Search

The $B(E2,{2}^{+}\ensuremath{\rightarrow}{0}^{+})$ transition strengths of the $T=1$ isobaric triplet $^{70}\mathrm{Kr},$ $^{70}\mathrm{Br},$ $^{70}\mathrm{Se},$ 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 $\mathrm{JUN}45+\mathrm{LNPS}$ 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 $^{70}\mathrm{Br},$ rather than $^{70}\mathrm{Kr}$. 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. Our results do not support a shape change of $^{70}\mathrm{Kr}$ with respect to the other members of the isobaric multiplet.

7 pags., 4 figs., 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 32Mg 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., N.K. acknowledges support of the Grant-in-Aid for JSPS Fellows (18J12542) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan. K.W. acknowledges support from the Ministerio de Ciencia e Innovación (Spain) through the Ramón y Cajal program RYC-2017-22007. A.P. is supported in part by the Ministerio de Ciencia, Innovación y Universidades (Spain), Severo Ochoa program SEV-2016-0597 and grant PGC-2018-94583. The SDPF-M calculations were enabled by the CNS-RIKEN joint project for large-scale nuclear structure calculations and were performed mainly on the Oakforest-PACS supercomputer. N.S. acknowledges support from “Priority Issue on post-K computer” (hp190160) and “Program for Promoting Researches on the Supercomputer Fugaku” (hp200130) by JICFuS and MEXT, Japan. J.A.T. acknowledges support from the U.K. Science and Technology Facilities Council Grant No. ST/L005743/1. This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Nuclear Physics, under Grant No. DE-SC0020451 and by the U.S. National Science Foundation (NSF) under Grant No. PHY-1306297. GRETINA was funded by the U.S. DOE, Office of Science. Operation of the array at NSCL was supported by the U.S. NSF under Cooperative Agreement No. PHY-1102511 (NSCL) and DOE under Grant No. DE-AC02-05CH11231 (LBNL).

The Ge80 structure was investigated in a high-statistics β-decay experiment of Ga80 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 02+ 639-keV level suggested as evidence for low-energy shape coexistence in Ge80. Large-scale shell model calculations performed in Ge78,80,82 place the 02+ level in Ge80 at 2 MeV. The new experimental evidence combined with shell model predictions indicate that low-energy shape coexistence is not present in Ge80.

The interpretation of nuclear observables in the laboratory frame in terms of the intrinsic deformation parameters beta and gamma is a classical theme in nuclear structure. Here we use the quadrupole invariants (Kumar), calculated within the framework of the configuration-interaction shell model, to clarify the meaning and limitations of nuclear shapes. We introduce a novel method that enables us to calculate accurately higher-order invariants and, therefore, the fluctuations in both beta and gamma. We find that the shape parameter beta often has a non-negligible degree of softness, and that the angle gamma 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., Comment: Accepted in Physical Review C. Title changed. Added sections on triaxiality and sphericity

Isomeric states in 59,61Ti have been populated in the projectile fragmentation of a 345 AMeV 238U beam at the Radioactive Isotope Beam Factory. The decay lifetimes and delayed gamma-ray transitions were measured with the EURICA array. Besides the known isomeric state in 59Ti, two isomeric states in 61Ti are observed for the first time. Based on the measured lifetimes, transition multipolarities as well as tentative spins and parities are assigned. Large-scale shell model calculations based on the modified LNPS interaction show that both 59Ti and 61Ti belong to the Island of Inversion at N=40 with ground state configurations dominated by particle-hole excitations to the g_9/2 and d_5/2 orbits., Phys. Lett. B accepted

International audience; The N=20 island of inversion is an excellent playground for testing shell model calculations. The Mg chain is a region of shell evolution still far from being well understood. In this paper we present preliminary results of a single-neutron knockout experiment from 31Mg performed at GANIL to study the structure of 31Mg and of the core 30Mg. The level scheme and longitudinal momentum distributions were mesured and spectroscopic factors were deduced. Negative parity states arise at low energy and the spectroscopic factor for the isomeric in 30Mg was determined to be smaller than foreseen in the standard picture. The preliminary experimental results are compared to state-of the art shell model calculations revealing opposed interpretations.

