Track-Effect Theory of Scintillation Efficiency

A theoretical account is presented of the pulse-height characteristics of NaI(Tl) scintillation counters subjected to energetic heavy-ion bombardment ($Z\ge 5$, $\frac{E}{A}=1-10\mathrm{}$ MeV/nucleon) at room temperature. The falling off of scintillation efficiency $\frac{\mathrm{dL}}{\mathrm{dE}}$ with decreasing energy and the charge dependence at fixed energy are simultaneously accounted for by introducing the concept of a cylinder of high energy-deposit density surrounding the particle track. Inside the cylinder competitive events, favored by high ionization density, are assumed to dominate those which produce the characteristic luminescence emission. Agreement with experiment is best for high-$Z$ particles. Cylinder radii vary over the range $110\lesssim R_c\mathrm{}(Z,v)\mathrm{}\lesssim 390$ Å. Estimates of the fraction of the total energy loss available for efficient light production yield the values $0.20\lesssim F_0\mathrm{}(Z,v)\mathrm{}\lesssim 0.50$, while the critical value of energy-deposit density defining the high-density cylinder is approximated to be 5.32 × ${10}^7$ ${\mathrm{e}\mathrm{r}\mathrm{g}/\mathrm{c}\mathrm{m}}^3$. Also, a brief discussion is presented regarding interpretation of the heavy-ion pulse-height characteristics of pure alkali halides at low temperature, and those of anthracene and NE 102 plastic scintillators, in terms of the track-effect theory.