  A device with the parent $^{229}$Th source was constructed to search for
variations of the daughter $^{213}$Po half-life ($T_{1/2} = 4.2$ $\mu$s). A
solar-daily variation with amplitude $A_{So}=(5.3 \pm 1.1) \times 10^{-4}$, a
lunar-daily variation with amplitude $A_L = (4.8 \pm 2.1) \times 10^{-4}$, and
a sidereal-daily variation with amplitude $A_S = (4.2 \pm 1.7) \times 10^{-4}$
were found upon proceeding the data series over a 622-day interval (from July
2015 to March 2017). The $^{213}$Po half-life mean value is found to be
$T_{1/2} = 3.705 \pm 0.001$ $\mu$s. The obtained half-life is in good agreement
with some of the literature values obtained with great accuracy.
