A superconducting-solenoid isotope spectrometer for production of neutron-rich nuclei ((136)Xe + (nat)C, E/A = 30 MeV/u).

Abstract

This dissertation in experimental nuclear physics describes the production of exotic, neutron-rich isotopes towards to the limits of particle stability---the neutron-dripline---in the region of the periodic table from neon to zinc (10 &le; <italic>Z</italic> &le; 30). Isotopes up to and beyond the most neutron-rich known at the time were produced (e.g. C8029u, N7628i, M6827g and C6626r ). The reaction studied was a mass-asymmetric collision: <super>136</super>Xe<super> +24</super> on a thick (114 mg/cm<super>2</super>) <italic><super>nat</super></italic>C target at an energy of E/A = 30 MeV/u, conducted at the National Superconducting Cyclotron Laboratory (NSCL) in E. Lansing, MI, USA. A novel superconducting-solenoid spectrometer, BigSol Isotope Spectrometer, was built to collect, separate and identify the neutron-rich isotopes. This device is based on the University of Michigan's seven-Tesla superconducting magnet, BigSol. The device features a large-bore (40 cm), long time-of-flight path length (6.31 m), and position-sensitive detectors at the entrance and focal-plane. Reaction-product fragments were collected over an angular range from 0.7&deg; &le; theta<italic>_lab</italic> &le; 6&deg; with respect to the primary-beam direction. Particle-by-particle identification of isotopes was achieved through software limitation of magnetic dispersion (Delta(<italic>B</italic>rho)/<italic>B</italic>rho &ap; 1.6%) of the fragments analyzed, together with high-resolution silicon focal-plane detectors (Delta<italic>E</italic>/<italic>E</italic> < 10<super>-3 </super>), and by time-of-flight measurements taken between the entrance parallel-plate gas avalanche counter (2D-PPAC) and a silicon focal-plane Delta<italic> E</italic> detector. Isotopic separation was achieved for some 200 distinct isotopes collected at magnetic rigidities of <italic>B</italic>rho = 1.36 and 1.76 T-m, despite the large distribution of the isotopes' ionic charge states. Novel data reduction techniques which avoid placing any restrictive cuts whatsoever on the data were developed. Solenoid-specific methods of achieving reliable isotopic identifications using calibration beams of isotopes which were mass-to-charge analogs of the cyclotron's primary beam were developed. This device and type of reaction provide novel means for mapping the region of the table of isotopes toward the neutron dripline, beyond the current experimental limit at neon (<italic>Z</italic> = 10), and for producing new radioactive nuclear beams (RNBs) for secondary experiments. This would provides stringent tests of nuclear mass-model predictions which extrapolate from knowledge derived mainly from stable isotopes. In addition one can anticipate the appearance of new magic-number shell closings, shell quenchings, new regions of nuclear deformity and isomerism, diffuse and extended neutron 'halos' and other exotic structures in the vicinity of the neutron dripline. This information is important for understanding the astrophysical 'r-process' of nucleosynthesis of the heavy elements in supernovae.