[Paper Review] Concerning the Time Dependence of the Decay Rate of 137Cs

J. H. Jenkins, Ephraim Fischbach+3 more|arXiv (Cornell University)|Nov 9, 2012

Radioactive Decay and Measurement Techniques2 references4 citations

TL;DR

This study analyzes 10 years of 137Cs decay rate data from PTB (1999–2008) using time-frequency spectrograms and power-spectrum analysis, finding no significant annual oscillation. In contrast, 133Ba measured on the same system shows strong annual and harmonic periodicities, indicating that decay rate variability is nuclide-specific and not due to systematic effects, supporting the hypothesis of a solar influence on certain isotopes.

ABSTRACT

The decay rates of 8 nuclides (85Kr, 90Sr, 108Ag, 133Ba, 137Cs, 152Eu, 154Eu, and 226Ra) were monitored by the standards group at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany, over the time frame June 1999 to November 2008. We find that the PTB measurements of the decay rate of 137Cs show no evidence of an annual oscillation, in agreement with the recent report by Bellotti et al. However, power spectrum analysis of PTB measurements of a 133Ba standard, measured in the same detector system, does show such evidence. This result is consistent with our finding that different nuclides have different sensitivities to whatever external influences are responsible for the observed periodic variations.

Motivation & Objective

• To investigate whether 137Cs decay rates exhibit periodic variations, particularly annual oscillations, using long-term PTB measurements.
• To compare 137Cs decay behavior with other nuclides (especially 133Ba) measured under identical conditions to isolate systematic effects.
• To determine whether observed periodicities in decay rates are due to environmental factors or intrinsic nuclear phenomena.
• To assess the consistency of decay rate variability across different isotopes and detector systems.
• To evaluate the hypothesis that solar influences, such as neutrino flux or solar oscillations, may modulate nuclear decay rates.

Proposed method

• Power-spectrum analysis using the Lomb-Scargle method on residual decay data after half-life fitting.
• Time-frequency spectrograms generated via RONO normalization and sequential likelihood power-spectrum analysis on 500-measurement segments.
• Comparison of 137Cs and 133Ba decay data collected simultaneously with the same detector and electronics at PTB.
• Use of spectrograms to detect intermittent or non-steady periodicities, especially annual and sub-annual frequencies.
• Analysis of data from multiple nuclides (8 in total) including 85Kr, 90Sr, 108Ag, 152Eu, 154Eu, and 226Ra for cross-comparison.
• Cross-validation with results from Ellis (2010), Alburger et al. (1980), and Bellotti et al. (2012) to assess consistency and systematics.

Experimental results

Research questions

• RQ1 Does the decay rate of 137Cs exhibit any significant annual or sub-annual periodicity over a 10-year measurement period?
• RQ2 Why does 133Ba show strong annual oscillations while 137Cs does not, despite being measured on the same detector system?
• RQ3 Can the observed periodicities in decay rates be attributed to environmental or instrumental effects, or do they point to a physical mechanism like solar influence?
• RQ4 Are the amplitudes and phases of periodic variations in decay rates consistent across different nuclides, or do they vary significantly?
• RQ5 Do the observed periodicities align with known solar frequencies, such as Rieger-type oscillations or solar rotation harmonics?

Key findings

• The spectrogram of 137Cs decay rate data shows only a slight, non-significant suggestion of annual oscillation between 2002 and 2004, with no conclusive evidence of periodicity.
• In contrast, 133Ba data from the same detector system exhibit a strong, sustained annual oscillation from 2003 to 2005, with additional evidence of a 2-year-1 harmonic, possibly indicating a Rieger-type oscillation.
• The absence of annual periodicity in 137Cs but its presence in 133Ba under identical experimental conditions strongly argues against systematic or environmental causes.
• The differential behavior between 137Cs and 133Ba, despite shared detector and electronics, supports the hypothesis that decay rate variability is nuclide-specific and not due to measurement artifacts.
• The data are consistent with the hypothesis that solar influences—such as modulated neutrino flux or solar oscillations—may affect certain isotopes differently, as seen in other nuclides like 226Ra and 32Si/36Cl.
• The study reinforces that not all nuclides exhibit time-varying decay rates, and when they do, the patterns (amplitude, phase, frequency) differ significantly across isotopes.