光電倍增管反應模擬研究及香港亞伯丁宇宙線實驗校正

Abstract

近年來，液態閃爍體粒子探測器被廣泛應用於許多大型粒子偵測器當中，例如大亞灣計畫以及香港亞伯丁宇宙線偵測器。此類探測器多半以光電倍增管作為訊號採集以及放大，其校正與監控對實驗數據的可信度有很重要的影響。Bellamy的研究團隊於1994年發表了一篇以反應函數擬合從探測器得到的能譜來監控光電倍增管的方法[1]，該反應函數包含了光電倍增管大部份重要的變數，每一項變數剛好對應到一項光電倍增管的物理特性。然而，對於一些比較複雜的探測器系統，反應函數以不同起始值擬合相同能譜，會給出不同的結果，我們認為該函數因參數較多，在擬合上本會產生許多解，只是正確的解該落在哪我們並不清楚。所以，我們使用蒙地卡羅模擬來確認不同起始值對擬合結果的影響，進而歸類出較符合物理的解。本論文將探討反應函數，蒙地卡羅模擬方法，以及兩點關於香港亞伯丁探測器的應用。

Recently, scintillation detectors are extensively used in many projects with particle detector such as Dayabay and Aberdeen. Usually in such detectors, photomultiplier tubes (PMT) are used for the detection of light. The paper by Bellamy et al. [1] gives a good tool, i.e., PMT response function,to simplify the calibration process. The response function already considers almost every variable of spectrometric channel from PMT. Each variable is directly proportional to one of PMT’s parameters. However in some case, using response function to fit spectra from the same system could give different results especially when initial values taken in the fitting are varied. Our conclusion is that there are many local minima in the fitting. Monte Carlo simulation is a good scheme to understand the issue of multiple local minima. In this thesis, we shall introduce the response function, and use Monte Carlo simulation to deal with local minima. At last, we shall present two applications to Aberdeen cosmic ray experiment.