Search for Possible Solar Influences in Ra-226 Decays

TL;DR

This study analyzed Ra-226 decay measurements over 18 years to find periodic variations, revealing annual patterns that may be influenced by environmental factors or solar processes, but not necessarily indicating new physics.

Contribution

It provides evidence of annual variations in Ra-226 decay rates and links these to solar r-mode oscillations, suggesting environmental influences rather than new physics.

Findings

Annual variations observed in 4 detectors

Variations show phase differences and amplitude changes over time

Spectral peaks align with solar r-mode oscillation frequencies

Abstract

Measurements of Ra-226 activity from eight HPGe gamma ray detectors at the NC State University PULSTAR Reactor were analyzed for evidence of periodic variations, with particular attention to annual variations. All measurements were made using the same reference source, and data sets were of varying length taken over the time period from September 1996 through August 2014. Clear evidence of annual variations was observed in data from four of the detectors. Short time periodograms from the data sets suggest temporal variability of both the amplitude and frequency of these variations. The annual variations in two of the data sets show peak values near the first of February, while surprisingly, the annual variations in the other two are roughly out of phase with the first two. Three of the four detectors exhibited annual variations over approximately the same time period. A joint statistic constructed by combining spectra from these three shows peaks approximating the frequencies of solar r-mode oscillations with $\nu_R = 11.74$ cpy, $m=1$, and $l=3,5,6.$ The fact that similar variations were not present in all detectors covering similar time periods rules out variations in activity as the cause, and points to differing sensitivities to unspecified environmental parameters instead. In addition to seasonal variations, the modulation of environmental parameters by solar processes remains a possible explanation of periodogram features, but without requiring new physics.