A precision experiment to investigate long-lived radioactive decays

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 β 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 × 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 \order{-4}.

No correlation between Solar flares and the decay rate of several β-decaying isotopes

“…From the continuously monitored slow control parameters we find that the variation [17]. We therefore conclude that systematic influences due to slow control parameters remain <2 · 10 −5 .…”

“…In this work, we present radioactive decay data for the month of September 2017, measured at two different locations with identical and independent NaI(Tl) detectors. The complete detector setups are discussed in detail in [17]. Each of the setups contain four cylindrical (76×76)mm NaI(Tl) detector pairs.…”

“…Waveforms from each event are integrated to reconstruct the deposited energy and a spectrum is produced. We use a fitting routine which considers a Gaussian absorption peak, together with a background spectrum and the Compton spectrum, obtained from a Monte Carlo simulation performed with GEANT4, to obtain the number of counts inside the full absorption peak in one-hour bins [17].…”

“…For the 60 Co source monitored by the UZH setup we also 2 search during the second (X8.2) flare of September 10th. Other sources monitored by the setups at UZH, Purdue University, USA and at CBPF Rio de Janeiro, Brazil [17] are not used here since either data was not taken during the flares, the activity of the sources was low, or the detector saturated at high energies.…”

Testing claims of the GW170817 binary neutron star inspiral affecting β-decay rates

“…In this work, we present a search for correlations in the decay rates from a ∼ 0.8 kBq 44 Ti 2 , a ∼ 0.5 kBq 60 Co and a ∼ 0.8 kBq 137 Cs source, monitored by a NaI(Tl) detector setup in a 5 h time interval following the observation of the neutron star inspiral on August 17, 2017. The detector setup [10] located at Nikhef (Amsterdam, the Netherlands), consists of four cylindrical (76×76) mm NaI(Tl) detector pairs shielded by 5 cm of lead. Three detector pairs measure the de-excitation photons after the β-decay of the sources while the fourth detector pair monitors the ambient radioactive background.…”