In the laboratory, a more useful measurement is the decay rate R, usually measured in di...

In the laboratory, a more useful measurement is the decay rate R, usually measured in disintegrations per second, counts per minute, etc. Thus, the decay rate is defined as R = -dN/dt. Using the equation dN/dt = -λN, it is easily seen that R = λN. Furthermore, differentiating the solution with respect to t reveals that

in which is the decay rate at t = 0. That is, because R and N are proportional, they both decrease with time according to the same exponential law. Use this idea to help solve Exercise.

A 1.0 g sample of Radium 226 is measured to have a decay rate of disintegrations/s. What is the half-life of 226Ra in years? Note: A chemical constant, called Avogadro's number, says that there are atoms per mole, a common unit of measurement in chemistry. Furthermore, the atomic mass of .