Radioactivity
Higher than the natural ambient/background radiation, it originates from building materials or is inhomogeneous at geological faults and underground watercourses. It causes cell damage (tumors), cell death, etc. Radioactivity (=ionizing radiation) is measured in sieverts per hour (Sv/h) or simply as a count rate (pulses/second [Ips] or pulses/minute [Ipm]).
