Experimental study of X-ray dose reduction factor when using various size bismuth and lead particles

Low-energy X-rays are widely used during clinical examinations, therefore we need to reduce exposure dose to medical staff by using radiation shielding products. Current X-ray shielding materials are fabricated by embedding high-atomic-number metal particles into a base material. It is valuable to derive knowledge concerning metal particles and shielding ability from actual experimentation. This is necessary because it is unrealistic to mimic many particles in the Monte-Carlo simulation. Understanding the effect of the particle size on the dose reduction factor is important, but at this time this systematic clarification has not been achieved. In this study, we aim to investigate the effect of metal particle size on X-ray shielding ability. 28 investigational shielding products were prepared by embedding metal particles into clay. Lead, bismuth and bismuth oxide having particle diameters between 1.8 μm and 211.3 μm were used. The effective mass thicknesses related to the metals (lead or bismuth) were set at 2,400 g/m2, 1,200 g/m2 and 600 g/m2, resulting in the maximum dose reduction factors of 94.5%, 84.8% and 68.0%, respectively. The dose reduction factors of these investigational shielding products were measured using "International Standard Testing Geometry" with a tube voltage of 70 kV. As a result, we found that a high dose reduction factor can be obtained when the particle size is 40 μm or less. Furthermore, we found that the shielding ability decreased when the metal particles were embedded in various base materials such as polymer sheets, and that the loss was 2.4% or less. Our findings provide insight into the development of novel X-ray shielding products and guarantee the reliability of previous studies that used Monte-Carlo simulations.