A STUDY OF THE TWO-STEP MECHANISM OF THE DOUBLE IONISATION OF NOBLE GASES M. GRIN and C. DAL CAPPELLO Institut de Physique, Laboratoire de Physique Mol=E9culaire et des= Collisions, Technop=F4le 2000, 1 Rue Arago, 57078 Metz Cedex 03, France e-Mail : cappello@ipc.sciences.univ-metz.fr =20 An ab initio calculation of the differential cross section for the double ionisation of noble gases is performed by using the first and second Born approximation. A comparaison with the recent experiments of El Marji et al shows that the agreement is good.