Hi Maurice Winn; Re: "Yes DJ, but when there's a lot of the stuff close together, that half life must reduce a lot. The critical mass has to be close enough that neutrons from one must be wearing down the adjacent mass quicker than if there was just a pinhead of the stuff."
This is a great comment. A little math shows that yes, it would be possible for a small fission bomb to bleed away 1% of its power each year without any need for special cooling. But I don't think that most fission bombs are designed that close to the edge:
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Most of the WE 177s were built between 1966 and 1982, with an estimated 25 year shelf life.
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cdi.org
I would guess that the shelf-life is due, not to radioactivity decay, but instead to problems with other components. Every bought a 25 year-old car? Hell, ever gone out with a 25 year-old woman?
Oh, here's a link that cuts straight to the chase:
For obvious secrecy and security reasons, radiation measurements on real warheads are rarely published. In the so-called "Black Sea Experiment" in the late 1980s, however, Soviet authorities allowed Soviet and U.S. experts to take measurements from the nuclear warhead on a ship-based cruise missile, to assess its detectability.[8] With the hand-held and transportable gamma ray detectors the American team used in the experiment, they concluded that the warhead could only be detected about 6 meters away. Soviet scientists using a larger helicopter-borne neutron detector, however, were able to detect a neutron signal significantly above the background rate more than 70 meters above the ship.[9] That neutron signal was coming essentially entirely from the plutonium in the warhead – an all-HEU warhead would not have been detected by that means, and would have been detectable at even shorter range by the hand-held and transportable gamma detectors. In short, given the fundamental physics of the situation, finding hidden nuclear weapons at ranges of more than a few hundred meters from the detector – and much less for HEU or an HEU bomb – is simply a job that cannot be done. To find a hidden nuclear weapon, or the materials to make one, you need to know at least roughly where to look.
nti.org
The above makes it clear that there is no significant change to the half-life of the uranium.
-- Carl
I've heard that fusion bombs do have short shelf-lifes, though. |
