In radiation physics classes, point sources are typically used, for which it is relatively easy to describe the signal obtained by a radiation detector, such as the NaI(Tl) scintillation detector. The use of large extended radiation sources is generally avoided due to the mathematical complexity that their description may involve. However, the use of Monte Carlo simulation methods allows this limitation to be overcome. Potassium chloride, containing the ⁴⁰K isotope, is an ideal candidate for carrying out this type of experiment. The source activity is obtained through the detection of the 1460.8 keV gamma-photon emitted in the ⁴⁰K decay. In the first experiment, a cylindrical container is used, placing the NaI(Tl) detector in its center and filling the remaining space with potassium chloride. In a second, more complex case, a large radioactive source consisting of a container filled with a mixture of sand and potassium chloride, with the NaI(Tl) detector placed in the center of the mixture, is used. In this case, the mass of potassium chloride is approximately 1/5 of the sand mass. In both experiments, the detection efficiency is obtained by Monte Carlo simulation. A careful analysis of the experimental data allows to obtain a good agreement between the measured and calculated value of the activity.

中文翻译：

---

桶中的放射性


在辐射物理课程中，通常使用点源，相对容易描述由辐射探测器（例如 NaI(Tl) 闪烁探测器）获得的信号。由于其描述可能涉及数学复杂性，通常避免使用大型扩展辐射源。然而，蒙特卡罗模拟方法的使用可以克服这个限制。含有 ⁴⁰ K 同位素的氯化钾是进行此类实验的理想选择。通过检测 ⁴⁰ K衰变中发射的1460.8 keV伽马光子获得源活动。在第一个实验中，使用圆柱形容器，将 NaI(Tl) 检测器放置在其中心，并用氯化钾填充剩余空间。在第二种更复杂的情况下，使用一个大型放射源，该放射源由一个充满沙子和氯化钾混合物的容器组成，NaI(Tl)探测器放置在混合物的中心。在这种情况下，氯化钾的质量大约是沙子质量的1/5。在这两个实验中，检测效率都是通过蒙特卡罗模拟获得的。对实验数据的仔细分析可以使活性的测量值和计算值之间获得良好的一致性。