Evaluation of X ray unit shielding by means of an industrial thulium 170 radioactive source

Shielding thickness distribution and flaws are not readily available for evaluation during inspection work because the lead is usually no longer visible after the room finishing is completed. This is also often the case for concrete slabs or walls. When the evaluation cannot be performed adequately with an X-ray unit, an appropriate radioactive source can be used. Many used sup(99m)Tc with a very short half-life of 6 h and 144Ce, whose transmission curves for lead make it difficult to differentiate between 0.8 and 1.6 mm Pb which are often used commercially in North America. We present here transmission data obtained for 170Tm (Tsub(1/2)=127 d; 84 KeV) through various thicknesses of laminated lead sheets, lead glass, ordinary plate glass, concrete slabs, gypsum boards as well as simulated wall sections (60 x 60 cm) made of spaced gypsum boards only or shielded with various available lead thicknesses commonly found in North american buildings. The results show that 170Tm makes it possible to differentiate between 0.8 and 1.6 mm Pb, and a shielding evaluation is possible up to 4.0 mm Pb as long as the building material attenuation is taken into account in order to avoid lead equivalency overestimation