



But as he passed a collection of rocks, minerals and fossils that were on display in the classroom, Neff's Geiger counter almost "exploded".

One of the lumps of the uranium that sparked an evacuation at 12 schools


It sparked a city-wide check, with 373 schools notified by education officials, and at least 11 others unwittingly had the rocks.

The antinuclear campaigner had wanted to demonstrate how radioactive the watches were when he turned up at the Missionaries of the Sacred Heart School in Salzburg, the Austrian city on the border with Germany.

The expert, Thomas Neff, said: "I brought the old watch from the sixties which lights brightly at night because of the radiation."

He said the watch had been carefully sealed so that nothing could leak out, and despite that the Geiger counter had notched up 1,200 counts per minute, 20 times the normal value.

More than 300 schools in Salzburg, Austria, were notified of the emergency and 12 evacuated

Yet as he walked close to the classroom display, Neff's Geiger counter reached over 102,000 counts per minute, sparking the evacuation.

If the non-measurable alpha-radiation were to be included, the actual radiation exposure should be at least 250,000 counts per minute, according to local media.

Thomas Neff said: "If you had this rock the whole year in your bag, you would get around 210 millisievert exposure. The exposure to radiation from natural sources is only 2.8 millisievert in a whole year in Austria."

To put this into perspective, in the US the maximum allowable yearly occupational dose is 50 millisievert, while 100 millisievert exposure per year is the lowest yearly dose linked to a likely increase in cancer risk. Yet for severe radiation poisoning, at least 2,000 millisievert would be needed.

Radiation warning sign
None of the schools were aware the rocks contained radioactive material, officials said

Education chiefs said that none of the schools had realised the danger of the radioactive rock that they had on display.]

The radiological laboratory in Austria said: "The radioactive screening and the risk assessment show a basic risk potential in Salzburg schools in case of improper storage."

All of the radioactive rock samples are currently in the radiological laboratory at the University of Graz, with one exception.

A fish fossil that also turned out to be radioactive can still be shown in the biology area in a state school after it was deemed to be low enough to not pose any risk.