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Measured binary quasifission mass spectra in reactions with actinide nuclides show a large peak in yield near the doubly-magic $^{208}$Pb. This has generally been attributed to the enhanced binding energy of $^{208}$Pb causing a valley in the potential energy surface, attracting quasifission trajectories. To investigate this interpretation, binary quasifission mass spectra and cross-sections have been measured at near-barrier energies for reactions of $^{50}$Ti with actinide nuclides from $^{238}$U to $^{249}$Cf. Cross-sections have also been deduced for sequential fission (a projectile-like nucleus and two fragments from fission of the complementary target-like nucleus). Binary cross-sections fall from ∼70% of calculated capture cross-sections for $^{238}$U to only ∼40% for $^{249}$Cf, with a compensating increase in sequential fission cross-sections. The data are consistent with the $^{208}$Pb peak originating largely from sequential fission of heavier fragments produced in more mass-asymmetric primary quasifission events. These are increasingly suppressed as the heavy quasifission fragment mass increases above $^{208}$Pb. The important role of sequential fission calls for re-interpretation of quasifission characteristics and dynamics in superheavy element synthesis reactions.

International audience; The nature of quadrupole and octupole collectivity in $^{222}$Rn was investigated by determining the electric-quadrupole (E2) and octupole (E3) matrix elements using subbarrier, multistep Coulomb excitation. The radioactive $^{222}$Rn beam, accelerated to 4.23 MeV/u, was provided by the HIE-ISOLDE facility at CERN. Data were collected in the Miniball $\gamma$ -ray spectrometer following the bombardment of two targets, $^{120}$Sn and $^{60}$Ni. Transition E2 matrix elements within the ground-state and octupole bands were measured up to 10 ¯h and the results were consistent with a constant intrinsic electric-quadrupole moment, 518(11) $e$ fm$^2$ . The values of the intrinsic electric-octupole moment for the $0^+ \to 3^-$ and $2^+ \to 5^-$ transitions were found to be respectively $2360^{+300}_{-210}$ $e$ fm$_3$ and $2300^{+300}_{-500}$ $e$ fm$^3$ while a smaller value, $1200^{+500}_{-900}$ $e$ fm$^3$ , was found for the $2^+ \to 1^-$ transition. In addition, four excited non-yrast states were identified in this work via γ -γ coincidences.

International audience; Excited states in the extremely neutron-deficient nucleus Te107 have been identified from two separate experiments using the recoil-decay tagging technique. Two connected structures were observed on the basis of γγ-coincidence relations and tentatively assigned as built on the mixed-parentage νg7/2d5/2 and νh11/2 intruder configurations. The observed structures were compared with large-scale shell-model calculations and total Routhian surface calculations. Collective behavior was discovered to persist in the νh11/2 band of Te107 which highlights the shape-polarizing effect of a single valence neutron occupying the h11/2 intruder orbit as the N=50 shell closure is approached.

The competition between the dominant mass-asymmetric and rarer narrow mass-symmetric fission modes in actinide nuclei are controlled by deformed and spherical shell effects. The low energy fission of 80180Hg was recently observed to be strongly mass-asymmetric, indicating that despite spherical shell gaps in fragments around 4090Zr, the system does not fission mass-symmetrically. Several theoretical approaches have been used to explain this unexpected result.To investigate the underlying mechanism, systematic measurements of fission mass distributions for isotopes of Os, Pt, Hg and Pb, formed in fusion reactions with p, $^{12}$C, $^{32}$S, $^{40,48}$Ca projectiles, have been made for excitation energies above the fission saddle-point (Eeff⁎) between 2.8 and 28.2 MeV. Evidence for mass-asymmetric fission is widespread, manifested as flat topped mass distributions or significant deviations from a single Gaussian shape. The systematic trends seen cannot be attributed to quasifission. Comparing two-Gaussian fits at a wide range of E$^{⁎}$, it is concluded that the fit centroids reflect the low energy character of mass-asymmetric fission in the sub-lead region.Quantitative comparisons were made with microscopic calculations by Scamps and Simenel (2019) [33] of fission mass-asymmetries attributed to the influence of shell gaps in both neutrons (N=52, 56 for compact octuple deformations) and protons (Z=34 and Z=42, 44, 46 with large quadrupole deformations). For the predominant fission mode in the calculations, having one elongated and one compact fragment, the results are in extremely good agreement with all experimental values. This provides strong support for both the calculations, and the exploration of mass-asymmetric fission systematics through heavy ion fusion reactions. The total kinetic energy distributions for $^{176}$Pt and $^{180}$Pt do not show any evidence of a low TKE mass-symmetric fission mode, as had been reported for $^{178}$Pt by Tsekhanovich et al. (2019) [39].

6 pags., 5 figs., 1 tab., There is sparse direct experimental evidence that atomic nuclei can exhibit stable "pear" shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in Ra222,228 nuclei using the method of sub-barrier, multistep Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of E3 matrix elements for different nuclear transitions is explained by describing Ra222 as pear shaped with stable octupole deformation, while Ra228 behaves like an octupole vibrator., The support of the ISOLDE Collaboration and technical teams is acknowledged. This work was supported by the following Research Councils and Grants: Science and Technology Facilities Council (UK) Grants No. ST/P004598/1, No. ST/L005808/1, No. ST/ R004056/1; Federal Ministry of Education and Research (Germany) Grants No. 05P18RDCIA, No. 05P15PKCIA, and No. 05P18PKCIA and the “Verbundprojekt 05P2018”; National Science Centre (Poland) Grant No. 2015/18/M/ ST2/00523; European Union’s Horizon 2020 Framework research and innovation programme 654002 (ENSAR2); Marie Skłodowska-Curie COFUND Grant (EU-CERN) 665779; Research Foundation Flanders and IAP Belgian Science Policy Office BriX network P7/12 (Belgium); GOA/2015/010 (BOF KU Leuven); RFBR (Russia) Grant No. 17-52-12015; and the Academy of Finland (Finland) Grant No. 307685.

The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical $r$-process in producing nuclei heavier than $A\sim190$. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in $^{207}$Hg have been probed using the neutron-adding ($d$,$p$) reaction in inverse kinematics. The radioactive beam of $^{206}$Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of $^{207}$Hg marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the $r$-process., Comment: 6 pages, 5 figures

There is sparse direct experimental evidence that atomic nuclei can exhibit stable pear shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole ($E3$) matrix elements have been determined for transitions in $^{222,228}$Ra nuclei using the method of sub-barrier, multi-step Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of $E$3 matrix elements for different nuclear transitions is explained by describing $^{222}$Ra as pear-shaped with stable octupole deformation, while $^{228}$Ra behaves like an octupole vibrator. There is sparse direct experimental evidence that atomic nuclei can exhibit stable pear shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole ($E3$) matrix elements have been determined for transitions in $^{222,228}$Ra nuclei using the method of sub-barrier, multi-step Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of $E$3 matrix elements for different nuclear transitions is explained by describing $^{222}$Ra as pear-shaped with stable octupole deformation, while $^{228}$Ra behaves like an octupole vibrator.

A charge plunger device has been commissioned based on the DPUNS plunger (Taylor et al., 2013) using the in-flight mass separator MARA at the University of Jyväskylä. The 152Sm(32S,4n)180Pt reaction was used to populate excited states in 180Pt. A lifetime measurement of the 21+ state was performed by applying the charge plunger technique, which relies on the detection of the charge state-distribution of recoils rather than the detection of the emitted γ rays. This state was a good candidate to test the charge plunger technique as it has a known lifetime and depopulates through a converted transition that competes strongly with γ-ray emission. The lifetime of the 21+ state was measured to be 480(10)ps, which is consistent with previously reported lifetimes that relied on the standard γ-ray techniques. The charge plunger technique is a complementary approach to lifetime measurements of excited states that depopulate through both γ-ray emission and internal conversion. In cases where it is not possible to detect Doppler-shifted γ rays, for example, in heavy nuclei where internal conversion dominates, it may well be the only feasible lifetime analysis approach. peerReviewed

International audience; Lifetimes of low- and high-spin states in the odd-A nucleus Hf177 were measured during the EXILL&FATIMA campaign using a spectrometer equipped with eight HPGe-Clover detectors and 16 fast-timing LaBr3(Ce) detectors. For the determination of lifetimes in the pico- to nanosecond regime, the well-established generalized centroid difference method was used. Lifetimes of the 9/2−, 9/2+, 11/2−, 11/2+ states were remeasured, the lifetimes of the 13/2−, 17/2−, 13/2+, 15/2+, and 17/2+ states were determined for the first time and an upper limit for the 19/2+ state has been established. From these lifetimes absolute reduced transition probabilities were extracted and compared to particle-rotor-model calculations and quasiparticle-phonon-model calculations showing the importance of including multipole-multipole interactions in the description of odd-A nuclei in the rare earth region.

