Radioactive material sealed in a metal case has gone missing from a parking lot at a road construction site in Ashikaga, Tochigi Prefecture, the government said Sunday.
There is a danger of slight exposure to radiation if the material is taken out of the case and touched, but no danger if it is kept 1 meter away, according to the science ministry.
The material is used for a device that measures ground density, the ministry said.
It went missing when a construction worker left it unattended for about 30 minutes Friday morning.
The incident was not reported to the Ashikaga police until Saturday night.
Whoever has the material is urged to call the ministry or police and refrain from touching it.