Surficial Chemical States of Li₃N Synthesized on Lithium Target for Boron Neutron Capture Therapy

Abstract

  To remove high level of contaminants by O and C from Li₃N surface for Boron Neutron Capture Therapy target, high temperature thermal desorption was conducted up to 1123 K in ultra high vacuum and the following results were derived; (1) During thermal desorption up to 1023 K, typical three peaks of vacuum pressure disturbance due to vaporization of contaminants were observed in vacuum pressure-temperature curve. (2) Over-layered contaminants having lower melting point than 1023 K on Li₃N surface is completely removed by high temperature thermal desorption up to 1123 K in ultra high vacuum. (3) From these desorption results, it is suggested that these contaminants corresponding to these vaporization peaks are H₂O and Li compounds having lower melting point than 1023 K, of which LiOH and Li₂CO₃ were synthesized by decomposition process of Li₃N with residual H₂O and CO₂ in low temperature.

Fig. 2

XPS wide–scan spectra for lithium deposited layer bombarded with 1 keV N₂⁺ ions for various fluences. The fluences were: (a) 0 atoms cm⁻², (b) 4.2×10¹⁵ atoms cm⁻², (c) 4.6×10¹⁶ atoms cm⁻², and (d) 6.3×10¹⁷ atoms cm⁻².