III. Scintillation Detectors（三世。）.pdf

III. Scintillation Detectors Sources: J.B. Birks, The Theory and Practice of Scintillation Counting, New York, 1964 G.F. Knoll, Radiation Detection and Measurement, New York, 1989 S.E. Derenzo, Scintillation Counters, Photodetectors and Radiation Spectroscopy, IEEE Short Course Radiation Detection and Measurement, 1997 Nuclear Science Symp. • Incident particles or photons excite atoms or molecules in the scintillating medium. • Excited states decay under emission of photons, which are detected and converted into electric signals. 1. Scintillation materials Both organic and inorganic materials, can be solid, liquid or gaseous a) organic scintillators (e.g. plastics) states of interest are energy levels of individual molecules, i.e. no interactions with neighbors ⇒ excitation and emission spectra practically the same whether in solid, liquid or gaseous state. Introduction to Radiation Detectors and Electronics Copyright  1998 by Helmuth Spieler III. Scintillation Detectors Typical energy levels (from Birks, as redrawn by Derenzo) a) At room temperature practically all electrons in ground state. (since energy of S1 states 0.025 eV) b) Incident radiation populates S states 1 vibrational levels within S1 band decay radiation-less to S base state, which in turn decays under emission of 1 light to the S band. 0 c) S1 can also decay to adjacent triplet levels. Since their energy is significantly lower, the decay time is much longer. Introduction to Radiation Detectors and Electronics Copyright  1998 by Helmuth Spieler III. Scintillation Detectors Why isn’t e