风化壳淋积型稀土矿中^(138)La原位γ能谱法最小可探测活度的计算

Calculation of the Minimum Detectable Activity of La in Weathered Crust Elution-deposited Rare Earth Ores with In-site γ Spectrometer

镧在赣南稀土矿中含量十分丰富,其中^(138)La作为镧的主要同位素,衰变过程中释放0.788 MeV(发射比0.344)和1.44 MeV(发射比0.656)的伽马射线。本文通过理论计算与蒙卡模拟相结合的方法建立一套针对^(138)La的现场伽马能谱测量方法。首先,利用数学理论计算得到探测器探测距离的最佳位置(距地0cm)和可探测范围(?60×20 cm)。其次,根据赣南地区七个典型稀土矿的U,Th,40K比活度数据,采用蒙特卡洛模拟获得U系,Th系,40K的天然放射性本底"秒谱"。最后,计算了^(138)La的最小可探测活度,在1000 s测量时间下^(138)La的最小可探测活度可降低至在29.88 Bq/kg~121.69 Bq/kg。

Rare earth lanthanum is very rich in southern Jiangxi rare earth ore. ^(138)La is the main radioactive isotope of lanthanum, which released 0.788 MeV(34.4%) and 1.44 MeV(65.6%) gamma rays during the decay process. In this article, an in-site detection method of La gamma spectrum was designed by theoretical calculation and Monte Carlo simulation. Firstly, a mathematical model of in-site detection was built to obtain the best detecting distance(0 cm from the ground) and detectable range(φ60×20 cm). Then, based on the U, Th and 40K specific activity data of seven typical rare earth mines in Jiangxi Province, the "peak efficiency" characteristics of natural gamma radiation were constructed by Monte Carlo simulation method.Finally, under the measurement time of 1000 s, the minimum detectable activity of ^(138)La was calculated to be 29.88 Bq/kg~121.69 Bq/kg.