  We have used Rayleigh power spectrum analysis of the monthly solar neutrino
flux data from (1) SAGE detector during the period from 1st January 1990 to
31st December 2000; (2) SAGE detector during the period from April 1998 to
December 2001; (3) GALLEX detector during the period from May 1991 to January
1997; (4) GNO detector during the period from May 1998 to December 2001; (5)
GALLEX-GNO detector (combined data) from May 1991 to December 2001 and (6)
average of the data from GNO and SAGE detectors during the period from May 1998
to December 2001. (1) exhibits periodicity around 1.3, 4.3, 5.5, 6.3, 7.9, 8.7,
15.9, 18.7, 23.9, 32.9 and 48.7 months. (2) shows periodicity around 1.5, 2.9,
4.5, 10.1 months. For (3) we observe periodicity around 1.7, 18.7 and 26.9
months. For (4) periodicity is seen around 3.5, 5.5, 7.7 and 10.5 months. (5)
gives periodicity around 1.7, 18.5, 28.5 and 42.1 months while (6) shows
periodicity around 4.3, 6.9, 10.3 and 18.1 months. We have found almost similar
periods in the solar flares, sunspot data, solar proton data which indicates
that the solar activity cycle may be due to the variable character of nuclear
energy generation inside the sun.
