A novel experimental system for the KDK measurement of the 40K decay scheme relevant for rare event searches

Potassium-40 ($^{40}$K) 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. $^{40}$K also plays role in geochronological dating techniques. branching ratio of the electron capture directly to ground state argon-40 has never been measured, which can cause difficulty interpreting certain results or lead lack precision depending on field and analysis technique. KDK (Potassium (K) Decay (DK)) collaboration measuring this decay. A composite method silicon drift detector with an enriched, thermally deposited source inside Modular Total Absorption Spectrometer. This setup characterized terms energy calibration, gamma tagging efficiency, live time false negatives positives. complementary, homogeneous, discussed; it employs KSr$_2$I$_5$:Eu scintillator as detector.