Positron-induced droplet formation in gaseous He

A semiclassical theory is presented for positron-induced droplets in helium gases. The initial low-temperature drop is estimated to be 12A in radius in 4He, containing about 150 atoms. The corresponding numbers for 3He are 14A and 180 atoms. With increasing gas density and/or temperature the droplet grows and finally merges with the surrounding gas. The temperature dependence of the onset gas density for clustering is calculated. (author)