The depth for X-ray penetration is only dependent on X-ray wavelength and material composition
Prove: I = I0 X exp(-ux), where u is linear absorption coeff., x is the sample thickness, I0 is the beam intensitiy, I is the transmission intensity.
figure: ----> I0 IIIIIIIIIIIIIIIIIIII -----> I x
suppose: X-ray passes a material and reduces the amount of transmitted X-ray intensity by half.
1/2 x I0 = I0 x exp ( -u x) --> ln1 - ln2 = -ux, ln1 = 0, ln2 = 0.693, therefore, x = 0.693/u
you can check the u value on some websites which is only depdent on the wavelength, then you can calculate the sample thickness and the intensitiy transmitted.