Question

A patient is given 0.050 mg of tecgnetium -99m ( where m means mestastable- an unstable but long-lived state) a radioactive isotope with a half-life of about 6.0 hours. How long until the radioactive isotope decays to 7.8×10^-4 mg ?​

Answer 1

36 hrs

Explanation:

It will need to decay 6 half-lives, which is 36 hrs

0.050/2 = 0.025 (6 hrs)

0.025/2 = 0.0125 (6 hrs)

0.0125/2 = 0.00625 (6 hrs)

0.00625/2 = 0.003125 (6 hrs)

0.003125/2 = 0.0015625 (6 hrs)

0.0015625/2 = 0.00078 = 7.8 x 10^-4 (6 hrs)