Average Physical Enhancement by Nanomaterials under X-ray Irradiation

Abstract

We for the first time used highly water-soluble silica-covered gold nanoparticles (AuNP@SiO2) in water to successfully isolate average physical enhancement from other enhancements such as nanoscale physical enhancement, chemical enhancement, and antienhancement and obtained the highest enhancement slope of 1.03 per weight percent (wp–1) and the highest experimental enhancement factor of 4.5-fold (εexpt = 4.5 and εexpt= 0 for no enhancement) at 7.5 wp of gold in water. The slope and εexpt agree with the theoretically predicted values obtained from simulation of enhancement of X-rays by gold nanoparticles in water, and the experimental enhancement coefficient (γ = εexpt/εtheo, 0 ≤ γ ≤ 1) is approximately 0.90. The enhancement dependency on X-ray energy, silica layer thickness, and sample thickness were studied experimentally and theoretically. The results presented here elucidate the mechanism of the average physical enhancement by nanomaterials under X-ray irradiation.