Interaction of Fission Fragments with Organic Scintillators

Abstract

A pulse‐shape discriminator circuit was used for the measurement of the pulse heights of the slow components of light pulses from organic scintillators excited by different types of particles: electrons, protons, alpha particles, and fission fragments. Three types of organic scintillators were employed: a crystal (stilbene), a liquid (7 g PPO and 0.5 g M₂‐POPOP in 1 liter of toluene), and a plastic (NE‐150). The relationship of the pulse heights of the slow components for excitation with electrons, protons, and alpha particles was similar for all three scintillators. However, fission fragments produced a slow component pulse height similar to protons in stilbene and the plastic but more like electrons in the liquid. The pulse‐height distributions of total light pulses from the scintillators excited by the alpha and spontaneous fission emissions of Cf²⁵² were measured. The alpha‐particle and fission‐event spectra were resolved only with the liquid scintillator giving a pulse‐height spread of the fission distribution peak of 40%. From the maximum of the fission sepctra it was calculated that the most probable energy of fission produced the same pulse height as an electron with 1/75th that energy would produce. The alpha particles and the fission events were counted with 100% efficiency and a value of 31.0±0.5 was obtained for the alpha to fission disintegration ratio of Cf²⁵².