Study of cosmogenic radiocarbon concentration variations in the Earth's   atmosphere during solar activity of Mounder minimum (1645-1715)
  Variations of radiocarbon concentration have been studied in annual rings for the last 350 years (1600-1950)on the basis of our experimental research using methods of spectral analysis. From this interval of time special attention is paid to the so-called period of the Maunder minimum (1645-1715) of solar activity. In the experimental series of corresponding period two types of periodicity are revealed: 20 year and 8 year. 
S. Tsereteli, V. Bochorishvili, M. Samkharadze, G. Khoriauli