Direct quantitative analysis of a cesium pencil in a simulated hot-cell using a remote-LIBS system equipped with a miniature collimator

Abstract

¹³⁷Cs-containing borosilicate glass encapsulated in an SS tube, known as a Cs-pencil, is replacing the traditional ¹³⁷CsCl powder used in blood irradiators for enhanced nuclear safety. Accurate quantification and investigation of the homogeneity of ¹³⁷Cs distribution are integral aspects of its quality assessment. Herein, the first quantitative measurement of Cs-pencils using a remote-laser-induced breakdown spectroscopy (LIBS) system equipped with a miniature collimator is reported, which involves no sample preparation. A simulated hot-cell structure forcing the remote acquisition of the signal at >1 m was constructed for this analysis. The relationship between the signal intensity and solid angle of the collection created by the collimator with the remote distance was evaluated, and the result was verified both experimentally and theoretically. Moreover, studies were carried out to characterize the spectral noise embedded in the LIBS spectrum. The results reveal the inadequacy of the fitting algorithms in high noise spectra. With the use of a 266 nm laser for ablation and under ambient Ar conditions, the accuracy and precision for the determination of Cs was found to be 2.5–5% at the 1–1.5 m remote distances. The results obtained herein demonstrate that the miniature collimator-equipped remote-LIBS is suitable for analyzing the Cs-pencil produced by fissionogenic ¹³⁷Cs and has significant potential to be employed as a routine analytical technique in the nuclear industry.