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Evaporation residue cross sections for 124,126,127, 128Sn+64Ni and 132Sn+Ni have been measured to study the effects of neutron excess in neutron-rich radioactive nuclei on the fusion probability. A comparison of the reduced evaporation residue cross sections for 126Sn + 64Ni and 132Sn + 58Ni, which make the same compound nucleus, shows that the fusion probability is indistinguishable for reactions involving the same atomic elements, Sn and Ni, but different isotope combinations. For the reactions with MNi, the fusion probability does not decrease with increasing neutron excess in Sn, contrary to the result of the stable beam Sn + Zr measurement. [ABSTRACT FROM AUTHOR]

The β-decay properties of neutron-rich fission fragments of Cu, Zn, and Ga isotopes were studied at the Holifield Radioactive Ion Beam Facility. Beams of 75-79Cu, 79-81Zn, and 83-85Ga were formed and delivered to two new end-stations at the facility. The Low-energy Radioactive Ion Beam Spectroscopy Station is a traditional on-line low energy (200 keV) beam line with 4 clover Ge detectors, two half-cylindrical plastic β-detectors, and a moving tape collector. In addition, many of the beams were accelerated to above 2 MeV/u and delivered to a micro-channel plate and transmission ion chamber located just in front of the same detector setup. In both cases, fine adjustment of an isobar separator was used to enhance the isotope of interest. Excited levels in the daughters and β-delayed neutron branching ratios were measured and used to confirm isotope identification. The decays from 79Cu and 85Ga were observed for the first time as was the 84Ge 2+1 level populated by β and βn decay channels. [ABSTRACT FROM AUTHOR]

The properties of β-γ and β-delayed neutron emission from 76-79Cu and 83-85Ga were measured at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. Selected results on the decay properties of copper isotopes are briefly presented and discussed. [ABSTRACT FROM AUTHOR]

Single-neutron transfer reactions have been measured on two N = 50 isotones at the Holifield Radioactive Ion Beam Facility (HRIBF). The single-particle-like states of 83Ge and 85Se have been populated using radioactive ion beams of 82Ge and 84Se and the ( d, p) reaction in inverse kinematics. The properties of the lowest-lying states --including excitation energies, orbital angular momenta, and spectroscopic factors-- have been determined for these N = 51 nuclei. [ABSTRACT FROM AUTHOR]

We describe an experiment optimized to determine the transition probabilities for excitation of the first excited 2+ state in 132Sn. The large excitation energy (4.04MeV) and consequent small excitation cross-section, together with the modest beam intensity available makes this a challenging experiment. The preliminary result is B( E2;0+ → 2+) = 0.11±0.03 e2 b2. The high efficiency and generalized nature of the setup enabled us to also measure the first 2+ state in the two-neutron nucleus 134Sn. We have determined a value of B( E2;0+ → 2+) = 0.029±0.005 e2 b2 which shows no sign of the asymmetry with respect to the N = 82 shell closure exhibited by the Te isotopes. [ABSTRACT FROM AUTHOR]

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of measurements around the 132Sn region, including Coulomb excitation and single-nucleon transfer. The B( E2;0+ → 2+) values for first 2+ excited states of even-even neutron-rich 132-136Te and 126-130Sn have been measured by Coulomb excitation in inverse kinematics. Neutron transfer onto a 134Te beam from 9Be and 13C targets, to populate single-particle states in 135Te, has also been studied. Gamma rays from the 13C(134Te, 12C) reaction were used to identify the ν i13/2 state in 135Te, at an energy of 2109 keV. These and other results, and plans for future experiments with these neutron-rich beams, are presented. [ABSTRACT FROM AUTHOR]

132Te has been studied through β- decay of 132Sb radioactive beam at HRIBF leading to a significantly revised level scheme. A number of newly identified, likely 2+ states allows for a test of recent quasiparticle random phase approximation calculations with a density-dependent pairing force. In addition, the removal of a previously proposed 3- state allows for a simple shell model interpretation of the low-lying negative-parity states. [ABSTRACT FROM AUTHOR]

Evaporation residue cross-sections measured with short-lived 132Sn on 64Ni at energies near and below the Coulomb barrier were found to be enhanced as compared to those measured with stable Sn isotopes on 64Ni. Subsequent measurements of fission following fusion of 132Sn with 64Ni and extending the measurement of evaporation residues to higher energies were carried out. [ABSTRACT FROM AUTHOR]

