Alab technician had a sample of radioactive americium. he knew it was one of the isotopes listed in the table below but did not know which one. the sample originally contained 0.008 g of the isotope, but 120 minutes later it contained 0.002 g. a. how many half-lives have passed? b. what is the half-life of the sample? c. which isotope did he have?

a. 2

b. 1 hour

c. Am-237

Explanation:

Half life is the time taken by a reactant to reduce to its original concentration. It is designated by the symbol .

Formula used :

where,

a = amount of reactant left after n-half lives = 0.002

= Initial amount of the reactant = 0.008 g

n = number of half lives  = ?

Putting values in above equation, we get:

Thus two half lives have passed.

2. If two half lives have passed in 120 minutes

one half life will be passed in = or 1 hour

3. As half life is characteristic of a particular isotope.

Given : the half life of isotope Am-237 is 1 hour or 60 minutes. thus the isotope was Am-237.