KDK: Potassium for Dark Matter

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We propose to investigate a conventional nuclear process that may debunk a controversial claim for detection of the exotic dark matter thought to make up most of the universe. The radioactivity of potassium could contribute more background than previously thought to the very sensitive experiments looking for dark matter. Among other things, our project requires a radioactive source equivalent to two bananas. Potassium-40 (40K) is a naturally-occurring isotope. Low-energy X-rays from its electron capture decay to the ground state of argon-40 (40Ar) represent a significant radioactive background in various rare-event searches such as DAMA. However, its branching ratio has never been measured, though it is critical to the interpretation of the longstanding, yet controversial, claim for dark matter discovery by DAMA. Measuring this branching ratio is the goal of the KDK (potassium decay) experiment. KDK will involve a 40K radioactive source, a small X-ray detector, and a large veto to tag the gammas from the competing electron-capture decay to the excited state of 40Ar. There is an excellent window of opportunity to carry out this measurement before August 2017 and the dismantling of the MTAS facility at Oak Ridge National Laboratory (TN), a veto with a uniquely high efficiency. We therefore request funds for the 40K source, the X-ray detector, vacuum infrastructure, and a circulating chiller. The items requested here, and the X-ray detector in particular, as well as the analysis of the data, will form the bulk of the work in a Master's dissertation, and will be used by an undergraduate summer student as well.