International audience; In this study we propose a common mechanism for the disappearance of shell closures far from stabilty. With the use of Large Scale Shell Model calculations (SM-CI), we predict that the region of deformation which comprises the heaviest Chromium and Iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence space including the full pf-shell for the protons and the full sdg shell for the neutrons, which represents a come-back of the the harmonic oscillator shells in the very neutron rich regime. Our calculations preserve the doubly magic nature of the ground state of 78Ni, which, however, exhibits a well deformed prolate band at low excitation energy, providing a striking example of shape coexistence far from stability. This new Island of Inversion (IoI) adds to the four well documented ones at N=8, 20, 28 and 40.

The $(\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{He},t)$ charge-exchange reaction populating ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$ states has been examined at 420 MeV incident energy for a series of double-$\ensuremath{\beta}$ decaying nuclei, i.e., $^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{96}\mathrm{Zr}$, $^{100}\mathrm{Mo}$, $^{128}\mathrm{Te}$, $^{130}\mathrm{Te}$, and $^{136}\mathrm{Xe}$. The measurements were carried out at the Grand Raiden spectrometer of the Research Center for Nuclear Physics at the University Osaka with typical spectral resolution of 30--40 keV. It is found that the charge-exchange reaction leading to ${2}^{\ensuremath{-}}$ spin-dipole states is selective to the $\ensuremath{\sigma}\ensuremath{\tau}$ part of the interaction much similar to the observed selectivity to Gamow-Teller transitions. In the present case, the $\mathrm{\ensuremath{\Delta}}L=1$ peak cross sections at finite momentum transfers are used to extract the spin-isospin part of the low-lying transition strength near the Fermi surface (i.e., ${E}_{x}\ensuremath{\le}5$ MeV). Relative strength values are confronted with various model calculations, i.e., the interacting shell model, the quasiparticle random-phase approximation, and the Fermi surface quasiparticle model. The impact on the nuclear matrix elements for the neutrinoless double-$\ensuremath{\beta}$ decay is discussed.

I will discuss the impact of the research on exotic nuclei carried out at ISOLDE and later on, following its impulse, in many laboratories worldwide, in our present knowledge of the nuclear dynamics. I will put particular emphasis on the occurrence of islands of inversion (IoI) at several magic numbers for the neutrons, far from stability. I will also discuss the appearance of new local shell closures in the calcium and silicon isotopic chains, and qualify their status as new doubly magic nuclei.

In this article we analyze the nuclear matrix elements (NME) of the neutrinoless double beta decays ( 0 ν β β ) of the nuclei 48 Ca, 76 Ge, 82 Se, 124 Sn, 128 Te, 130 Te and 136 Xe in the framework of the interacting shell model (ISM). We study the relative value of the different contributions to the NME's, such as higher order terms in the nuclear current, finite nuclear size effects and short range correlations, as well as their evolution with the maximum seniority permitted in the wave functions. We discuss also the build-up of the NME's as a function of the distance between the decaying neutrons. We calculate the decays to 0 1 + final states and find that these decays are at least 25 times more suppressed with respect to the ground state to ground state transition.

In this article, we analyze some nuclear-structure aspects of the 0ν double-beta decay nuclear matrix elements (NME). We give results for the decays of 48Ca , 76Ge , 82Se , 124Sn , 128Te , 130Te , and 136Xe , using improved effective interactions and valence spaces. We examine the dependence of the NMEs on the effective interaction and the valence space, and analyze the effects of the short-range correlations and the finite size of the nucleon. Finally, we study the influence of the deformation on the values of the NMEs.

The determination of accurate nuclear matrix elements for ββ decay processes is a challenge for nuclear theory and can have a strong impact in neutrino physics. Large Scale Shell Model (LSSM) calculations are among the best tools for such determination and recent developments have allowed to extend its application domains. In particular, systematic studies of nuclear matrix elements calculations have been now undertaken in this framework for most of the ββ emitters. These calculations are crucial in the determination of the most favorable emitters in the forthcoming generation of ββ experiments. The present paper focuses on the recent advances and remaining difficulties of shell model calculations for the neutrinoless mode. Stability and predictive power of the results will be discussed.

