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The structure of the nucleus 925F was investigated through in-beam γ-ray spectroscopy of the fragmentation of 26Ne and 27,28Na ion beams. Based on the particle-γ and particle-γγ coincidence data, a level scheme was constructed and compared with shell model and coupled-cluster calculations. Some of the observed states were interpreted as quasi-single-particle states built on top of the closed-shell nucleus 24O, while the others were described as states arising from coupling of a single proton to the 2+ core excitation of 24O. [ABSTRACT FROM AUTHOR]

The structure of nucleus 25F was studied by use of in-beam -ray spectroscopy of the fragmentation of a 36S beam. The emitted rays were detected by BaF2 detectors. In the -ray spectrum obtained a wide bump between 3 and 4.5 MeV energy was observed corresponding to a set of γ rays, including their first and second escape peaks. In order to resolve the peaks and to determine the high-energy structure of 25F, the experimental spectra were compared to Geant4 simulations taking the complex line shape into account. The observed decomposition of the bump is in good agreement with the results of the two-step fragmentation experiment [Zs. Vajta et al., submitted to Phys. Rev. C]. Furthermore, an additional transition was observed at 2140(30) keV. [ABSTRACT FROM AUTHOR]

The structure of the 44S nucleus has been studied at GANIL through the one proton knock-out reaction from a 45Cl secondary beam at 42 A-MeV. The &ggr; rays following the de-excitation of 44S were detected in flight using the 70 BaF2 detectors of the Château de Cristal array. An exhaustive &ggr; &ggr; -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 y-ray transitions connecting the prolate deformed 2+2 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 44S. [ABSTRACT FROM AUTHOR]

Abstract: The structure of the very neutron-rich nuclei 39Si and 41Si has been investigated via in-beam γ-ray spectroscopy and few-nucleon knockout from radioactive beams. The observation of low-lying states in 39Si is a clear evidence for a drastic lowering of the intruder neutron state when going from to . The energy of the only γ-ray transition (672(14) keV) observed in 41Si is significantly lower than that of the first excited state in 47Ca (2014 keV) suggesting a deformed ground state for 41Si. These results are consistent with large-scale shell-model calculations implying that strong proton–neutron correlations are the main reason for the lowering of the intruder configurations over the normal ones. [Copyright &y& Elsevier]

The results obtained from electron and in-beam spectroscopy experiments reveal that the 44S nucleus is located in a transitional region between the spherical 44Ca and the oblate 44Si. The comparison of the results with Large Scale Shell Model calculations points towards prolate-spherical shape coexistence where the ground state becomes the intruder configuration due to quadrupole excitations across the Z = 14 and N = 28 shell gaps. [ABSTRACT FROM AUTHOR]

Abstract: Excitation functions of the reaction products were measured for the reactions induced by 4,6He projectiles on 208,206Pb targets, leading to the same compound nucleus. This was accomplished by using the stacked-foil activation technique. The identification of the reaction products (accumulated in the Pb targets) was done by their radioactive α-decays. The excitation functions for the various products were obtained at energies including the sub-Coulomb barrier region. A large value of the fusion cross section was observed in the case of the reaction induced by the weakly bound 6He projectile. [Copyright &y& Elsevier]

The Advanced Time Delayed method has been used to measure the lifetimes of excited states in the exotic nuclei 134Sb, 135Sb and 136Te populated in the beta decay of 134Sn, 135Sn and 136Sn, respectively. High purity Sn beams were extracted at the ISOLDE separator using a novel production technique utilizing the molecular SnS+ beams to isolate Sn from contaminating other fission products. Among the new results we have identified the 1/2+ state in 135Sb and its E2 transition to the lower-lying 5/2+ state was found to be surprisingly collective. This measurement represents also one of the first applications of the LaBr3 scintillator to ultra fast timing. [ABSTRACT FROM AUTHOR]

Energy integrated reaction cross-section measurements of around sixty neutron-rich nuclei covering the region of closed shells N = 20 and N = 28 were performed at intermediate energy (30-65 A . MeV) using direct method. In this experiment, silicon detectors were used as active targets. The reduced strong absorption radii, r02, for 19 new nuclei (27F, 27,30Ne, 33Na, 28, 34-35Mg, 36-38Al, 38-40Si, 41-42P, 42-44S and 45Cl) are deduced for the first time. An additional 60 radii, also measured in this experiment, are compared to results from literature. A new quadratic parametrization is proposed for the nuclear radius as a function of the isospin in the region of closed shells N = 8 and N = 28. According to this parametrization, the skin effect is well reproduced and anomalous behaviour on the radii are observed in 23N, 29Ne, 33Na, 35Mg, 44S, 45Cl and 45Ar nuclei. [ABSTRACT FROM AUTHOR]

A new SPEG mass measurement experiment has been performed to determine masses closer to the neutron drip-line in the mass region A ∼ 10-50. The precision of 37 masses has been improved and 8 masses were measured for the first time. The region covered was motivated by the study of shell structure and of shape coexistence in the region of closed shells N = 20 and N = 28. The evolution of the two neutron separation energies and the shell correction energy have been studied as a function of the neutron number. The results thus obtained provide a means of identifying, in exotic nuclei, new nuclear structure effects that are well illustrated by the changes of the conventional magic structure. [ABSTRACT FROM AUTHOR]

