摘要
By monitoring the ionizing radiation from minute to minute in S^o Jos6 dos Campos, SP, Brazil （230 S, 450 W） using Geiger counter, during January to August 2015, it has confirmed the presence of radon gas in these measures. The observation confirms the existence of a periodicity of 24 hours through the technique （Fast Fourier Transform） applied to the data set, and this cycle can be better visible in longer dry periods. On rainy days or with heavy fog in the region, this periodicity is modified or even disappears. As Geiger do not detect alpha particles due to absorption in the walls of the sensor tube, it measured X and gamma rays coming from the radon gas progeny. Radon gas （222Rn） has a half-life of 19.7 minutes to decays in 214Bi emitting gamma ray energy （45%） with 0.609 MeV which is monitored daily by Geiger. Also 222Rn decays in 26.8 minutes in 214pb giving （37%） with 0.35 MeV and others with less energy. It is confirmed the good performance ofa Geiger tube with LND 712 working with about 500 VDC rated voltage.
