This is a single entry representing 35 letters related to the Atomic Scientists' Association. Many of them deal with publicity surrounding the A-bomb and nuclear weapons. BR is not directly mentioned or one of the correspondents. The correspondence covers the period October 1949 to April 1950.

Cambridge University, Churchill College, Churchill Archives Centre; Joseph Rotblat Archives, RTBT 10/17/03/03. The 36 images for the 35 letters are numbered (1) to (36).