For nuclear weapons to do their job of deterring conflict, an enemy has to believe one is willing to use them, the scientists say.
But the bombs stockpiled during the Cold War are so destructive that potential enemies may think no one would be willing to use them, the scientists wrote in a paper in the British journal Comparative Strategy addressing the central paradox of nuclear weapons.
It's an argument made before by advocates of modernization of the U.S. nuclear arsenal, but the paper offers the most detailed, publicly available analysis by U.S. weapons scientists of the amount of damage that would be caused by new "reduced collateral damage" weapons.
The pitch actually mirrors the argument of people who oppose so-called mini nukes. Because it might be easier to justify their use, they worry that lower-yield weapons will blur the line between conventional and nuclear weapons. Anti-nuclear advocates credit that distinction with preventing any use of nuclear weapons in war since the U.S. attack on Nagasaki in 1945.
The Los Alamos paper was published last week as House and Senate negotiators approved legislation that would allow lab weapons designers to begin work on designs for the type of low-yield weapons discussed by the scientists.
The Los Alamos authors — Bryan Fearey, Paul White, John St. Ledger and John Immele — say the paper reflected their views, not the policies of the lab or the federal government.
"We're not the first ones to put this dialogue on the table," White said.
The basic technical problem addressed in the paper is the relationship between the explosive yield of nuclear weapons and the accuracy with which they can be delivered. The lower the accuracy, the larger a blast is required to be sure a target is destroyed.
In one example, the scientists discuss the blast needed to destroy a shallowly buried enemy bunker.
A typical weapon in the current U.S. arsenal can be accurately delivered within about 300 feet of its target. To destroy such a bunker, that requires a blast equivalent to about 15 kilotons of TNT.
The scientists say that would spread deadly radiation over a five-mile radius.
By delivering the weapon more accurately — within 30 feet — they say a blast of only one-half kiloton would be enough to destroy the bunker. The radiation zone would be reduced to a little more than a mile.
The question today is whether such new highly accurate low-yield weapons can be achieved with modifications to existing weapons or by designing entirely new ones.
"New is not necessarily a requirement to achieve new objectives," White said.
But critics of low-yield weapons contend that smaller nuclear blasts might not reduce health risks if the weapons explode underground. The reason is that earth-penetrating weapons that seek enemy bunkers may produce smaller explosions, but will expel a large amount of contaminated soil.
Opponents of new nuclear research also contend that any new weapons will create more security problems than they solve, by undermining the United States' efforts to prevent nuclear proliferation.
The action by Congress last week lifted a decade-old ban on the research of low-yield nuclear weapons, though it would require the administration to go back to Congress before development work could begin.
It also authorized $15 million for continued research into the Robust Nuclear Earth Penetrator, a powerful nuclear weapon capable of penetrating deep underground bunkers.