Newton’s metal as a new home-made shielding material

Abstract

The protection of critical organs inside the radiated area during radiotherapy applications is very important. Lipowitz’s metal (also called cerrobend) is widely used. It consists of 50% bismuth, 26.7% lead, 13.3% tin and 10% cadmium. The physical density at 20 °C is 9.4 g/cm3 (70 °C melting point). Cadmium has been recognized as a source of environmental pollution and poisonous cadmium gas is emitted during fabrication of the material into custom blocks. The determining factor in the release of metallic oxide fumes is temperature. The higher the temperature, the greater the potential for release of metallic oxide fumes. To overcome the toxic effect of cadmium in Lipowitz’s alloy during casting, low melting point Newton’s metal (cadmium-free) is used. This study is carried out to compare the two alloys. The first alloy is the cerrobend alloy used in the National Cancer Institute of Cairo University, imported from Medical Technology Company, USA. Secondly, we deal with Newton’s metal which has a composition of 50% Bi, 31.2% Pb and 18.8% Sn known in industry as a low melting point solder. The measurements taken using 60Co and 6 MV X-ray show that Bi50Pb31.2Sn18.8 alloys have good physical properties (low melting point, high attenuation coefficient, adequate values of hardness). They are easy to fabricate into shapes, and friendly to the environment, so that they may be used as a substitute for Lipowitz’s metal in radiotherapy.