Suppose a laboratory has a 26-gram sample of polonium-210.The half-life of polonium-210 is about days. a. How many half-lives of polonium-210 occur in 276 days? b. How much polonium is left in the sample after 276 days?

a) Two half lives, b)

Step-by-step explanation:

a) The polonium-210 has a half life of 138.4 days. Therefore, 1.994 half lives have past.  

b) Mass decay is described by the following exponential model:

The time constant for the isotope is:

The mass of the isotope after 276 days is: