By February 1945, a small group of scientists had succeeded in producing a small amount of material in a rudimentary separator in the RIKEN complex—material which RIKEN's cyclotron indicated was "not" uranium-235.The separator project came to an end in March 1945, when the building housing it was destroyed by a fire caused by the USAAF's "Operation Meetinghouse" raid on Tokyo. No attempt was made to build a uranium pile; heavy water was unavailable, but Takeuchi Masa, who was in charge of Nishina's separator, calculated that light water would suffice if the uranium could be enriched to 5–10% uranium-235.