Normal-ordering approximations and translational (non)invariance
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
SEARCH · Engineering Papers
Results for “Nuclear Structure”
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Experimental and shell-model study of excited states in Fe 29 26 55 and related notes on Cu 26 29 55
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Shapes, softness, and nonyrast collectivity in 186 W
Nonyrast, excited states in neutron-rich 186 W were populated via inelastic-scattering reactions using beams of 136 Xe nuclei accelerated to 725 and 800 MeV. Levels populated in the reactions were investigated via particle-γ coincidence techniques using the Gammasphere array of high-purity germanium detectors and the compact heavy-ion counter, CHICO2. The K π = 2 + (γ ), K π = 0 + and K π = 2 – (octupole) rotational side bands were extended to spins 14h¯, 12h¯, and 13h¯, respectively. A staggering pattern observed in the energies of levels in the K π = 2 + band was found to be consistent with a potential that gets softer to vibration in the γ degree of freedom with increasing spin. Furthermore, the odd-even staggering of states in the K π = 2 – band was found to exhibit a phase opposite to that seen in the γ band; an effect most probably associated with Coriolis coupling to other, unobserved octupole vibrational bands in 186 W.
150 ≤ A ≤ 189↗
Investigation of the ground-state spin inversion in the neutron-rich Cl 47 , 49 isotopes
A first γ -ray study of Cl 47 , 49 spectroscopy was performed at the Radioactive Isotope Beam Factory with Ar 50 projectiles at 217 MeV/nucleon, impinging on the liquid hydrogen target of the MINOS device. Prompt deexcitation γ rays were measured with the NaI(Tl) array DALI2 + . Through the one-proton knockout reaction Ar 50 ( p , 2 p ) , a spin assignment could be determined for the low-lying states of Cl 49 from the momentum distribution obtained with the SAMURAI spectrometer. A spin-parity J π = 3 / 2 + is deduced for the ground state of Cl 49 , similar to the recently studied N = 32 isotope K 51 . The evolution of the energy difference E ( 1 / 2 1 + ) - E ( 3 / 2 1 + ) is compared to state-of-the-art theoretical predictions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Spectroscopy of 10 N with the invariant-mass method
Proton decays of $^{10}$N states has been investigated with the invariant-mass technique using data from two reactions. In the first experiment, $^{10}$N states were created via multi-nucleon knockout from a fast $^{13}$O beam. The second experiment involved proton pickup from a $^9$Be target to a fast $^9$C beam. Both data sets produce similar distributions with a peak centered at a decay energy of 2.8 MeV and a width of $\approx 2.5$ MeV. This result is consistent with a previous study using multi-nucleon transfer reaction which was originally fit with an $\ell$ = 0 resonance but later interpreted as an $\ell$=1 resonance. This later interpretation is affirmed as the proton pickup reaction should favor $\ell$ = 1. This strength is located near the predicted energies of two $\ell$ = 1 resonances in calculations using complex scaling and the Gamow shell model. Furthermore, the multi-nucleon knockout data also show excess strength below the main peak which is interpreted as contributions from one or more $\ell$ = 0 resonances.
