Plastic Scintillation Detector for Fast Beta/Electron Detection
This manual was written as part of a student lab exercise in the KJM-FYS 5920 course at the University of Oslo in the autumn 2010.
Co-author (student): Tomas
Lab supervisor: Hilde-Therese Nyhus (PhD-student)
Responsible teacher: Prof. Jon Petter Omtvedt
User Manual for Plastic Scintillation Detector for Fast Beta/Electron Detection
Organic Scintillators are characterized by their very rapid decay time. It is in the order of a few nanoseconds or less. They contain linked or condensed benzene-ring structure. se fig.
The transitions made by the free valence electrons of the molecules emits scintillation light which the compound is transparent for and therefor can be registered by an observer. The most common organic scintillators are the the anthracene crystals which has the highest light output of all organic scintillators and is therefore chosen as a reference.
Plastic scintillators are the most used organic scintillators and are low-cost and can easily be shaped in any size and form. As most organic scintillators, they have a short decay times, 2-3 ns, which is short even for organic scintillators. Plastic also have a high light output and narrow light emission spectra.
In this exercise we use the NE 102a plastic scintillator. It has a decay constant of 2.4 ns and a light output of 65% compared to anthracene. The plastic was first throughly cleaned with "isopropanol" and then mounted to the PMT (photomultiplier tube) using optical grease (BC-630). It is important to twist the plastic on, to avoid air bubbles to form between the plastic and the PMT. A double layer of aluminum foil was put around the plastic and the PMT. It is important to get the detectors front as flat as possible and the foil was fastened by black insulating tape which covered the whole detector, except the front.