E1 excitations in A = 15 nuclei

Journal Article · Sat Nov 01 04:00:00 EST 1975 · Phys. Rev., C, v. 12, no. 5, pp. 1410-1422

OSTI ID:4122917

Harakeh, M H; Paul, P; Kuan, H M; Warburton, E K

The $sup 14$C(p, )$sup 15$N reaction was studied from E/sub p/ = 2.8 to 30 MeV corresponding to E/sub x/ = 13 to 38 MeV in $sup 15$N covering the region of the lowest T = 3/2 states as well as the giant dipole resonance (GDR). The $sup 14$N(p, $gamma$$)$$sup 15$O reaction measurements were extended for excitation regions from E/sub x/ = 24 to 33.5 MeV, thus covering the analogous regions in $sup 15$O and $sup 15$N. Angular distributions obtained in the first reaction at the resonance energies of E/sub p/ = 4.83, 5.62, 6.65, 6.925, 10.0, 11.0, 12.35, 13.6, and 16.4 MeV indicated large negative a$sub 2$ coefficients in all cases. The new narrow (GAMMA/sub c.m./) = 90 keV) resonance at 6.925 MeV has J/sup $pi$/ = 3/2$sup +$ and T = 1/2. A careful comparison of the $sup 15$N($gamma$, p$sub 0$$)$$sup 14$C and $sup 15$O($gamma$, p$sub 0$$)$$sup 14$N reactions is used to extract the T = 3/2 and 1/2 components of the GDR in A = 15. Most of the T = 3/2 E1 strength is located near E/sub x/ = 26 MeV. A microscopic calculation of J/ sup $pi$/ < or = 5/2$sup -$ states with T = 1/2 and 3/2 in a 2h-1p and 1h basis of good isospin gives good agreement with the observed depleted B(E1) values from the lowest T = 3/2 states and reproduces the location of the collective T = 3/2 E1 states near 26 MeV. It also describes well the distribution of T = 1/2 collective E1 strength. Using this agreement with the theory, which contains no adjusted parameters an effective symmetry potential of U = 28 MeV is extracted from the isospin energy splitting. This value is smaller than the typical 60 MeV found in heavier nuclei but agrees with a recent model-independent limit and with other cases of absolute value T/sub z/ vertical-bar = 1/2 nuclei. (AIP)

• Research Organization: Physics Department, State University of New York, Stony Brook, New York 11794
• NSA Number: NSA-33-010680
• OSTI ID: 4122917
• Journal Information: Phys. Rev., C, v. 12, no. 5, pp. 1410-1422, Journal Name: Phys. Rev., C, v. 12, no. 5, pp. 1410-1422; ISSN PRVCA
• Country of Publication: United States
• Language: English

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