Uranium hydride bomb
Unlike all other fission-bomb types, the concept relies on a chain reaction of slow nuclear fission (see neutron temperature).
Bomb efficiency was harmed by the slowing of neutrons since the latter delays the reaction, as delineated by Rob Serber in his 1992 extension of the original Los Alamos Primer.
It made use of uranium deuteride particles coated with paraffin (to reduce the pyrophoricity of UD3 aka U2H3) and boron-10 carbide (B4C) wax distributed uniformly throughout the solid core.
[3]: 258 In reality the result was that the slower neutrons delayed the reaction time too much by reducing the number of fission generations accomplished; especially as the core expanded to reach its snowplow region (where all nuclear reactions cease), more neutrons could escape from the turbulent surface of the core, and before enough energy (for military applications) could be produced.
The predicted yield was around 1 kilotonne of TNT (4.2 TJ),[7] if the core operated as originally expected; the first rough estimate for the behavior of the "hydride" bomb appeared in 1944, when James Conant forecast that 1 kt of energy would be obtained from about 9 kg of UD3.
[8] Post-war, LANL physicists continued research on the subject at low priority; while a Monte-Carlo simulation in December 1949[3]: 258 showed that the core could in principle work and result in a weapon considerably smaller than the MK 5, strong skepticism arose as the inherently low efficiency of the fuel would not improve even remotely as theoretically envisioned when a hollow core and boosting were incorporated, and a proposed test of such a core in an MK 4 high-explosive assembly was ultimately stricken from the preliminary shot schedule of operation Greenhouse.
Optimism in the new lab prompted UCRL to even propose a class of such "small weapons" making use of the material, dubbing it as the "Geode".
The fuel was selected so that UCRL's thermonuclear program would not compete with LASL's on scarce materials at the time, specifically lithium.
[Note 5][10]: 24 If successful, the devices could also lead to a compact primary containing minimal amount of fissile material, and powerful enough to ignite Ramrod[10]: 149 the other Mark 22 nuclear bomb prototype designed by UCRL at the time.
For a hydride-type primary, the degree of compression would not make deuterium to fuse, thus the design would be essentially a pure fission weapon, not a boosted one.
