  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 $\mathcal{O}(10^{-4})$.