The excited states of odd-odd 82As are studied in the β decay of 82Ge. An isotopically pure beam of 83Ga was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The atoms of 82Ge are created after β-delayed neutron emission in the decay of 83Ga. The number of 82Ge atoms is found by normalization to the 1348-keV γ ray. Detailed analysis of the decay scheme is compared with shell-model calculations with several commonly used fpg shell interactions. [ABSTRACT FROM AUTHOR]

The β-decay properties of neutron-rich 87As produced in the proton-induced fission of 238U were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The low-energy excited states in N = 53 87Se and N = 52 86Se were identified through β-γ and β-delayed neutron-γ decay of 87As, respectively. The experimental systematics of low-energy levels of N = 53 isotones, Z = 34 87Se, and Z = 32 85Ge, and along with an analysis of shell-model calculations, allow us to discuss the main features of excited states expected for the next N = 53 isotone, 83Zn. [ABSTRACT FROM AUTHOR]

The β-decay properties of neutron-rich 85Ga produced in proton-induced fission of 238U were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Data consisted of β - γ and β - γ - γ coincidences were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station after high-resolution on-line mass separation. For the first time, the excited states in the N = 53 isotone 85Ge were established from β-delayed γ decay of 85Ga. The level scheme of the N = 52 isotone 84Ge was improved and includes now 0+, 2+, (2)+, 4+, and (0)+ states populated in the β-delayed-neutron-γ decay of 85Ga. Advanced shell-model calculations were used to analyze experimental data on 85Ge and 84Ge. [ABSTRACT FROM AUTHOR]

Short-lived neutron-rich nuclei including 93Br, 93Kr, and 94Kr were produced in proton-induced fission of 238U at the Holifield Radioactive Ion Beam Facility in Oak Ridge. Their ß decay was studied by means of a high-resolution online mass separator and β-γ spectroscopy methods. The half-life of T1/2 = 152(8) ms and β-delayed branching ratio of Pn = 53' % measured for 93Br differs from the previously reported values of T1/2 = 102(10) ms and Pn = 68(7)%. At the same time the half-life of 94Kr Tlß = 227( 14) ms and both the half-life of T\ß = 1.298(54) s and β-delayed branching ratio of Pn = 1.9-0.2+0.6% of 93Kr are in very good agreement with literature values. The decay properties of 93Br include previously unreported γ transitions following β-delayed neutron emission. [ABSTRACT FROM AUTHOR]

The fusion cross sections of radioactive 134Te + 40Ca were measured at energies above and below the Coulomb barrier. The evaporation residues produced in the reaction were detected in a zero-degree ionization chamber providing high efficiency for inverse kinematics. Both coupled-channel calculations and comparison with similar Sn + Ca systems indicate an increased sub-barrier fusion probability that is correlated with the presence of positive Q-value neutron transfer channels. In comparison, the measured fusion excitation functions of 130Te + 58,64Ni, which have positive Q-value neutron transfer channels, were accurately reproduced by coupled-channel calculations including only inelastic excitations. The results demonstrate that the coupling of transfer channels can lead to enhanced sub-barrier fusion but this is not directly correlated with positive Q-value neutron transfer channels in all cases. [ABSTRACT FROM AUTHOR]

The β-decay properties of several neutron-rich germanium and arsenic isotopes were measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The measurements of almost-pure radioactive sources were enabled by the combination of ion-source chemistry and two-stage mass separation. The half-life of 86Ge (226±21 ms) was determined for the first time, while those of 84,85Ge and 84-87As were remeasured. The results are compared to theoretical predictions of the gross theory of β decay, the finite-range droplet model, and the new calculations using the energy density functional DF3a with continuum quasiparticle random-phase approximation (CQRPA). We confirm the robustness and good predictive power of the latter model for nuclei near closed shells. These DF3a+CQRPA calculations were used recently to analyze r-process isobaric abundances. [ABSTRACT FROM AUTHOR]

