Apparent Diurnal Variation in Background Radiation

Between 1998 and 2001 I measured background radiation in Fourmilab's computer lab with a Geiger-Müller tube interfaced to a computer. Analysing the data revealed both an apparent divergence from a Gaussian distribution of counts per minute and a variation in background radiation with time of day. This page presents the data, analysis, speculation on possible causes, and provides a link whence you can download the data and programs for your own investigations.