Radioactive isotopes are often introduced into the body through the bloodstream. their spread through the body can then be monitored by detecting the appearance of radiation in different organs. one such tracer is 131i, a β− emitter with a half-life of 8.0

d. suppose a scientist introduces a sample with an activity of 345 bq and watches it spread to the organs.

We are asked for the decay rate (which means the same as activity) after 24 days. The half life is 8 days. After 8 days the activity is halved: A = 425/2 = 212.5Bq ;)

this age may represent the age of the earth's accretion, of core formation, or of the material from which the earth formed. this dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.