This graph presents the attenuation of 50, 70, 100, 125 and 150 kVp X-rays as a function of concrete thickness. The vertical axis is logarithmic and represents K, the quotient of exposure at a unit distance and workload in units of Roentgens per milliampere-minute (R per mA-min at 1 metre). The horizontal axis represent the thickness of concrete in centimetres (cm). The graph shows that logarithm of K decreases as the thickness of concrete increases.