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

TL;DR

This paper introduces a new experimental system to measure the $^{40}$K decay scheme, crucial for rare event searches and geochronology, by combining silicon detector and scintillator methods for precise branching ratio determination.

Contribution

The paper presents a novel combined experimental setup for measuring the $^{40}$K decay branching ratio with improved accuracy and characterization techniques.

Findings

Characterized the silicon drift detector setup for energy calibration and efficiency.

Developed a complementary scintillator-based measurement method.

Achieved preliminary measurements of the $^{40}$K decay scheme.

Abstract

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 a role in geochronological dating techniques. The branching ratio of the electron capture directly to the ground state of argon-40 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 $^{40}$K 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.