We present Large Scale Shell Model calculations using the effective interaction LNPS, which reproduce nicely the experimental data available in the N=40 island of deformation. We deal as well with the triple (shape?) coexistence in the low energy spectrum of 68Ni, showing that the highly deformed band based upon the excited 0+ state at 2627 keV is in fact the doorway to the island. The onset of prolate quadrupole collectivity and shape coexistence in the heavy N=Z nuclei, is explained by means of the realizations of the pseudo plus quasi SU3 symmetry, with special emphasis on the shape mixing in the ground state of 72Kr, This work is partly supported by a grant of the MICINN (Spain) (FPA2011-29854), by the Nupnet network SARFEN (PRI-PIMMNUP-2011-1361) and by MINECO’s (Spain) Programme ”Centros de Excelencia Severo Ochoa” grant SEV-2012-0249

The evolution of the N = 28 neutron shell closure is studied in the N = 28 isotones from neutron drip line's 40Mg to N = Z doubly magic 56Ni. It is found that the N = 28 closure vanishes at Z = 12 in favor of a deformed ground state. For Z = 14 and Z = 16 closed shell and intruder configurations are almost degenerate, leading to highly mixed ground states and to very low lying excited 0 + states. For Z > 20 the intruder states are always above the closed shell ground states. We examine their structure and their possible existence as collective yrare bands of well-defined particle–hole character.

We study in this Letter the double beta decay of 136Xe with emission of two neutrinos which has been recently measured by the EXO-200 Collaboration. We use the same shell model framework, valence space, and effective interaction that we have already employed in our calculation of the nuclear matrix element (NME) of its neutrinoless double beta decay. Using the quenching factor of the Gamow–Teller operator which is needed to reproduce the very recent high resolution 136Xe (3He, t) 136Cs data, we obtain a nuclear matrix element M 2 ν = 0.025 MeV − 1 compared with the experimental value M 2 ν = 0.019 ( 2 ) MeV − 1 .

It is argued that there exist natural shell model spaces optimally adapted to the operation of two variants of Elliott' SU3 symmetry that provide accurate predictions of quadrupole moments of deformed states. A selfconsistent Nilsson-like calculation describes the competition between the realistic quadrupole force and the central field, indicating a {\em remarkable stability of the quadruplole 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 $^{56}$Ni to $^{96}$Cd reveals that the region of prolate deformation is bounded by a pair of transitional nuclei $^{72}$Kr and $^{84}$Mo in which prolate ground state bands are predicted to dominate, though coexisting with oblate ones, Replacement I) Title simplified. II) Major revision: structure of paper kept but two thirds totally rewritten (same number of pages); 20 references added

DSAM lifetimes have been determined in the middle of 1f7/2 shell for the cross-conjugated nuclei 47 Va nd 49 Cr, populated with the reaction 28 Si on 28 Si at 115 MeV using a Au backed target. B(E2) and B(M1) reduced rates agree very well with large scale shell model predictions. The interplay between spherical and collective structures is discussed.  2001 Elsevier Science B.V. All rights reserved.

We study the ββ decays of 76 Ge, 82 Se, 136 Xe, 124 Sn, 128 Te, 130 Te in the shell model framework. Bounds on the neutrino mass are obtained and it is found that, among them, 82 Se and 124 Sn are the most favoured isotopes to detect the neutrinoless mode.

The ( SM ) 2 (Strasbourg-Madrid Shell Model) calculations in the full pf -shell are reviewed. We examine first some issues concerning codes and interactions. Then we list the predictions that have been experimentally verified, and give a description of the main findings concerning rotational motion. The last section introduces some new material on binomial level densities, and on convergence properties in the Lanczos basis. It will be shown how the largest calculation done so far could be made more economically.

The magnetic dipole response of N =28 isotones is obtained for 48 Ca, 50 Ti, 52 Cr and 54 Fe by means of shell model calculations in the full pf -shell. Spin quenching factors derived in all four nuclei by comparison to experimental strengths from electron scattering agree well with each other. The deduced effective g -factor g s eff =0.75(2) g s free is consistent with findings for the Gamow-Teller strength in this mass region. The ability of state-of-the-art shell-model calculations to describe the gross properties and the fragmentation of the complex experimental B ( M 1) strength distributions is investigated.

