[Paper Review] Evidence against correlations between nuclear decay rates and Earth-Sun distance

E. B. Norman, Edgardo Browne+3 more|arXiv (Cornell University)|Oct 17, 2008

Radioactive Decay and Measurement Techniques6 references77 citations

TL;DR

This study reanalyzes 15 years of gamma-ray decay data from 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am to test if their decay rates correlate with Earth-Sun distance, as previously suggested by Jenkins et al. The authors find no evidence for such correlations and set 3σ upper limits on any amplitude of annual modulation at 0.004% to 0.06%, strongly disfavoring proposed mechanisms involving solar neutrinos or unknown solar fields.

ABSTRACT

We have reexamined our previously published data to search for evidence of correlations between the rates for the alpha, beta-minus, beta-plus, and electron-capture decays of 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am and the Earth-Sun distance. We find no evidence for such correlations and set limits on the possible amplitudes of such correlations substantially smaller than those observed in previous experiments.

Motivation & Objective

• To test the hypothesis that nuclear decay rates of long-lived isotopes vary annually in correlation with Earth-Sun distance.
• To investigate whether such variations could be caused by solar neutrino flux or an unknown solar field.
• To reanalyze high-precision gamma-ray decay data collected over 15 years to detect subtle periodic modulations.
• To use isotope ratio analysis to minimize systematic effects from detector or electronics drift.
• To set stringent upper limits on the amplitude of any such correlation, improving on prior experimental claims.

Proposed method

• Collected gamma-ray spectra using high-purity germanium detectors over extended periods (1–2 years) for 44Ti, 121Snm, and 108Agm.
• Measured net peak areas by subtracting background regions from peak regions to extract decay signal.
• Used reference isotopes with well-known half-lives (e.g., 241Am, 133Ba) to form ratioed data, minimizing instrumental drift effects.
• Corrected measured ratios for expected exponential decay using λeff = λ1 - λ2 to isolate potential periodic variations.
• Applied χ²/ν tests to compare the null hypothesis (no variation) against the Jenkins hypothesis (annual variation correlated with 1/R²_ES).
• Varied the amplitude of the proposed annual variation to determine 3σ upper limits via ∆χ² = 9 criterion.

Experimental results

Research questions

• RQ1 Is there a statistically significant correlation between nuclear decay rates and Earth-Sun distance?
• RQ2 Do alpha, beta-minus, beta-plus, and electron-capture decays of different isotopes show synchronized annual modulations?
• RQ3 Can the observed annual variations in prior studies be explained by instrumental drift or systematic effects?
• RQ4 What are the upper limits on the amplitude of any such correlation, given the precision of our data?
• RQ5 Does the ratio of decay rates from two different isotopes show annual variations if the decay rates are correlated with Earth-Sun distance?

Key findings

• No evidence was found for correlations between decay rates of 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am and Earth-Sun distance.
• The null hypothesis (no annual variation) is strongly favored, with χ²/ν values of 1.08, 1.09, and 1.23 for the 22Na/44Ti, 241Am/121Snm, and 133Ba/108Agm data sets, respectively.
• The Jenkins hypothesis (annual variation correlated with 1/R²_ES) is rejected, with χ²/ν values of 3.39, 5.25, and 20.8 for the same data sets.
• 3σ upper limits on the amplitude of any Earth-Sun distance-correlated variation were determined to be 0.06% for 22Na/44Ti, 0.024% for 241Am/121Snm, and 0.004% for 133Ba/108Agm.
• These upper limits are 2.5 to 37 times smaller than the amplitudes reported in earlier studies by Alburger et al., Siegert et al., and Falkenberg.
• The results strongly disfavor proposed mechanisms involving solar neutrino flux or an unknown solar field as the cause of decay rate variations.