The Big Time by Fritz Leiber

After about 0.1 millisecond (one ten-thousandth part of a second) has elapsed, the radius of the ball of fire is some 45 feet, and the temperature is then in the vicinity of 300,000 degrees Centigrade. At this instant, the luminosity, as observed at a distance of 100,000 yards (5.7 miles), is approximately 100 times that of the sun as seen at the earth's surface. the ball of fire expands very rapidly to its maximum radius of 450 feet within less than a second from the explosion. -- Los Alamos

Brother, that was all we needed to make everybody but Kaby and the two ETs start yelping at once, me included. It may seem strange that Change People, able to whiz through time and space and roust around outside the cosmos and knowing at least by hearsay of weapons a billion years in the future, like the Mindbomb, should panic at being shut in with a little primitive mid-20th Century gadget. Well, they feel the same as atomic scientists would feel if a Bengal tiger were brought into their laboratory, neither more nor less scared.