This report reviews the physical interactions through which residual radioactivity can be de veloped in the shielding vault of the NRDL 70 inch AVF cyclotron and discusses in general terms the design characteristics that affect the magni tude of the ultimate residual radiation field that will be found. By comparison with measure ments at other cyclotrons, estimates of the ex pected maximum residual gamma-radiation fields are reported. From the results it appears that, under certain conditions of operation of the NRDL cyclotron, residual radiation fields after shut down may possibly present a serious hazard, but it should be possible, through careful design of specific parts of the cyclotron, to keep the magnitude of this radiation below hazardous levels. (Author).