International audience; Lifetimes of excited states of the phosphorus isotopes 1533,34,35,36P have been measured by using the differential recoil-distance method. The isotopes of phosphorus were populated in binary grazing reactions initiated by a beam of S36 ions of energy 225 MeV incident on a thin Pb208 target mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA γ-ray tracking array was used to detect γ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were made within the range from about 1 to 100 ps. The number of states for which lifetime measurements were possible was limited by statistics. For P33, lifetime limits were determined for the first 3/2+ and 5/2+ states at 1431 and 1848 keV, respectively; the results are compared with previous published lifetime values. The lifetime of the first 2+ state of P34 at 429 keV was determined and compared with earlier measurements. For P35, the states for which lifetimes, or lifetime limits, were determined were those at 2386, 3860, 4101, and 4493 keV, with Jπ values of 3/2+, 5/2+, 7/21−, and 7/22−, respectively. There have been no previous published lifetimes for states in this nucleus. A lifetime was measured for the stretched π(1f7/2)⊗ν(1f7/2)Jπ=(7+) state of P36 at 5212 keV and a lifetime limit was established for the stretched π(1d3/2)⊗ν(1f7/2)Jπ=(5−) state at 2030 keV. There are no previously published lifetimes for states of P36. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF effective interaction. In addition, measured branching ratios, published mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. In general, there is good agreement between experiment and the shell model; however there is evidence that the shell-model values of the M1 transition rates for the 3/21+→1/2+ (ground state) and 5/21+→3/21+ transitions in P33 underestimate the experimental values by a factor between 5 and 10. In P35 there are some disagreements between experimental and shell-model values of branching ratios for the first and second excited 7/2− states. In particular, there is a serious disagreement for the decay characteristics of the second 7/2− state at 4493 keV, for which the shell-model counterpart lies at 4754 keV. In this case, the shell-model competing electromagnetic decay branches are dominated by E1 and M1 transitions.

International audience; The nature of low-lying 3− levels in Nd144 was investigated in the Nd143(n,γγ) cold neutron-capture reaction. The combination of the high neutron flux from the research reactor at the Institut Laue-Langevin and the high γ-ray detection efficiency of the EXILL setup allowed the recording of γγ coincidences. From the coincidence data precise branching ratios were extracted. Furthermore, the octagonal symmetry of the setup allowed angular-distribution measurements to determine multipole-mixing ratios. Additionally, in a second measurement the ultra-high resolution spectrometer GAMS6 was employed to conduct lifetime measurements using the gamma-ray induced Doppler-shift technique (GRID). The confirmed strong M1 component in the 33−→31− decay strongly supports the assignment of the 33− level at 2779keV as low-lying isovector octupole excitation. Microscopic calculations within the quasiparticle phonon model confirm an isovector component in the wave function of the 33− level, firmly establishing this fundamental mode of nuclear excitation in near-spherical nuclei.

International audience; The first excited level of 96Mo was investigated in a high-statistics experiment using the 95Mo(n, γγ) cold neutron capture reaction. The measurements used the high cold neutron flux from the research reactor at Institut Laue-Langevin and employed the highly-efficient EXILL array to detect γ-ray coincidences. The recorded statistics allow identification of decay branches with only a small relative intensity including the E3 decay. With the knowledge of the newly measured branching ratio and the known transition probability, the lifetime of the level was determined and, subsequently, the strength of the other decay branches of the octupole phonon were calculated. The extracted electromagnetic decay strengths are compared to the systematics of the stable even–even molybdenum isotopes and values calculated in a Skyrme-force based quasiparticle random phase approximation and in a cluster approach. Additionally, the decay branch to the low-lying quadrupole isovector level was observed.

In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of $^{132}$Sn. The spectroscopic strength of single-hole states in $^{131}$Sn was determined from the measured differential cross sections of the tritons from the neutron-removing $^{132}$Sn(d, t)$^{131}$Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3/2+, 1/2+ and 5/2+ states were found to be consistent with their maximal values of (2j+1), confirming the robust N=82 shell closure at $^{132}$Sn. We compared the spin-orbit splitting of neutron single-hole states in $^{131}$Sn to those of single-particle states in $^{133}$Sn determined in a recent measurement of the $^{132}$Sn(d, p)$^{133}$Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength.

International audience; The transitional nucleus Xe131 is investigated after multinucleon transfer in the Xe136+Pb208 and Xe136+U238 reactions employing the high-resolution Advanced γ-Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and as an elusive reaction product in the fusion-evaporation reaction Sn124(B11,p3n)Xe131 employing the High-efficiency Observatory for γ-Ray Unique Spectroscopy (HORUS) γ-ray array coupled to a double-sided silicon strip detector at the University of Cologne, Germany. The level scheme of Xe131 is extended to 5 MeV. A pronounced backbending is observed at ℏω≈0.4MeV along the negative-parity one-quasiparticle νh11/2(α=−1/2) band. The results are compared to the high-spin systematics of the Z=54 isotopes and the N=77 isotones. Large-scale shell-model calculations employing the PQM130, SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in Xe129−132 provide insight into the changing nuclear structure along the Xe chain towards the N=82 shell closure. Proton occupancy in the π0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon.

