The value of d is believable considering that the cylinder has diameter of 7.62 cm. Given that the thickness may vary from 7.62 cm in the center to almost 0 on the sides, the square thickness should be a bit greater than the half of the diameter.
    Since d is the thickness of the scatterer, the unit area can be determined. Then, \(N_{\gamma}\) is simply the corrected peak count with peak to total ratio, \(\epsilon = 0.53\), per unit area which can be expressed as