Search

The ATLAS facility is being augmented with two new separators in order to take full advantage of recent and future anticipated beam intensity upgrades to the accelerator. A novel concept is used for the Argonne Gas-Filled Analyzer (AGFA), which employs only two magnetic elements; a quadrupole singlet for vertical focusing and a multipole magnet that provides a dipole field for the separation and a quadrupole field for horizontal focusing of the reaction products. The design allows for placing Gammasphere or GRETINA at the target position. This arrangement enables studies of prompt gamma-ray emission from weakly populated trans-fermium nuclei and those near the doubly-magic N=Z=50 shell closures measured in coincidence with the recoils registered in the AGFA focal plane. The Argonne In-flight Radioactive Ion Separator (AIRIS) is a magnetic chicane that will be installed immediately downstream of the last ATLAS cryostat. It will be used to separate radioactive ion beams generated in flight by the primary beam at an upstream high-intensity production target. These beams will be further purified by a downstream RF sweeper and transported to a number of target stations including HELIOS, the Enge spectrograph, the FMA and Gammasphere.

We have studied the nucleus 14B using the 13B(d,p)14B and 15C(d,3He)14B reactions. The two reactions provide complementary information about the negative-parity 1s1/2 and 0d5/2 neutron single-particle states in 14B. The data from the (d,p) reaction give neutron-spectroscopic strengths for these levels, and the (d,3He) results confirm the existence of a broad 2- excited state suggested in the literature. Together these results provide estimates of the sd-shell neutron effective single-particle energies in 14B.

The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E∗ of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier.

Transfer and inelastic scattering reactions using light-ion beams and stable or long-lived targets have traditionally provided detailed information on the structure of nuclei near the line of beta stability. Such studies can now be extended to nuclei away from the line of β-stability as radioactive beams are becoming available at a number of facilities around the world, including the CARIBU facility at Argonne. These measurements must, however, be carried out in inverse kinematics, resulting in a loss of the effective experimental resolution when conventional detection schemes are employed. The HELIOS spectrometer is based on a new concept, that is especially well suited for such studies by reducing the resolution problem, providing simple particle identification, and giving high detection efficiency with moderate Si detector area. In this talk, the HELIOS concept and results from the first series of experiments will be presented.

We have for the first time studied the fusion-fission excitation functions for the systems 14,15C + 232Th at energies in the vicinity of the Coulomb barrier. At energies below the barrier, the fusion cross section of the halo nucleus 15C showed an enhancement by a factor of 2-5, while the fusion cross section for 14C shows a similar trend to that of 12,13C.