The 50 � N,Z � 82 region of the Segrè chart, spanning the nuclei “northwest” of doubly-magic 132Sn, is an intriguing study ground to test the suitability and predictive power of nuclear models at both low and high spins. Low-spin excited states in the nearly spherical nuclei near proton- and neutronshell closures are well described as anharmonic vibrations [1] with a gradual change to rotational structures further away from the closed shells. Further on, quasiparticle excitations play a key role and are responsible for the presence of yrast-trap isomers. These long-lived states interrupt and fragment the decay flux in spectroscopic investigations. High-j couplings involving the unique-parity h11/2 neutron-hole orbital give rise to a wealth of high-spin states with multi-quasiparticle character. In particular, detailed knowledge of isomers is crucial to ascertain the active quasiparticle configurations in the specific nucleus.

Angular distributions of γ-rays for selected transitions in 40, 41, 42Ar isotopes have been studied with the PRISMA magnetic spectrometer coupled to the CLARA γ array. These transitions were populated in Ar isotopes reached via neutron transfer in the 40Ar + 208Pb reaction. By comparison with the shape of the experimental angular distribution of the known E2 transitions we established more firmly the spin and parity of excited states. In particular, in 41Ar for the (11/2-) state through the (11/2-) -> 7/2- transition whose structure was discussed in terms of a phonon-fermion coupled state. The comparison with the expected fully aligned spin indicated that a high level of spin alignment has been reached.

International audience; The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134−xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7−) and (10+) isomers in Xe132 and above the 11/2− isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2≫1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

International audience; Excited states in La147, populated in spontaneous fission of Cf252, have been reinvestigated by means of γ-ray spectroscopy, using high-fold γ-ray coincidences measured with the Gammasphere array of Ge detectors. The 229.5-keV level, which has been assigned spin parity 9/2− in a recent evaluation, is shown to have spin parity 11/2−. Consequently, the ground state has spin parity 5/2+. Excited levels in La147 have been arranged into a parity-doublet structure, showing that at medium excitation energy the La147 nucleus may have octupole deformation. The B(E1) rates in La147, which are factor of four lower than in La145, suggest that the electric dipole moment in La147 is depressed by an extra mechanism, probably connected with the population of particular neutron orbitals.

International audience; Rapid shape changes are observed for neutron-rich nuclei with A around 100. In particular, a sudden onset of ground-state deformation is observed in the Zr and Sr isotopic chains at N = 60: Low-lying states in N 58 nuclei are nearly spherical, while those with N 60 have a rotational character. Nuclear lifetimes as short as a few picoseconds can be measured using fast-timing techniques with LaBr3(Ce) scintillators, yielding a key ingredient in the systematic study of the shape evolution in this region.We used neutron-induced fission of 241Pu and 235U to study lifetimes of excited states in fission fragments in the A ∼ 100 region with the EXILL-FATIMA array located at the PF1B cold neutron beam line at the Institut Laue-Langevin. In particular, we applied the generalized centroid difference method to deduce lifetimes of low-lying states for the nuclei 98Zr (N = 58), 100Zr,and 102Zr (N 60). The results are discussed in the context of the presumed phase transition in the Zr chain by comparing the experimental transition strengths with the theoretical calculations using the interacting boson model and the Monte Carlo shell model.

International audience; New excited states in $^{142}$Ba and $^{144}$Ce are investigated by means of prompt $\gamma$-ray spectroscopy of the radiation following spontaneous fission of $^{252}$Cf. Measurements of angular correlations and the observed branchings allowed the assignment of spins and parities with confidence. The new measurements are reinforced by shell-model calculations where energy levels, electric transitions, and magnetic moments are consistent with experimental data. The presence of collectivity in the N=86 isotones is confirmed by clear signatures of soft triaxial γ bands in both nuclei.

International audience; The high-spin structures and isomers of the N=81 isotones Xe135 and Ba137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+U238 and (ii) Xe136+Pb208 MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the Xe136+Pt198 MNT reaction employing the γ-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a B11+Te130 fusion-evaporation reaction with the HORUS γ-ray array at the University of Cologne. The high-spin level schemesof Xe135 and Ba137 are considerably extended to higher energies. The 2058-keV (19/2−) state in Xe135 is identified as an isomer, closing a gap in the systematics along the N=81 isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of B(E2,19/2−→15/2−)=0.52(6) W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels.

The α decay of Th222 populating the low-lying Jπ=3− state, and also a proposed 1− state, in Ra218 has been observed. The observations suggest an excitation energy of 853 keV for the 1− state, which is 60 keV above the 3− state. The hindrance factors of these α decays give a possible boundary to the region of ground-state octupole deformation in the light-actinide nuclei. The relative positions of the Jπ=1− and 3− states suggest they are produced by an octupole-vibrational mechanism, as opposed to α clustering or rotations of a reflection-asymmetric octupole-deformed shape.

