomb excitation reactions. The direct measurement of the lifetime of low-lying excited states in odd-even Sn isotopes provides a new and precise guidance for the theoretical description of the nuclear structure in this region. Lifetime measurements have been performed in 105 Sn for the first time with the coincidence Recoil Distance Doppler Shift technique. The lifetime results for the $7/2^+_1$ first excited state and the $11/2^+_1$ state, $2^+ (^{104}$Sn) Ⓧ $v1g_{7/2}$ multiplet member, are discussed in comparison with state-of-the-art shell model and mean field calculations, highlighting the crucial contribution of proton excitation across the core of 100 Sn. The reduced transition probability B(E2) of the $11/2^+_1$ core-coupled state points out an enhanced staggering with respect to the B(E2; $2^+_1$ → $0^+_1$) in the even-mass 104 Sn and 106 Sn isotopes.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
First Evidence of Axial Shape Asymmetry and Configuration Coexistence in Zn 74 : Suggestion for a Northern Extension of the N = 40 Island of Inversion
The excited states of N=44 74 Zn were investigated via γ-ray spectroscopy following 74 Cu β decay. By exploiting γ-γ angular correlation analysis, the 2$_2^+$, 3$_1^+$, 0$_2^+$, and 2$_3^+$ states in 74 Zn were firmly established. The γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 2$_2^+$, 3$_1^+$, and 2$_3^+$ states were measured, allowing for the extraction of relative B(E2) values. In particular, the 2$_3^+$→0$_2^+$ and 2$_3^+$→4$_1^+$ transitions were observed for the first time. Here the results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the N=40 gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize 74 Zn in its ground state. Furthermore, an excited K=0 band with a significantly larger softness in its shape is identified. A shore of the N=40 "island of inversion" appears to manifest above Z=26, previously thought as its northern limit in the chart of the nuclides.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
In-beam $$\gamma $$-ray spectroscopy of $$^{94}$$Ag
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.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
In-beam γ-ray spectroscopy of 32 Mg via direct reactions
Background: The nucleus 32 Mg (N=20 and Z=12) plays a central role in the so-called “island of inversion,” where in the ground states sd-shell neutrons are promoted to the fp-shell orbitals across the shell gap, resulting in the disappearance of the canonical neutron magic number N=20. Purpose: The primary goals of this work are to extend the level scheme of 32Mg, provide spin-parity assignments to excited states, and discuss the microscopic structure of each state through comparisons with theoretical calculations. Method: In-beam γ-ray spectroscopy of 32 Mg was performed using two direct-reaction probes: one-neutron (two-proton) knockout reactions on 33 Mg ( 34 Si). Final-state exclusive cross sections and parallel momentum distributions were extracted from the experimental data and compared with eikonal-based reaction model calculations combined with shell-model overlap functions. Results: Owing to the remarkable selectivity of the one-neutron and two-proton knockout reactions, a significantly updated level scheme for 32 Mg, which exhibits negative-parity intruder and positive-parity normal states, was constructed. The experimental results were confronted with four different nuclear structure models. Conclusions: In some of these models, different aspects of 32 Mg and the transition into the island of inversion are well described. However, unexplained discrepancies remain, and, even with the help of these state-of-the-art theoretical approaches, the structure of this key nucleus is not yet fully captured.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Evolution of shape and collectivity along the Ge isotopic chain: The case of 80 Ge
In this work, the shape and collectivity of 80 Ge were investigated via a sub-barrier-energy Coulomb excitation measurement using the JANUS setup at the NSCL ReA3 facility. The 80 Ge spectroscopic quadrupole moment $Q_{s}(2^{+}_{1})$ of the $2^{+}_{1}$ state was measured for the first time, and the precision of the 80 Ge $B(E2; 0^{+}_{1}$ → $2^{+}_{1}$) transition strength was increased. The experimental $Q_{s}(2^{+}_{1})$ value indicates a large, prolate deformation for 80 Ge, which is consistent with large-scale shell-model calculations performed for comparison. These results provide important benchmarks for models that try to describe nuclear shape in neutron-rich nuclei near the magic number N=50.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Coexisting normal and intruder configurations in 32 Mg
Situated in the so-called “island of inversion,” the nucleus 32 Mg is considered as an archetypal example of the disappearance of magicity at N = 20. We report on high statistics in-beam spectroscopy of 32 Mg with a unique approach, in that two direct reaction probes with different sensitivities to the underlying nuclear structure are employed at the same time. More specifically, states in 32 Mg were populated by knockout reactions starting from 33 Mg and 34 Si, lying inside and outside the island of inversion, respectively. The momentum distributions of the reaction residues and the cross sections leading to the individual final states were confronted with eikonal-based reaction calculations, yielding a significantly updated level scheme for 32 Mg and spin-parity assignments. By fully exploiting observables obtained in this measurement, a variety of structures coexisting in 32 Mg was unraveled. Comparisons with theoretical predictions based on shell-model overlaps allowed for clear discrimination between different structural models, revealing that the complete theoretical description of this key nucleus is yet to be achieved.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
In-beam γ-ray spectroscopy of 68 Fe from charge exchange on 68 Co projectiles
Excited states in the neutron-rich nucleus 68 Fe were populated using a 9 Be( 68 Co, 68 Fe + γ)X charge-exchange reaction at 95 MeV/u. The new γ-ray transitions reported here for the first time complement data from β-decay studies and nucleon knockout reactions. In comparison to shell-model calculations with the LNPS effective interaction, two candidate states for the $6$$^{+}_{1}$ level emerge. Here, the distinct population pattern of excited states and the magnitude of the cross section, σ inc = 0.51(6) mb, make this reaction a promising one for future in-beam γ -ray spectroscopy. Reaction calculations with nuclear structure input from a new, locally optimized Hamiltonian, f7j4a, together with general considerations for heavy-ion-induced charge-exchange reactions appear consistent with most of the observations, although challenges remain.
