A small amount of radioactive, weapons-grade plutonium has gone missing from a university in Idaho.

Idaho State University was using the radioactive chemical element, which was about the size of a 10p piece, for research.

The US Nuclear Regulatory Commission said the university could not account for about a 30th of an ounce (one gram) of the material, which is used in nuclear reactors and to make nuclear bombs.

While the amount is too small to make a nuclear bomb, it could be used to make a dirty bomb to spread radioactive contamination, said Victor Dricks, a spokesman for the agency.

“The NRC has very rigorous controls for the use and storage of radioactive materials as evidenced by this enforcement action,” he said of the proposed fine of $8,500 (£6,280) for failing to keep track of the material.

Dr Cornelis Van der Schyf, vice president for research at the university, blamed partially completed paperwork from 15 years ago as the school tried to dispose of the plutonium.

“Unfortunately, because there was a lack of sufficient historical records to demonstrate the disposal pathway employed in 2003, the source in question had to be listed as missing,” he said in a statement. “The radioactive source in question poses no direct health issue or risk to public safety.”

Nuclear waste is stored in underground containers at the Idaho Nation (AP Photo/Keith Ridler)

Idaho State University has a nuclear engineering program and works with the US Department of Energy’s Idaho National Laboratory, considered the nation’s primary nuclear research lab and located about 65 miles northwest of the school.

The plutonium was being used to develop ways to ensure nuclear waste containers were not leaking and to find ways to detect radioactive material being illegally brought into the US following the 11 September, 2001, terror attacks, the school said.

The university, which has 30 days to dispute the proposed fine, reported the plutonium missing on 13 October, according to documents released by the Nuclear Regulatory Commission.

The agency said a school employee doing a routine inventory discovered the university could only account for 13 of its 14 plutonium sources, each weighing about the same small amount.

Russia's floating 'nuclear Titanic': in pictures Show all 9 1 /9 Russia's floating 'nuclear Titanic': in pictures Russia's floating 'nuclear Titanic': in pictures The floating nuclear power plant, the 'Akademik Lomonosov', is towed out of the St. Petersburg shipyard. AP Russia's floating 'nuclear Titanic': in pictures Workers on the nuclear atomic icebreaker "Arktika" operated by Rosatomflot watch the floating nuclear power plant "Akademik Lomonosov" being towed . Reuters Russia's floating 'nuclear Titanic': in pictures The 'Akademik Lomonosov', the first in a series of floating nuclear plants planned, will be fuelled, tested and in 2019 towed 5,000 kilometres through the Northern Sea Route and put to use near Pevek, in the Chukotka Region. EPA Russia's floating 'nuclear Titanic': in pictures The Akademik Lomonosov is to be loaded with nuclear fuel in Murmansk. AP Russia's floating 'nuclear Titanic': in pictures The floating nuclear power plant. AP Russia's floating 'nuclear Titanic': in pictures Fishermen sail on a boat past the floating nuclear power plant "Akademik Lomonosov". Reuters Russia's floating 'nuclear Titanic': in pictures The floating nuclear power plant, the 'Akademik Lomonosov'. AP Russia's floating 'nuclear Titanic': in pictures The plant, owned and operated by Russian state controlled nuclear giant Rosatom, will pass through Estonian, Danish, Swedish and Norwegian waters towards Murmansk. EPA Russia's floating 'nuclear Titanic': in pictures The floating nuclear power plant "Akademik Lomonosov" Reuters

The school searched documents and found records from 2003 and 2004 saying the material was on campus and awaiting disposal. However, there were no documents saying the plutonium had been properly disposed.

The last document mentioning the plutonium, dated 23 November, 2003, said the Idaho National Laboratory didn’t want the plutonium and the school’s technical safety office had it “pending disposal of the next waste shipment.”

The school also reviewed documents on waste barrels there and others transferred off campus since 2003, and opened and examined some of them.

Finally, officials searched the campus but did not find the plutonium.

“We suspect that it ended up in a landfill for radioactive materials,” Mr Dricks, the commission spokesman, told Live Science website.