Why is it said that the greater the atomic number, the greater the density and the greater the tissue thickness, the stronger the attenuation of X-ray blocking ability?

Because the density is doubled, the number of atoms and electrons per unit volume is doubled, and the interaction probability of particles is doubled, the attenuation ability of X-rays is stronger.

X-ray attenuation is also related to the atomic number of matter, the number of electrons in a certain thickness and the energy of X-ray itself.

Atomicnumber (atomic number) refers to the serial number of an element in the periodic table of elements, with the symbol Z, which is numerically equal to the number of nuclear charges (i.e. protons) of the nucleus or the number of extranuclear electrons of neutral atoms. For example, the atomic number of carbon is 6, and its nuclear charge (proton number) or extranuclear electron number is also 6.