I have a new column (“Putin’s Doomsday Machine”) up on Status-6/Kanyon — the Russian underwater drone that is apparently armed with a very dirty thermonuclear weapon. I wasn’t really able to do the science justice in the column, so I wanted to add a few thoughts here.
There are really two different things going on. First, there is the question of how the Russians might produce the persistent radioactive contamination described in the weapon’s mission statement. That is a concept called “salting.” Second, there is the added impact of detonating the device underwater, in the harbor of a major metropolitan area. That relates to the “base surge” seen during the Baker test conducted as part of Operation Crossroads at Bikini. Together, these two phenomenon combine for a very nasty weapon.
I
Salting
As I noted in the column, one method to increase the amount of long-lived radioistopes produced in the explosion is to jacket the bomb in something like cobalt. Glasstone and Dolan, The Effects of Nuclear Weapons (1962) provide a concise, explicit explanation of this phenomenon:
9.11 The composition of the fallout can also be changed by “salting” the weapon to be detonated. This consists in the inclusion of significant quantities of certain elements, possibly enriched in specific isotopes. for the purpose of producing induced radioactivity. There are several reasons why a weapon might be salted. For example, salting has been used in some weapons tests to provide radioactive tracers for various purposes, such as the study of the paths and relative compositions of the early and delayed stages of fallout. By the choice of elements, to give radioactive products of suitable half lives and radioactivity, the characteristics of early fallout from a nuclear weapon could be modified for application in radiological warfare (§ 9.110).
The element usually suggested is cobalt, although elements with shorter half-lives have been mentioned including gold, tantalum and zinc. (I was reminded that I have such a nice collection of various editions — 1950, 1957, 1962 and the 1977.)
II
Base Surge and Rainout
The other aspect that bears mentioning is that an underwater explosion will produce a “base surge,” as well as a rainout, that are a very effective ways to deposit significant amounts of radiation on surrounding areas. Again, from Glasstone and Dolan:
9.121 In a shallow underwater explosion, radioactive contamination will arise from the visible and invisible base surge, which remains near the water surface, and from the radioactive airborne cloud, which is produced by condensation of the vented weapon residues (Chapter II). The radioactive cloud does not ascend as high as it would for a surface (or low air) burst of the same yield and so a large proportion of of the fission product activity rains out in a short time within a radius of a few thousand yards of surface zero. In the Bikini BAKER test (§ 2.61), the contaminated fallout (or rainout) consisted of both solid particles and of a slurry of salt crystals in drops of water. This contamination was difficult to dislodge and had there been personnel on board the ships used in the test, they would have been subjected to considerable doses of radiation if the fallout were not removed immediately. Since the BAKER shot was fired in shallow water, the bottom material may have helped in the scavenging of the radioactive cloud, thus adding to the contamination.
To see this phenomenon, take a look at this video of the BAKER test. You can see the visible base surge extend outward. Imagine that rolling through Manhattan and Brooklyn.
III
Operation Crossroads
Speaking of Operation Crossroads, I happen to have a copy of the official pictorial record of the test series, published by the Office of the Historian, Joint Task Force One. It has a bunch of really great images. There are two particularly nice shots of the base surge that I wanted to share with you.
