A Precision Experiment to Investigate Long-Lived Radioactive Decays

TL;DR

This experiment rigorously measures long-term radioactive decay rates using multiple detectors across continents to detect potential variations and systematic influences with high precision.

Contribution

It introduces a stable, multi-site experimental setup with advanced data acquisition for precise long-term decay rate measurements, addressing previous uncertainties and claims of decay anomalies.

Findings

Systematic uncertainties are well-characterized and controlled.

The experiment achieves sensitivity below 10^{-4} in detecting decay rate variations.

No significant time-dependent decay rate variations were observed.

Abstract

Radioactivity is understood to be described by a Poisson process, yet some measurements of nuclear decays appear to exhibit unexpected variations. Generally, the isotopes reporting these variations have long half lives, which are plagued by large measurement uncertainties. In addition to these inherent problems, there are some reports of time-dependent decay rates and even claims of exotic neutrino-induced variations. We present a dedicated experiment for the stable long-term measurement of gamma emissions resulting from $\beta$ decays, which will provide high-quality data and allow for the identification of potential systematic influences. Radioactive isotopes are monitored redundantly by thirty-two 76 mm $\times$ 76 mm NaI(Tl) detectors in four separate temperature-controlled setups across three continents. In each setup, the monitoring of environmental and operational conditions facilitates correlation studies. The deadtime-free performance of the data acquisition system is monitored by LED pulsers. Digitized photomultiplier waveforms of all events are recorded individually, enabling a study of time-dependent effects spanning microseconds to years, using both time-binned and unbinned analyses. We characterize the experiment's stability and show that the relevant systematics are accounted for, enabling precise measurements of effects at levels well below $\mathcal{O}(10^{-4})$.