Nilsson-SU3 self-consistency in heavy N=Z nuclei

It is argued that there exist natural shell-model spaces optimally adapted to the operation of two variants of Elliott's SU3 symmetry that provide accurate predictions of quadrupole moments of deformed states. A self-consistent Nilsson-like calculation describes the competition between the realistic quadrupole force and the central field, indicating a remarkable stability of the quadrupole moments - which remain close to their quasi- and pseudo-SU3 values - as the single-particle splittings increase. A detailed study of the N=Z even nuclei from Ni56 to Cd96 reveals that the region of prolate deformation is bounded by a pair of transitional nuclei Kr72 and Mo84 in which prolate ground-state bands are predicted to dominate, though coexisting with oblate onesThis work is partly supported by Spanish Grants No. FPA2011-29854 from MICINN and No. SEV-2012-0249 from MINECO, Centro de Excelencia Severo Ochoa Programm

Ground-state electromagnetic moments of calcium isotopes

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMBackground: The neutron-rich calcium isotopes have gained particular interest as evidence of closed-shell structures has recently been found in two exotic nuclei, at N=32 and N=34. Additionally, the study of such neutron-rich systems has revealed new aspects of nuclear forces, in particular regarding the role of three-nucleon forces. Purpose: We study the electromagnetic properties of Ca isotopes around the neutron number N=32. Methods: High-resolution bunched-beam collinear laser spectroscopy was used to measure the optical hyperfine spectra of the Ca43-51 isotopes. Results: The ground-state magnetic moments of Ca49,51 and quadrupole moments of Ca47,49,51 were measured for the first time, and the Ca51 ground-state spin I=3/2 was determined in a model-independent way. Our experimental results are compared with state-of-the-art shell-model calculations using both phenomenological interactions and microscopic interactions derived from chiral effective field theory. Conclusions: The results for the ground-state moments of neutron-rich isotopes are in excellent agreement with predictions of interactions derived from chiral effective field theory including three-nucleon forces. Lighter isotopes illustrate the presence of particle-hole excitations of the Ca40 core in their ground state. Our results provide a critical test of modern nuclear theories, and give direct answer to the evolution of ground-state electromagnetic properties in the Ca isotopic chain across three doubly closed-shell configurations at N=20, 28, 32 of this unique systemThis work was supported by the IAP-project P7/12, the GOA grant 15/010 KU Leuven, NSF Grant No. PHY-1068217, the BMBF Contracts No. 05P12RDCIC and No. 06DA70471, the Max-Planck Society, the EU FP7 via ENSAR No. 262010, the DFG through Grant No. SFB 634, ERC Grant No. 307986 STRONGINT, the Helmholtz Alliance HA216/EMMI, and MINECO (SPAIN) (FPA2011-29854). Computations were performed on JUROPA at the Julich Supercomputing Center. We would like to thank the ISOLDE technical group for their support and assistance. International Research Fellowship of the Japan Society for the Promotion of Science (JSPS) and JSPS KAKENHI Grant No. 26.0432

Neutrinoless double-beta decay

This paper introduces the neutrinoless double-beta decay the rarest nuclear weak process and describes the status of the research for this transition, both from the point of view of theoretical nuclear physics and in terms of the present and future experimental scenarios. Implications of this phenomenon on crucial aspects of particle physics are briefly discussed. The calculations of the nuclear matrix elements in case of mass mechanisms are reviewed, and a range for these quantities is proposed for the most appealing candidates. After introducing general experimental concepts—such as the choice of the best candidates, the different proposed technological approaches, and the sensitivity—we make the point on the experimental situation. Searches running or in preparation are described, providing an organic presentation which picks up similarities and differences. A critical comparison of the adopted technologies and of their physics reach in terms of sensitivity to the effective Majorana neutrino mass is performed. As a conclusion, we try to envisage what we expect round the corner and at a longer time scaleThis work was partially supported by the MICINN (Spain) (FPA2011-29854) ; by the Comunidad de Madrid (Spain) (HEPHACOS S2009-ESP-1473); by the Spanish Consolider-Ingenio 2010 Program, CPAN (CSD2007-00042

The land of deformation south of 68^{68}Ni

We study the development of collectivity in the neutron-rich nuclei around $N=40$, where experimental and theoretical evidences suggest a rapid shape change from the spherical to the rotational regime, in analogy to what happens at the {\it island of inversion} surrounding $^{31}$Na. Theoretical calculations are performed within the interacting shell model framework in a large valence space, based on a $^{48}$Ca core which encompasses the full $pf$ shell for the protons and the $0f_{5/2}$, $1p_{3/2}$, $1p_{1/2}$, $0g_{9/2}$ and $1d_{5/2}$ orbits for the neutrons. The effective interaction is based on a G-matrix obtained from a realistic nucleon-nucleon potential whose monopole part is corrected empirically to produce effective single particle energies compatible with the experimental data. We find a good agreement between the theoretical results and the available experimental data. We predict the onset of deformation at different neutron numbers for the various isotopic chains. The maximum collectivity occurs in the chromium isotopes, where the large deformation regime starts already at $N=38$. The shell evolution responsible for the observed shape changes is discussed in detail, in parallel to the situation in the $N=20$ region

Intruder configurations in Ne at the transition into the island of inversion: Detailed structure study of Ne

Detailed γ-ray spectroscopy of the exotic neon isotope 28Ne has been performed for the first time using the one-neutron removal reaction from 29Ne on a liquid hydrogen target at 240 MeV/nucleon. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 28Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N=20 and N=28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chainCEX2020-001007-S, PID2021-127890NB-I0

