Abstract
A feasibility study was made of an important aspect of the Coulomb-dissociation method, which has been proposed for the determination of the rate of the astrophysically important 12C(α, γ)16O reaction. A crucial aspect is the disentanglement of nuclear and Coulomb interactions on one hand and the separation of dipole and quadrupole contributions on the other. As a first step the resonant breakup via two well-known 2+ states of 16O was measured. The differential cross section of 208Pb(16O, 16O*)208Pb and the angular correlations of the fragments 12C and α in the center of mass were measured and compared to theoretical predictions calculated in DWBA and the coupled-channel method. The best agreement was found for the state at 11.52 MeV associated to a one-step excitation from the ground state, while the 9.84 MeV requires coupling to the first-excited 2+ state and is not well described.
Highlights
A feasibility study was made of an important aspect of the Coulomb-dissociation method, which has been proposed for the determination of the rate of the astrophysically important 12C(α, γ )16O reaction
The aim was twofold: first, to test the possibility to fit the angular distributions with distorted-wave Born approximation (DWBA) or coupled-channel (CC) calculations that include the nuclear and Coulomb interactions and the interferences between their contributions; second, to measure the angular correlations of the fragments in the breakup center of mass
It has been shown [8,10,11] that the angular correlation of the fragments is very sensitive to the interference between the contributions of the various multipolarities involved in the excitation process
Summary
A feasibility study was made of an important aspect of the Coulomb-dissociation method, which has been proposed for the determination of the rate of the astrophysically important 12C(α, γ )16O reaction. Measurements have been carried out down to a center-of-mass energy of = 1 MeV with relatively low statistics, requiring uncertain extrapolation of the fusion excitation function down to = 300 keV, i.e., the astrophysically relevant region. Such measurements at larger center-of-mass energies ∼ 4 MeV require a spectrograph with large angular opening and momentum bite, as we will discuss below.
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