[mcclung]

The only really interesting thing about this is the claim that it was weapons grade uranium. I wonder if they mean the same thing other people do when they say that (for me, 90+% U-235), or if the mention of californium means it was blended?

[InclinedPlane]

Weapons grade HEU is typically 80% or above, though strictly speaking anything above about 20% is pretty easy to make a nuke out of provided you have enough material.

Also, back in the day it was quite normal for such small research reactors to use HEU (specifically, about 93% enrichment), and such reactors were pretty commonplace at the time. See: http://en.wikipedia.org/wiki/Research_reactor

[uvdiv]

There's only on the order of 1 mg of Cf-252 in the source (my estimate) -- enough for the order of 10^9 neutrons/second. It's not a meaningful amount of fissile material. By weapons-grade they mean the uranium in the neutron multiplier is >90% U-235.

Cf-252: http://www.nndc.bnl.gov/chart/reCenter.jsp?z=98&n=154

[falling]

as you can read from what I think is the original source (http://www.democratandchronicle.com/article/20120511/NEWS01/...) californium was the neutron source and uranium was used in the multiplier.

«A steady stream of neutrons is needed for these purposes. Kodak used small research reactors, including one at Cornell University, and possessed a dollop of californium-252, a radioactive isotope that endlessly sheds neutrons.

But it wanted a more potent in-house system, so in 1974 it acquired a californium neutron flux multiplier, known as a CFX. Small plates of highly enriched uranium multiplied the neutron flow from a tiny californium core.»

[mcclung]

Reading the original source completely changes everything. Thank you.