High-spin states in the odd-odd $N=Z$ nucleus ${}^{50}\mathrm{Mn}$ have been identified. At low spin, the $T=1$ isobaric analogue states of ${}^{50}\mathrm{Cr}$ are established up to ${I}^{\ensuremath{\pi}}{=4}^{+}.$ At high spin, the $T=0$ band built on the low-lying ${I}^{\ensuremath{\pi}}{=5}^{+}$ isomer in ${}^{50}\mathrm{Mn}$ becomes energetically favored and this band is observed up to its ${f}_{7/2}$-shell termination at ${I}^{\ensuremath{\pi}}{=15}^{+}.$ Spherical shell model calculations in the full $\mathrm{pf}$ shell are found to be in excellent agreement with the experimental results. In addition, a weak side band in ${}^{50}\mathrm{Mn}$ is observed to spin ${(12}^{\ensuremath{-}})$ and is interpreted as a possible octupole vibrational structure.

High-spin states have been investigated in the A=47 mirror pair 4723V24 and 4724Cr23. The Coulomb energy difference (CED) between the two nuclei has been examined up to the band-terminating state of J π = 31 2 − and compared with that of their cross-conjugate nuclei, the mirror pair 4924Cr25 and 4925Mn24. The CED results are interpreted in terms of band-crossing and band-termination phenomena. A comparison of the cross-conjugate pairs indicates for the first time that the CED can reflect the changing nuclear deformation as a function of spin. CED calculations from full pf-shell calculations are presented for the first time and are shown to be in good quantitative agreement with the data.

We describe the properties of the neutron rich nuclei around N=28 in the shell mode framework. The valence space comprises the $sd$ shell for protons an the $pf$ shell for neutrons without any restriction. Good agreement is found with the available experimental data. The N=28 shell closure, even if eroded due to the large neutron excess, persists. The calculations predict that $^{40}$S and $^{42}$S are deformed with $\beta=0.29 $ and $\beta=0.32$ respectively., Comment: 17 pages and 19 figures, LateX, RevTeX

9 pages, 2 figures, 2 tables.-- PACS nrs.: 21.60.Cs; 23.40.−s; 27.30.+t; 29.30.Ep., Low-energy beta-delayed protons from Ar-33 have been measured for the first time. The data reveal states, which, despite unfavourable barrier penetrability values, strongly decay to the first excited 2+ state in S-32. The observation is discussed in terms of the standard shell model. A natural explanation is provided by the large spectroscopic amplitudes, involving s(1/2) and d(3/2) orbitals, as well as the l = 0 barrier penetrability, favouring the decay to the 2+ state., This work has been financially supported by the Academy of Finland and the CICYT (Spain, under contract AEN94-0833-C02-02).

We have calculated the Gamow-Teller matrix elements of 64 decays of nuclei in the mass range {ital A}=41{endash}50. In all the cases the valence space of the full {ital pf} shell is used. Agreement with the experimental results demands the introduction of an average quenching factor {ital q}=0.744{plus_minus}0.015 slightly smaller but statistically compatible with the {ital sd}-shell value, thus indicating that the present number is close to the limit for large {ital A}. {copyright} {ital 1996 The American Physical Society.}

The 48Ca → 48Ti two neutrino double-beta decay rate is calculated exactly in the full fp shell with the hamiltonian describing well the spectroscopy of the A = 48 system. The resulting half-life is very near the experimental lower limit. In order to find out whether the shell model can at all accommodate longer 2ν half-lives we modify the hamiltonian in several ways, keeping, however, the acceptable agreement with the main spectroscopic indicators intact. We conclude that, within such an approach, the longest possible half-life is about 1020 yr, only a factor of three longer than the present limit. We stress that any possible modifications of the hamiltonian must be restricted by the comparison with available data on energy levels and transitions rates.

We shall discuss the meaning of the 'nuclear shape' in the laboratory frame proper to the spherical shell model. A brief historical promenade will bring us from Elliott's SU3 breakthrough to today's large scale shell model calculations. A section is devoted to the algebraic model which extends drastically the field of applicability of Elliot's SU3, providing a precious heuristic guidance for the exploration of collectivity in the nuclear chart. Shape coexistence and shape mixing will be shown to occur as the result of the competition between the main actors in the nuclear dynamics; the spherical mean field, and the pairing and quadrupole–quadrupole interactions. These ideas will be illustrated with examples in magic nuclei (40Ca and 68Ni); neutron rich semi-magic (32Mg, and 64Cr); and in proton rich N = Z (72Kr).

