Scientists exploded a nuclear weapon beneath the Nevada desert Monday in a "very successful" test, the fourth announced detonation by the United States this year.

The detonation at the Nevada Test Site was conducted at 6:10 a.m., and the earth above ground zero at the blast site collapsed at 6:59 a.m., Jim Boyer, Department of Energy spokesman, said.No radiation escaped into the atmosphere, he said.

No motion was felt by residents in Las Vegas, 85 miles from ground zero. The test was not announced in advance.

The test, code named "Palisade," was No. 691 since the Nevada Test Site became operational in 1951.