Cobalt-60 Radiation in Delhi : What is Cobalt 60 ?

Cobalt-60 Radiation in Delhi : What is Cobalt 60 ?

Cobalt-60 (60Co) is a radioactive isotope of cobalt. Due to its short half life of 5.27 years 60Co is not found in nature. It is produced artificially by neutron activation of 59Co. 60Co decays by negative beta decay to the stable isotope nickel-60 (60Ni). The activated Ni-atom emits two gamma rays with energies of 1.17 and 1.33 MeV.

Corresponding to its half life the radioactive activity of one gram of 60Co is 44 TBq (about 1100 curies). The absorbed dose constant is related to the decay energy and time. For 60Co it is equal to 0.35 mSv/(GBq h). It allows to calculate the equivalent dose, which depends on distance and activity.

Example: a 60Co source with an activity of 2.8 GBq, which is equivalent to 60 µg of pure 60Co, generates a dose of 1 mSv in one meter distance within one hour. Swallowing of 60Co reduces the distance to millimeters, and the same dose is achieved within seconds.

Test sources, such as those used for school experiments, have an activity <100 kBq. Devices for nondestructive material testing uses sources with activities of 1 TBq and more.

The high ?-energies result in a significant mass difference between 60Ni and 60Co of 0.003 u. The short life time contributes further to the high decay energy. It amounts to nearly 20 W/g, nearly 30 times larger than 238Pu.