The half life period of radium is 1580 years. How do you imterpret this statement?

Explanation

Whatever quantity of radium is taken, it shall become half after the expiry of 1580 years. The following table explains the statement:
`{:("Quantity of radium","Quantity of radium"),("at parent","after 1580 years"),(100 "atoms",50 "atoms"),(50 "gram",25"gram"),(5 "mole",2.5 "mole"):}`