Application of monolithic polycapillary focusing optics in MXRF

摘要

Abstract: A monolithic polycapillary focusing optic, consistingof hundreds of thousands of small tapered glasscapillaries, can collect a large solid angle of x-raysfrom a point source and guide then through thecapillaries by multiple total reflections to form anintense focused beam. Such a focused beam has manyapplications in microbeam x-ray fluorescence (MXRF)analysis. Two monolithic polycapillary focusing opticswere tested and characterized in a MXRF set- up using amicrofocusing x-ray source. For the CuK$-$alpha$/ line,the measured focal spot sizes of these optics were 105micrometers and 43 micrometers full-width-half-maximum,respectively. When the source was operated at 16W, theaverage CuK$-$alpha$/ intensities over the focal spotswere measured to be 2.5 $MUL 10$+4$/photons/s/micrometers$+2$/ and 8.9 $MUL 10$+4$/photons/s/micrometers$+2$/, respectively. When wecompared the monolithic optics to straightmonocapillary optics with approximately the same outputbeam sizes, intensity gains of 16 and 44 were obtained.The optics were applied to the MXRF set-up to analyzetrace elements in various samples and a minimumdetection limit of about 2 pg was achieved for thetransition elements (V, Cr, Mn, and Fe). The opticswere also used to map the distributions of traceelements in various samples. !12