Multi-quasiparticle high-K states, several of which are isomeric, were observed in Hf180 with the Gammasphere array. Lifetimes in the ns-μs range were determined using centroid-shift and decay measurements within a μs coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to Kπ=(18−) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well.

Multi-quasiparticle high-K states, several of which are isomeric, were observed in Hf180 with the Gammasphere array. Lifetimes in the ns-μs range were determined using centroid-shift and decay measurements within a μs coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to Kπ=(18-) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well.

Detailed spectroscopic information in the N~82 region is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in 134Xe is investigated after multinucleon transfer (MNT) and actinide fission. 134Xe was populated as (i) a transfer product in 136Xe+238U, and 136Xe+208Pb MNT reactions and (ii) as a fission product in the 136Xe+238U reaction employing the high-resolution Advanced Gamma Tracking Array (AGATA). Trajectory reconstruction has been applied for the complete identification of beamlike transfer products with the magnetic spectrometer PRISMA. The 136Xe+198Pt MNT reaction was studied with the gamma-ray spectrometer GAMMASPHERE in combination with the gas detector array Chico. Several highspin states in 134Xe on top of the two long-lived isomers are discovered based on gamma-gamma coincidence relationships and information on the gamma-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of 134Xe is extended up to an excitation energy of 5.832 MeV with tentative spin-parity assignments up to 16+. Previous assignments of states above the 7- isomer are revised. Latest shell model calculations employing two different effective interactions reproduce the experimental findings quite well and support the new spin and parity assignments.

The neutron-rich nuclei 34, 35, 36, 37, 38P were populated in binary grazing reactions initiated by a beam of 36S ions at 215 MeV incident on a thin 208Pb target. The combination of the PRISMA magnetic spectrometer and the CLARA array of escape-suppressed Ge detectors was used to detect gamma rays in coincidence with projectile-like nuclear species. Further evidence to support the observed gamma decay of excited states of the populated phosphorus isotopes is provided by gamma-gamma coincidence measurements based on the results of an earlier thick-target deep-inelastic experiment. Level schemes for 34, 35, 36, 37, 38P are presented and discussed within the context of state-of-the-art shell-model calculations. In particular, new spin and parity assignments are proposed for a number of excited states of 36P. The evolution with neutron number of the energy difference of the low-lying 3/2+ and 1/2+ states in the odd-A isotopes of phosphorus, and the relationship to nuclear collectivity, is discussed. The evolution with neutron number of the shell-model wave functions of the first 1/2+, 3/2+, and 5/2+ states of the odd-A phosphorus isotopes and of the first 3−, 4−, and 5− states of the even-A isotopes is also explored.

Excited states have been studied in the deformed proton emitter 113Cs. Gamma-ray transitions have been unambiguously assigned to 113Cs by correlation with its characteristic proton decay, using the method of recoil-decay tagging. Two previously identified rotational bands have been observed and extended to tentative spins of 45/2 and 51/2 h¯, with excitation energies over 8 MeV above the lowest state. These are the highest angular momenta and excitation energies observed to date in any nucleus beyond the proton drip-line. Transitions in the bands have been rearranged compared to previous work. A study of aligned angular momenta, in comparison to the predictions of Woods–Saxon cranking calculations, is consistent with the most intense band being based on the π g7/2[422]3/2+ configuration, which would contradict the earlier πh11/2 assignment, and with the second band being based on the πd5/2[420]1/2+ configuration. The data suggest that the band based upon the πh11/2 configuration is not observed. peerReviewed

5 pags., 6 figs., Single-neutron states in the , isotope 79Zn have been populated using the 78Zn(d, p)79Zn transfer reaction at REX-ISOLDE, CERN. The experimental setup allowed the combined detection of protons ejected in the reaction, and of γ rays emitted by 79Zn. The analysis reveals that the lowest excited states populated in the reaction lie at approximately 1 MeV of excitation, and involve neutron orbits above the shell gap. From the analysis of γ-ray data and of proton angular distributions, characteristic of the amount of angular momentum transferred, a configuration was assigned to a state at 983 keV. Comparison with large-scale-shell-model calculations supports a robust neutron shell-closure for 78Ni. These data constitute an important step towards the understanding of the magicity of 78Ni and of the structure of nuclei in the region., This work was supported by the European Commission through the Marie Curie Actions Contracts Nos. PIEFGA-2011-30096 (R.O.) and PIEFGA-2008-219175 (J.P.), by the Spanish Ministerio de Ciencia e Innovación under contracts FPA2009-13377-C02 and FPA2011-29854-C04, by the Spanish MEC Consolider – Ingenio 2010, Project No. CDS2007-00042 (CPAN), by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF KU Leuven), by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office (BriX network P7/12), by the European Union Seventh Framework Programme through ENSAR, contract no. RII3-CT-2010-262010, and by the German BMBF under contracts 05P09PKCI5, 05P12PKFNE, 05P12RDCIA and 06DA9036I. R.O., R.C., J.F.W.L., V.L. and J.F.S. also acknowledge support from STFC, Grant Nos. PP/F000944/1, ST/F007590/1, and ST/J000183/2.