Background: The g factors and lifetimes of the 2+1 states in the stable, proton-rich Sn isotopes have been measured, but there is scant information on neutron-rich Sn isotopes. Purpose: Measurement of the g factor and the lifetime of the 2\ state at 1.141 MeV in neutron-rich I26Sn (Γ1/2 = 2.3 χ 105y). Purpose: Measurement of the g factor and the lifetime of the 2+1 state at 1.141 MeV in neutron-rich 126Sn (T1/2 = 2.3 χ 105y). Method: Coulomb excitation in inverse kinematics together with the transient field and the Doppler shift attenuation techniques were applied to a radioactive beam of 126Sn at the Holifield Radioactive Ion Beam Facility. Results: g(2+1) = -0.25(21) and r(2+1) = 1.5(2) ps were obtained. Conclusions: The data are compared to large-scale shell-model and quasiparticle random-phase calculations. Neutrons in the h 11/2 and d3/2 Orbitals play an important role in the structure of the 2+1 state of 126Sn. Challenges, limitations, and implications for such experiments at future rare isotope beam facilities are discussed. [ABSTRACT FROM AUTHOR]

The β-decay properties of neutron-rich Cu isotopes produced in proton-induced fission of 238U were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The data were collected using high-resolution online mass separation, reacceleration, and digital β-γ spectroscopy methods. An improved decay scheme of N = 49 78Cu and the first observation of N = 50 79Cu β-delayed neutron decay followed by a gamma transition are reported. Spin and parity (5-) are deduced for 78gsCu. The β-delayed neutron branching ratios (Pβn) for the 77Cu and 79Cu precursors are analyzed with the help of nuclear structure models. [ABSTRACT FROM AUTHOR]

Time delays in fission induced by bombardment of Mo with 170- and 180-MeV 32S, 225- and 240-MeV 48Ti, and 300-MeV 58Ni have been measured by observation of crystal blocking of fission fragments. In contrast to earlier measurements with a W target, the results are consistent with fission of a compound nucleus in competition with mainly neutron emission. Most of the fissions happen on a time scale much shorter than attoseconds but there is a significant component of fission with much longer lifetimes. The measurements are reproduced with a standard statistical model, including a Kramers correction to fission widths from the viscosity of hot nuclear matter. These new results support the interpretation of our earlier measurements with a W target, which indicate that there is a transition in heavy-ion-induced fission at large atomic number and mass, from multichance fission in the standard Bohr-Wheeler picture to fission without formation of a compound nucleus. The process is slowed down by nuclear viscosity, with measured delays of order attoseconds. [ABSTRACT FROM AUTHOR]

The 2+2 state in 132Te is identified as the one-phonon mixed-symmetry state in a projectile Coulomb excitation experiment presenting a firm example of a mixed-symmetry state in unstable, neutron-rich nuclei. The results of shell-model calculations based on the low-momentum interaction VlOW_k are in good agreement with experiment demonstrating the ability of the effective shell-model interaction to produce states of mixed-symmetry character. [ABSTRACT FROM AUTHOR]

High-precision measurements of (01 ||M/(Е2)||2) matrix elements from the Coulomb excitation of 124,126,128Sn on a 12C target are presented. The extracted B(E2) values decrease monotonically from the neutron midshell toward the 132Sn double-shell closure, despite a near constancy in the first 2+ level energy. Furthermore, Coulomb excitation of l24,126,128Sn on an enriched 50Ti target, combined with the results from the l2C target, provide a measure of the static quadrupole moments, Q(21+) (expected to be zero for a spherical shape). These new results confirm that the unstable neutron-rich 126,128Sn isotopes have deformations consistent with zero. The present study marks the first report on measured 21+ static quadrupole moments for unstable closed-shell nuclei. [ABSTRACT FROM AUTHOR]

The β-decay properties of the very neutron-rich nucleus 85Ge, produced in the proton-induced fission of 238U, were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The level scheme of 8533As52 populated in 85Ge βγ decay was reconstructed and compared to shell-model calculations. The investigation of the systematics of low-energy levels in N = 52 isotones together with shell-model analysis allowed us to provide an estimate of the low-energy structure of the more exotic N = 52 isotone 81Cu. [ABSTRACT FROM AUTHOR]

The β-decay properties of the very neutron-rich 84Ge nucleus were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Several new γ-transitions and levels were added to its decay scheme and the order of the two lowest-lying levels in the daughter 84As was corrected. For the first time γ radiation following β-delayed neutron emission was observed. The shell-model calculations and apparent β transition intensities were used to guide the spin assignment to the 84As levels, in particular for the low-energy part of the level scheme. The new spin-parity (2-) proposed for the ground state of 84As is supported also by the systematics of N=51 isotones. [ABSTRACT FROM AUTHOR]