How do you calculate Current Relative Intensity using half-life of an element if you know the relative intensity of the isotope when it was prepared.

All the information I have is provided below.

Table 1 lists the relative intensities of gamma-ray lines from the mixed Eu/Sb source when prepared in 1981 (see Table D1). From the given half lives of these isotopes calculate their current relative intensities.

Table 1 lists the relative intensities of gamma-ray lines from the mixed Eu/Sb source when prepared in 1981 (see Table D1).

From the given half lives of these isotopes (Appendix D) calculate their current relative intensities.

A mixed source (ID# SRM 4275- 174) prepared at the National Standards Institute in 1981 will be used comprising mostly isotopes of europium and antimony, whose half-lives are 8.49 yrs. (154-Eu) and 2.75 yrs. ( 125-Sb).

The isotopes are in the form of dried deposits of chlorides and sulfides, approximately 0.3 mm in diameter, sandwiched between two thin polyester films and mounted on a 5-cm diameter aluminum frame.