Strength function for the giant isovector monopole resonance

Journal Article · Wed Feb 01 04:00:00 EST 1984 · Phys. Rev. C; (United States)

DOI:https://doi.org/10.1103/PhysRevC.29.425· OSTI ID:6580989

MacDonald, W M; Birse, M C

The theory of the strength function for giant resonances is extended to exhibit the explicit energy dependence of the width and shift functions for the giant isovector monopole. An integral sum rule on the width GAMMA/sub M/(E) relates its normalization to the second moment M/sub 2/ of the strength function and leads to a relation GAMMA/sub M/(E/sub M/)GAMMA/sub s//4 = M/sub 2/ between M/sub 2/ and the width at the maximum, which involves the width GAMMA/sub s/ of the distribution in energy of the spreading matrix elements. An estimate of GAMMA/sub M/(E/sub M/)approx. =8 MeV based on the absorptive part of the optical potential together with random-phase approximation calculations of M/sub 2/ leads to the result GAMMA/sub s//2approx. =2h..omega.., supporting the intermediate coupling model of Lane, Thomas, and Wigner. Using the sum rule expressions of Lane and Mekjian to evaluate the Coulomb matrix element M/sub A/M between an isobaric analog state and its corresponding isovector monopole, we test this strength function for the isovector monopole by calculating the spreading widths for the ground state analogs of nuclei from /sup 38/Cl to /sup 208/Pb. The good agreement with the systematic dependence upon mass number and isospin resolves the long-standing discrepancy between the estimate GAMMA/sub M/(E/sub M/)approx.8--10 MeV and the value GAMMA/sub M/(E/sub A/)< or =2 MeV needed to account for the spreading widths of the isobaric analog state.

• Research Organization: Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742
• OSTI ID: 6580989
• Journal Information: Phys. Rev. C; (United States), Journal Name: Phys. Rev. C; (United States) Vol. 29:2; ISSN PRVCA
• Country of Publication: United States
• Language: English

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