The "colbalt treatments" used in medicine for arresting certain types of cancer rely upon the ability of gamma rays to destroy canercous tissues. Cobalt-60 decays with the emission of Beta particles and gamma rays, with a half life of 5.27 years. How much of a 4.78 microgram sample of Co-60 remains after 30 years?
1. 0.1098 micrograms remains after 30 years
2. 0.1067 micrograms remains after 30 years
3. 0.0925 micrograms remains after 30 years
4. 0.0832 micrograms remains after 30 years
5. 0.0667 micrograms remains after 30 years