In this contribution an experimental study of the deep-inelastic reaction 96 40Zr+124 50 Sn at 530 MeV, using the GASP and PRISMA-CLARA arrays, is presented. The experiments populate a wealth of projectile-like and target-like binary fragments, in a large neutron-rich region around N ≥ 50 and Z ≈ 40. Preliminary results on the study of the yrast and near-yrast states for 95Nb will be shown, along with a comparison of the experimental yields obtained in the experiments.

Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85 MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in 182−188Hg were extracted. Information on the deformation of the ground and the first excited 0+ states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0+ state was noted in 182,184Hg. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established., The authors would like to thank the ISOLDE facility for providing excellent beams. This work was supported by the FWO-Vlaanderen (Belgium), an FWO Pegasus Marie Curie Fellowship (L. P. G.), by GOA/2010/010 (BOF KULeuven), by the IAP Belgian Science Policy (BriX network P6/23 and P7/12), by the European Commission within the 7th Framework Programme through I3-ENSAR (Contract No. RII3-CT-2010-262010), by the U. K. Science and Technology Facilities Council, by the German BMBF under Contracts No. 06DA9036I, No. 05P12RDCIA, No. 06KY205I, No. 05P09PKCI5, No. 05P12PKFNE, No. 05P12WOFNF, and No. 09MT9156, Academy of Finland (Contract No. 131665), by the Spanish MINECO through FPA2010-17142 project and the Spanish Project No. FIS2011-28738-C02-02.

The structure of 58Fe was investigated at Gammasphere using 48Ca(13 ,14C,xn) fusion-evaporation reactions at a beam energy of 130 MeV. The level scheme has been revised and extended to J∼17 and an excitation energy of 16.6 MeV. Regular band structures consisting of low-energy ΔJ=1 transitions have been observed at moderate spin (J∼8-15) and are candidates for magnetic rotational bands. Self-consistent tilted-axis-cranking calculations within a relativistic mean-field theory were applied to investigate these bands and were found to reproduce the experimental results well. In other parts of the level scheme, quasirotational bands composed of stretched-E2 transitions have been extended to high spin, and other new bands have been identified. Positive-parity experimental states were compared to predictions of the spherical shell model using the GXPF1A, KB3G, and FPD6 effective interactions in the fp model space. The projected shell model, with a deformed quasiparticle basis including the neutron νg9/2 orbital, was applied to interpret regular ΔJ=2 band structures that extend beyond the maximum spin available for π[(f7/2)-2]- ν[(p3/2f 5/2p1/2)4] configurations and exhibit features characteristic of rotational alignment. It is clear that the νg9/2 intruder orbital plays a crucial role in describing the quasirotational structures in this nucleus, even starting as low as J∼5.

Excited states have been identified in the very neutron-deficient Z=58 nucleus 123Ce. This is the most neutron-deficient odd-A cerium isotope in which excited states have been identified. The states have been unambiguously assigned to 123Ce by detecting de-excitation γ rays in coincidence with evaporated charged particles and neutrons. Three rotational bands, each consisting of at least eight E2 transitions, have been observed. The bands have tentatively been assigned to be based on neutrons in g7/2 and h11/2 orbitals. Two of the bands have been assigned to be signature partners, although no interband transitions have been observed. The aligned angular momenta of the bands have been studied in comparison with neighboring nuclei and with the results of Woods-Saxon cranking calculations. Observation of the deformation-dependent π(h11/2)2 quasiparticle alignment at 0.36MeV/ in each of the bands suggests a quadrupole deformation of β2 0.3, in good agreement with theoretical predictions for the suggested possible configuration assignments.

Gamma-ray transitions have been observed in the proton-emitting N=Z+2 (Tz=1) isotope 112Cs. The transitions have been unambiguously assigned to 112Cs by correlation with the characteristic proton decay, using the method of recoil-decay tagging with mass selection. The measured proton-decay energy and half-life are Ep=810(5) keV and T1/2=470(50) μs, respectively, which are consistent with previous measurements. Five γ-ray transitions have been observed which appear to form a rotational sequence. The energy differences between excited states in the sequence are consistent with an assignment as the favored signature of the ν(h 11/2) π(h11/2) structure. Tentative evidence for fine structure in the 112Cs proton decay is also observed.