6 ≤ A ≤ 19↗
Neutron occupancies and single-particle energies across the stable tin isotopes
The occupancies and vacancies of the valence neutron orbitals across the stable tin isotopic chain from 112 ≤ A ≤ 124 have been determined. These were inferred from the cross sections of neutron adding and -removing reactions. In each case, the reactions were chosen to have good angular momentum matching for transfer to the low- and high-` orbitals present in this valence space. Here, these new data are compared to older systematic studies. The effective single-neutron energies are determined by combining information from energy centroids determined from the adding and removing reactions. Two of the five orbitals are nearly degenerate, below N = 64, and approximately two MeV more bound than the other three, which are also degenerate.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Application of an efficient generator-coordinate subspace-selection algorithm to neutrinoless double- β decay
The generator coordinate method begins with the variational construction of a set of nonorthogonal mean-field states that span a subspace of the full many-body Hilbert space. These states are then often projected onto states with good quantum numbers to restore symmetries, leading to a set with members that can be similar to one another, and it is sometimes possible to reduce this set without greatly affecting results. Here, we propose a greedy algorithm that we call the energy-transition-orthogonality procedure (ENTROP) to select subsets of important states. As applied here, the approach selects on the basis of diagonal energy, orthogonality, and contribution to the matrix element that governs neutrinoless double-β decay. We present both shell-model and preliminary ab initio calculations of this matrix element for the decay of 76Ge, with quadrupole deformation parameters and the isoscalar pairing strength as generator coordinates. ENTROP converges quickly, reducing significantly the number of basis states needed for an accurate calculation.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Charge radii, moments, and masses of mercury isotopes across the N = 126 shell closure
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Search for in-band transitions in the candidate superdeformed band in Si 28
Background: Superdeformed (SD) bands are suggested by theory around Ca 40 and in lighter alpha-conjugate nuclei such as Mg 24 , Si 28 , and S 32 . Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in Ca 40 and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. Additionally, the key evidence of superdeformation would be the observation of transitions with high B ( E 2 ) transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant. Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in Si 28 through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths. Methods: Excited states in Si 28 were populated in the Si 28 ( α , α ' ) reaction using a 130-MeV He 4 beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of 9 . 1 ° to favor the population of states with J ≈ 4 . Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large LaBr 3 detectors. Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in Si 28 in the vicinity of 10 MeV. However, while the candidate 4 + SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate 2 + SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of B ( E 2 ) < 43 W.u. could be established. This contradicts AMD predictions of ≈ 200 W.u. for such a transition. Conclusion: The present study strongly rejects the hypothesis that the candidate set of states identified in Si 28 represents an SD band, which demonstrates the potential of the methodology devised here.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Signature splitting of the g 7 / 2 [ 404 ] 7 / 2 + bands in Ba 131 and Ce 133
Excited states in Ba 131 and Ce 133 were studied using in-beam γ -ray spectroscopy through the Sn 122 ( C 13 , 4 n ) Ba 131 and Te 125 ( C 12 , 4 n ) Ce 133 reactions, respectively. A strongly coupled band, associated with the ν g 7 / 2 [ 404 ] 7 / 2 + configuration, was identified in Ba 131 and Ce 133 . It is the first time to observe the ν g 7 / 2 [ 404 ] 7 / 2 + bands in the N = 75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the π g 7 / 2 [ 404 ] 7 / 2 + bands in the odd- A Ta and Re isotopes. Here, extensive cranked shell model and quasiparticle-plus-triaxial-rotor model calculations reveal the origin of the signature splitting, which depends not only on the triaxiality, but also on the configuration mixing with nearby low- j orbitals.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Effective shell-model interaction for nuclei “southeast” of 100 Sn
We construct an effective shell-model interaction for the valence space spanned by single-particle neutron and single-hole proton states in 100 Sn. Starting from chiral nucleon-nucleon and three-nucleon forces and single-reference coupled-cluster theory for 100 Sn we apply a second similarity transformation that decouples the valence space. The particle-particle components of the resulting effective interaction can be used in shell model calculations for neutron deficient tin isotopes. The hole-hole interaction can be used to calculate the N=50 isotones south of 100 Sn, and the full particle-hole interaction describes nuclei in the region southeast of 100 Sn. We compute low-lying excited states in selected nuclei southeast of 100 Sn, and find reasonable agreement with data. The presented techniques can also be applied to construct effective shell-model interactions for other regions of the nuclear chart.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Effective field theory approach to rotational bands in odd-mass nuclei
In this work, we extend an effective field theory developed to describe rotational bands in even-even nuclei to the odd-mass case. This organizes Bohr and Mottelson's treatment of a particle coupled to a rotor as a model-independent expansion in powers of the angular velocity of the overall system. We carry out this expansion up to fourth order in the angular velocity and present results for 99 Tc, 159 Dy, 167,169 Er, 167,169 Tm, 183 W, 235 U, and 239 Pu. In each case, the accuracy and breakdown scale of the effective field theory can be understood based on the single-particle and vibrational energy scales in that nucleus.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Shell model analysis of the B ( E 2,2 + → 0 + ) values in the A = 70, T = 1 triplet 70 Kr, 70 Br, and 70 Se
The B(E2, 2 + → 0 + ) transition strengths of the T=1 isobaric triplet 70 Kr, 70 Br, 70 Se, recently measured at the RIKEN Radioactive Isotope Beam Factory (RIBF), are discussed in terms of state-of-the-art large scale shell model calculations using the JUN45 and JUN45 + LNPS plus Coulomb interactions. In this Letter we argue that, depending on the effective charges used, the calculations are either in line with the experimental data within statistical uncertainties, or the anomaly happens in 70 Br, rather than 70 Kr. In the latter case, we suggest that it can be due to the presence of a hitherto undetected 1 + T = 0 state below the yrast 2 + T = 1 state. Furthermore, our results do not support a shape change of 70 Kr with respect to the other members of the isobaric multiplet.
