Tuesday, November 01, 2005


One of my nuclear physicist readers has emailed me to offer the following technical correction to the "Suitcase nukes" story in the WSJ's Opinion Journal that I referred to below:

You are correct to note that the suitcase nukes story is bunk and that real suitcase nukes have an extremely limited shelf life - but the Opinion Journal article on why it is bunk gets the physics all wrong. A suitcase nuke has to make use of a small quantity of plutonium with isotopics that are referred to as "super-grade" well above the normal weapons grade level (super grade is around 97% Pu-239 as opposed to 93% Pu-239 for normal weapons grade) - the Pu-239 has a half-life of 24,000 years. The Opinion Journal's explanation of why the suitcase nukes have a limited shelf-life is simply ludicrous.

The real reason is that the nukes themselves operate at extremely fine tolerances and their yield is incredibly dependent upon the absolute perfection of their internal geometries. As the higher isotopes of the Pu decay (most importantly Pu-241 going to Am-241) the heat output of the Pu part of the core changes drastically and the geometry changes slightly - this makes the weapn prone to two problems that are referred to as spalling and jetting. As the weapon itself operates right on the limit of having too little material to give an actual nuclear explosion, any material lost to spalling or jetting will prevent the weapon from going off at all. The steps necessary to remake the suitcase weapon to get back its old yield are at least as complex as building it in the first place.

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