High resolution particle spectroscopy in 208Pb

Abstract

By using the Q3D magnetic spectrograph of the Maier-Leibnitz-Laboratorium at München, particle-hole states in 208Pb are investigated. With the reaction 208Pb(p, p') at energies 14 < Ep < 18MeV an instrumental resolution of δEp′Ep′ = 3 · 10−4 is achieved for protons without energy loss in the target. For lower energies Ep′ an exponential tail with a width proportional to the effective target thickness appears. Below Ex = 8.2 MeV more than 250 states in 208Pb are observed. Excitation energies are derived with uncertainties of 0.1 keV for strongly excited states by calibration with known data from Nuclear Data Sheets. 208Pb(p, p') via isobaric analog resonances (IAR) in 209Bi allows to determine the neutron particle-hole components of each state in 208Pb. The selective excitation in an IAR yields the parity for each state. Spin and dominant neutron particle-hole configurations of a state are determined from the mean cross section and the shape of the angular distribution for 208Pb(p, p'). From about 120 particle-hole states predicted by the shell model in 208Pb below Ex = 6.1 MeV, about 50 states with negative parity and 30 states with positive parity are identified.