Rutherford Scattering: Why is Count Rate 10x at 1mm Slit?

[quietrain]

why is it that in rutherford scattering experiment, if i change my slit width from 5mm to 1mm with everything else the same, i get a 10 times difference in the count rate for the same angle say 30degrees?

for example, 1 count takes about 100seconds for the 1mm slit width

but 1 count takes only 10s for the 5mm slit width.

if the difference of width is 5 times only, then the area will also be 5 times only , with length the same.

so how come i get a 10 times difference? shouldn't it be 5 times only?

thanks!

 

[Valerie Park]

The reason for the 10x increase in count rate when you reduce the slit width from 5 mm to 1 mm is due to the inverse square law of radiation. The inverse square law states that the intensity of radiation (in this case, alpha particles) at a certain distance from its source is inversely proportional to the square of its distance from the source. As the slit width is decreased, the distance between the alpha particle source and the detector increases, which causes the intensity of the alpha particles reaching the detector to be reduced. This results in a 10x decrease in the count rate.