Test of a High Power Target Design

%IS343 :\\ \\ A high power tantalum disc-foil target (RIST) has been developed for the proposed radioactive beam facility, SIRIUS, at the Rutherford Appleton Laboratory. The yield and release characteristics of the RIST target design have been measured at ISOLDE. The results indicate that the yields are at least as good as the best ISOLDE roll-foil targets and that the release curves are significantly faster in most cases. Both targets use 20 -25 $\mu$m thick foils, but in a different internal geometry.\\ \\Investigations have continued at ISOLDE with targets having different foil thickness and internal geometries in an attempt to understand the release mechanisms and in particular to maximise the yield of short lived isotopes. A theoretical model has been developed which fits the release curves and gives physical values of the diffusion constants.\\ \\The latest target is constructed from 2 $\mu$m thick tantalum foils (mass only 10 mg) and shows very short release times. The yield of $^{11}$Li (half-life of 8.7 ms) was measured to be 7000 per $\mu$C of incoming protons. This is 14 times better than that of a "standard" ISOLDE roll-foil target using 2$\mu$m thick foil and with a mass of 111mg. Further tests are to be made at ISOLDE with this target to measure the yields of other short lived isotopes such as beryllium, sodium and aluminium.\\ \\These tests are very important to the development of future targets at ISOLDE and other facilities and, coupled with the theoretical model, allow predictions of the performance of new designs.