RPA quasi-elastic responses in infinite and finite nuclear systems

Quasi-elastic responses in nuclear matter and in C-12 and Ca-40 nuclei are calculated with the ring approximation to investigate the finite-size effec ts on the electromagnetic quasi-elastic responses. A method to simulate the se effects in infinite-systems calculations is proposed. The sensitivity of the results to the various terms of the residual interaction is studied. T he results of nuclear matter random-phase approximation calculations are co mpared with those obtained in the ring approximation to demonstrate the imp ortance of the exchange terms.