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Recent experimental results related to the quadrupole collectivity in neutron-rich carbon isotopes are analyzed in a phenomenological approach. fi(E2;21+ → 01+) transitions rates derived from lifetime measurements are interpreted in terms of the mixing of basic neutron and proton 2+ excitations. A seniority inspired scheme is used to describe the neutron component. The observed increase in collectivity can be explained with a corresponding increased role of proton excitations. This is likely due to the reduction of the proton p3/2-p1/2 spin-orbit splitting caused by the tensor and two-body spin-orbit components of the force between the protons and the added neutrons in the (d5/2 + S1/2) shells. [ABSTRACT FROM AUTHOR]

The geometry of the shears mechanism in nuclei is derived from the nuclear shell model. This is achieved by taking the limit of large angular momenta (classical limit) of shell-model matrix elements. [ABSTRACT FROM AUTHOR]

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which 235U (thick target) was Coulomb-excited. The program involved standalone experiments with Gammmasphere and with the 8pi Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a 40Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., [631]l/2, [624]7/2, and [622]5/2) strongly populated by E3 excitation. The CHICO data have been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many M1 matrix elements could be extracted from the γ-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of E3 collectivity on Coriolis interactions. [ABSTRACT FROM AUTHOR]

Rotational and electromagnetic properties of the yrast band in 102Pd are analyzed in terms of a phenomenologi-cal phonon model that includes anharmonic terms. Both the moment of inertia and B(E2)'s are well reproduced by the model, providing an independent confirmation of the multiphonon picture recently proposed. The (empirical) dependence of the phonon-phonon interaction on the phonon frequency, in Ru, Pd, and Ru isotopes, follows the expectations from particle-vibration coupling. [ABSTRACT FROM AUTHOR]

The role of the pairing interaction in multi-quasiparticle isomeric states was examined by calculating β-decay half-lives with the superfluid tunneling model. We found that this model reproduces the experimental β-decay half-lives with an accuracy typical of current β-decay models. In spite of the simplicity of the model, we are able to demonstrate how the reduction of pairing in multi-quasiparticle isomers has a remarkable effect on β-decay half-lives. Taking this effect into account may be important for spin and parity assignments of β-decaying multi-quasiparticle isomers. [ABSTRACT FROM AUTHOR]

A measurement of the direct two-proton removal from 42Si has provided the first structural information on the N = 28 isotone 40Mg. The value for the inclusive cross section for two-proton removal from 42Si of 40+27-17 μb is significantly lower than that predicted by structure calculations using the recent SDPF-MU shell-model effective interaction combined with eikonal reaction theory. This observed discrepancy is consistent with the interpretation that only one of the predicted low-lying 0+ states in 40Mg is bound. A two-state mixing analysis describing two-proton knockout cross sections along N = 28 provides support for the interpretation of a prolate-deformed 40Mg ground state. [ABSTRACT FROM AUTHOR]

We studied transition rates for the lowest 1/2+ and 5/2+ excited states of C17 through lifetime measurements with the GRETINA array using the recoil-distance method. The present measurements provide a model-independent determination of transition strengths giving the values of B(M1;1/2+→3/2g.s.+)=1.04-0.12+0.03×10-2µN² and B(M1;5/2+3/2g.s.+)=7.12-0.96+1.27×10-2µN². The quenched M1 transition strength for the 1/2+→3/2g.s.+ transition, with respect to the 5/2+3/2g.s.+ transition, has been confirmed with greater precision. The current data are compared to importance-truncated no-core shell model calculations addressing effects due to continuum and three-body forces. [ABSTRACT FROM AUTHOR]

