Column of Water Length

Column of Water Needed to Cut Photon Count in Half at 10 MeV

e ^{-n σ t}

[math]\displaystyle{ n = \frac{density}{weight(mols)} \times N = \frac{atoms}{cm^{3}} }[/math]

[math]\displaystyle{ n = \frac{atoms}{cm ^{3}} => \frac{ \frac{g}{cm^{2}} }{ \frac{g}{mol}} \times \frac{atoms}{mol} => \frac{atoms}{cm^{3}} }[/math]