Description of the simplest photonuclear reactions within the particle-hole dispersive optical model

Abstract

A recently developed particle-hole dispersive optical model is applied to describe the cross sections of photoabsorption, direct + semidirect photoneutron and inverse reactions accompanied by excitation of the isovector giant dipole and quadrupole resonances in medium-heavy-mass spherical nuclei. The model is an extension of the standard and nonstandard versions of the continuum-random-phase approximation by including the spreading effect in a phenomenological way. It contains the following ingredients: the Landau-Migdal particle-hole interaction and a phenomenological mean field consistent with this interaction, isovector velocity-dependent forces taken in the simplest form and the imaginary part of an effective single-particle optical-model potential determining the corresponding dispersive part. All the model parameters are taken from the other data and from the description of photoabsorption, while the direct + semidirect photoneutron and inverse reactions are described without the use of specific adjustable parameters. Calculation results obtained for a few neutron-closed-shell nuclei are compared with the corresponding experimental data.

Properties of high-energy isoscalar monopole excitations in medium-heavy mass spherical nuclei

“…The parameterization of the energy dependence of the imaginary part of the effective optical-model potential W (ω), is given in Refs. [7,8,12]. The intensity parameter α = 0.07 MeV −1 is found from the description within the model of the observed ISGMR (FWHM) exp = 2.88 MeV [15].…”

“…The results of R(r = r , ω) are compared with the quasi-classical reduced double transition densities R qc,i (r = r ) obtained according to Eqs. (9)- (12). The energy dependence of the reduced averaged double transition density appears within the PHDOM due to taking into account Landau damping and spreading effect.…”

“…In accordance with Refs. [7,8,12], the expression for the "free" p-h propagator A β 0 (r, r , ω) can be presented in the following form (the isobaric index β is omitted for brevity):…”

Damping of simple modes of high-energy nuclear excitations: dispersive optical models and their implementations

“…(3): P(ω) = (2/π)W(ω) ln(ω/B). In implementations of the PHDOM [7,8], for W(ω) we use the more sophisticated parameterization, which contains also an adjustable "gap" parameter ∆. (It is supposed, that the spreading effect appears at a finite excitation energy ω min = ∆).…”

“…The first intensive implementation of the PHDOM was concerned with the description of simplest photonuclear reactions (photo-absorption, DSD (γ, n) and inverse reactions) accompanied by excitation of the isovector giant dipole and quadrupole resonances (IVGDR and IVGQR, respectively) [7]. In such a case, the external fields are well-known and PHDOM equations can be directly exploited.…”