What does the term λ_eff indicate in the context of Xe-135 population changes?

The term λ_eff represents the effective decay rate of xenon-135 (Xe-135), particularly in the context of how it influences reactor operation. Xe-135 is a significant neutron absorber due to its presence as a fission product. When discussing its population changes, λ_eff accounts for both the decay of Xe-135 and its production from the decay of other isotopes, primarily iodine-135 (I-135).

In a nuclear reactor, the dynamics of neutron economy are critical, and the effective decay rate is crucial for understanding how Xe-135 impacts reactivity. As fission occurs, neutrons are produced which can be absorbed by xenon-135. Its presence can lead to negative reactivity if its population rises, which in turn affects the overall power output of the reactor. The effective decay rate encapsulates how reactor operation may adjust in response to changes in the concentration of Xe-135, enabling reactor operators to manage and anticipate changes in reactivity.

Overall, λ_eff is essential for predicting how effectively reactor control can be maintained in the face of changes in xenon-135 concentration, thereby ensuring safe and stable operation of nuclear reactors.