Dipole strength distribution in Pb206 for the evaluation of the neutron capture cross section of Pb205

Abstract

The dipole strength distribution of 206 Pb was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The analysis of the measured γ-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of γ-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground state transitions. The extracted photo-absorption cross section show enhanced dipole strength at the excitation energies around 5.5 and 7 MeV, which may related to a pygmy dipole resonance. The present (γ, γ′) data combined with (γ, n) data from the literature were used for confining input parameters of the statistical calculation code CCONE to derive the neutron capture cross section of the unstable 205 Pb nucleus.

Structure of negative parity states at $${\mathbf {6}\,\lesssim \, \mathbf {E}_\mathbf {x} <{\mathbf {7.0}} }$$ MeV in $$\mathbf {^{208}}{} \mathbf{Pb}$$

“…The 1 − states. Higher excited states are known for spin 1 − [1, 89,90,[92][93][94]. The number of identified states agrees with the expectations by the SDI calculation [17,18] up to E x = 7.2 MeV except for the additional yrast state (M = 1).…”

“…Several states with spins 1 − , 2 − , and 3 − are known at 6.2 < E x < 7.0 MeV [1,46,[89][90][91][92][93][94]. Two states with spins 4 − and 5 − were suggested by the big cross sections [40].…”

Electric and magnetic dipole strength in Fe54

“…4. As found in previous studies [5,6,12,27,[39][40][41][42] the continuum in the spectrum of γ rays scattered from 54 Fe is considerably higher than the background due to atomic scattering. This continuum is formed by a large number of unresolved transitions with small intensities that are a consequence of the increasing nuclear level density at high excitation energies in connection with the finite detector resolution.…”

Reference database for photon strength functions

“…Data can be found in Refs. [155,[225][226][227] for NRF data, [51,228,229] for Oslo data, [83-85, 110-113, 125, 126, 230-237] for photodata and [13,14] for (p,γ) data. Data correspond to the total dipole PSFs, except ARC data which yield E1 PSFs. ]…”

“…Fig.41(Color online) Experimental PSFs for 4 nuclei,90 Zr,181 Ta,196 Pt and206 Pb, for which data from different methods exist. Data can be found in Refs [155,[225][226][227]. for NRF data,[51,228,229] for Oslo data,[83-85, 110-113, 125, 126, 230-237] for photodata and[13,14] for (p,γ) data.…”