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The mean lifetime of the 21+ state in the near drip-line nuclide 20C was measured for the first time using the Recoil Distance Method with intermediate energy radioactive beams via a knockout reaction. The measured value of τ21+ = 9.8±2.8(stat)-1.1+0.5(syst) ps gives a reduced transition probability of B(E2;21+→0g.s.+) = 7.51.7+3.0(stat) e2fm4. This value is in good agreement with shell model calculations using a p-sd shell model space and isospin-dependent (N-Z) effective charges. [ABSTRACT FROM AUTHOR]

We have studied the weak-decay channels of fusion/evaporation in light projectile/light target systems in order to provide reliable predictions for gamma-spectroscopy experiments. [ABSTRACT FROM AUTHOR]

Both the quasi-continuum of γ rays as well as the ridges from the feeding (and decay) of superdeformed and normal bands have been extracted in the nucleus 152Dy. A model has been developed that simultaneously describes all these spectra as well as the feeding intensity of the superdeformed bands. Through the calculation of the continuum of γ rays at finite temperature, the rotational damping width in the normal and superdeformed wells are extracted. This is the first time the rotational damping width in a superdeformed well has been measured in the A∼150 mass region. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Wobbling is an excitation mode unique to triaxial nuclei. Even though it is a general consequence of triaxiality in nuclei, it has so far only been observed in the odd-mass Lu isotopes around 163Lu. The principal evidence for the wobbling mode is based on the pattern of rotational bands characterized and described by a wobbling phonon number and the decay between different bands belonging to the same family. A new measurement revealed lifetimes of states in an excited wobbling band for the first time and gave access to absolute transition probabilities for both in-band and interband transitions. A general recipe how to derive quadrupole moments for triaxial nuclei from experimental data is discussed. The results show a remarkable similarity of the quadrupole moments for the different bands, further supporting the wobbling scenario. A decrease of the quadrupole moments is observed with increasing spin. This is attributed to an increase in triaxiality with spin, which can at the same time explain the dependence of the interband transitions on spin. Such an increase in triaxiality is qualitatively reproduced by cranking calculations to which the experimental results are compared. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Two Gammasphere experiments have been performed in order to establish the possible triaxial nature of strongly deformed (SD) bands in 174Hf. A lifetime measurement confirmed the large deformation of the four previously observed bands in this nucleus. In addition, a thin-target, high-statistics experiment was carried out to search for linking transitions between the SD bands. No such transitions, which represent an experimental signature for wobbling modes, were observed. Four new SD bands were found in 174Hf together with a single SD band in 173Hf. These results indicate that the strongly deformed sequences of N ≈ 102 Hf isotopes behave differently than the TSD bands found in Lu nuclei near N = 92. The interpretation of these bands in terms of possible stable triaxial deformation is confronted with the experimental findings and UC predictions. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have performed three separate experiments at LBNL’s 88-Inch Cyclotron over a period of several years in which 235U (thick target) was Coulomb-excited. It involved stand-alone experiments with Gammasphere and with the 8PI Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with an 40Ar beam at 180 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]1/2, [624]7/2 and [622]5/2) strongly populated by E3 excitation. The CHICO data has been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many E1 and M1 matrix elements could be extracted from the γ-ray branching ratios. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Fragmentation reactions, typically performed at energies ∼E/A > 50 MeV, produce neutron-rich nuclei but leave little angular momentum in the residues. In this work we have examined the product distribution and angular momentum input for a 12C beam at 30 MeV/A on a thick (40 mg/cm2) target of 51V, testing the feasibility of in-beam gamma-ray spectroscopy study of target fragments at this lower energy. This technique allows the study of some neutron-rich nuclei to moderate spins, complementing the beam fragmentation studies. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

