atomic weight Aand Avogadro’s number 6.02 × 1023 atoms per g·atom as
follows:
(3.7)
When two or more radionuclides are present in a sample, the measured
count of such a sample comprises counts of all individual radionuclides.
A semilogarithmic plot of the activity of a two-component sample versus
time is shown in Figure 3.3. The half-life of each of the two radionuclides
can be determined by what is called the peeling or stripping method. In
this method, first, the tail part (second component) of the curve is extra-
polated as a straight line up to the ordinate, and its half-life can be deter-
mined as mentioned previously (e.g., 27 hr). Second, the activity values on
this line are subtracted from those on the composite line to obtain the activ-
ity values for the first component. A straight line is drawn through these
points, and the half-life of the first component is determined (e.g., 5.8 hr).
N
W
A
=× ×602 10.^23
24 3. Kinetics of Radioactive Decay
Fig. 3.3. A composite radioactive decay curve for a sample containing two radionu-
clides of different half-lives. The long-lived component (a) has a half-life of 27 hr
and the short-lived component (b) has a half-life of 5.8 hr.