Trinity Site: 1945-1995.
Page: 7

intact.

Today Jumbo rests at the entrance to ground zero so all can see it.
The ends are missing because, in 1946, the Army detonated eight 500-
pound bombs inside it. Because Jumbo was standing on end, the bombs
were stacked in the bottom and the asymmetry of the explosion blew the
ends off.

To calibrate the instruments which would be measuring the atomic
explosion and to practice a countdown, the Manhattan scientists ran a
simulated blast on May 7. They stacked 100 tons of TNT onto a 20-foot
wooden platform just southeast of ground zero. Louis Hemplemann
inserted a small amount of radioactive material from Hanford into
tubes running through the stack of crates. The scientists hoped to
get a feel for how the radiation might spread in the real test by
analyzing this test. The explosion destroyed the platform, leaving a
small crater with trace amounts of radiation in it.



Bomb Assembly


On July 12 the two hemispheres of plutonium were carried to the George
McDonald ranch house just two miles from ground zero. At the house,
Brig. Gen. Thomas Farrell, deputy to Maj. Gen. Leslie Groves, was
asked to sign a receipt for the plutonium. Farrell later said, "I
recall that I asked them if I was going to sign for it shouldn't I
take it and handle it. So I took this heavy ball in my hand and I
felt it growing warm, I got a certain sense of its hidden power. It
wasn't a cold piece of metal, but it was really a piece of metal that
seemed to be working inside. Then maybe for the first time I began to
believe some of the fantastic tales the scientists had told about this
nuclear power."

At the McDonald ranch house the master bedroom had been turned into a
clean room for the assembly of the bomb core. According to Robert
Bacher, a member of the assembly team, they tried to use only tools
and materials from a special kit. Several of these kits existed and
some were already on their way to Tinian, the island in the Pacific
which was the base for the bombers. The idea was to test the
procedures and tools at Trinity as well as the bomb itself.

At one minute past midnight on Friday, July 13, the explosive assembly