A COLD WAR relic was last night flying above North Korea trying to answer the question the world is asking: did Kim Jong Il tell the truth about his inaugural nuclear test? The last surviving Constant Phoenix, a nuclear-test sniffing aircraft commissioned by President Eisenhower, has so far failed to detect radioactive isotopes from the atmosphere.

There was still “no definitive proof” that a nuclear device had been detonated at an underground facility in northeast North Korea, according to Western intelligence sources. “For a first nuclear test, one would have expected radioactivity to have been released into the atmosphere, unless the device was small enough for the North Koreans to have contained all the radioactivity underground,” said one source.

If no trace of radiation is discovered by the Constant Phoenix, it would indicate that the size of the detonation was more in line with the estimate given by the South Koreans — less than one kiloton of TNT.

Had the explosion been the equivalent of the Hiroshima bomb, about 15 kilotons — as suggested by the Russians — the intelligence sources said that there would normally have been some radioactive evidence in the atmosphere.

“However, whatever the size, it would be quite an achievement on the North Koreans’ part if they have managed to contain all the radioactivity, but at this stage there is no indisputable proof either way,” one intelligence source said.

The US is using every possible technological device to resolve the issue of what the North Koreans achieved at their nuclear facility.

A single WC-135W Constant Phoenix, an adapted KC135 tanker flown by the US Air Force’s 55 Wing, based at Offutt in Nebraska, is now flying out of Kadena airbase in Okinawa on a daily mission to scoop up evidence from the atmosphere.

The only one left from a fleet of American radiation-sniffing aircraft used to monitor Russian nuclear tests during the Cold War, the Constant Phoenix is equipped with a system that includes special filter paper that can pick up radioactive isotopes.

These can then be analysed in laboratories to discover whether they are related to a man-made event — a nuclear test. The atmosphere contains natural radioactivity.

Alerted to the possibility of a test, the US would have deployed other spy planes to monitor all North Korean military radio and communications traffic. A big military event such as a nuclear test would likely be preceded by total silence — another give-away of an imminent development.

The CIA used to have a special arrangement with the Chinese to monitor Russian nuclear tests at a site in northern China because of the mutual benefit to Beijing and the US.

If that deal still exists, analysis of the seismic impact of the test will also help Washington to decide exactly what North Korea has achieved.

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