Excited states in l67Lu were populated in the l23Sb(48Ca,4n) reaction at 203 MeV and decay γ rays measured using the Gammasphere spectrometer array. Two triaxial strongly deformed bands were identified previously and interpreted as zero- and one-phonon wobbling excitations. As a result of more extensive band search, the level scheme has been considerably extended to include ten new rotational bands and some 630 γ-ray transitions. A number of interband linking transitions were revealed, so that all but two bands could be connected with each other. Configurations are proposed for all new bands based on measured observables, with the help of cranked shell model calculations. A γ-ray sequence, previously suggested as a triaxial strongly deformed band based on quasiparticle excitations coexisting with the wobbling excitation in the triaxial potential well, has now been determined to be a signature partner of a coupled band, associated with a normal deformed five-quasiparticle configuration. The possibility of two new bands being associated with triaxial deformation is discussed. [ABSTRACT FROM AUTHOR]

The first lifetime measurement used to study the magnetic response of halo nuclei is presented. The lifetime of the first excited state of the one-neutron halo nucleus 19C has been measured by two complementary Doppler-shift techniques with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA). The B(M 1 ; 3/2+ →1/2g,s+) strength of 3.21(25)x 10-3µ²N determined for this decay represents a strongly hindered M1 transition among light nuclei. Shell-model calculations predict a strong hindrance due to the near-degeneracy of the S1/2 and d5/2 orbitals among neutron-rich carbon isotopes, while tensor corrections and loosely bound effects are necessary to account for the remaining strength. [ABSTRACT FROM AUTHOR]

In even-mass Te isotopes with 114 ≤ A ≤ 122 the experimentally observed yrast Iπ = 16+ states have been interpreted as favored noncollective oblate states based on the fully aligned π[(g7/2)²]6+ ⊗ ν[(h11/2)²]10+ configuration. For 124Te the highest-spin positive-parity state known has lπ = 10+. An extension of the yrast cascade of 124Te is needed to spin at least 16+ in order to answer the question of whether this noncollective oblate state lies along the yrast line in this isotope. The level structure of 124Te has been studied via prompt y-ray spectroscopy. 124Te was produced in the fission of the compound systems formed in two heavy-ion-induced reactions, 24Mg (134.5 MeV) + 173Yb and 23Na (129 MeV) + 176Yb. γ-ray spectroscopy was accomplished with the Gammasphere array. The yrast cascade of, 24Te was extended up to 5481-keV excitation energy with a tentative 16+ assignment for the highest observed state. This state does not exhibit the characteristics of the favored noncollective oblate states with Iπ = 16+ observed in the lighter doubly even Te isotopes, indicating that such a state is probably no longer yrast in 124Te. [ABSTRACT FROM AUTHOR]

Limited information is currently known on medium- and higher-spin states for 135Cs, a neutron-rich nucleus amenable to shell-model calculations due to its proximity to the shell closures in 132Sn. In order to extend the level structure of 135Cs to higher excitations, this nucleus was studied via prompt y- ray spectroscopy of fragments following the fission of the compound nucleus 226Th formed in the 18O (91 MeV) + 208Pb fusion-fission reaction. Medium-spin states up to spin (23/2) and ~3.3 MeV excitation energy have been established. The observed states were compared with those in the neighboring N = 82137Cs nucleus, as well as with states in the neighboring N = 80 isotones. The coupling of the odd proton occupying the g7/2 orbital to the yrast states in the 134Xe and 136Ba cores could account for the lower excited states of 135Cs. The experimental results are compared with predictions from shell-model calculations. [ABSTRACT FROM AUTHOR]

Excited states in 16C were populated via the 9Be(17N,16C + γ)X one-proton knockout reaction. The lifetime of the 21+ state in 16C was measured using the recoil distance method. The extracted lifetime of τ21+ = 11,4-0.9+0.8(stat) ± 0.7(systBp)-1.5+0.0(systfeeding) ps yields a deduced B(E2;21+ → O1+ ) = 4.21-0.26+0.34(stat)-0.24+0.28(systsBp)-0.00+0.64(systfeeding) e²fm4 value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the 16C 21+ state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 22+ state and the 21+ and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN + NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the γ-ray branching ratios. [ABSTRACT FROM AUTHOR]

