The latest radioactive fragment found on Sandside Beach near the Dounreay nuclear plant in Caithness is among the "hottest" yet detected.
The Dounreay site is being decommissioned
The particle of Caesium-137 was picked up during a sweep of the beach.
It was the third recovered since monitoring resumed in August following a lengthy gap.
The latest find brings the legacy of pollution from the plant to 97 used reactor fuel particles and an unidentified radioactive object.
After being taken back to a laboratory at the former fast reactor complex, last Friday's find was found to have an activity count of 380,000 Becquerel (Bq).
Becquerel is a measurement of radioactivity.
Last week's discovery compares to the most active 500,000 Bq particle, which was recovered in February.
The majority unearthed at Sandside have been below 100,000 Bq.
Public health authorities and the Scottish Environment Protection Agency (Sepa) have not judged the risk posed by the pollution to justify closing off public access to the beach.
The independent Dounreay Particles Advisory Group has assessed the risk of someone coming into contact with a potentially harmful particle as 80 million to one.
The UK Atomic Energy Authority (UKAEA) was earlier this year fined £100,000 at Wick Sheriff Court after admitting three charges relating to the rogue discharges of the particles between 1963 and 1984.