I have got to design an experiment to measure the thickness of an aluminium sheet with Beta radiation. Basically, it's Beta Thickness gauging and I can use I = I0e^-x to find the thickness if i measure the incident intensity of the radiation and then the intensity of the attenuated ray as it leaves the aluminimum sheet. I also of course have to know the linear attenuation coefficient of aluminium to do this. I do however have a few questions. I know Beta radiation is stopped by a thin sheet of aluminium which I learnt last year, so do i have to a use a source which gives the highest energy beta particles??? What type of source would this be and why would you use it?? Also, I have to calibrate the apparatus. I have no idea what this means. Am I calibrating the geiger counter here??? Do i just measure the background radiation before i start and subtract that off experimental results to give the actual count. How else would you calibrate, anything referring to the formula above?? It's also asked for a calibration graph. Does anybody know what one of these is? One last thing... anybody know the linear attenuation cooefficient value for aluminium, can't find it on the net anywer! Be appreciated if any1 cud help. Thanks!