1944: Developing the Bomb

1944: Developing the Bomb

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B Reactor Workers

1944 Oct 27

J. Robert Oppenheimer approves plans for a bomb test in the Jornada del Muerto valley at the Alamagordo Bombing Range. General Leslie Groves approves 5 days later, provided that the test be conducted in Jumbo.

1944 Oct 12

The first B-29s arrive in the Mariana Islands to begin bombing Japan. Japan has so far remained free from air attacks (except for the symbolic Doolittle raid in 1942).

1944 Sept 27-30

After several hours of operation at 100 megawatts, the B Reactor pile inexplicably shuts down, then starts up again by itself the next day. Within a few days this is determined to be due to poisoning by the highly efficient neutron absorber Xenon-135, a radioactive fission product. The reactor must be modified to add extra reactivity to overcome this effect before production can begin.

1944 Sept 26

Loading uranium into the first full scale plutonium reactor, the B Reactor, at Hanford, WA is completed. This reactor contains 200 tons of uranium metal, 1200 tons of graphite, and is cooled by 5 m^3 of water/sec. It designed to operate at 250 megawatts, producing some 6 kg of plutonium a month. Fermi supervises reactor start-up.

1944 Sept 22

The first RaLa implosion test shot is made in Los Alamos, NM. This diagnostic technique used 100 curies of radiolanthanum produced by the X-10 Graphite Reactor at Oak Ridge, TN to provide an intense gamma source for making observations of implosion (essentially an internal x-ray generator). This is the largest radioisotope source ever assembled in the world up to this time.

1944 Sept

President Franklin Roosevelt and British Prime Minister Winston Churchill sign the Hyde Park aide-memoire, pledging to continue researching atomic technology.

1944 Sept

During the fall Robert Christy suggests the "Christy gadget", the use of a solid core that is raised to supercriticality solely by compressing the metal to twice normal density. This conservative implosion design avoids instability and spalling problems, but the period of maximum compression is brief and requires a "modulated initiator" (a neutron generator that emits a burst at a precise moment). Earlier shell designs could have relied on spontaneous fission and still achieved reasonable efficiency.

1944 Sept

At this point the K-25 Plant is half built, but no usable diffusion barriers have been produced. The Y-12 Plant is operating at only 0.05% efficiency. The total production of highly enriched uranium to date is a few grams.

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