The element strontium has at least 16 isotopes. One of these isotopes is strontium-89. This isotope has a half-life of 52 days.
State what is meant by isotopes.
Calculate the probability per second of decay of a nucleus of strontium-89.
A laboratory prepares a strontium-89 source. The activity of this source is measured 21 days after preparation of the source and is found to be 
. Determine, for the strontium-89 source at the time that it was prepared,
the activity,
the mass of strontium-89.
.
.
.
