Direct proton decay of the isoscalar giant dipole resonance

Abstract

The direct proton decay of the isoscalar giant dipole resonance (ISGDR) has been studied in 208Pb using the (α,α′p) reaction at a bombarding energy of 200 MeV. Through observation of direct-decay protons from the ISGDR in coincidence with scattered α-particles, the population of proton–hole states in 207Tl was studied, allowing us to test recently performed continuum-RPA (CRPA) calculations for the ISGDR and thereby to learn about its microscopic structure. The energy and width of the ISGDR were also determined to be 22.1±0.3 MeV and 3.8±0.8 MeV, respectively. A new resonance of quadrupole character was observed at Ex=26.9±0.7 MeV with a width of 6.0±1.3 MeV.