Practice question

Solid scintillation uses thallium-activated sodium iodide crystals that produce light flashes when interacting with penetrating photons. Tritium, carbon-14, and sulfur-35 emit low-energy beta particles unable to penetrate crystal housing and efficiently interact, better suited for liquid scintillation where sample is intimately mixed. Cobalt-60 emits strong gamma rays of 1.17 and 1.33 MeV that penetrate crystal and generate ample scintillation photons detectable by photomultiplier. Therefore strong gamma emitters like cobalt-60 and sodium-24 are preferred isotopes for calibration and measurement with solid scintillation systems.