A gamma-ray energy tracking array (GRETA) is a new concept for the detection of gamma radiation. In such an array, the individual interactions of all the gamma rays are identified by their energies and positions. Then, using tracking algorithms based on the properties of gamma ray interactions, the scattering sequences are reconstructed, GRETA will give high peak efficiency, peak-to-background ratio, and position resolution. Recent research and development efforts have demonstrated that the construction of a gamma ray tracking array is feasible, and the construction of an array GRETINA, which covers 1/4 of 4π solid angle, is started. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have developed a new method to study the order-to-chaos transition in rotational nuclei. We measure the area of the valley in the narrow valley-ridge structure observed in γ-γ coincidence spectra from Yb nuclei. We relate this area to the ratio of the interaction potential between levels to the average level spacing. The measured ratios, 0.15 to 1.5, span the range from nearly ordered to nearly fully chaotic. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Multinucleon transfer reactions between a thin 100Mo target and a 136Xe beam at an energy of 700 MeV have been used to investigate the evolution of structure with increasing angular momentum in a range of nuclei with A∼100. The use of kinematically complete experiments coupled with isomer tagging allow the selection of specific exit channels. The evolution from quasi-vibrational states at low spins to quasi-rotational structures following the population of a low-Ω, ‘rotationally aligned’ h11/2 neutron configuration is demonstrated to be a standard feature of the region using the so-called E-Gamma Over Spin (E-GOS) empirical prescription. This treatment is extended to odd-A nuclei. [ABSTRACT FROM AUTHOR]

The excitation energy, spin and parity of the yrast superdeformed (SD) band in 152Dy have been established. The excitation energy of the lowest observed level in this band is found to be 10,644 keV with an assigned spin and parity of 24+. In addition, nine transitions of dipole character have been identified, which connect the excited superdeformed band 6 in 152Dy to the yrast SD band. The excitation energy of the lowest level in the excited SD band 6 is 14,239 keV. The spin and parity of this state has been determined to be either 29- or 31-. The measured properties of SD band 6 are consistent with an interpretation in terms of a rotational band built on an octupole vibration. A comparison with an RPA calculation by Nakatsukasa et al. suggests that the spin of the lowest SD band 6 level is 31-. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The structure of stable and neutron-rich nuclei with Z∼42 and N∼58 have been studied following binary heavy-ion reactions between a 136Xe beam and a thin, self-supporting 100Mo target. Discrete states at spins of 20h and above have been identified and these data allow both gamma-ray fold and binary-fragment particle angular distribiution analyses to be made. On the basis of these results, suggestions are made for future directions of this research extending to higher spin states in this region where more exotic nuclear shapes are predicted. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In a mixture of three Yb nuclei, we find the rotational damping widths vary from 180 keV at 1.1 MeV γ-ray energy to 290 keV at 1.5 MeV, and the average compound damping widths (or spreading widths) vary from 40 keV at 1.1 MeV γ-ray energy to 60 keV at 1.3 MeV. The simulations also suggest extensive motional narrowing. [ABSTRACT FROM AUTHOR]

We review the experimental data on binding-energy differences for nuclei along the N = Z line with emphasis on the odd-odd nuclei. Qualitative pair blocking arguments are used to discuss the effect of np pairing correlations. Calculations based on a single-j shell model support these general arguments that seem to rule out the formation of a condensate of isoscalar np pairs. [ABSTRACT FROM AUTHOR]

The excitation energy, spin and parity of the yrast superdeformed band 1 in [sup 152]Dy have been established. The evidence comes mainly from the measured properties of a 4011 keV single-step transition connecting the yrast superdeformed level fed by the 693 keV transition to the 27[sup -] yrast state. Four additional, weaker, linking γ rays have been placed as well. The excitation energy of the lowest superdeformed band 1 member is 10,644 keV and its spin and parity are determined to be 24[sup +]. A further nine transitions of dipole character have been identified, which connect the excited superdeformed band 6 in [sup 152]Dy to the yrast SD band 1. The excitation energy of the lowest level in the excited SD band 1 is 14,239 keV. The lowest state in band 6 has been determined to be of negative parity and odd spin (29[sup -] or 31[sup -]). The measured properties of band 6 are consistent with an interpretation in terms of an octupole vibrational band. A comparison with an RPA calculation by Nakatsukasa et al. suggests that the spin of the lowest SD band 6 level is 31[sup -]. [ABSTRACT FROM AUTHOR]

