Because of the novelty and complexity of the plutonium implosion device that was to be exploded during the Trinity test, Manhattan Project officials, directed by Kenneth Bainbridge, realized that a calibration explosion using ordinary high-explosives would be useful. The test, which called for slightly over 100 tons of TNT, was designed to practice timing sequences and calibrate the instruments that would detect energy release, thermal radiation and other factors that were independent of nuclear radiation.
The team placed 100 tons of TNT on a tower 20 feet in the air, arranged in the form of a massive cube. The detonation occurred on May 7, after an observation plane launched from the Alamogordo Army Air Field was in position. The explosion was visible 60 miles away at the air field, but was barely felt at the base camp, only 10 miles away from the detonation site.
Ralph Nobles, a physicist who helped set up the 100-ton TNT test, shared an amusing anecdote about the test preparations.
"They had a 'gear pump' set up on a table and were pumping the tracer solution into uniform grid of pipes which had been built in the TNT cube, through a plastic hose. For some reason the pressure built-up too high in the plastic hose attached to the pump, and the hose popped off the pump and started wildly flailing around and spraying radioactive tracer solution in all directions.
The radioactive tracer, though not highly dangerous, was not something in which one wanted to get soaked! So the nearby radio chemists started running away from the pump, to escape the radioactive liquid from the hose. The MP up here, on top of the TNT cube, saw the chemists running away, and must have assumed they were running because the TNT was about to explode! Whereupon, he dropped his rifle and started moving so that his helmet flew off. He literally ran 'out from under his helmet' and I have never seen 40 feet of stairs descended faster. He couldn't have reached the ground much faster by jumping.
However, he didn't stop at the ground and as he ran past my jeep, I wondered why he hadn't jumped in and yelled, 'that thing is about to blow, let's get the hell out of here,' but he didn't slow down or even seem to notice that we were there! When I last saw him, he appeared to be trying to set a running speed record!"
Copyright Ralph Nobles, 8/3/14