The structure of the $^{44}$S nucleus has been studied at GANIL through the one proton knock-out reaction from a $^{45}$Cl secondary beam at 42 A$\cdot$MeV. The $\gamma$ rays following the de-excitation of $^{44}$S were detected in flight using the 70 BaF${_2}$ detectors of the Ch\^{a}teau de Cristal array. An exhaustive $\gamma\gamma$-coincidence analysis allowed an unambiguous construction of the level scheme up to an excitation energy of 3301 keV. The existence of the spherical 2$^+_2$ state is confirmed and three new $\gamma$-ray transitions connecting the prolate deformed 2$^+_1$ level were observed. Comparison of the experimental results to shell model calculations further supports a prolate and spherical shape coexistence with a large mixing of states built on the ground state band in $^{44}$S., Comment: 6 pages, 5 figures, accepted for publication in Physical Review C

High-spin states of 40K have been populated in the fusion-evaporation reaction 12C(30Si,np)40K and studied by means of γ-ray spectroscopy techniques using one triple-cluster detector of the Advanced Gamma Tracking Array at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. Several states with excitation energy up to 8 MeV and spin up to 10 have been discovered. These states are discussed in terms of J=3 and T=0 neutron-proton hole pairs. Shell-model calculations in a large model space have shown good agreement with the experimental data for most of the energy levels. The evolution of the structure of this nucleus is here studied as a function of excitation energy and angular momentum, This work was financed by EURONS AGATA (Contract No. 506065-R113), the Swedish Research Council under Contracts No. 621-2008- 4163, No. 621-2011-4522, No. 822-2005-3332, and No. 821- 2010-6024, the Japan Society for the Promotion of Science (JSPS) Kakenhi Grant No. 23·01752, Ankara University (BAP Project No. 05B4240002), the Polish Ministry of Science and Higher Education under Grants No. DPN/N190/AGATA/2009 and No. N N202 073935, the German BMBF under Grants No. 06K-167, No. 06KY205I, and No. 06KY9136I, the Knut and Alice Wallenberg Foundation Contract No. 2005.0184, and STFC (UK). A. Gadea and E. Farnea acknowledge the support of MICINN, Spain, and INFN, Italy, through the AIC-D-2011-0746 bilateral action. A. Gadea’s activity has been partially supported by the Generalitat Valenciana, Spain, under Grant PROMETEO/2010/101. A. Gadea, A. Jungclaus, A. Poves, and B. Quintana acknowledge support from the MICINN, Spain, under Grant FPA2011-29854. A. Poves is partially supported by the Comunidad de Madrid (Spain) (HEPHACOS S2009-ESP-1473). G. Jaworski acknowledges the support of the Center for Advanced Studies of Warsaw University of Technology. B. Cederwall acknowledges the support of the Goran Gustafsson Foundation.

We describe the "islands of inversion" that occur when approaching the neutron drip line around the magic numbers N=20, N=28 and N=40 in the framework of the Interacting Shell Model in very large valence spaces. We explain these configuration inversions (and the associated shape transitions) as the result of the competition between the spherical mean field (monopole) which favors magicity and the correlations (multipole) which favor deformed intruder states. We also show that the N=20 and N=28 islands are in reallity a single one, which for the Magnesium isotopes is limited by N=18 and N=32., Comment: Proceedings of the Nordic Conference in Nuclear Physics 2011, Stockholm, to appear in Physica Scripta

A shell model calculation for 6−11 Li and 7−14 Be isotopes is performed using a density dependent Skyrme interaction and Hartree-Fock single-particle wave functions. Without any parameter fit, quite good agreement with the experimental binding energies and matter radii is obtained. Only 10 Li and 13 Be are found to be unstable with respect to neutron emission. The calculated radius of 11 Li is too small and possible causes of this exception are discussed.