High-spin states in [sup 108]Cd were studied following the reaction [sup 64]Ni([sup 48]Ca,4n) at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. Two rotational bands have been observed at very high angular momentum. Measurements of fractional Doppler shifts yielded lower limits for the quadrupole moments and showed that the observed structures are at least as deformed as the superdeformed structures e.g. in the A ≈ 150 region, and possibly exceed a 2:1 axis ratio. The existence of very extended shapes has been predicted by cranked Strutinsky calculations, and recent projected shell model calculations suggest that the πi[sub 13/2] hyper-intruder orbital is occupied in these newly observed bands. [ABSTRACT FROM AUTHOR]

A particle plus triaxial rotor model was applied to odd-odd nuclei in the A ∼ 130 region in order to study the unique parity πh[sub 11/2] ⊗vh[sub 11/2] rotational bands. With maximum triaxiality assumed and the intermediate axis chosen as the quantization axis for the model calculations, the two lowest energy eigenstates of a given spin have chiral properties. The independence of the quantity S(I) on spin can be used as a new criterion for chirality. In addition, a diminishing staggering amplitude of S(I) with increasing spin implies triaxiality in neighboring odd-A nuclei. Chiral quartet bases were constructed specifically to examine electromagnetic properties for chiral structures. A set of selection rules unique to chirality was derived. Doublet bands built on the πg[sub 9/2] ⊗vh[sub 11/2] configuration have been discovered in odd-odd [sup 104]Rh using the [sup 96]Zr([sup 11]B, 3n) reaction. Based on the discussed criteria for chirality, it is concluded that the doublet bands observed in [sup 104]Rh exhibit characteristic chiral properties suggesting a new region of chirality around A ∼110. In addition, magnetic moment measurements have been performed to test the πh[sub 11/2] ⊗vh[sub 11/2] configuration in [sup 128]Cs and the πg[sub 9/2]⊗vh[sub 11/2] configuration in [sup 104]Rh. [ABSTRACT FROM AUTHOR]

High-spin states have been studied in [sup 72,73]Kr using [sup 40]Ca+[sup 40]Ca and [sup 36]Ar+[sup 40]Ca reactions at 160, 164 and 145 MeV respectively. The properties and configurations of the bands observed are interpreted with the aid of unpaired cranked Nilsson-Strutinsky/cranked relativistic mean-field calculations and paired total routhian surface and cranked relativistic Hartree-Bogoliubov calculations. In [sup 73]Kr the three previously known structures have been extended to a spin of ∼30h and a fourth structure, which is believed to be the signature partner to the g[sub 9/2] band, has been identified. The negative parity bands show evidence for an unusual type of band crossing. It is currently unclear whether this is a consequence of T=0 n-p pairing. At the highest spins the unpaired calculations can reproduce the observed data, suggesting that there is little evidence for pairing correlations in this spin regime. In [sup 72]Kr a new band has been identified that has the properties expected from the missing doubly aligned S-band configuration. The properties of this band can be reproduced by the unpaired CNS/CRMF calculations, again suggesting that the structure has little pairing. However, paired calculations appear to be necessary to reproduce the properties of the previously known structure in this nucleus. The [sup 72]Kr results are also compared with projected shell model calculations. [ABSTRACT FROM AUTHOR]

We have studied the continuous gamma radiation from reactions of [sup 48]Ca beams on targets of [sup 50]Ti, [sup 64]Ni, [sup 96]Zr, and [sup 124]Sn at very high angular momentum. In all but the heaviest target, the nuclear moments of inertia rise rapidly with increasing angular momentum and the data suggest that the gamma ray energies may reach a maximum value. Whether this arises from a gradual transition towards a highly deformed Jacobi-like shape, or from other effects, is unclear. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recent high-spin studies in the mass 60 region of highly deformed and superdeformed shapes are discussed. The experimental data are from reaction channel selected γ-spectroscopic measurements at Gammasphere. Points of special attention are rotational bands in nuclei below the Z=28 shell gap and measurements of transition quadrupole moments throughout the region. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]