59 ≤ A ≤ 89↗
Accessing the shape of atomic nuclei with relativistic collisions of isobars
Nuclides sharing the same mass number (isobars) are observed ubiquitously along the stability line. While having nearly identical radii, stable isobars can differ in shape, and present different quadrupole deformations. We show that even small differences in these deformations can be probed by relativistic nuclear collisions experiments, where they manifest as deviations from unity in the ratios of elliptic flow coefficients taken between isobaric systems. Collider experiments with isobars represent, thus, a unique means to gain precise knowledge of the geometric shape of atomic nuclei.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Electron scattering on A = 3 nuclei from quantum Monte Carlo based approaches
We perform first-principle calculations of electron-nucleus scattering on 3 He and 3 H using the Green's function Monte Carlo method and two approaches based on the factorization of the final hadronic state: the spectral-function formalism and the short-time approximation. These three methods are benchmarked among each other and compared to the experimental data for the longitudinal and transverse electromagnetic response functions of 3 He, and the inclusive cross sections of both 3 He and 3 H. Since these three approaches are based on the same description of nuclear dynamics of the initial target state, comparing their results enables a precise quantification of the uncertainties inherent to factorization schemes. At sufficiently large values of the momentum transfer, we find an excellent agreement of the Green's function Monte Carlo calculation with experimental data and with both the spectral-function formalism and the short-time approximation. Here, we also analyze the relevance of relativistic effects, whose inclusion becomes crucial to explain data at high momentum and energy transfer.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Converged ab initio calculations of heavy nuclei
We propose a novel storage scheme for three-nucleon (3N) interaction matrix elements relevant for the normal-ordered two-body approximation used extensively in ab initio calculations of atomic nuclei. This scheme reduces the required memory by approximately two orders of magnitude, which allows the generation of 3N interaction matrix elements with the standard truncation of E 3max =28, well beyond the previous limit of 18. We demonstrate that this is sufficient to obtain the ground-state energy of 132 Sn converged to within a few MeV with respect to the E 3max truncation. In addition, we study the asymptotic convergence behavior and perform extrapolations to the un-truncated limit. Finally, we investigate the impact of truncations made when evolving free-space 3N interactions with the similarity renormalization group. We find that the contribution of blocks with angular momentum J rel > 9/2 to the ground-state energy is dominated by a basis-truncation artifact, which vanishes in the large-space limit, so these computationally expensive components can be neglected. For the two sets of nuclear interactions employed in this work, the resulting binding energy of 132 Sn agrees with the experimental value within theoretical uncertainties. This work enables converged ab initio calculations of heavy nuclei.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Nuclear matter as a liquid phase of spontaneously broken semiclassical SU ( 2 ) L × SU ( 2 ) R chiral perturbation theory: Static chiral nucleon liquids
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