The first excited states of 9Be and 9B

Abstract

It is found here that the 1/2+ first excited state of 9Be is a virtual state with the energy of -23.5 KeV. The line shape for the excitation of the state is approximated with a simple analytic form based on the effective range expansion. The partner in 9B of this state is found to be a resonance with a maximum in the peak at about 1.1 MeV, FWHM of 1.5 MeV, and complex energy of 0.6-i0.75 MeV. The line shape for its excitation is calculated in terms of the p-8Be phase shift. The phase shifts are obtained from N-8Be effective potentials deduced from the data on on the photodisintegration of 9Be. A possibility for direct extraction of the energy of the resonant state from experimental data is also discussed, and an expression for a residue at a virtual state pole in terms of a quadrature taken over the virtual state eigenfunction is given.

Comments: 13 pages, Latex, 2 Postscript figures, to appear in Eur. Phys. J. A, a possibility to reconstruct the resonant pole position directly from experimental data is discussed in the present version in addition