Large collectivity in 29Ne at the boundary of the island of inversión

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiereThe heavy-ion inelastic scattering of the neutron-rich nucleus 29Ne to its excited states was studied using a 100.1 MeV/u 29Ne rare isotope beam on 181Ta and 9Be targets. The combined setup consisting of the GRETINA array, the TRIPLEX device and the S800 Spectrograph facilitates the simultaneous measurements of the two inelastic reactions, providing the first measurement of the transition strengths for this isotope. A sizable E2 strength B(E2↑) which amounts to 163(30) e2 fm4 was determined in the excitation to the 931-keV state, demonstrating a large degree of collectivity. The present results of B(E2↑) are compared to various shell-model calculations, confirming the role of intruder configurations in 29Ne at the boundary of the island of inversionThe authors would like to thank K. Wimmer for providing us the input for FRESCO calculations and A. Moro for giving access to an unpublished version of the FRESCO code. This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Nuclear Physics, under Grant No. DE-SC0020451, the U.S. National Science Foundation (NSF) under Grant No. PHY1565546 (Operation of the NSCL) and PHY2110365, and by the DOE National Nuclear Security Administration through the Nuclear Science and Security Consortium, under Award No. DE-NA0003180. GRETINA was funded by the DOE, Office of Science. Operation of the array at NSCL was supported by DOE under Grants No. DE-SC0019034 (NSCL) and No. DE-AC02-05CH11231 (LBNL). A.P. acknowledges the Grant CEX2020-001007-S funded by MCIN/AEI/10.13039/501100011033 and PGC2018-094583. Y.U. and N.S. acknowledge KAKENHI Grant No. 20K03981 from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. N.S. acknowledges support from “Program for Promoting Researches on the Supercomputer Fugaku” (JPMXP1020200105, hp210165, and hp220174) by JICFuS and MEXT, Japan. T.M. acknowledges the support by the Croatian Science Foundation under project No. IP-2018-01-125

Mirror energy differences above the 0 f7/2 shell: First γ -ray spectroscopy of the Tz = −2 nucleus 56Zn

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMExcited states in 56Zn were populated following one-neutron removal from a 57Zn beam impinging on a Be target at intermediate energies in an experiment conducted at the Radioactive Isotope Beam Factory at RIKEN. Three γ rays were observed and tentatively assigned to the 6+ → 4+ → 2+ → 0+ yrast sequence. This turns 56Zn into the heaviest Tz = −2 nucleus in which excited states are known. The excitationenergy differences between these levels and the isobaric analogue states in the Tz = +2 mirror partner, 56Fe, are compared with large-scale shell-model calculations considering the full p f valence space and various isospin-breaking contributions. This comparison, together with an analysis of the mirror energy differences in the A = 58, Tz = ±1 pair 58Zn and 58Ni, provides valuable information with respect to the size of the monopole radial and the isovector multipole isospin-breaking terms in the region above doubly-magic 56N

Structure of 36Ca under the Coulomb magnifying glass

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMDetailed spectroscopy of the neutron-deficient nucleus Ca36 was obtained up to 9 MeV using the Ca37(p,d)Ca36 and the Ca38(p,t)Ca36 transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce light ejectiles (the deuteron d or triton t) that were detected in the MUST2 detector array, in coincidence with the heavy residues identified by a zero-degree detection system. Our main findings are (i) a similar shift in energy for the 11+ and 21+ states by about -250 keV, as compared with the mirror nucleus S36; (ii) the discovery of an intruder 02+ state at 2.83(13) MeV, which appears below the first 2+ state, in contradiction with the situation in S36; and (iii) a tentative 03+ state at 4.83(17) MeV, proposed to exhibit a bubble structure with two neutron vacancies in the 2s1/2 orbit. The inversion between the 02+ and 21+ states is due to the large mirror energy difference (MED) of -516(130) keV for the former. This feature is reproduced by shell model calculations, using the sd-pf valence space, predicting an almost pure intruder nature for the 02+ state, with two protons (neutrons) being excited across the Z=20 magic closure in Ca36 (S36). This mirror system has the largest MEDs ever observed, if one excludes the few cases induced by the effect of the continuu

Absence of low-energy shape coexistence in 80Ge: The nonobservation of a proposed excited 02+ level at 639 keV

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMExcited-state spectroscopy from the first experiment at the Facility for Rare Isotope Beams (FRIB) is reported. A 24(2)-μs isomer was observed with the FRIB Decay Station initiator (FDSi) through a cascade of 224- and 401-keV γ rays in coincidence with Na32 nuclei. This is the only known microsecond isomer (1 μs≤T1/2<1 ms) in the region. This nucleus is at the heart of the N=20 island of shape inversion and is at the crossroads of the spherical shell-model, deformed shell-model, and ab initio theories. It can be represented as the coupling of a proton hole and neutron particle to Mg32, Mg32+π-1+ν+1. This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of Mg32, where the onset of spherical-to-deformed shape inversion begins with a low-lying deformed 2+ state at 885 keV and a low-lying shape-coexisting 02+ state at 1058 keV. We suggest two possible explanations for the 625-keV isomer in Na32: a 6- spherical shape isomer that decays by E2 or a 0+ deformed spin isomer that decays by M2. The present results and calculations are most consistent with the latter, indicating that the low-lying states are dominated by deformationCEX2020-001007-S, PID2021-127890NB-I0