During my A level physics class we were discussing the attenuation coefficient of x-rays and a question arose that I can't find an answer to anywhere. If someone could help answer what effect physical state (ie gas/liquid/solid ect) has on the attenuation coefficient of x-rays it would be much appreciated? The only simplistic answer that arose was that perhaps because of the spacing difference between the molecules/atoms in other states this may cause "lesser" physical states to have lower attenuation coefficients. But then argueable to a certain extent this can be resolved by lowering the temperature, raising the pressure and keeping the volume constant to allow different states in the same area to exist. Any thoughts?