A) By mass spectral analysis, a sample of strontium is known to contain 2.64x1010atoms of Sr-90 as the only radioactive element. The absolute disintegration rate of this sample is measured as 1238 disintegrations per minute. Calculate the half-life (in years) of Sr-90.
B) How long will it take (in years) for the disintegration rate of this sample to drop to 886 disintegrations per minute?
C) How long will it take (in years) for the disintegration rate of this sample to drop to 886 disintegrations per minute?