Thickness measurement for thick actinide targets

We report the measurement of the thickness and com position of several film s of actinide material used for measuring photofission cross sections in tw o experiments performed at the Saskatchewan Accelerator Laboratory (SAL) an d at the Thomas Jefferson National Accelerator Facility (JLab). We characte rized films of Np-237, Th-232, U-238, U-235, and U-233. The films had thick nesses of the order of 1 mg/cm(2), and were deposited on aluminum foils 100 mum thick. By the activities and the energy losses of the alpha -particles emitted by the films we were able to determine the composition of each fil m and to measure its thickness with a precision of up to 2%. (C) 2001 Elsev ier Science B.V. All rights reserved.