Proton-transfer Study of Unbound ^19Ne States via ^2H(^18F,?+^15O)n REACTION
The nuclear structure of ^19Ne near the proton threshold is of interest for understanding the rates of proton-induced reactions on ^18F in novae. Analogues for several states in the mirror nucleus ^19F have not yet been identified in ^19Ne, indicating the level structure of ^19Ne in this region is incomplete. The proton-transfer reaction ^18F(d,n)^19Ne and neutron-transfer reaction ^18F(d,p)^19F have been measured simultaneously at Ec.m. = 14.9 MeV. The experiments were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory (ORNL) by bombarding a 720-µg/cm^2 CD2 target with a radioactive ^18F beam. The ^19Ne ions of interest are highly excited and promptly decay by breakup into ? and ^15O particles. The same holds true for states in ^19F which decay into ? and ^15N particles. These charged particles were detected in coincidence in position-sensitive E-^”E silicon telescopes. Particle identification, coincidence, and Q-value requirements enable us to distinguish the reaction of interest from other reactions. The reconstruction of relative energy of the detected particles reveals the excited states of ^19Ne and ^19F which are populated.
We have observed fifteen ^19Ne levels from the ^18F(d,n)^19Ne measurement with five levels below the proton threshold. Eighteen ^19F levels have been observed with the ^18F(d,p)^19F measurement. Angular distributions were extracted for all the levels observed in both nuclei and converted to differential cross sections using all necessary normalizing parameters. However, Distorted Wave Born Approximation (DWBA) calculations of the differential cross section were only done for levels with enough statistics to allow a meaningful comparison to the calculation. The spectroscopic factors determined from this analysis for these levels are reported.
The R-matrix analysis of the ^18F(p,?)^15O reaction, taking into the account new information from this experiment as well as other recent measurements indicate that the astrophysical S-factoris considerably less than than previously thought by about a factor of 2 - 5 within the temperature range of typical nova. The astrophysical S-factor was numerically integrated to produce an improved ^18F(p,?)^15O reaction rate. The uncertainty on the ^18F(p,?)^15O reaction rate due to interference between the 3/2^+ resonances is found to have been reduced when compared to the most recent work of Chae et al.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:proton transfer reaction width rate unbound levels around threshold in 19ne astrophysical s factor
Date of Publication:04/23/2009