Using a source with a higher activity would have decreased the relative standard deviation of the data. Time restricted experimentation, allowing only three or four data points in each set. The activity of the source dropped on the second day of experimentation, probably due to a smal misalignment between the Geiger counter and the source. As a result, it was unreasonable to combine the data taken on the two days, thus two smaller data sets were produced instead of one larger one. The Co-60 source emits a beta particle as well as a gamma ray in its decay process.
Beta particles are larger and more easily shielded.
The beta particles may have passed through the smaller thicknesses of material but were probably shielded almost completely by greater thicknesses. This effect would account for the curved appearance of some of the plotted data, and introduce error into the attenuation coefficient, the slope of the fit line. Bibliography Beiser, Arthur. Modern Physics .