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Nuclear Yield/Weight Ratios |
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Nuclear Yield/Weight Ratios |
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Fissionable Fuels |
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Name |
Oralloy
(Oak Ridge Alloy) |
Plutonium 239 |
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Cost |
$53/gram (1996) |
$4.65/milligram (1998; 99%+) |
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Energy Release from 100% Efficient Reaction |
17 kt/kg |
20 kt/kg |
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Minimum Critical Mass |
14.1 to 13.5 kg |
4.4 kg |
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Density |
18.8 g/cm3 |
19.7 g/cm3 |
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Description |
Silvery-Gray Metal. |
Silvery-White Metal. Produces 2.4 W/kg of heat from radioactive decay, so special precautions must be taken in design of devices to avoid self-generated heat from ruining them. |
Minimal yields of fission devices, with the minimum critical masses given above:
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Efficiency |
93.5% U-235 |
Plutonium 239 |
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0.5% |
1.15 kt |
0.44 kt |
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1% |
2.3 kt |
0.88 kt |
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2.5% |
5.7 kt |
2.2 kt |
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5% |
11.5 kt |
4.4 kt |
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10% |
23 kt |
8.8 kt |
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20% |
46 kt |
17.6 kt |
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30% |
69 kt |
26.4 kt |
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40% |
92 kt |
35.2 kt |
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50% |
115 kt |
44 kt |
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60% |
138 kt |
52.8 kt |
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70% |
161 kt |
61.6 kt |
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80% |
184 kt |
70.4 kt |
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95% |
218 kt |
83.6 kt |
As you can see from the above table, the only way to produce a low-yield nuclear weapon that is usable as a short-range battlefield nuclear device is to use a plutonium core; and heavily tamp the device with materials that inhibit full fission, resulting in the yield you want.
As might be expected, this results in a relatively bulky (for the yield) weapon, and one that requires lavish use of fissile material (several critical masses), in order to get a reliable initiation. The danger of operating at such minimal critical masses and at such inefficiencies deliberately, is that your device will “fizzle” and produce a yield of only a few tons as the chain reaction is choked off by the inhibitor tampers.
So called “Dial-a-Yield” nuclear devices might even work by extending or withdrawing fission tampers within the device to control it's yield = e.g. full insertion results in it's minimum yield, while inserting it partially would result in an intermediate yield, and zero insertion would result in the full yield.
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Fusionable Fuels |
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Name |
Liquid Deuterium |
Lithium-6 |
Lithium-7 |
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Cost |
$500 kg |
$1.30/gram (1997; 95-96%) |
$6.70/gram (1997; 99%) |
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Energy Release from 100% Efficient Reaction |
82.2 kt/kg |
64 kt/kg |
40.3 kt/kg |
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Density |
0.169 g/cm3 |
0.534 g/cm3 |
0.534 g/cm3 |
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Description |
Cryogenic Fuel. |
Whitish, slightly blue powdery light salt. Is pressed into a ceramic and then machined into shapes as necessary for devices. |
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Early Nuclear Weapon Yield/Weight Ratios
Mark One (Little Boy) – A plug consisting of 25.2 kilograms (42% of the critical mass) was fired into a series of concentric rings containing the remaining 58% (34.8 kilograms) of the critical mass. About 700 grams completely fissioned out of a total of 60 kilograms of Uranium-235, for a efficiency of 1.2% and a yield/weight ratio of 0.23 kt/kg.
Model 1561 (Fat Man) – A sub-critical mass of 6.2 kilograms of Plutonium was “squeezed” by a complex series of explosive detonations into a critical mass. Of 6.2 kilograms of Plutonium, about 1.3 kilograms fissioned completely, for an efficiency of 21% and a yield/weight ratio of 2.8 kt/kg.
Bibliography:
US Nuclear Weapons: The Secret History by Chuck Hansen
Cary
Sublette's Nuclear Weapons Archive