We discuss the variation of the nuclear matrix element (NME) for the neutrinoless double beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay of $^{76}\mathrm{Ge}$ when the wave functions are constrained to reproduce the experimental occupancies of the two nuclei involved in the transition. In the interacting shell model description the value of the NME is enhanced about 15% compared to previous calculations, whereas in the QRPA the NME's are reduced by 20%--30%. This diminishes the discrepancies between both approaches. In addition, we discuss the effect of the short-range correlations on the NME in light of the recently proposed parametrizations based on a consistent renormalization of the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ transition operator.

The neutron-rich isotopes with $Z\ensuremath{\leqslant}20$, in particular those with neutron numbers around $N=28$, have been the focus of a lot experimental and theoretical scrutiny during the past few years. Shell-model calculations using the effective interaction SDPF-NR were able to predict or to explain most of the properties featured by these nuclei. Prominent among them is the disappearance of the $N=28$ shell closure for $Z\ensuremath{\leqslant}16$. We have incorporated into SDPF-NR some modifications, either on purely theoretical grounds or guided by new experimental information. The proposed interaction SDPF-U offers enhanced reliability with respect to the earlier version.

Détecteur VAMOS, détecteur EXOGAM; Results from the gamma spectroscopy of $^{47,48}$Ar exemplifying new limits of sensitivity for characterizing neutron-rich nuclei at energies around the Coulomb barrier are presented. The present results along with interacting shell model calculations, highlight the role of cross shell excitations and indicate the presence of a non axial deformation in $^{48}$Ar.

We analyse results of complete shell-model calculations of 1+ excitations on the basis of Elliott's SU(3) model. We present and discuss results for three nuclei in the sd shell (20Ne, 22Ne, 24Mg) and one nucleus in the fp shell (44Ti). The SU(3) model is compared to the two-rotor model. It is shown that results for scissors-like excitations in the SU(3) and two-rotor model are in fair agreement. Comparing the results of shell model calculations to the SU(3) model results, we find that the lowest 1+ states in 20Ne and 44Ti are dominated by the single scissors mode of the SU(3) limit. In the case of 22Ne there are two SU(3) scissors states, both show up in the realistic 1+ spectrum. For 24Mg there are three SU(3) scissors states that overlap weakly with the realistic 1+ excitations.

The energies of the excited states in very neutron-rich Si-42 and P-41,P-43 have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of S-42,S-44 at 39A MeV. The low 2(+) energy of Si-42, 770(19) keV, together with the level schemes of P-41,P-43, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that Si-42 is best described as a well-deformed oblate rotor.

Large-scale shell-model calculations, with dimensions reaching ${10}^{9}$, are carried out to describe the recently observed deformed (ND) and superdeformed (SD) bands based on the first and second excited ${0}^{+}$ states of $^{40}\mathrm{Ca}$ at 3.35 and 5.21 MeV, respectively. A valence space comprising two major oscillator shells, $\mathit{sd}$ and $\mathit{pf}$, can accommodate most of the relevant degrees of freedom of this problem. The ND band is dominated by configurations with four particles promoted to the $\mathit{pf}$ shell (4p-4h in short). The SD band by 8p-8h configurations. The ground state of $^{40}\mathrm{Ca}$ is strongly correlated, but the closed shell still amounts to 65%. The energies of the bands are very well reproduced by the calculations. The out-band transitions connecting the SD band with other states are very small and depend on the details of the mixing among the different $n\mathrm{p}\text{\ensuremath{-}}n\mathrm{h}$ configurations; in spite of that, the calculation describes them reasonably. For the in-band transition probabilities along the SD band, we predict a fairly constant transition quadrupole moment ${Q}_{0}(t)~170\phantom{\rule{0.3em}{0ex}}e$ fm${}^{2}$ up to $J=10$ that decreases toward the higher spins. We submit also that the $J=8$ states of the deformed and superdeformed bands are maximally mixed.

In an effort to understand the magical status of $N=32$ and $N=34$ at the very neutron rich edge, experiments have been carried out in the titanium isotopes up to $A=56$. The measured staggering of the $B(E2)$'s is not reproduced by the shell model calculations using the best effective interactions. We argue that this may be related to the choice of the isovector effective charge and to the value of the $N=34$ neutron gap.

