George Smith in The Village Voice:
Sharon Weinberger’s Imaginary Weapons is another tale of military technology… It’s a fascinating investigation into the investment in the hafnium bomb, a device that entranced the military because salesmen promised a weapon with the bang of an atomic bomb in the size of a golf ball. As with Halter’s book, one defining feature of the story is the military’s enthusiastic pursuit of the dubious. In Imaginary Weapons, this is tied to the philosophy that the U.S. cannot afford to be taken by “technological surprise” by any adversary. This idea has fostered blind unreason and a penchant for pursuing any and all weapons projects, no matter how irrational.
In any case, “hafnium isomer” is a radioactive material that barely exists. It is expensive and difficult to make in even microscopic amounts, yet scientists receiving Pentagon funding became convinced it could be a wonder weapon in the war on terror. The hafnium bomb would be useful for sterilizing biological terror weapons hidden in underground bunkers. Another motivation was the logic—straight out of Dr. Strangelove—that America must not fall behind in a hafnium bomb gap to terrorists or rival nations. That there was no proof of any of this did not matter.
More here.