The level structures of the N = 50, 83As, 82Ge, and 81Ga isotones have been investigated by means of multi-nucleon transfer reactions. A first experiment was performed with the CLARA–PRISMA setup to identify these nuclei. A second experiment was carried out with the GASP array in order to deduce the γ -ray coincidence information. The results obtained on the high-spin states of such nuclei are used to test the stability of the N = 50 shell closure in the region of 78Ni (Z = 28). The comparison of the experimental level schemes with the shell-model calculations yields an N = 50 energy gap value of 4.7(3) MeV at Z = 28. This value, in a good agreement with the prediction of the finite-range liquid-drop model as well as with the recent large-scale shell model calculations, does not support a weakening of the N = 50 shell gap down to Z = 28.

Excited states in V55 and Cr55 have been populated via pn and 2n evaporation channels, respectively, following the fusion of a Ca48 beam at 172 MeV with a Be9 target. Level schemes have been deduced for the two nuclides to excitation energies of 7467 (V55) and 12226 keV (Cr55), with spins of 27/2 + and 33/2+, respectively. Negative-parity states are compared with shell-model calculations using three different effective interactions in the full fp model space. Negative-parity levels of Cr55 are explained in terms of single-particle fp-shell configurations outside N=28 and N=32 cores. Positive-parity states in both isotopes show evidence for the involvement of neutron g9/2 configurations. In the case of Cr55, a quasirotational structure based on the 1/2+[440] Nilsson orbital is observed up to the terminating state. In V55, positive-parity states do not exhibit well-developed collective features, and the observation of octupole decays is an indication of their importance in transitions from neutron g 9/2 configurations to the fp shell. Experimental results are compared with the predictions of a traditional shell model, the projected shell model, and total-Routhian-surface calculations.

Excited states in the neutron-rich isotopes Mn57-60 have been studied with fusion-evaporation reactions induced by Ca48 beams at 130 MeV on C13,14 targets. Level schemes have been deduced reaching spins of ∼16□ and ∼27□/2 in the odd-odd and odd-even isotopes, respectively. States with natural parity within an fp model space are compared to the predictions of large-scale shell-model calculations using the recently developed GXPF1A effective interaction. Quasirotational structures are evident in all of the isotopes and are discussed in terms of the deformation-driving potential of the ν1g9/2 intruder orbital. It is apparent that an enlarged model space, incorporating at least the 1g9/2 intruder state, is necessary to reproduce the observed experimental systematics in a more satisfactory manner.

Yrast states up to (6+) in the neutron-rich 40S nucleus have been studied using binary grazing reactions produced by the interaction of a 215 MeV beam of 36S ions with a thin 208Pb target. The novel experimental setup that combines the large acceptance magnetic spectrometer, PRISMA, and the high-efficiency γ -ray detection array, CLARA, was used. A new γ -ray transition at an energy of 1572 keV was observed and tentatively assigned to the (6+) → (4+) transition. A comparison of experimental observations and the results of large-scale 0hω sd-pf shell-model calculations indicates that one- and two-proton excitations from the 2s1/2 to the 1d3/2 orbitals play an important role in reproducing the 40S yrast level structure and the published B(E2 ; 0+g.s.→ 2+) value. The structure of the yrast states of the even-A isotopes of sulfur is interpreted in terms of the configurations of valence protons and neutrons within the context of large-scale 0hω sd-pf shell-model calculations.

Yrast states in the neutron-rich 33Si nucleus have been studied using binary grazing reactions produced by the interaction of a 215 MeV beam of 36S ions with a thin 208Pb target. An experimental setup which combines the large acceptance magnetic spectrometer, PRISMA, and the high efficiency gamma-ray detection array, CLARA, was used in the experiment. Four new gamma-ray photopeaks at energies of 971, 1724, 1772, and 2655 keV were observed and assigned to the 33Si level scheme. The experimental level scheme is compared with the results of p-sd-pf large-scale shell-model calculations using the recently developed PSDPFB effective interaction ; good agreement is obtained. The structure of the populated states of 33Si is discussed within the context of an odd-neutron coupled to states of the 32Si core.

Lifetimes of low-lying excited states of the neutron-rich 44, 46Ar nuclei, populated via multinucleon transfer reactions, are measured by means of the differential recoil distance Doppler shift method. The extracted electromagnetic transition probabilities are compared with previous intermediate-energy Coulomb-excitation measurements and with large-scale shell-model calculations. The increase in the deduced B(E2 ; 2+→0+) transition probability from 44Ar to the closed-shell nucleus 46Ar contradicts the earlier results of Coulomb-excitation experiments. Shell-model calculations using different effective interactions agree with the new measured values.

