Proton Decay of the Isobaric Analog of the Ground State ofPb208Populated by the (p,n

Abstract

The relative widths for the proton (p) decay of the isobaric analog of the 208 Pb ground state have been remeasured with significantly improved accuracy using the charge-exchange reaction m Ph(p,n) rather than 201 Pb(p,p) and (p,p f ) excitation functions to populate the isobaric analog level. For the first time the sequential process ip,np) has been observed both with a heavy (A ~ 200) target nucleus and also with a target nucleus which is even-even rather than even-odd. The total cross section for the isobaric-analogstate reaction 208 Pb(£,?2) 208 Bi has also been measured for the range of proton bombarding energies between 25.2 and 47.3 MeV.

Proton decay of the isobaric analogs of the ground states of207Pb and208Pb

“…It would appear that processes other than population of the IAS are contributing to the } yield. In addition to this discrepancy, the widths of the IAS of 2~176 and 2~ as measured in (p,n~) experiments [8,9,11], are considerably greater than the widths obtained in (p,n) experiments [4,6] or in 2~ [1] and 2~ [2,3] resonance experiments. To explain these discrepancies, it has been suggested [5] that proton decay of analogs of excited states may contribute to the } yield.…”

“…Indirect observation of an IAS is therefore possible, and has been made, by detecting proton decay (~) of the isobaric analog state [7][8][9][10][11][12]. The cross section for partial decay by } emission from the IAS of 2~ [8, 13] has been reported to be greater than the (p,n) cross section [6,14] for formation of the same IAS. A similar anomaly exists for the IAS of 2~ [5,6,9].…”

“…Figure 1 shows the neutron TOF spectrum for the 2~ target gated by protons between 10 and 12 MeV. The strong peak at 6 MeV corresponds to excitation of the target ground-state analog in ;~ The gating protons include the ~ decays of the IAS to the first three states of 2~ the only states with non-negligible population [8,11]. The continuum background extending down to our threshold at 1.5 MeV indicates that an appreciable number of protons in the energy range 10-12 MeV are of non-IAS origin.…”

Neutron-skin thickness of $^{208}$Pb, and symmetry-energy constraints from the study of the anti-analog giant dipole resonance

“…The expected γ-decay properties of the states excited in 208 Bi are shown in Fig. 1 together with the protondecay branching ratios of the IAS [19][20][21].…”

Production of and isotopes in proton-induced reactions on nuclei

“…Black symbols correspond to the experimental data of Refs. [19,26,27,29,35,36,[41][42][43]. Red crosses give the predictions of the standard version of the INCL4 model, and blue squares give those of the modified version.…”