The first government search in decades for a nuclear bomb lost off the Georgia (search) coast in 1958 found no trace of the sunken weapon, the Air Force said in a report Friday.

The report, released nine months after scientists tested radiation levels off Tybee Island (search), concluded the 7,600-pound bomb cannot explode and should be left at sea.

"We still think it's irretrievably lost. We don't know where to look for it," Dr. Billy Mullins, an Air Force (search) nuclear weapons adviser who led the search, told a news conference.

A damaged B-47 bomber jettisoned the Mark-15 nuke into a sound about 15 miles from Savannah after colliding with a fighter jet during a training flight.

The military never recovered the bomb and gave up searching until last year, when a retired Air Force pilot claimed his private search team had detected unusually high radiation levels in the sound.

Government scientists investigated, taking radiation readings and soil samples Sept. 30 from water in an area the size of four football fields. The report said varying radiation levels were observed, but they were from natural elements in the sediment on the sea floor.

"The best course of action in this matter is to not continue to search for it and to leave the property in place," said the report by the Air Force Nuclear Weapons and Counterproliferation Agency.

The Air Force has said the bomb contains uranium and about 400 pounds of conventional explosives, though it lacks the plutonium capsule needed to trigger a nuclear blast. The amount of uranium was undisclosed.

In 2001, the Air Force declared the bomb "irretrievably lost" and estimated it lies buried beneath 8 to 40 feet of water and 5 to 15 feet of mud and sand.

The report issued Friday by the Air Force Nuclear Weapons and Counterproliferation Agency said dropping the search and leaving the bomb was "the best course of action."