Spectroscopy of {sup 20}F levels
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
- Brookhaven National Laboratory, Upton, New York 11973 (United States)
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
From a study of the {sup 19}F({ital n},{gamma}) reaction with thermal neutrons incident on a Teflon target, 168 {gamma} rays have been detected and incorporated into a level scheme of {sup 20}F consisting of 35 previously known levels and a new one at 5939 keV. Two low-energy primary {ital E}1 transitions of energies 584 and 665 keV together account for more than half of the total capture cross section. They populate, respectively, states at 6018 and 5936 keV (both {ital J}{sup {pi}}=2{sup {minus}}). These states are also excited strongly in the {sup 19}F({ital d,p}) reaction. From each of these states, 17 {gamma} rays were observed to the lower-lying states. These {gamma} rays constitute the largest number of branches reported from any nuclear bound state. A weak (6{+-}1{mu}b){gamma} ray of energy 4630.6{+-}0.9 keV, placed as a transition between the neutron-capturing state (which is a 0{sup +} and 1{sup +} mixture) and the 1971-keV, (3{sup -}) state, might represent the first observation of a primary {ital M}2 transition in the ({ital n},{gamma}) reaction. The total thermal-neutron-capture cross section of {sup 19}F was measured as 9.51{+-}0.09 mb; and the neutron separation energy of {sup 20}F as 6601.35{+-}0.04 keV. Estimates of direct neutron capture have been made using physically realistic optical-model parameters. These model estimates are in reasonable agreement with the measured (partial) cross sections. While constructing the ({ital n},{gamma}) level scheme, the existing data on bound levels in {sup 20}F were critically evaluated. The lifetime values for many levels are poorly known. The lifetimes for 25 levels were measured by the Doppler-shift-attenuation method using the inverse reaction {sup 2}H({sup 19}F, {ital p}{gamma}) on implanted deuterium targets. The experimental level properties such as excitation energies, {ital J}{sup {pi}} assignments, branching ratios, and lifetimes are compared with the results from a large-basis shell-model calculation.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- DOE Contract Number:
- AC02-76CH00016; AC05-84OR21400; W-7405-ENG-36
- OSTI ID:
- 282824
- Journal Information:
- Physical Review, C, Vol. 53, Issue 2; Other Information: PBD: Feb 1996
- Country of Publication:
- United States
- Language:
- English
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