  Analysis results of data of long-term radioactivity measurements of 3H, 56Mn,
32Si, 36Cl, 60Co, 137Cs, 90Sr-90Y, 226Ra, 238Pu and 239Pu sources are
presented. For beta-radioactive sources, their activity in addition to the
exponential drop is characterized by rhythmic variations with a period of 1
year and magnitude of 0.1-0.35% from the average value. These oscillations
attain maximum values between January and March, with corresponding minimum
values occurring from July to September. Spectral analysis of 7-year long
measurements of count rates of beta-radioactive sources 90Sr-90Y as well as
15-year long measurements of beta-gamma radiation of 226Ra revealed presence of
rhythmic variations with a period of about a month and magnitude 0.01%.
Magnitude of diurnal oscillations did not exceed 0.003%. Analysis of
measurements data for alpha radioactive sources 238Pu and 239Pu did not reveal
any statistically reliable periodic patterns. Possible factors underlying these
rhythmic oscillations in beta-radioactivity are discussed.
