Search for the time dependence of the 137Cs decay constant

TL;DR

This study monitored 137Cs decay over several years underground, finding no significant time-dependent variations in decay rate and confirming the known half-life with high precision.

Contribution

It provides the most stringent limits to date on decay rate oscillations of 137Cs, improving previous constraints by over an order of magnitude.

Findings

No decay oscillation amplitude larger than 9.6×10⁻⁵ detected

Excluded 1-year period oscillations with amplitude >8.5×10⁻⁵ at 95% C.L.

Measured 137Cs half-life as 29.96 ± 0.08 years, consistent with literature.

Abstract

Starting from June 2011, the activity of a 137Cs source has been measured by means of a HPGe detector installed deep underground in the Gran Sasso Laboratory. In total about 5100 energy spectra, one hour measuring time each, have been collected. These data allowed the search for time variations of the decay constant with periods from a few hours to 1 year. No signal with amplitude larger than 9.6{\cdot}10-5 at 95% C.L. has been detected. These limits are more than one order of magnitude lower than the values on the oscillation amplitude reported in literature. In particular, for 1 year period an oscillation amplitude larger than 8.5{\cdot}10-5 has been excluded at 95% C.L., independently of the phase. The same data give a value of 29.96{\pm}0.08 years for the 137Cs half life, in good agreement with the world mean value of 30.05{\pm}0.08 years.