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研制了一台大面积低本底α屏栅电离室,其阴极表面积为1500cm~2,收集极对地电容约20pF,充以1.8大气压的 P_(10)气体(90%氩+10%甲烷)。分析了几种主要因素对能量分辨率的贡献,在源自吸收贡献为30keV 情况下,对~(210)Poα源的能量分辨率约为41keV。在4—6MeV 能区内装置的本底为6.1cph,在5MeV 处50keV 谱宽内的本底为0.1cph。采用新试制的氧化锆除氧炉循环净化负电性气体,以保证长时间稳定工作。对~(210)Po 电沉积小源测得的分辨率约为35—45keV;对于厚度为40μg/cm~2的1500 cm~2大源测得的分辨率平均为69keV,和估算值相符。最低可测放射性强度为10~(-14)—10~(-15)Ci。
A large area low background alpha grid ionization chamber with a cathode surface area of 1500cm ~ 2 and a collector - to - ground capacitance of about 20pF was charged with 1.8 atmosphere of P 10 gas (90% argon + 10% methane). The contributions of several main factors to the energy resolution were analyzed. The energy resolution for ~ (210) Poα source was about 41keV when the absorption contribution was 30keV. The background of the device in the 4-6 MeV energy range was 6.1 cph and the background at 50 keV spectral width at 5 MeV was 0.1 cph. A new trial of zirconia oxygen furnace cycle purification of negative electrical gas to ensure long-term stability. The resolution of ~ (210) Po electrodeposition is about 35-45 keV. The resolution of 1500 ke ~ 2 source with thickness of 40 μg / cm ~ 2 is 69 keV, which is consistent with the estimated value. The lowest detectable radioactivity intensity is 10 ~ (-14) -10 ~ (-15) Ci.