Isotope that decays one daughter isotope

1. First, for each parent isotope that decays one daughter isotope is created.
2. Secondly, it is important to notice in the rate expression that the number of decays is not a constant function of time (say for example the way a second is always 1/60th of a minute). Rather, the number of decays over a given time period changes with the number of parents present (simple example: 1/2 the students leave every 5 minutes during this lecture). Thus, decay is not a linear function of time, rather it is ‘curved’. The concept of half-life (t 1/2) is an important concept to remember. Half-life is the time required for half of the substance to decay to a stable daughter.

Given these basic points students can follow the construction of a Parent and Daughter vs. Time graph. This graph illustrates two major points regarding radiometric dating:

1. First, the point of intersection between the parent and daughter curves (both have equal no. of atoms) illustrates the concept of a half-life.
2. Second, this exercise graphically represents the change in Parent-Daughter ratio with time. With every half-life, there will be less parent atoms and correspondingly more daughters.

Sample Solution