The Placzek transient is a phenomenon studied in nuclear engineering. The Placzek transient occurs when a population of monoenergetic neutrons of energy E elastically scatter within a homogeneous medium. In each collision the neutrons impart a fraction of their energy to the nuclei in the medium, losing up to a maximum of
\DeltaEmax=(1-\alpha)E
\alpha=\left(
A-1 | |
A+1 |
\right)2
where A is the atomic number of the medium. In nuclear engineering, neutrons that have not yet undergone a collision are called the 1st generation, those that have undergone a single collision are the 2nd generation, those that have undergone two collisions are the 3rd generation, and so on. The neutrons from each generation collectively form the total neutron population within the medium.
The Placzek transient is a discontinuity of the neutron flux, and derivatives of the flux, at integer multiples of
\alphaE
Emin=\alphaE
Emin
\alphaE
\alphaE
The Placzek transient can be derived analytically by solving for the neutron flux using a piecewise function solution to a differential equation involving a Heaviside step function in energy intervals of width
(1-\alpha)E