A kinematic-coincidence detector system for sub-barrier heavy-ion reaction studies

A detector system has been developed to study sub-barrier heavy-ion transfer reactions by means of the coincident detection of both reaction products. Scattered ions are momentum-analyzed by an Enge split-pole magnetic spectrometer, and the recoils are detected in a 3.5 m long time-of-flight arm. Ion trajectories through the spectrometer are determined by an angle measurement at the focal plane, which together with the measured time-of-flight through the spectrometer provides independent measurements of the momentum and velocity of the scattered particles. This raytracing method allows the spectrometer to be operated with a large (10.3 msr) entrance solid angle without significantly degrading the velocity and momentum measurements. Two-body kinematic coincidence is used to measure the mass of the recoil and the reaction Q-value distribution. This detector system has been used to measure the cross sections and Q-value distributions for sub-barrier quasielastic transfer reactions in the system 58Ni + 162Dy. Mass resolution of better than 0.8 u (FWHM) is obtained, resulting in adequate channel separation. The Q-value resolution is approximately 1.4 MeV (FWHM) for ≈ 50 μg/cm2 thick Dy targets. Prospects for the improvement of the performance of such detector systems are discussed.