High-spin states in ${}^{46}\mathrm{Ti}$ have been investigated with the reaction ${}^{28}\mathrm{Si}{(}^{24}\mathrm{Mg},\ensuremath{\alpha}2p)$ at 100 MeV, using the GASP \ensuremath{\gamma}-ray array and the charged-particle detector ISIS. The positive parity yrast sequence has been observed up to the ${14}^{+}$ terminating state and several high-energy transitions have been established above the termination state. Both the signatures of a negative parity band have been observed up to the ${16}^{\ensuremath{-}}$ and ${17}^{\ensuremath{-}}$ terminating states, plus one more transition from an ${18}^{\ensuremath{-}}$ state at 19.086 MeV excitation. The observed states are interpreted within the frame of large scale shell model calculations in the full $\mathrm{pf}$ space (positive parity) and as particle-hole excitations from the ${d}_{3/2}$ shell (negative parity).

The nuclei in the middle of the 1f7/2 shell are shown to have rotational features. Progresses made recently at GASP in their spectroscopy, and in particular in lifetime measurement, are reviewed. The agreement of Large Scale Shell Model calculations with experiments is in general excellent. As an example, the case of 50 Cr is illustrated where a observed bandcrossing is discussed as well as its connection with recent Coulomb Energy Differences data in the 50 Fe -50 Cr mirror pair.

The neutron-rich ${}^{66,68}\mathrm{Ni}$ have been produced at GANIL via interactions of a $65.9A\mathrm{MeV}$ ${}^{70}\mathrm{Zn}$ beam with a ${}^{58}\mathrm{Ni}$ target. Their reduced transition probability $B({E2;0}_{1}^{+}\ensuremath{\rightarrow}{2}^{+})$ has been measured for the first time by Coulomb excitation in a ${}^{208}\mathrm{Pb}$ target at intermediate energy. The $B(E2)$ value for ${}^{68}{\mathrm{Ni}}_{40}$ is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the $B(E2)$ values and indicates the erosion of the $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}40$ harmonic-oscillator subshell by neutron-pair scattering.

Excited states in Ar-38 have been investigated by means of the heavy-ion fusion-evaporation reaction Si-28 +O-16. The level scheme reveals a subtle interplay between spherical, deformed, and superdeformed shapes. Large-scale shell-model calculations in the sd-fp space are invoked to study the microscopic aspects of deformation and shape changes.

Recent shell model calculations for the neutron-rich nuclei around the magic numbers N = 20, N = 28 and N = 40 are reviewed. We stress two points: i) The crucial role played by the monopole part of the effective interaction that determines the evolution of the spherical mean field. In particular, the reduction in the quasiparticle gaps at the magic numbers can erode or even erase the shell closures. ii) The rich variety of structures that can be found in these situations, with coexisting deformed and spherical states, rapid changes of behaviour with N or Z, and the massive occurrence of intruder states as ground states.

The N=20 and N=28 “islands of inversion” are described by large scale shell model calculations which mix configurations with different Nħ ω or equivalently with different number of particles promoted from the sd -shell to the pf -shell. We pay particular attention to the properties of the states at fix Nħ ω which turn out to be the real protagonists of the physics at N=20. In particular we study the appearance of spherical, deformed and superdeformed structures in 32 Mg at fixed 0p-0h, 2p-2h and 4p-4h configurations. Finally we submit that the islands of deformation at N=20 and N=28 merge in the Magnesium isotopes

In the present paper we introduce a simple model to describe the process of beta delayed nucleon emission. A standard shell model calculation can be used to describe the beta decay of the precursor and the single particle structure of the particle unbound levels of the emitter nucleus. The single particle width for nucleon emission is then obtained from the Gamow wave functions of a suitable single particle potential. We compare our theoretical predictions with recent experimental data on beta delayed protons produced in the beta decay of 31 Ar.

We discuss the present status of the description of the structure of the very neutron rich nuclei, in the framework of modern large scale shell model calculations. Particular attention is paid to the interaction related issues, as well as to the problems of the shell model approach at the neutron drip line. We present detailed results for nuclei around N=20 and, more briefly, we discuss some salient features of the regions close to N=8, 28 and 40. We show that most experimental features can be understood in a shell model context., Comment: 10 pages, to appear in Nuclear Physics A