Alex WellersteinVerified account

I’ve seen both 80% and 84% HEU on Little Boy not sure which is actual or how much a difference it makes.https://twitter.com/casillic/status/1040411913606320129?s=21 …

A) note error in Pu mass for FM. B) I think the upper enrichment limit of HEU rings hit toward 90% but not sure- I SUMMON @wellerstein! C) the average enrichment may be technically classified still? (Relates to A)? D) Error? Somewhere? E) it was 84%? But

The math carrie sutherland does jives with 80% IIRC but t may not have been able to differentiate in any case. Bittom line: I tell people 80% but I would now have to go to @wellerstein’s primary docs to double check.

The rings were lower enriched, the solid chunk in the middle was higher, unless I’m having a brain malfunction. Searching for cite...

Both cylinders were hollow. The most enriched was in the center.

Cadmium was used as the neutron absorber to reduce predet. I presume b/c affinity for lower energy Ns and because it becomes saturated more quickly than boron-10?

https://nuclearweaponarchive.org/Nwfaq/Nfaq8.html … Insert: inner stack of 6 cylindrical rings stationary inside the target assembly “The insert had an enrichment of 86%, the projectile was enriched to 82% for an average enrichment for the core of 83.5%, equal to slightly more than three critical masses.”