Gamma ray detection sensitivity of superheated drop detectors, 1

Abstract

The gamma-ray detection sensitivity of a Superheated Drop Detector (SDD) has been investigated. SDD was composed of droplet of octafluoropropane (C3F8) as the sensitive liquid and glycerol as the droplets supporting medium. The gamma-ray detection sensitivity has been calculated using Monte Carlo code ITS3.0, and the calculation results have been compared with some published experimental results. The mechanism and equations for the nucleation process of superheated liquids up to growing up to a visible bubble from a vapor cavity by radiation was described. The creation of a bubble was determined by the stopping power of the charged particle produced. The value of the electron stopping power in C3F8 has been obtained using ITS3.0 code. It was found that the electron stopping power increases monotonously with decreasing electron energy. The gamma-ray detection sensitivity of the detector has been determined by calculating the electron flux in the detector by incident gamma rays using ITS3.0. The comparison of the calculated results with the existing experimental data showed that the presence of a few percent of heavy elements in the supporting medium has an important influence on the sensitivity in the lower energy region of the gamma-rays.

過熱液滴検出器(SDD)のガンマ線検出感度を検討した。SDDは感応液体であるオクタフルオロプロパン(C3F8)の液滴と液滴支持媒質であるグリセリンから成る。ガンマ線検出感度をモンテカルロ・コードITS3.0を使って計算し、計算結果を既報の実験結果と比較した。放射線により蒸気空洞から可視気泡に成長するまでの過熱液体の核生成過程に関するメカニズムと方程式を解説した。気泡の生成は発生した荷電粒子の阻止能により決まることを指摘した。C3F8内の電子阻止能の値をITS3.0で求めた。電子阻止能は電子エネルギーの減少に伴い単調に増加することが分かった。検出器のガンマ線検出感度は入射ガンマ線による検出器内の電子フラックスをITS3.0で計算して決定した。既存の実験データと計算結果との比較は、支持媒質中に存在する数パーセントの重元素がガンマ線の低速領域における感度に重大な影響を与えることを示した。