為了降低由清華大學反應器(1012 n cm-1s-1)的中子束造成 38Cl, 24Na及 42K對 γ能譜上的干擾，建立一個應用於超熱中子活化分析(Epithermal Neutron Activation Analysis, ENAA)的最佳化條件，以 1 mm 厚鎘套(Cd)及 3.2 mm厚的硼-聚乙烯 (Boroned polyethylene,BPE)為封套以尋求標準品鮮苔(lichen IAEA-336)及明日葉之生物樣本內的砷-76( T1/2 = 26.3 hr)，溴 -80(T1/2 = 17.7 min)，錳-56(T1/2 = 2.58 hr)，碘-128(T1/2 = 24.9 min)、銻-122(T1/2 = 2.68 d)等元素建立確實又快速的同時多元素最佳化分析條件。結果證明 150 mg的樣本中碘及溴以照射 10分鐘、冷卻 10分鐘、計測 5分鐘，而於砷及銻是以 350 mg的樣本照射 24小時、冷卻 30至 60小時、計測 20分鐘，得到的最小可測值 minimum detectable concentrations (MDC)的最佳化分析方法。
Optimal conditions for analysis of As, Br, Mn, I and Sb contents in lichen and angelica keiskei (AK) were investigated using Epithermal Neutron Activation Analysis (ENAA). The minimum detectable concentrations (MDCs) of 76As(T1/2 = 26.3 hr), 80Br(T1/2 = 17.7 min), 56Mn(T1/2 = 2.58 hr), 128I(T1/2 = 24.9 min) and 122Sb(T1/2 = 2.68 d) were calculated at optimized conditions. This was accomplished by wrapped the irradiated target with 1 mm Cd cover and 3.2 mm Borated polyethylene (BPE) neutron filters which were adopted to screen original reactor fission neutrons and reduce of 38Cl,24Na, and 42K background activity. These results indicated that the MDCs of Br and Mn, I, measured under 10 min activation and 5 min counting followed by 10 min decay. MDCs of As, Sb were analyzed by 350 mg irradiated in 24 hr counting 20 min following by 30 to 60 hr decay was optimal for irradiation in a 1012 n cm-1s-1 thermal neutron flux.
