 The KDK experiment by KDK collaboration (2021)

TIPP 2021 presentation: indico.cern.ch/event/981823/contributions/4295324/attachments/2250469/3818551/KDK_TIPP_2021_pub.pdf

Its potassium-40 decay scheme gives the approximate atomic mass-energy differences of $1.311$ MeV to calcium-40 and $1.505$ MeV to argon-40, and distinguishes capture to an excited argon level from the rare positron branch. The positron kinetic-energy endpoint additionally subtracts $2m_e$ from the atomic mass difference.