Annual Variation In Polonium Decay Rates?

Polonium is atomic element 84 which is a radioactive metal with no stable isotopes and several unstable ones (i.e. isotopes are variations of a chemical element with the same number of protons but different numbers of neutrons). One of those isotopes (Po-210) is the penultimate daughter of natural uranium-238 and was discovered in 1898 by Marie and Pierre Curie. But its short half-life of 138 days means that it is almost completely absent in nature. Polonium is usually produced in milligram quantities by the neutron irradiation of bismuth.

More or less by hypothesis, the radioactive decay of elements is an internal process which is indifferent to the environment. 

But a study at the underground low-background conditions of the Baksan Neutrino Observatory has detected annual and other kinds of periodic variation in the half-lives of three different Polonium isotopes, specifically, annular, solar-daily, lunar-daily and sidereal-daily variations, which would suggest that some sort of cosmic ray bombardment from the Sun, mitigated by shielding from the Earth and Moon, influences the decay rates of these radioactive isotopes. 

The effect sizes are modest, but statistically significant (more than two but less the four sigma), with a period consistent with one year (that could have a physical reality) in each case, but significantly varying phases that could relate, for example, to geometric Moon-Earth configurations relative to the Sun.

As the conclusion to the paper explains (the last highlighted sentence is clearly an error that includes the words "do not" where it clearly means the opposite of what it says):

Conclusion that half-life values of the 214Po, 213Po and 212Po isotopes are feel annular variations with similar amplitudes could be done on a base of a comparison of graphs on the Fig. 1. It is shown that two independent sequential sets of the 214Po τ -values (τ ≡ T1/2 ) obtained in the spaced laboratories can be described by sinusoidal functions. 

A sine function approximates a set of the 214Po τ -values with a time duration of ∼ 973 days obtained at the BNO has an amplitude A = (5.0 ± 1.5) · 10^−4 , a period ω = (365 ± 8) days and a phase ϕ = (170 ± 7) days relative to the 1st January, 2012 year. The function approximates a set of τ -values with a time duration of 1460 days obtained at the KhNU has an amplitude A = (4.9±1.8)·10^−4 , a period ω = (377±13) days and a phase φ = (77±10) days. 

The 213Po τ -value set with a time duration of ∼ 1700 days can be described by a sinusoidal function with an amplitude A = (3.9 ± 1.2) · 10^−4 , a period ω = (370±13) days and a phase φ = (130±9) days. 

The 212 Po τ -value set with a time duration of ∼ 670 days can be described by a sinusoidal function with an amplitude A = (7.5±1.6)·10^−4 , a period ω = (375 ± 13) days and a phase φ = (40 ± 10) days. 

Observed differences of the phases of the approximated sine functions have not any unambiguous explanations and define necessity of further investigations. These differences are complicate a search of the common factors caused the viewed variations. None of environmental factors examined up to now (pressure, air humidity and temperature, layer of air ionization, earth magnetic field variations, set-up instability) do not show correlations with the observed 214Po, 213Po and 212Po half-life values variations. Investigations are continuing.