Excited states of 38Cl were populated in binary grazing reactions during the interaction of a beam of 36S ions of energy 215 MeV with a 208Pb target. The combination of the PRISMA magnetic spectrometer and the CLARA γ-ray detector array was used to identify the reaction fragments and to detect their decay via γ-ray emission. A level scheme for 38Cl is presented and discussed within the context of the systematics of neighboring nuclei and is compared with the results of state-of-the-art shell-model calculations.

The yrast sequence of the neutron-rich dysprosium isotope 168Dy has been studied using multi-nucleon transfer reactions following collisions between a 460-MeV 82Se beam and a 170Er target. The reaction products were identified using the PRISMA magnetic spectrometer and the gamma rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground state rotational band of 168Dy have been confirmed and the yrast band extended up to 10+. A tentative candidate for the 4+ to 2+ transition in 170Dy was also identified. The data on these nuclei and on the lighter even-even dysprosium isotopes are interpreted in terms of Total Routhian Surface calculations and the evolution of collectivity in the vicinity of the proton-neutron valence product maximum is discussed., 15 pages, 7 figures, submitted to Phys. Rev. C

Excited states in 95Y, populated following the spontaneous fission of 248Cm and 252Cf and following fission of 235U induced by thermal neutrons, were studied by means of γ spectroscopy using the EUROGAM2 and GAMMASPHERE multidetector Ge arrays and the LOHENGRIN fission-fragment separator, respectively. We have found a new (17/2−) isomer in 95Y at 3142.2 keV with a half-life of T1/2 = 14.9(5) ns. Another isomer was identified in 95Y at 5022.1 keV and it was assigned a spin-parity (27/2−). For this isomer a half-life of T1/2 = 65(4) ns was determined and four decay branches were found, including an E3 decay. A new E3 decay branch was also found for the known, 1087.5-keV isomer in 95Y, for which we measured a half-life of 51.2(9) μs. The B(E3) and B(E1) transition rates, of 2.0 and 3.8 × 10−7 W.u., respectively, observed in 95Y are significantly lower than in the neighboring 96Zr core, suggesting that octupole correlations in this region are mainly due to the coupling of proton deltaj = 3 orbitals. Shell-model calculations indicate that the (27/2−) isomer in 95Y corresponds to the πg9/2ν(g7/2h11/2) maximally aligned configuration and that all three isomers in 95Y decay, primarily, by M2 transitions between proton g9/2 and f5/2 orbitals.

Excited states in 159Sm, populated following the spontaneous fission of 252Cf have been studied by means of gamma spectroscopy, using the Gammasphere array. In 159Sm we have identified an isomeric level with a half-life of T1/2=116(8) ns at an excitation energy of 1276.8 keV and observed a rotational band on top of this isomer. On the basis of the observed properties of the isomer and the band on top of it we propose that the 1276.8-keV level in 159Sm corresponds to the 11/2-[505] neutron extruder configuration. The new excitation scheme of 159Sm is compared to quasiparticle rotor model calculations.

The decay of a new 3.2-μs, (4−) isomeric state at 1298.0 keV has been observed using γ -ray spectroscopy at the Lohengrin mass spectrometer of the Institut Laue-Langevin. By comparison with theoretical calculations this state was assigned a ν5/2[642] ⊗ ν3/2[521] dominant configuration. Prompt γ -ray data from a spontaneous fission experiment have also been analyzed allowing the observation of a collective band on top of this isomeric state, the identification of a new band on top of the previously reported (5−) isomer of 156Nd and the extension of collective bands on top of (5−) isomers of the neighboring 156,158Sm nuclei. Quasiparticle rotor model calculations reported in this work correctly predict the energies and decay patterns of these bands. A new (5−) isomer in 160Sm has also been observed. The calculations predict ν5/2[642] ⊗ ν5/2[523] dominant configurations for all these (5−) isomers.

Gamma rays from Ti52 have been studied with Gammasphere and the Fragment Mass Analyzer using reactions induced by a Ca48 beam on a Be9 target. The data have been used in combination with information from deep-inelastic reactions of Ca48 beams on a thick U238 target at an energy about 25% above the Coulomb barrier. The Ti52 level scheme was expanded considerably, and the lifetimes of some of the identified states were determined for the first time. The excitation of two protons and two neutrons outside the Ca48 core provide new tests of effective interactions in the full pf-shell model space. The positive-parity states in Ti52 were compared to theoretical predictions obtained with the GXPF1A, FPD6, and KB3G effective interactions. The comparisons favor, to a degree, the results computed with the GXPF1A interaction.