Californium Rounds

“The description of atomic bullets can be found in science fiction, but few people know that such munitions were reality in the USSR. One such bullet could melt an armoured tank, while several atomic bullets would destroy a multistory building. Why did the Soviet Union have to cease the production of such powerful ammo?”


This article is complete nonsense. Russians may be great engineers and mathematicians, but they are also consummate bullshitters, and this piece contains not a microgram of Правда.

Where to start?

Californium, element 98, was first synthesised in 1950. It has seven principal isotopes with atomic mass between 248 and 254 and half lives ranging from 17.81 days (253Cf) to 898 years (251Cf). The main isotope of Californium produced for practical applications is 252Cf, with a half-life of 2.645 years and decay modes of alpha emission (96.9%) and spontaneous fission (3.09%). Cf-252 is a spontaneous neutron emitter, producing 2.3 million neutrons per second per microgram. This makes it an ideal start-up neutron source for nuclear reactors, and for neutron radiography of metal components. It is also used for some forms of radiation therapy, as it can deliver neutrons directly to a tumor.

Californium-252 is calculated to have the smallest critical mass of any known isotope which has been produced in quantity: 2.73 kilograms for an unreflected sphere 6.9 cm in diameter. Note that the actual critical mass is more than 1500 times greater than the “1.8 grams” claimed in the Pravda fantasy article. Each spontaneous fission releases an average of 3.7 neutrons, not the “5–8” claimed in the fable.

Now, perhaps you can see the problem trying to squeeze 2.73 kg in a 6.9 cm ball into the barrel of a rifle ranging from 7.62 to 14.3 mm. With a good neutron reflector as a tamper the critical mass would be reduced somewhat, but the tamper itself would increase the size of the core further. The claimed core of “5–6 grams” and “8 mm” is delusional.

Now, imagine the fate of the stalwart Soviet nuclear rifleman. Below is the cask used at Oak Ridge National Laboratory in the U.S. to transport one gram of Cf-252.


This apparatus weighs around fifty tons, which is required to shield those in its vicinity from the intense neutron emission of that quantity of Cf-252, around 2.3 trillion neutrons per second for one gram of Cf-252. And for a critical mass of more than 2 kilograms? Don’t even think about it. The rifleman would be instantaneously killed by the neutron flux, just as if he were standing next to a neutron bomb.

The intense neutron background of Cf-252 would make it extraordinarily difficult to design an implosion system which would assemble a critical mass without predetonation occurring as the core approached criticality. It’s difficult enough with the neutron flux from Pu-240 contamination in plutonium core weapons, and Cf-252 is thousands of times worse.

The “Californium six-gun” is, like the mythical Hafnium hand grenade, an imaginary weapon.



But…but…‘Hafnium Hand Grenade’ just sounds so good…

Never mind…sob!


Phased plasma rifle in the 40-Watt range:


I was googling around to find information on a weapon system in the science fiction Traveller RPG, Cf collapsing rounds, when I found this article. In the game they are dependent on advanced tech to control the strong force.

While it’s false, there is a deeper truth that this is exactly the kind of thing the old Soviet Union would have tried (“The USSR, a military industrial complex with a state attached”) and probably left a lot of radioactive pollution behind.