Giant dipole resonance parameters of ground-state photoabsorption: Experimental values with uncertainties

Abstract

Updated values and corresponding uncertainties of Isovector Giant Dipole Resonance (GDR) parameters which are obtained by the least-squares fitting of theoretical photoabsorption cross sections to experimental data are presented. The theoretical photoabsorption cross sections are taken as a sum of the components corresponding to the excitation of the GDR and quasideuteron photodisintegration. The current compilation is an extension and improvement of the earlier compilations of Lorentzian parameters for ground-state photoneutron and photoabsorption cross sections and covers experimental data made available up• GDR parameters were added for 271 datasets, including 24 new isotopes that were absent previously, i.e.• The GDR values for 40 datasets were corrected by revising the energy interval of fitting and modifying the uncertainty estimates.• The GDR parameters from 8 datasets, namely 15 N, 19 F, 26 Mg, 51 V, 59 Co, 127 I, 141 Pr, 197 Au were excluded due to the poor quality of the fit to experimental data.

Reference database for photon strength functions

“…A compilation of such data can be found in Ref. [106]. However, when no data exists, systematics of the GDR parameters is used.…”

“…The prescription for calculating the high-energy quasi-deuteron contribution, i.e., the photoabsorption cross section leading to the production of a neutron -proton pair can be found in Ref. [106].…”

“…Lorentz and Breit-Wigner shapes of the photoabsorption cross sections can be derived from different theoretical approaches [7,135]. The Lorentzian shape can be transformed to a Breit-Wigner form but with a shape width that depends on the photon energy, resonance energy and width of the Lorentzian [106]. A Lorentz shape is more suitable for fitting the photonuclear data because the standard Breit-Wigner expression is obtained without taking account of time reversal invariance and is adequate for describing a strong resonance state when the width is small with respect to the resonance energy [136].…”

Developing reliable reaction gamma-ray data

“…The data are being assessed to ensure compatibility near the neutron thresholds, as well as to resolve discrepancies observed between different types of measurements and extraction methods, such as (γ,γ) and data obtained with the Oslo method. Global models (Lorentzian-type SLO/SMLO [4], QRPA [6]) have also been developed in the entire energy range. Figure 2 shows such an example where photon strength data from different sources are compared.…”

“…The new compilation is an extension and improvement of earlier compilations and also includes recommendations [4]. …”