Broad Beam Attenuation in Concrete for 50 to 300-Kvp X-Rays and in Lead for 300-Kvp X-Rays

Abstract

Broad Beam Attenuation Data in Concrete, 50 to 300 kvp For x-ray installations up to 400 kvp it has been the general practice to use lead as the shielding material; at the lower voltages lead is a very effective barrier, since attenuation is largely due to photoelectric absorption. With the increased use of concrete for structural purposes in walls, floors, and ceilings of new buildings, it may be desirable to use concrete rather than lead as the barrier material. In existing structures, concrete may provide all or part of the necessary protection. Attenuation data for lead have been generally available. For concrete, attenuation data have been available for the higher voltages but not generally for low voltages. The reason for this lack of information in the lower voltage range lies in the fact that the data must be obtained with large fields (at least 3 feet in diameter) at the barrier. Large sheets of concrete of thin section are not easily made and do not lend themselves to the repeated handling required in experimental studies. Wyckoff, Kennedy, and Bradford (1) and Miller and Kennedy (2) described the need for broad-beam attenuation data in barrier design. Miller and Kennedy also called attention to the fact that, since attenuation at the lower voltages in materials of low atomic number is largely due to Compton scattering, it should be possible to take attenuation data in other material of low atomic number and, by applying the necessary corrections, derive data for concrete. The correction applied would take into account differences in density, atomic number, and atomic weight. The correction factor so derived would be essentially constant over a wide range of energies. The logical material for such a study would be aluminum, which can be procured and handled in large sheets of almost any thickness. The atomic number of aluminum is 13, compared with 14 for silicon, the major element in concrete. The density for aluminum is 2.70 compared with 2.35 for concrete made to the usual 147 pounds per cubic foot specification. The atomic weight of aluminum is 26.98 and for silicon 28.09.