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Russia is reportedly developing sub-kiloton yield tactical nuclear weapons that can be shot from the upgraded guns of its future T-14 tanks. According to Defense One:
"The Russians ... maintain their tactical nuclear stockpile in ways that we have not," Hix said. Potomac Institute head Philip Karber, who helped write the Pentagon's Russia New Generation Warfare Study, offered a bit more explanation when Defense One spoke to him in January. While the United States retains just a few of its once-large arsenal of tactical nukes, Karber estimates that Russia currently has anywhere from 2,000 to 5,000 of the weapons. "Look at what the Russians have been doing in low-fission, high-fusion, sub-kiloton tactical nuclear technology," he said. "It appears that they are putting a big effort...in both miniaturizing the warheads and using sub-kiloton low-yield warheads."
Why is that significant? By shrinking the warhead, you can shoot it out of a wider variety of guns, including, potentially, 152-millimeter tank cannons. "They've announced that the follow-on tank to the Armata will have a 152-millimeter gun missile launcher. They're talking about it having a nuclear capability. And you go, 'You're talking about building a nuclear tank, a tank that fires a nuke?' Well, that's the implication," said Karber.
The U.S. developed their own tactical nuclear weapons, such as 127, 155, 200, and 280 mm nuclear artillery shells, during the Cold War. The U.S. withdrew nuclear artillery from service in 1991, and Russia followed suit in 1992.
(Score: 5, Informative) by butthurt on Thursday April 13 2017, @08:20AM (1 child)
With a steel neutron reflector, a 4.5 kg sphere of plutonium-239 can form a critical mass.
https://www.euronuclear.org/info/encyclopedia/criticalmass.htm [euronuclear.org]
That's under "fixed conditions" meaning without compression. In a nuclear weapon, a sub-critical plutonium mass is compressed by explosives, whereupon it attains criticality. Hence less than 4.5 kg is needed, if a similar reflector is used.
By one estimate, a sphere of 63 mm radius (126 mm diameter) is sufficient. That's without a reflector and without compression, with which a smaller sphere will suffice.
https://wws.princeton.edu/system/files/research/documents/Chyba_Simple%20Calculation%20of%20the%20Critical%20Mass.pdf [princeton.edu]
So you can see that forming such a sphere within a 152 mm shell is plausible.
I speculate that, rather than starting with a sphere and compressing it isotropically, they may be starting with an elongated shape--ellipsoidal or biconical perhaps--and compressing the ends more vigourously than the middle. Or if they are doing isotropic compression they've developed peculiarly powerful conventional explosives for that--because the casing doesn't leave much space for a spherical charge. Perhaps someone with more knowledge of the subject can offer more authoritative information here.
(Score: 2) by butthurt on Thursday April 13 2017, @11:03AM
Yes, I've read the same thing. However I happened upon a page about a series of tests in the USSR in 1953. "Tellurium-120" is said to be a code word for plutonium:
An RDS-5 device with the main charge from tellurium-120 with the weight of 0.8 kg with a normal neutron background with the purpose of validating the possibility of obtaining an explosion of the main charge of a hollow design containing 0.8 kg of tellurium-120 and determining the full TNT equivalent.
-- http://russianforces.org/blog/2012/10/interesting_document_on_soviet.shtml [russianforces.org] (emphasis removed and my own emphasis added)
Don't follow the atomhistory.ru link, for it has become porn.