Iodine – 125 emits gamma rays when it decays to Tellerium-125 and has a half-life of 60 days. If a 0.020 g pellet of iodine – 125 is implanted into a prostate gland, how much iodine – 125 remains there after one year

0.0003125 g

Explanation:

Given data:

Half life of iodine-125 = 60 days

Mass of iodine pellet  = 0.020 g

Mass of iodine remain after one year = ?

Solution:

one year = 365 days

Number of half lives = Time elapsed/ half life

Number of half lives = 365 days/ 60 days

Number of half lives = 6

At time zero = 0.020 g

At 1st half life = 0.020 g/2 = 0.01 g

At 2nd half life = 0.01 g / 2 = 0.005 g

At 3rd half life = 0.005 g/2 = 0.0025 g

At 4th half life = 0.0025 g / 2 = 0.00125 g

At 5tht half life = 0.00125 g / 2 =  0.000625 g

At 6th half life = 0.000625 g/ 2 = 0.0003125 g