MEASUREMENTS IN THE BEAM DIRECTION OF THE AR-40 PROJECTILE FRAGMENTATION AT 44-MEV A/

Accurate beam-direction measurements ((0 +/- 3) mrad) have been perfor med on the Ar-40 projectile fragmentation on a Ni target, at 44 MeV/u, by using the telescopic mode on the double spectrometer LISE at GANIL . Sampling results on Al and Au targets are also presented. Velocity d istributions are analysed for fragments of masses from 10 to 45. As ex pected from a study of the forward-angle physics, the presented beam-d irection measurements (0-degrees) and the grazing-angle ones (3-degree s) exhibit important differences. The most probable velocities are fou nd much closer to the beam one at O-degrees than at 3-degrees. The vel ocity-integrated mass yields obtained in the beam direction exhibit a regular exponential rise from A approximately 18 to A approximately 40 ; they are found larger or much larger than at the grazing angle, at v ariance with the less populated light proton-rich fragments. Integrate d yields are found dependent on these new results. A non-dissipative p rocess has to be invoked in the beam direction. The role of diffractio n is to be examined. No unique mechanism can explain the whole set of results now available. [G