Los Alamos National Laboratory

Los Alamos National Laboratory

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Detonation: From the Bottom Up

In the nuclear testing era, scientists never thoroughly characterized the properties of the nuclear weapons because the weapons were tested and regularly replaced.
July 1, 2013
Detonation: From the Bottom Up

An unarmed Minuteman III ICBM is launched from a silo during a test at Vandenberg Air Force Base, California. (Photo: U.S. Air Force)


  • Managing Editor
  • Clay Dillingham
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U.S. nuclear weapons are like Ferraris: complex and lightweight, with high performance but little margin for error.

Nuclear testing was a wonderful tool. It was also the world’s biggest shortcut. It meant that nuclear scientists didn’t have to understand all the details of a nuclear weapon and how it functions. During the nuclear testing era, they knew enough about how the weapons worked to make a new weapon and make predictions about its yield. They then detonated it to see if it worked. It usually did, but sometimes it didn’t, and they didn’t always understand why. Basically, they solved the problem of building a new weapon from the top down. If it worked, they froze the design at this point and built more weapons exactly like it. If it didn’t work, they tried something different and tested again.

In the post-testing era, they realized that without the top-down approach, they would have to understand how nuclear weapons function from the bottom up—that is, gather all the basic science to understand the behavior of everything inside the weapon and then use that information to calculate how and why the weapon worked (or didn’t work). This is what the Stockpile Stewardship Program is all about: using the bottom-up approach to assess whether aging U.S. weapons will work.