Optical interfaces in GD-OES system for vacuum far ultraviolet detection

Abstract

A Glow Discharge Optical Emission Spectrometry device has been designed for glove box adaptation in CEA Valduc to analyze carbon, hydrogen, nitrogen and oxygen at low concentration in nuclear materials. Vacuum ultraviolet region of the spectrum (between 120 and 160 nm) was chosen for light elements analysis with the aim to avoid optical interferences with matrix emission lines (20000 lines in the visible region for plutonium element). For this purpose, two different systems of collection have been developed: a first based on two focusing lenses and a second having an optical interface based on mirrors. In the present paper, the whole set-up integrated in a glove box is described. Optical limits, such as absorption and chromatic and geometric aberrations, of the first system of collection and transmission of light (two MgF₂ focusing lenses), are presented, as well as the new optical interface based on mirrors developed in order to reduce the defects of the lens system. Calibration graphs performed for carbon, nitrogen and oxygen in non-nuclear materials were plotted with the lenses' system and the corresponding sensitivities were calculated. First results obtained with the new optical box are also presented. This system allows an increase in the number of photons transmitted from the source to the analyser. Numerical calculations and first experimental results particularly prove its efficiency for the transmission of the hydrogen line (121 nm).