However this half life still requires cobalt sources to be replaced about every 5 years .
The main reason for its wide use in radiotherapy is that it has a longer half - life , 5.27 years , than many other gamma emitters .
This half life still requires cobalt sources to be replaced about every 5 years .
The main reason for its wide use in radiotherapy is that it has a longer half - life , 5.27 years , than many other gamma emitters .