Dipole absorption by many-particle many-hole states: A study in the nuclei oxygen-16 and calcium-40.

Format:

Book

Thesis/Dissertation

Author/Creator:

Brown, Keith David.

Contributor:

University of Pennsylvania.

Language:

English

Subjects (All):

Nuclear physics.

0610.

Local Subjects:

0610.

Physical Description:

139 pages

Contained In:

Dissertation Abstracts International 51-08B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

A search has been conducted for the giant E1 resonances (GDR's) built on the prolate deformed, four-particle four-hole first excited states of $\sp{16}$O ($E\sb{x}$ = 6.05 MeV, $J\sp{\pi}$ = 0$\sp{+}$) and $\sp{40}$Ca ($E\sb{x}=3.35$ MeV, $J\sp\pi=0\sp+$) in order to study the dependence of the properties of excited state GDR's on the structure of the underlying states. To examine the $\sp{16}$O(0$\sbsp{2}{+}$) GDR, proton capture on $\sp{15}$N was measured in the energy range from $E\sb{p}$ = 10.0 to 22.0 MeV, and $\sp3$He capture on $\sp{13}$C in the energy range from $E\sb{\rm 3\sb{He}}$ = 3.5 to 24.0 MeV. The $\sp{40}$Ca(0$\sbsp{2}{+}$) GDR was examined using proton capture on $\sp{39}$K in the energy range from $E\sb{p}$ = 7.2 to 19.2 MeV. All these experiments used large solid angle electron detection systems to identify $\gamma$ rays from capture to the first excited states by coincident observation of an electron or positron from the decay of that state.

A pronounced concentration of dipole strength is observed in the $\sp{15}$N($p$,$\gamma\sb1$)$\sp{16}$0 reaction at excitation energies between 23 and 27 MeV which is interpreted as the giant isovector E1 responance built on the $\sp{16}$O(0$\sbsp{2}{+}$) state. Significant capture strength is observed in the $\sp{13}$C($\sp3$He,$\gamma\sb1$)$\sp{16}$O reaction only for energies below 27 MeV of excitation. In the $\sp{39}$K($p$,$\gamma\sb1$)$\sp{40}$Ca reaction, there is a concentration of capture cross section between $E\sb{x}$ = 18 and 23 MeV, which is interpreted as the giant isovector E1 resonance built on the $\sp{40}$Ca(0$\sbsp{2}{+}$) state.

A similar coincidence technique has been used to measure the proton spectroscopic factor of the $\sp{40}$Ca(0$\sbsp{2}{+}$) state. The value of $S\sb{p}$ is found to be 0.12 $\pm$ 0.03. The integrated strengths of both the $\sp{15}$N($p$,$\gamma\sb1$)$\sp{40}$Ca and $\sp{39}$K($p$,$\gamma$)$\sp{40}$Ca reactions are larger than would be predicted by proportionality to the respective spectroscopic factors, suggesting that there are contributions to the cross sections from mechanisms other than direct-semidirect capture. The $\gamma$-ray energy for both first excited GDR's is lower than that for the respective ground state GDR's, in contradiction to the Brink hypothesis.

Notes:

Source: Dissertation Abstracts International, Volume: 51-08, Section: B, page: 3906.

Supervisor: D. P. Balamuth.

Thesis (Ph.D.)--University of Pennsylvania, 1990.

Local Notes:

School code: 0175.

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Restricted for use by site license.