γ strength function and level density of Pb208 from forward-angle proton scattering at 295 MeV

Abstract

Background: Gamma strength functions (GSFs) and level densities (LDs) are essential ingredients of statistical nuclear reaction theory with many applications in astrophysics, reactor design, and waste transmutation.Purpose: The aim of the present work is a test of systematic parametrizations of the GSF recommended by the RIPL-3 data base for the case of 208 Pb. The upward GSF and LD in 208 Pb are compared to γ decay data from an Oslo-type experiment to examine the validity of the Brink-Axel (BA) hypothesis.Methods: The E1 and M1 parts of the total GSF are determined from high-resolution forward angle inelastic proton scattering data taken at 295 MeV at RCNP, Osaka, Japan. The total LD in 208 Pb is derived from the 1 − LD extracted with a fluctuation analysis in the energy region of the isovector giant dipole resonance.Results: The E1 GSF is compared to parametrizations recommended by the RIPL-3 data base showing systematic deficiencies of all models in the energy region around neutron threshold. The new data for the poorly known spinflip M1 resonance call for a substantial revision of the model suggested in RIPL-3. The total GSF derived from the present data is larger in the PDR energy region than the Oslo data but the strong fluctuations due to the low LD resulting from the double shell closure of 208 Pb prevent a conclusion on a possible violation of the BA hypothesis. Using the parameters suggested by RIPL-3 for a description of the LD in 208 Pb with the back-shifted Fermi gas model, remarkable agreement between the two experiments spanning a wide excitation energy range is obtained.Conclusions: Systematic parametrizations of the E1 and M1 GSF parts need to be reconsidered at low excitation energies.The good agreement of the LD provides an independent confirmation of the approach underlying the decomposition of GSF and LD in Oslo-type experiments.

Systematics of the electric dipole response in stable tin isotopes

“…Therefore the level densities from proton scattering for 1 − states must be converted to total level densities for a comparison. The procedure for this conversion is described in [31]. In Fig.…”

Gamma Strength Functions and Level Densities from 300 MeV Proton Scatttering at 0°

“…A full account of the 208 Pb results can be found in Ref. [26]. In the case of 96 Mo with much larger level densities GSFs from both experiments iagree within uncertainties indicating that the BA hypthesis indeed holds.…”

Gamma Strength Functions and Level Densities from High-Resolution Proton Scattering under 0°

“…The former assumption is motivated by the strong suppression of isoscalar strength due to the anomalous nucleon magnetic moments, while the latter is well justified in the energy region of the spin M1 resonanance [17]. Figure 2 presents the E1 (blue), M1 (green), and E2 (red) GSF in 208 Pb [42]. The latter is deduced from the isoscalar E2 strength function given in Ref.…”

“…The data set has been reanalyzed recently, for details see Ref. [42]. There are overlapping results from both experiments in the energy region between 5 and 8 MeV (inlet of Fig.…”

“…A better suited case to test the BA hypothesis in the energy region of the PDR is 96 Mo, where the LD should be sufficiently high because of the considerable ground state [29,30] in comparison to the reanalyzed [42] results from the Oslo experiment [44]. The inlet shows an expanded view of the low-energy region 5 − 8 MeV.…”