J. Dias

High-resolution 40Ca(γ, p) measurements and the photoproton reaction mechanism

Abstract High-resolution measurements for the 40 Ca ( γ , p ) 39 K reaction have been performed at E γ =60 MeV. Five groups of states in the residual nucleus were identified. The angular cross sections for the 2 s 1 2 and the 1 d 3 2 hole state are reasonably well predicted in an RPA model. Both the shape and the magnitude of the angular cross sections of the remaining groups of states suggest the excitation of two-hole-one-particle states evidencing a two-body photoabsorption mechanism.

Determination of the random particle energy spectrum in tagged photon experiments

A new, improved method to define the random particle energy spectrum in tagged photon experiments is described. This procedure yields the random spectrum with very good statistical accuracy, and can be applied when no hard coincidence with the focal plane is required in order to accept events.

Microstructure in the electron beam and the shape of tagging TDC spectra

Abstract The effect of fast electron beam intensity fluctuations and of the dead time of the electron detectors on the shape of TDC spectra in tagged photon experiments is explained. Some consequences for the data analysis and for the use of multi-hit TDCs are also discussed.

Absorption of intermediate-energy photons by multi-particle clusters in 6Li

Abstract The results of a study of the 6 Li (γ, cc) (c, c : charged particle ) reaction with the tagged-photon technique are presented. It is shown that the (γ, pt) reaction can be understood within the framework of a semi-phenomenological quasi-alpha reaction model. The total (γ, pt) cross section is found to be larger than the 6Li(γ, pn)α cross section at the same photon energy. No evidence is found for a three-body absorption mechanism, but the possible role of final-state interactions in the (γ, pd) reaction is outlined.

The semi-inclusive 40Ca(γ, p) reaction

Abstract The experimentally determined semi-inclusive 40 Ca(γ, p) process at 60 MeV photon energy is interpreted in terms of two different approaches. Applying the hybrid model for pre-equilibrium reactions gives a fair description of the spectral shapes and the angular distributions. In a more microscopic approach, it is shown that a recently developed model for the 40 Ca(γ, pn) reaction yields at least half of the detected (γ, p) strength above the pn emission threshold.

Investigation of the40Ca(γ,N) reaction at 60 MeV

The values of the angle-integrated cross section for the decay to various low-lying states in39K following the40Ca(γ,π) reaction at a mean photon energy of 60 MeV are reported on, together with the values of the reduced Legendre coefficientsai. The40Ca(γ,gp) and40Ca(γ,n) reactions yield the same angular cross-section values and these agree with the corresponding RPA-calculations.

The 6Li(γ,p) reaction at intermediate photon energies

Abstract The 6 Li(γ,p) reaction was measured at average tagged photon energies of 〈 E γ 〉 = 59 and 75 MeV. Protons were detected at 5 different angles between 30° and 150°. Most of the observed strength is apparently due to the three-body breakup channels. In particular the semi-inclusive (γ,p(n)) and (γ,p(t)) channels are discussed.