Excited states in 18C were populated by the one-proton knockout reaction of an intermediate energy radioactive 19N beam. The lifetime of the first 2+ state was measured with the KöIn/NSCL plunger via the recoil distance method to be τ(21+) = 22.4 ± 0.9(stat)-2.2+3.3(syst) ps, which corresponds to a reduced quadrupole transition strength of B(E2; 21+ → 01+ = 3.64-0.14+0.15(stat)-0.47+0.40(syst) e²fm4. In addition, an upper limit on the lifetime of a higher-lying state feeding the 21+ state was measured to be τ < 4.6 ps. The results are compared to large-scale ab initio no-core shell model calculations using two accurate nucleon-nucleon interactions and the importance-truncation scheme. The comparison provides strong evidence that the inclusion of three-body forces is needed to describe the low-lying excited-state properties of this A = 18 system. [ABSTRACT FROM AUTHOR]

The article presents the study which examined the lifetime excited-state transition-rate measurements in neutron-rich 18 carbon (C). In the study, the recoil distance method (RDM) lifetime measurements were used due to their reliability as model-independent probes of nuclear structure. The study was carried out at the Michigan State University's National Superconducting Cyclotron Laboratory (NSCL).

The available experimental information on 34P has been greatly increased through the analysis of γ decays in coincidence with protons from the interaction of an 18O beam at 24 MeV with an 18O target. Light charged particles from the reaction were detected with Microball, and multiple γ-ray coincidences with Gammasphere. Many observed γ transitions have been identified and placed in the level scheme. Additionally, for most states, spins have been assigned based on measured γ-ray angular distributions while parities were inferred from lifetimes determined through Doppler-broadened line-shape analysis. Most of the states observed have been interpreted in terms of shell-model calculations using the WBP-a and SDPF-NR interactions having one particle in the 0f7/2 or 1P3/2 orbital. The two calculations agree almost equally well with the data resulting in root-mean-square differences of about 200 keV. However, a few high-lying states observed with long lifetimes challenge current calculations. Two of these may be associated with stretched πf7/2 ⊗ νf7/2 states, but the calculations overpredict their energies by 2-3 MeV. Furthermore, a long-lived 7919-keV state is established for which no explanation is available at present. [ABSTRACT FROM AUTHOR]

High-spin states in 120Te were populated in the reaction 80Se(>48Ca,&agr;4n))120Te at a beam energy of 207 MeV and &ggr;-ray coincidences were measured using the Gammasphere spectrometer. The previously known level scheme is extended to higher spin and new interband transitions and side-feeding branches are established. Five highly deformed rotational bands, extending up to almost l = 50, are observed for the first time. The bands are compared with similar structures found recently in neighboring nuclei. The experimental results are interpreted within the framework of the cranked Nilsson-Strutinsky model. Configuration assignments to several terminating states and to the high-spin bands are discussed. [ABSTRACT FROM AUTHOR]

The high-spin structure above the previously known 10+ isomers of the 118, 120, 122, 124Sn isotopes was studied via prompt γ-ray spectroscopy. All isotopes were populated as fragments following the fission of much heavier compound nuclei formed in three fusion-fission reactions. The 118, 120, 122Sn isotopes were also independently populated and studied as evaporation residues in the 124Sn(n, xnγ) reactions, with x = 3, 5, 7. Transitions above the previously known 10+ isomers were observed for the first time and the corresponding level schemes above these isomers were established up to 6646-, 5673-, 5386-, 5952-keV excitation energy for 118,120,122,124Sn, respectively. The experimental results are compared with predictions from shell-model calculations. [ABSTRACT FROM AUTHOR]

High-spin states have been studied in Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. populated through the 116Cd(23Na,4n) reaction at 115 MeV, using the Gammasphere γ-ray spectrometer. The negative-parity yrast band has been significantly extended to spin ~45ħ and excitation energy 21.5 MeV, showing evidence for several rotational alignments. The positive-parity yrast band of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., populated through the p4n channel of this reaction, was also populated to spin ~38ħ and excitation energy 18 MeV. Cranking calculations indicate that these nuclei are soft with respect to the triaxiality parameter γ and that several competing nuclear shapes occur at high spin. [ABSTRACT FROM AUTHOR]