Continuous distribution of αt relative kinetic energies in 7Li breakup reactions

Abstract

A newly developed technique has been used to probe a previously inaccessible region of the continuum in the at channels of 7Li breakup reactions. This was used to investigate reactions of 63 MeV 7Li with 58Ni, 120Sn, 144Sm, and 208Pb targets. Breakup pairs of α-particles and tritons emitted within a finite opening angle were analyzed according to their magnetic rigidity using a K = 150 Enge split-pole spectrograph. The αt coincidences were taken with two single-wire proportional counters mounted at different positions along the focal plane of the spectrograph. The large energy acceptance (Emax/Emin ≈ 8) of the spectrograph is crucial to the present coincidence measurements involving two particles with different q/m values. Very small relative energy components were studied without any detection threshold. A pronounced bump was observed immediately above the αt particle threshold. No strong indication of the post Coulomb acceleration was observed. The excitation of the continuum states as well as the 7−2 state in 7Li is discussed in terms of the distorted-wave Born approximation. The astrophysical implications of the data are also discussed regarding the Coulomb excitation of the continuum. The present technique offers the promise of very high sensitivity at small relative energies if it were applied in conjunction with ray-tracing, a thin target, and a dispersion-matched beam.