Delighted to find that South Terras mine lived up to repution.
Pic shows geiger counter reading 7.64 microSieverts per hour.
For this geiger-counter, set to display counts-per-minute, that's about 720CPM to 740CPM. Cornwall background radiation is about 35CPM; UK general is around 18CPM.
So this reading is about 30X background radiation level. Still low - but impressive.
This was by the pumping shaft - now overgrown and flooded to within a metre of ground level.
Reputed to be the highest natural radiation level in Britain.
Lots of detail about South Terras on the Internet - not replicated here.
(R. Smith, 07Apr2024)