Structural Evolution in the Neutron Rich-Nucleus 14B

Date of Award

8-2014

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. Alan H. Wuosmaa

Second Advisor

Dr. Dean Halderson

Third Advisor

Dr. Paul V. Pancella

Fourth Advisor

Dr. William G. Lynch

Abstract

The effective single–particle energies (ESPEs) of shell–model orbitals play a decisive role in nuclear structure calculations. The ESPEs set the scale for excited states, and they help determine the strength of configuration mixing for multi-particle states. The ESPEs depend on the proton and neutron ratio, and it is interesting to determine how the values of these energies evolve as a function of N/Z, particularly at the limit of nuclear stability. The nucleus 14B, with neutron separation energy of 0.969Mev, is the lightest bound N=9 isotone. The single neutron outside the closed p–shell provides an excellent opportunity to explore the 1s1=2 and 0d5=2 neutron single-particle states to, and beyond the limit of stability. In this mass region, for large N/Z, the ordering of the 1s1=2 and 0d5=2 orbitals is inverted as compared to the situation near stability. This inversion is seen, for example, from the ground-state spin of 1/2+ for 15C as compared to 5/2+ for 17O, both of which contain a single valence neutron in the sd shell. The same inversion is expected in 14B. The evolution structure of 14B has been investigated using two single-nucleon-transfer reactions: neutron adding with 13B(d ,p)14B, and proton removal with 15C(d ,3He)14B. From the (d ,p) reaction, the angular-momentum and relative spectroscopic factors were deduced for the lowest four negative-parity states, namely (21, 11, 31, 41)-. The (d ,3He) results confirm the existence of the broad 2-2 excited state suggested in the literature.

Both the (d ,p) and (d ,3He) measurements were conducted using the HELIcal Orbit Spectrometer (HELIOS) at the ATLAS (Argonne Tandem Linac Accelerator System) facility at Argonne National Laboratory. HELIOS is a large solenoid spectrometer specially designed to study transfer and other reactions in inverse kinematics. HELIOS takes advantage of the uniform magnetic field produced by a superconductor solenoid to transport the light-charged particles emitted at the target in helical orbits trajectories back to the solenoid axis where they are detected in the array of position-sensitive silicon detectors. The heavy beam-like ions 14B (13B) from bound (unbound) states in 14B were detected in the recoil detector at forward angles. The radioactive 13B and 15C beams were produced in the "in-flight" facility at ATLAS.

Access Setting

Dissertation-Open Access

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