For experiment 1:  Energy loss in air
  1.   Repeat measuring the spectra as a function of distance between the source and the detector by moving and inserting lego blocks and plates.  With care it is possible to have steps down to 1.2 mm in separation.  The studs on Lego bricks are 8.0 mm apart, bricks are 9.6 mm tall and plates are 3.2 mm thick.  The count rate drops significantly as the separation increases, both due to energy loss but also due to geometric effects.  
For experiment 2: Energy loss in mylar
  1. We use 2.5 micron thick polyester terephthalate films (mylar)\cite{spi_supplies} attached to paper.  Here we are able to measure the spectrum with up to 7 layers of mylar in between source and detector and measure the resulting spectrum.