SCIENCE FICTION HISTORY: HEINLEIN, ASIMOV, DE CAMP, ANALOG CLEARED OF LEAKING CLASSIFIED SECRETS

    Suffice it to say, there was no tempest in this particular teapot, not even much tea. As John W. Campbell Jr., editor of Astounding, pointed out to the FBI representatives in their first meeting, it required neither leaked security secrets or predictive genius for Cleve Cartmill to have described the functioning of an atomic bomb so accurately more than a year before WWII's biggest secret was revealed when it was dropped on

Japan. In "Deadline", the story in question, Cartmill had simply reworked a passage from one the many articles on nuclear physics and chain reactions openly published in the technical journals of the period and available in libraries throughout the U.S.A. The government's most closely guarded secret, in short, was known to every professional in the field, and if the Germans had wanted to know how to construct an atomic bomb, all they would have had to do was subscribe to those journals (which, it turns out, is just what they did to help advance their own atomic bomb  program).

Campbell even supplied the FBI with a copy of the publicly-circulated document that had served as the inspiration for "Deadline," the "Official U. S. Report: Atomic Energy for Military Purposes." In part, it read:

"DETONATION AND ASSEMBLY. As stated in Chapter II, it is impossible to prevent a chain reaction from occurring when the size exceeds the critical size.  For there are always enough neutrons (from cosmic rays, from spontaneous fission reactions, or from alpha-particle-induced reactions in impurities) to initiate the chain.  Thus until detonation is desired, the bomb must consist of a number of separate pieces each one of which is below the critical size either by reason of small size or unfavorable shape.  To produce detonation, the parts of the bomb must be brought together rapidly.  In the course of this assembly process the chain reaction is likely to start–because of the presence of stray neutrons–before the bomb has reached its most compact (most reactive) form.  Thereupon the explosion tends to prevent the bomb from reaching that most compact form.  Thus it may turn out that the explosion is so inefficient as to be relatively useless.  The problem, therefore, is two-fold: (1) to reduce the time of assembly to a minimum; and (2) to reduce the number of stray (predetonation) neutrons to a minimum."

You can compare this passage with the way Cartmill describes the same phenomenon by reading his story in our book Deadline and Other Controversial SF Classics..

After a few more interviews with the astonished Robert A. Heinlein, Isaac Asimov, L. Sprague de Camp, and Murray Leinster, the FBI wrote an end to its investigation, clearing all concerned, and turned to what surely must have been  weightier matters. 
It ought to be noted, in fairness to Cartmill, that if any government or bureaucracy were to properly understand his stories, they would find them all controversial and dangerous. For Cartmill questioned authority, and traditional explanations of things, and tried to tell his stories in such a way that the reader would begin to see their shortcomings in her or his own society and start to question them, too. So be warned, if you are completely comfortable with the people in charge and way things are now, and never want to doubt them, put down this book immediately and do not read any further.