Physics Letters B 268 (1991) 345-350 North-Holland PHYSICS LETTERS B Measurements of reaction cross sections for neutron-rich exotic nuclei by a new direct method A.C.C. Villari t Departamento de Fisica Nuclear, Instituto de Fisica da USP, C.P. 20516, 01498 SSo Paulo, SP, Brazil W. Mittig, E. Plagnol, Y. Schutz, M. Lewitowicz GAN1L, B.P. 5027, F-14021 Caen Cedex, France L. Bianchi, B. Fernandez, J. Gastebois, A. Gillibert CENS, DPhN/BE, F-91191 Gif-sur-Yvette, France C. Stephan, L. Tassan-Got IPN, B.P. 1, F-91406, Orsay Cedex, France G. Audi CSNSM, bdtiment 108, F-91405 Orsay Campus, France Wenlong Zhan IMP, Lanzhou, China A. Cunsolo, A. Foti Dipartimento di Fisica and INFN, Corso Italia 57, 1-95129 Catania, Italy A. Belezyorov, S. Lukyanov and Y. Penionzhkevich LNP, INR, P.O. Box 79, Moscow, USSR Received 24 April 1991 A new, simple, direct method for the measurement of reaction cross sections (aR) is presented. The aR for neutron-rich exotic nuclei were measured and the reduced strong absorption radii r 2 were deduced. A strong isospin dependence ofro 2 was observed for measured isobars with masses from A = 10 up to A = 18. For heavier nuclei, this dependence is strongly reduced. The evaluation of nuclear radii is of fundamental interest in nuclear physics. The observation of an un- expectedly large interaction radius for l lLi has sug- gested the image of a neutron halo [ 1,2 ] in this nu- cleus. This very exotic matter distribution could be interpreted as a precursor of neutron matter, as sug- #r Experiment performed at GANIL. t Partially supported by CNPq. gested by Myers [3 ]. Therefore, the correct evalua- tion and interpretation of experimental measure- ments of interaction cross sections (a~), and the related interaction radii (ri) are essential. At high energies ( ~ 800A MeV), ax was measured for several light (2 < Z< 5 ) isotopes using a trans- mission technique [ 1,4]. At intermediate energies ( ~ 60A MeV), ai measurements were carried out for a wider atomic number range (3 < Z < 15 ), using the 0370-2693/91/$ 03.50 © 1991 Elsevier Science Publishers B.V. All fights reserved. 345