J. van Driel

Binary l-matched reactions in 14N + 159Tb collisions

Abstract Various channels from the 14 N + 159 Tb reaction at 140 MeV were studied using γ-particle coincidences combined with γ-ray multiplicity measurements. A wide class of binary reactions ranging from typical incomplete fusion processes to few-nucleon capture reactions was selected and investigated. Energy spectra, absolute cross sections and average γ-ray multiplicities were measured for a large number of reaction channels. From a detailed kinematical analysis it was found that all the reactions quite precisely satisfy the “recoil formula” of Siemens et al. for hard-grazing collisions. It is attempted to describe this wealth of reaction data on the common footing of the sum-rule model that combines the idea of partial statistical equilibrium with a generalized concept of critical angular momentum. The experimental results seem to confirm the basic assumptions of the model.

A versatile detection system for a broad range magnetic spectrograph

The focal plane detector for the QMG/2 magnetic spectrograph of the Kernfysisch Versneller Instituut is described. It consists of two-dimensional position sensitive proportional detectors and scintillation detectors. The properties of the components of the set-up and of the system as a whole in conjunction with the associated electronics and software are presented. The system allows easy optimization of spectrograph focusing and correction of kinematic effects. The position resolution is about 1 mm for relatively highly ionizing particles (50 MeV α-particles), and slightly worse for low-ionizing particles (50 MeV protons).

Sequential ejectile decays and uncorrelated breakup processes in the 14N + 159Tb reaction

From a study of particle-particle correlations, involving position-sensitive detector telescopes, conclusive evidence for sequential ejectile decay was found, and the relative importance of sequential decay and of breakup processes, which were observed to be uncorrelated in angle, could be determined.

The (α, 2He) reaction on 12C, 24Mg, 26Mg, 28Si, 40Ca, 58Ni, 90Zr and 208Pb at Eα = 65 MeV☆

Abstract The two-neutron transfer reaction (α, 2 He) has been studied for a number of target nuclei ranging from 12 C to 208 Pb at E γ = 65 MeV. The reaction mechanism has been formulated in single-step, zero-range DWBA analogously to that for the (α, d) and ( 3 He, 2 He) reactions. Angular distributions are reasonably well described in this formalism and likely J π values are deduced for a number of levels. The optical-model potential for the 2 He is discussed. The continuum part of the spectra mainly arises from evaporation protons with some evidence for contributions from complete α-particle breakup.

Evidence for giant quadrupole excitation in 208Pb by 200 MeV 12C scattering

In inelastic 12C scattering from 208Pb a peak, corresponding in excitation energy, width and strength to the well-known GQR is observed. The underlying broad continuum is probably due to 13C breakup rather than to excitation of giant resonances with L > 2.

The 120Sn(α, p)123Sb reaction in a semi-microscopic description

Abstract The three-nucleon stripping reaction 120 Sn(α, p) 123 Sb is described in a semi-microscopic model in which only J π = 0 − coupled neutron pairs are included. This spectator model describes the differences in excitation strengths of the (α, p) and ( 3 He, d) reaction if the coupling between the transferred proton and the di-neutron is correctly taken into account.

Investigation of the (3He, 2He) reaction: Reaction mechanism and application to the reaction on 28Si☆

Abstract The single-neutron stripping reaction 28 Si( 3 He, 2 He) 29 Si has been studied at E 3 He = 52 MeV. In order to deduce absolute cross sections the proton relative energy distribution has been measured as well. The reaction mechanism has been formulated analogously to that for the ( 3 He, d) reaction. Two relative energy dependent functions have been introduced, which contain three-body and additional reaction mechanism information, respectively. Angular distributions are well described by single-step DWBA calculations, yielding spectroscopic factors in good agreement with those from other reactions. The optical-model potential for 2 He is discussed. The use of a folding optical-model potential is found to be important in describing the cross section dependence on the internal 2 He energy.

Single and mutual excitation of projectile and target in α-scattering

Abstract The projectile excitation of 4He exciting the J π = 0 + state at E x = 20.1 MeV (α ∗ ) and the mutual excitation of projectile and target has been studied in α-scattering from 24Mg, 28Si, 40Ca, 58Ni and 90Zr at Eα = 65 MeV. The monopole excitation of 4He has been detected by its breakup α ∗ → p + t in a coincidence setup. The double folding approach for the description of the single and mutual excitation is discussed in which the rather large effect of recoil in the microscopic calculation of the inelastic form factor is taken into account. The microscopic DWBA calculation yields a good description of the structure of the angular distributions for the single excitation, but fails to reproduce the absolute cross sections. A possible explanation in terms of a drastically larger absorption for the final (α∗ + target) channel is discussed. As compared to the single excitation the mutual excitation is enhanced and in two cases even more strongly than the single excitation. For larger angles this effect is well reproduced by our calculations; however, at small angles an anomalous behaviour in the cross section for mutual excitation is observed.

Unbound Li nuclei as ejectiles in α-induced pickup

Abstract Measurement of the relative energy distribution of the correlated decay products in the (α, Li ∗ ) reaction shows that when the breakup proceeds sequentially through definite final states in the Li ∗ nucleus, excitation energy spectra of the residual nuclei can be generated.