[miliantnutcase]

Probably enriched uranium. If they had plutonium I doubt it would be only 30kt.

[Gideon7]

Nobody has exploded a U235 bomb (Little Boy type) since the 1950s (AFAIK)

https://en.wikipedia.org/wiki/Gun-type_fission_weapon#Comparison_with_the_implosion_method

All bombs since the 1950s are implosion type using Pu.

The reason is because U235 bombs are just too unstable and dangerous to handle.