59 ≤ A ≤ 89↗
Octupole correlations near Te 110
The lifetime of the 2 + and 9 – , 11 – , 13 – , 15 – states in the neutron-deficient 110 Te was measured for the first time using the recoil distance Doppler shift technique. The reported value of the reduced transition probability B(E2; $0$$^{+}_{g.s}$ → 2 + ) = 4.3(8) × 10 3 e 2 fm 4 supports the systematic for even-mass Te isotopes and was interpreted in the framework of the large-scale shell model and cranked shell model calculations. The measured reduced transition probabilities in the negative-parity yrast band revealed the upward trend towards the high spins. Furthermore, the enhanced collectivity is discussed in terms of the tilted axis cranking approach and the symmetry configuration mixing method with the Gogny D1S interaction.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
In-beam γ-ray spectroscopy of 62,64 Cr
The region of neutron-rich Cr isotopes has garnered much attention in recent years due to a rapid onset of collectivity near neutron number N = 40. We report here on the first γ-ray spectroscopy beyond the ($4$ $^{+}_{1}$) state in 62,64 Cr, using nucleon removal reactions from several projectiles within a rare-isotope beam cocktail. A candidate for the 6 + state in 64 Cr is presented as well as one for, possibly, the second excited 0 + state in 62 Cr. The results are discussed in comparison to the LNPS shell-model predictions that allow for neutron excitations across the N = 40 harmonic oscillator gap into the g 9/2 and d 5/2 orbitals. Here, the calculated level schemes for 62,64 Cr reveal intriguing collective structures. From the predicted neutron particle-hole character of the low-lying states in these Cr isotopes, 62 Cr emerges as a transitional system on the path to the center of the N = 40 island of inversion.
59 ≤ A ≤ 89↗
Absence of Low-Energy Shape Coexistence in 80 Ge: The Nonobservation of a Proposed Excited 0 2 + Level at 639 keV
The 80 Ge structure was investigated in a high-statistics β-decay experiment of 80 Ga using the GRIFFIN spectrometer at TRIUMF-ISAC through γ, β-e, e-γ and γ-γ spectroscopy. No evidence was found for the recently reported 0 2 + 639-keV level suggested as evidence for low-energy shape coexistence in 80Ge. Large-scale shell model calculations performed in 78,80,82 Ge place the 0 2 + level in 80 Ge at 2 MeV. The new experimental evidence combined with shell model predictions indicate that low-energy shape coexistence is not present in 80 Ge.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Limits on assigning a shape to a nucleus
The interpretation of nuclear observables in the laboratory frame in terms of the intrinsic deformation parameters β and γ is a classical theme in nuclear structure. Here we use the quadrupole invariants, calculated within the framework of the configuration-interaction shell model, to clarify the meaning and limitations of nuclear shapes. In this work we introduce a novel method that enables us to calculate accurately higher-order invariants and, therefore, the fluctuations in both β and γ. We find that the shape parameter β often has a non-negligible degree of softness and that the angle γ is usually characterized by large fluctuations, rendering its effective value not meaningful. Contrary to common belief, we conclude that doubly magic nuclei are not spherical, because the notion of a well-defined shape does not apply to them.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Extending the Southern Shore of the Island of Inversion to F 28
Detailed spectroscopy of the neutron-unbound nucleus 28 F has been performed for the first time following proton/neutron removal from 29 Ne/ 29 F beams at energies around 230 MeV / nucleon . The invariant-mass spectra were reconstructed for both the 27 F(*) + n and 26 F(*) + 2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the 28 F ground state, with S n ( 28 F) = -199(6) keV, while analysis of the 2n decay channel allowed a considerably improved S n ( 27 F) = 162(60) keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of 28 F. Importantly, in the case of the ground state, the reconstructed 27 F + n momentum distribution following neutron removal from 29 F indicates that it arises mainly from the 1p 3/2 neutron intruder configuration. Finally, this demonstrates that the island of inversion around N = 20 includes 28 F, and most probably 29 F, and suggests that 28 O is not doubly magic.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