Optimalisering van fisiese eienskappe van vloeistofsintillasiedetektore

Abstract

The Physics Department of the Potchefstroom University for C.H.E. intends to install an underground muon telescope in a mine under a depth of rock with an effective absorbing thickness of 420 hg m-2 to study the ~nisotropy in the in= tensity of galactic cosmic rays. This experiment will primarily consist of the equipment, including sixty liquid scintillation counters, used in the neutrino experiment con= ducted by the Case-Wits-Irvine co-operation during the 1960's. Because some characteristics of the scintillation counters were unknown and because of the ageing of the scintillation liquid, a series of experiments had to be done to determine the properties of the equipment at present. Firstly, the relative response function of a counter was determined, while using an anticoincidence screen to elimi= nate associated particles. To determine the efficiency of this anticoincidence screen, the contribution of any remai= ning associated particles to the form of a pulse height dis= tribution was determined. It was found that the screen had such a high efficiency that the contribution of asso= ciated particles to the form of a pulse height distribution could be neglected. An attempt was made to measure a single photo-electron spec= trum for calibration purposes. While this did not succeed, the response function of the counter was determined by cal= culating the number of photo-electrons per channel from a well chosen normalized pulse height distribution. This distribution was approximated by a normal probability den= sity function. Secondly, the efficiency of a complete counter with four photomultipliers, (two at each end), was theoretically op= timized by determining the combination of coincidences be= tween the photomultipliers which had the highest efficiency over the whole area of the counter and the lowest noise rate. The conbination where the pulses of two opposing photomultipliers were added and brought in coincidence with the added pulse of the other two photomultipliers, proved to be the most efficient.