Potassium-40 (⁴⁰K) is a long-lived, naturally occurring radioactive isotope. The decay products are prominent backgrounds for many rare event searches, including those involving NaI-based scintillators. ⁴⁰K also plays a role in geochronological dating techniques. The branching ratio of the electron capture directly to the ground state of ⁴⁰Ar has never been measured, which can cause difficulty in interpreting certain results or can lead to lack of precision depending on the field and analysis technique. The KDK (Potassium (K) Decay (DK)) collaboration is measuring this decay. A composite method has a silicon drift detector with an enriched, thermally deposited ⁴⁰K source inside the Modular Total Absorption Spectrometer. This setup has been characterized in terms of energy calibration, gamma tagging efficiency, live time and false negatives and positives. A complementary, homogeneous, method is also discussed; it employs a KSr${}_2$I${}_5$:Eu scintillator as source and detector.

钾 40 ( ⁴⁰ K) 是一种长寿命的天然放射性同位素。衰变产物是许多罕见事件搜索的重要背景，包括那些涉及基于 NaI 的闪烁体。 ⁴⁰ K 还在地质年代学技术中发挥作用。电子捕获直接与⁴⁰ Ar基态的分支比从未被测量过，这可能导致解释某些结果的困难或可能导致精度不足，具体取决于领域和分析技术。KDK（钾（K）衰变（DK））合作正在测量这种衰变。一种复合方法具有硅漂移检测器，该检测器具有富集的热沉积 ⁴⁰模块化总吸收光谱仪内的 K 源。这种设置的特点是能量校准、伽马标记效率、实时时间以及假阴性和阳性。还讨论了一种互补的、同质的方法；它采用 KSr${}_2$一世${}_5$:Eu 闪烁体作为源和检测器。