The Cobolt-57 check sources are supplied as one inch plastic disks. The small quantity of radioactive material is sealed in radioactive isotope check source the plastic with epoxy to prevent leakage and contamination. The transmission window is sufficiently thin to transmit gamma emissions without undue absorption.

Co-57 is available in the activities:
1 microCurie
5 microCuries
10 microCuries
25 microCuries
50 microCuries
75 microCuries
100 microCuries