A KINEMATIC-COINCIDENCE DETECTOR SYSTEM FOR SUBBARRIER HEAVY-ION REACTION STUDIES

A detector system has been developed to study sub-barrier heavy-ion tr ansfer 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 ti me-of-flight arm. Ion trajectories through the spectrometer are determ ined by an angle measurement at the focal plane, which together with t he measured time-of-flight through the spectrometer provides independe nt measurements of the momentum and velocity of the scattered particle s. This raytracing method allows the spectrometer to be operated with a large (10.3 msr) entrance solid angle without significantly degradin g the velocity and momentum measurements. Two-body kinematic coinciden ce 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 transf er reactions in the system Ni-58 + Dy-162. Mass resolution of better t han 0.8 u (FWHM) is obtained, resulting in adequate channel separation . The Q-value resolution is approximately 1.4 MeV (FWHM) for approxima te to 50 mu g/cm(2) thick Dy targets. Prospects for the improvement of the performance of such detector systems are discussed.