RADIOACTIVITYDOE-HDBK-1019/1-93 Atomic and Nuclear PhysicsNP-01Page 38Rev. 0Figure 12 Combined Decay of Iron-56, Manganese-54, and Cobalt-60Plotting the manner in which the activities of each of the three nuclides decay over timedemonstrates that initially the activity of the shortest-lived nuclide (iron-59) dominates the totalactivity, then manganese-54 dominates. After almost all of the iron and manganese havedecayed away, the only contributor to activity will be the cobalt-60. A plot of this combineddecay is shown in Figure 12.RadioactiveEquilibriumRadioactive equilibriumexists when a radioactive nuclide is decaying at the same rate at whichit is being produced. Since the production rate and decay rate are equal, the number of atomspresent remains constant over time.An example of radioactive equilibrium is the concentration of sodium-24 in the coolantcirculating through a sodium-cooled nuclear reactor. Assume that the sodium-24 is beingproduced at a rate of 1 x 10 atoms per second. If the sodium-24 were stable and did not decay,6the amount of sodium-24 present after some period of time could be calculated by multiplyingthe production rate by the amount of time. Plotting the amount of material present would resultin the graph in Figure 13.However, sodium-24 is not stable, and it decays with a half-life of 14.96 hours. If nosodium-24 is present initially and production starts at a rate of 1 x 10 atoms per second, the rate6of decay will initially be zero because there is no sodium-24 present to decay. The rate of decayof sodium-24 will increase as the amount of sodium-24 increases.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business