The development of nuclear detection and stabilization circuits was described. Furthermore, gamma and alpha spectrometry methodologies were developed for field and laboratory measurements. By the use of techniques from other geophysical instruments as fluxgate and optical pumping magnetometers, it was possible to develop stabilization and linearization circuits for gamma ray spectrometers composed by scintillation crystals and multichannel analyzers. The developed system presents excellent thermal and temporal stability, leading to a high reproducibility of the measurements. Teflon PTFE electrets based ionization chambers were constructed for monitoring the alpha particles from soil emanated radon, from the uranium and thorium radioactive series. (author).