Uranium hydride bomb

The uranium hydride bomb was a variant design of the atomic bomb, that was first suggested by Robert Oppenheimer in 1939 and advocated and tested by Edward Teller.^[1] It used deuterium, an isotope of hydrogen, as a neutron moderator in a U235-deuterium compound. The chain reaction is a slow nuclear fission (see neutron temperature). Bomb efficiency is very adversely affected by the cooling of neutrons since it delays the reaction. ^{[citation needed]}

Two uranium hydride bombs are known to have been tested, the Ruth and Ray test explosions in Operation Upshot-Knothole. The tests produced a yield comparable to 200 tons of TNT each; both tests were considered to be fizzles.^[1][2] All other nuclear weapons programs have relied on fast neutrons in their weapons designs.

Tower for the RUTH test. The explosion failed even to level the testing tower, only somewhat damaging it.

Theory

The hydrogen in uranium hydride (UH₃) or plutonium hydride moderates (slows) the neutrons, thereby increasing the nuclear cross section for neutron absorption. The result would be a lower required critical mass, thereby reducing the amount of pure U235 or plutonium needed for an explosion.^[3] The result was that the slower neutrons delayed the reaction time too much, and reduced the efficiency of the weapon.^[3] It increased the time between subsequent neutron generation events necessary for rapid explosion. It creates a problem in the containment of the explosion; the inertia that is used to confine implosion type bombs will not be able to confine the reaction. The end result may be a fizzle instead of a bang. The predicted energy yield would be 1000 tons TNT equivalent.^[4]

1953 tests

During early phases of Manhattan Project, in 1943, uranium hydride was investigated as a promising bomb material; it was abandoned by early 1944 as it turned out such design would be inefficient.^[5] After World War II, Los Alamos physicists were skeptical of uranium hydride in weapons. Edward Teller remained interested, however, and he and Ernest Lawrence experimented with the devices in the early 1950s at UCRL (later Lawrence Livermore National Laboratory).

Two test devices were exploded in 1953 as part Operation Upshot-Knothole. The aim of the University of California Radiation Laboratory design was to produce an explosion powerful enough to ignite a thermonuclear weapon, with the minimal amount of fissile material. The core consisted of uranium hydride, with hydrogen, or in the case of Ray, deuterium acting as the neutron moderator. The predicted yield was 1.5 to 3 ktTNT for Ruth and 0.5–1 ktTNT for Ray. The bombs failed to have the predicted explosive power in practice.

Ruth, which used ordinary hydrogen-1, was the first device entirely designed at Livermore; it was fired on March 31, 1953 at 05:00 local time (13:00 GMT) at Mercury, Nevada. The explosive device, Hydride I, weighed 7,400 lb (3,400 kg) and was 56 inches (140 cm) in diameter and 66 inches (170 cm) long. The predicted yield was 1.5 to 3.0 kilotons, but the actual yield was only 200 tons. Wally Decker, a young Laboratory engineer, characterized the sound the shot made as "pop." The lower 100 ft (30 m) of the 300-foot (91 m) testing tower remained intact, although the upper third was vaporized.^[6]

A second device, Ray, used deuterium. It was fired on a 100-foot (30 m) tower on April 11, 1953. Although Ray managed to level the tower, the yield was similarly disappointing: again 200 tons, as opposed to the predicted 0.5–1 ktTNT.^[7]

References