Oliphant's team reached a strikingly different conclusion. He had delegated the task to two German refugee scientists, Rudolf Peierls and Frisch, who could not work on the university's secret projects like radar because they were enemy aliens, and therefore lacked the necessary security clearance.[12] They calculated the critical mass of a metallic sphere of pure uranium-235, and found that instead of tons, as everyone had assumed, as little as 1 to 10 kilograms (2.2 to 22.0 lb) would suffice, and would explode with the power of thousands of tons of dynamite.[13][14][15]