Interference effects among J = 3/2⁺ resonances in ¹⁹Ne system & Searching for resonances in the unbound ⁶Be nucleus

Author

Kyung Yuk Chae, University of Tennessee - Knoxville

Date of Award

12-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Mike W. Gudiry

Committee Members

Michael S. Smith, Pengcheng Dai, Chia C. Shih, Lawrence W. Townsend

Abstract

The ¹⁸F(p,α)¹⁵O reaction plays a crucial role in understanding γ-ray emission from novae. Because of the importance of understanding the ¹⁸F + p reactions, a number of studies of the A=19 isobars have been made using stable and exotic beams. The interference effects among J ^π = 3/2⁺ resonances in the ¹⁸F + p system, however, have never been measured, but they can change the S-factor by a factor of 20 at nova energies. R-matrix calculations indicate that the cross sections above the Ec.m. = 665 keV resonance are sensitive to the interference between the E_c.m. = 8, 38, and 665 keV resonances. In order to study the interference effects, an excitation function for the ¹H(¹⁸F,α)¹⁵O reaction has been measured in the energy range of E_c.m. = 663-877 keV using radioactive ¹⁸F beams at the Holifield Radioactive Ion Beam Facility (HRIBF). By measuring the ¹⁸F(p,α)¹⁵O cross section off resonance and comparing the cross section with theoretical calculations, we provide the first experimental constraints on the interference of 3/2⁺ resonances.

The ³He(³He,2p)⁴He reaction is responsible for destruction of ³He in stars, and strongly affects the calculated neutrino luminosity from the sun. Previous measure- ments demonstrated a rise in the ³He(³He,2p)⁴He S-factor at low energies, which could be due to a low energy resonance in the ³He + ³He (⁶Be) system, or be due to an electron screening effect. In the ⁶Be nucleus, however, no excited states have been observed above the first 2⁺ state at E_x = 1.67 MeV up to 23 MeV. But there is considerable evidence to support the presence of unknown excited states in ⁶Be. First of all, in the mirror nucleus ⁶He two excited states have been established below the t + t threshold at E_x = 12.3 MeV. Secondly, a recent measurement at Notre Dame University found tentative evidence for a ⁶Be level at 9.6 MeV. A search for the missing ⁶Be levels was performed by studying the d(⁷Be,t)⁶Be reaction with the radioactive ⁷Be beam at Oak Ridge National Laboratory HRIBF. No excited states in ⁶Be were found; however, we could set the upper limits on the reaction cross section.

Recommended Citation

Chae, Kyung Yuk, "Interference effects among J = 3/2⁺ resonances in ¹⁹Ne system & Searching for resonances in the unbound ⁶Be nucleus. " PhD diss., University of Tennessee, 2006.
https://trace.tennessee.edu/utk_graddiss/1920