Detection of beryllium treatment of natural sapphires by NRA

作者：Gutierrez P C^*; Ynsa M D; Climent Font A; Calligaro T

来源：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms , 2010, 268(11-12): 2038-2041.

DOI：10.1016/j.nimb.2010.02.053

• NRA
• Beryllium
• Diffusion
• Sapphire
• Gemstones

Since the 1990's, artificial treatment of natural sapphires (Al(2)O(3) crystals coloured by impurities) by diffusion of beryllium at high temperature has become a growing practice. This process permits to enhance the colour of these gemstones, and thus to increase their value. Detection of such a treatment - diffusion of tens of mu g/g of beryllium in Al(2)O(3) crystals - is usually achieved using high sensitivity techniques like laser-ablation inductively coupled plasma mass spectrometry (LA-ICP/MS) or laser-induced breakdown spectrometry (LIES) which are unfortunately micro-destructive (leaving 50-100-mu m diameter craters on the gems). The simple and non-destructive alternative method proposed in this work is based on the nuclear reaction (9)Be(alpha, n gamma)(12)C with an external helium ion beam impinging on the gem directly placed in air. The 4439 key prompt gamma-ray tagging Be atoms are detected with a high efficiency bismuth germanate scintillator. Beam dose is monitored using the 2235 keV prompt gamma-ray produced during irradiation by the aluminium of the sapphire matrix through the (27)Al(alpha, p gamma)(30)Si nuclear reaction. The method is tested on a series of Be-treated sapphires previously analyzed by LA-ICP/MS to determine the optimal conditions to obtain a peak to background appropriate to reach the required mu g/g sensitivity. Using a 2.8-MeV external He beam and a beam dose of 200 mu C, beryllium concentrations from 5 to 16 mu g/g have been measured in the samples, with a detection limit of 1 mu g/g.

• 出版日期2010-6