It was shortly before 11 a.m. on Jan. 12, 1965, when government scientists set off a spectacular nuclear explosion in the Nevada desert that sent a cloud of radiation all the way to the California coast, newly found documents showed.

The blast "produced a shower of incandescent sparks rarely seen in anything but a pyrotechnic display," stated a report from the Los Alamos Scientific Laboratory in New Mexico.The report, released Wednesday, is among the latest findings unearthed in the ongoing probe of the government's secretive human radiation experiments during the Cold War.

The test by the Atomic Energy Commission - in which part of a rocket's nuclear core was vaporized in Jackass Flats, Nev. - was conducted so scientists could study the reactor's behavior and the environmental effects of the radiation, the documents showed.

Also, in 1960, military planes were sent through radioactive rocket exhaust, and radiation doses to flight crews were measured, they showed.

"Elements of the nuclear-powered rocket program should qualify as human experiments," Rep. Edward Markey, D-Mass., who released the documents, wrote to Energy Secretary Hazel O'Leary.

After the explosion, the cloud was tracked by aircraft. Increased radioactivity in routine air samples was observed a few days later. Although estimated radiation doses to humans beyond the test site were well below current limits set by the Environmental Protection Agency, considerably more people were exposed than in other experiments.