How much does the radioactive core of a nuclear bomb shrink due to compression by conventional explosives before it goes critical?

Question

I saw a claim online that the conventional explosions used to detonate a nuclear bomb "significantly" compress the radioactive core, but I can't find any numbers indicating by how much the core actually shrinks in radius before going critical. I'm sure that it takes an enormous amount of pressure to physically reduce the volume of a solid uranium or plutonium sphere, so I wouldn't expect the total volume to decrease by very much, despite this claim. Are there numbers on this?

Answer 1

Flash photos of test implosions of the "Trinity"-type (Fat Man) core as shown in the book "How To Photograph An Atomic Bomb" indicate that the diameter of the core is reduced by at least half and possibly more at the peak squeeze point.

Answer 2

A relatively simple "Point kinetic model of the early phase of a spherically symmetric nuclear explosion" gives a volume compression factor $(R_\mathrm{initial}/R_\mathrm{minimum})^3$ of about $2.5$ for the Trinity Explosion, consistent with the factor of "2-3" commonly reported.