The neutron-rich nuclei 2157, 58Sc, 2258-60Ti, 2360-63V, 2462-66Cr have been produced at Ganil via interactions of a 61.8A MeV76Ge beam with a58Ni target. Beta-decay studies have been performed using combined ß- and ?-ray spectroscopy. Half-lives have been determined and ß-decay schemes are proposed for58Ti,61V and62Cr. From these studies, new hints for the existence of ß-decaying isomers in60V and in62Mn are provided. These results are compared to shell model calculations. The role of the pf7/2- ?f5/2 proton-neutron interaction is examined through its influence on the lifetime values. [ABSTRACT FROM AUTHOR]

A β-decay experiment on nuclei in the region of N=28 has been performed at the GANIL facility. New measured half-lives for the Si isotopes from N=25 to N=28 are reported and discussed in the light of the deformation occuring in this region. Comparison with QRPA calculations suggests that a weakening of the spin-orbit force occurs for the very neutron-rich Si isotopes. [Copyright &y& Elsevier]

The structure of the neutron-rich odd-even nuclei37, 39 15P 22,24 and43, 45 17Cl 26,28 nuclei has been investigated through in-beam ?-ray spectroscopy using the fragmentation of a 60.3A . MeV48Ca beam on a thin Be target. Level schemes as well as spin assignments are proposed for the nuclei studied in the present work. The experimental data are compared to shell model calculations and related to the onset of collectivity within thesdorbitals aroundN= 28. [ABSTRACT FROM AUTHOR]

The structure of theA/Z = 3 nucleus15B has been investigated using the in-beam-spectroscopy technique with a fragmentation reaction of a36S beam on a9Be target at 77.5. The fragments were identified and selected by their energy loss and time of flight using the SPEG spectrograph.-ray energies and intensities have been measured in coincidence with the projectile-like fragments. From this information as well as from the-coincidence relationships a level scheme is proposed for15B up to the neutron separation energy. The experimental results have been interpreted using shell model calculations in thepsdvalence space. Effects of the weakly bound nature of the valence neutrons have been observed. [ABSTRACT FROM AUTHOR]

Measurements of the beta-decay half-lives of neutron-rich nuclei (Mg&z.sbnd;Ar) in the vicinity of the N=28 shell closure are reported. Some 22 half-lives have been determined, 12 of which for the first time. Particular emphasis is placed on the results for the Si isotopes, the half-lives of which have been extended from N=25 to 28. Comparison with QRPA calculations suggests that 42Si is strongly deformed. This is discussed in the light of a possible weakening of the spin–orbit potential. [Copyright &y& Elsevier]

The shell closure N=20 has been studied by β-decay spectroscopy experiment performed at the GANIL facility. The experimental setup is described and first results on the beta-decay of 32Mg are presented. The extracted level scheme of 32Al is compared to Shell Model calculations and discussed in the light of the structural changes observed for the nuclei of the so-called island of inversion. Finally, neutron time-of-flight spectrum from the β-delayed neutron decay of 32Mg is presented. [Copyright &y& Elsevier]

The structure of the N≃28 45,4618Ar27,28 nuclei has been investigated through in-beam γ-ray spectroscopy using the fragmentation reaction of a 60 AMeV 48Ca beam on a thin Be target. γ-ray energies, intensities, γγ coincidences and γ-ray angular anisotropies have been measured. The level scheme of 45Ar is proposed for the first time, while that of 46Ar has been extended to states above the previously known 2+ first excited state. An isomeric state at 537 keV of 0.34+0.32−0.15 ns lifetime has been found in 45Ar from the line-shape analysis of the γ ray connecting the first excited state to the ground state. The experimental results are interpreted using shell-model calculations. [Copyright &y& Elsevier]

The fission cross sections for the [sup 6]He + [sup 209]Bi reaction as functions of the [sup 6]He-beam energy are measured. The experimental excitation functions for the reaction [sup 209]Bi([sup 6]He, 4n)[sup 211] At are also presented. The [sup 6]He secondary ion beam is obtained on the basis of the extracted-beam transport system of the U400-M accelerator (the Q4DQ spectrometer). A comparison of the experimental data obtained with available results for the [sup 6]He + [sup 209]Bi reaction shows that a pronounced enhancement of the fission cross sections in the above-barrier energy region is observed in the case of the reaction with the [sup 6]He beam. In order to fit the results of theoretical calculations to the experimental data, it is necessary to reduce the Coulomb barrier by 15% (20%). This corresponds to an increase of 1.5 (1.6) fm in the parameter r[sub 0] of the nuclear potential. [ABSTRACT FROM AUTHOR]

Proton reaction cross-section measurements on various stable and neutron-rich nuclei (4,6He, 7–9Li, 9–11Be, 21–24F, 22–26Ne, 25–29Na and 29–32Mg) were performed via the attenuation method at intermediate energies (∼35–75AMeV) and using a cryogenic hydrogen target. The results are discussed in the framework of different approaches of the nucleon–nucleus potential. [Copyright &y& Elsevier]

γ-ray and fast-timing spectroscopy were used to study levels in 30Al populated following the β- decay of Mg30. Five new transitions and three new levels were located in 30Al. A search was made to identify the third 1+ state expected at an excitation energy of ~2.5 MeV. Two new levels were found, at 3163.9 and 3362.5 keV, that are firm candidates for this state. Using the advanced time-delayed (ATD) βγγ(t) method we have measured the lifetime of the 243.8-keV state to be T1/2=15(4)ps, which implies that the 243.8-keV transition is mainly of M1 character. Its fast B(M1;2+ → 3+) value of 0.10(3) W.u. is in very good agreement with the USD shell-model prediction of 0.090 W.u. The 1801.5-keV level is the only level observed in this study that could be a candidate for the second excited 2+ state. [ABSTRACT FROM AUTHOR]