A museum which housed a mysterious radioactive rock was forced to shut an entire floor after radiation levels became too high.

The unidentified stone - suspected to contain uranium - has been stored away from the public in Folkestone Museum since it opened in 2017.

But radiation protection advisors are now assisting owners Folkestone Town Council (FTC) to dispose of the potentially dangerous object after it emitted “above the permitted level” of radiation.

A council spokesperson says staff and the public have not been placed at risk, with the item consistently housed in a secure location and now safely taken off-site.

Events unfolded when, during the summer, the authority acted upon health and safety advice to check radon levels in the town hall, where the museum is based, due to low levels being fairly common in the area.

But when readings of the radioactive gas came back “higher than they should be” the Guildhall Street venue’s lower floor was cordoned off to the public and staff from June 25 to August 6.

A council spokesperson told KentOnline: “Following the monitoring, the (radon) levels were considered higher than they should be in the lower level of the museum.

‘There is no record as to how the object came to be in the museum collection’

“While further investigations were made, as a precaution, the lower level of the museum was closed to the public and areas restricted for staff.”

When government-vetted radiation protection advisers were drafted in to help tackle the problem they were asked to scan the museum’s collection.

“One item was identified within the mineral collection - not within the public area - as being above the permitted level,” the spokesperson said.

“Although already secure, this has been further addressed by removal to a secure location until appropriate disposal measures can be addressed safely as per the advice of the radiation protection officer.

“There is no record as to how the object came to be in the museum collection.”

Now, the council has struck up a three-year contract with a radiation protection firm for guidance on storing and getting rid of the object.

Meanwhile, it plans on training a specialist “radiation officer” to join its rank of employees, according to official papers.

Always known to be radioactive, the rock is understood to have joined the mineral collection between the 1970s and 1980s to help complete a geological set exclusive to the area.

For decades, Kent County Council has been responsible for the items, including the radioactive stone, which was decanted from the old Tontine Street museum in 2016.

“It was immediately isolated in the toxic materials cabinet in a suitable container and placed on the relevant toxic/radioactive register by a previous employee who was a university-trained geologist,” the spokesperson explained.

“Proper handling precautions were taken and risks known at that point. However, we didn’t have an exact reading as the 2017 check was a Geiger sweep.”

But the more recent and accurate scan gave a gamma dose rate of 50 μSv/h, meaning it is likely a piece of naturally occurring uranium, they added.

Radon gas is everywhere in the UK.

Levels in the air we breathe outside are very low but can be higher inside buildings.

It produces a cloud of invisible radioactive dust which, when inhaled, can cause serious lung damage.

“People cannot see, taste or smell ionising radiation - most of its effects cannot be observed by eye,” according to the Museum of London.

“Radiation can only be detected using specialist monitoring equipment.

“With the correct equipment, it is usually easy for a trained person to identify radioactive objects.”

Under the law, if a radioactive material is discovered museums must seek specialist advice from radiation protection advisors.