PARTICLE-HOLE OPTICAL MODEL FOR STRENGTH FUNCTIONS OF HIGH-ENERGY GIANT RESONANCES

M.H. Urin1
1 Moscow Engineering Physics Institute (State University), Moscow, Russia
E-mail: urin@theor.mephi.ru

An attempt to formulate an optical model for phenomenological description of the spreading of the particle-hole (p–h) nuclear excitations at relatively high energies is undertaken. A Bethe–Salpeter-type equation for the p–h Green function in coordinate space is used as a starting point. The equation contains an additional p–h interaction (a specific polarization operator), which describes (p–h) scattering via virtual excitation of many-quasiparticle configurations. After energy averaging this short-range interaction acquires energy-dependent imaginary and real parts. The latter can be expressed in terms of the former via the corresponding dispersive relationship. The energy dependence of the intensity of the imaginary part of the interaction is parametrized in the same form, as it is used for the imaginary part of the effective optical-model potential within the continuum-RPA-based semi-microscopic approach to description of giant-resonance damping [1]. Within this approach the spreading effect is taken into account in the pole approximation (i. e. at the giant-resonance energy) by the substitution  in the continuum-RPA equations. Here,  is the excitation energy, and  determines the radial- and energy-dependent imaginary part of the above-mentioned potential. This imaginary part generates the respective real part via a proper dispersive relationship [2]. After an appropriate choice of the corresponding imaginary parts both approaches lead to similar results for the strength function of a giant resonance at its maximum. A difference might be noticeable at giant-resonance "tails". The last remarks are illustrated by some examples. A comparison of the single-quasiparticle and particle-hole optical models is also given.
This work is partially supported by the RFBR (grant no. 09-02-00926-a).

	1. M.H.Urin // Nucl. Phys. A. 2008. V.811. P.107. 
	2. B.A.Tulupov, M.G.Urin // Phys. At. Nucl. 2009. V.72. P.737.