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给出了所研制的便携式FT 648型绝对法测氡仪的物理原理。与相对法测氡仪不同,绝对法测氡仪依据仪器的结构参数、测量的运行参数与测量读数,直接得出被测气体的氡浓度值,而毋须事先用已知氡浓度的标准气体源对仪器进行刻度。将滤膜过滤效率Σ、α自吸收修正β、能谱修正系数S、探头的几何因子Ω、及重力沉降修正因子G引入托马斯双滤膜测氡公式,用这一改进了的托马斯公式处理测量结果,消除了原公式的系统偏差。用所研制的FT 648型绝对法测氡仪测定了北京地区氡浓度按小时的平均值,及日变化规律。日平均氡浓度为8.5Bq·m~(-3),得出了“马鞍形”氡浓度—时间关系曲线。
The physical principle of portable FT 648 absolute radon detector is given. Different from the radon detector, the absolute radon detector directly obtains the radon concentration of the measured gas according to the structural parameters of the instrument, the measured operating parameters and the measurement readings, without the need of using a standard gas source of known radon concentration Scale the instrument. The filter efficiency Σ, α self-absorption correction β, spectral correction factor S, the probe geometry factor Ω, and the gravity settlement correction factor G is introduced into the Thomas double membrane measurement radon formula, using this improved Thomas formula treatment measurement As a result, the system deviation of the original formula is eliminated. With the developed FT 648 absolute radon detector measured in Beijing radon concentration by the average, and the daily variation. The average daily radon concentration is 8.5Bq · m ~ (-3), and the “saddle” radon concentration-time curve is obtained.