This article presents a power-spectrum analysis of 2,350 measurements of the ^ { 90 } Sr/ ^ { 90 } Y decay process acquired over the interval 4 August 2002 to 6 February 2009 at the Lomonosov Moscow State University ( LMSU ) .
As we have found for other long sequences of decay measurements , the power spectrum is dominated by a very strong annual oscillation .
However , we also find a set of low-frequency peaks , ranging from 0.26 year ^ { -1 } to 3.98 year ^ { -1 } , which are very similar to an array of peaks in a power spectrum formed from Mt Wilson solar diameter measurements .
The Mt Wilson measurements have been interpreted in terms of r-mode oscillations in a region where the sidereal rotation frequency is 12.08 year ^ { -1 } .
We find that the LMSU measurements may also be attributed to the same type of r-mode oscillations in a solar region with the same sidereal rotation frequency .
We propose that these oscillations occur in an inner tachocline that separates the radiative zone from a more slowly rotating solar core .