EXPERIMENTAL CONFIRMATION OF CLUSTER-IMPACT FUSION

We have investigated deuteron-deuteron fusion induced by impact of (D2O)n+ and (H2O)n+ clusters with n = 1-150 on deuterated polyethylene targets at energies of 135-225 keV. Both the energy dependence and magnitude of the fusion yield measured with (D2O)115+ clusters confirm the results of Beuhler et al. [J. Phys. Chem. 94, 7665 (1990)]. Furthermore, we have observed that the size dependence of the (D2O)n+ fusion yields measured at the impact energy of 225 keV for small (n < 10) clusters follow the "thermonuclear" model proposed by Carraro et al. [Phys. Rev. A 42, 1379 (1990)] rather than the thick-target model. For H2O+ and (H2O)2+ at 225 keV, the yields roughly agree with the "knock-on" model by Carraro et al. No fusion event was observed for (H2O)n+ clusters with n = 4-50; however, n = 115 clusters produced an observable fusion rate. The ratio between fusion rates of (H2O)115+ and (D2O)115+ is 5% +/- 2%, in close agreement with the result, approximately 5%, measured by Beuhler et al. at 300 keV.