Coincidence X-ray Fluorescence (cxrf) Spectrometry for in Vivo Quantitative Measurement of Bone Lead

In previous work, the main interfering background for the in vivo lead in bone measurement was found to be from back-scattered Compton and Rayleigh source photons, which is, therefore, also the main problem for the improvement of sensitivity. Based on the physics of atomic transition, certain fractions of the characteristic K-series X-rays and L-series X-rays are in true coincidence. With an advanced CAMAC data acquisition system, experimental results are presented and preliminary quantitative methods for analyzing coincidence spectra are treated. A prototype coincidence spectrometer was proposed in previous work and is studied by benchmarked Monte Carlo simulation in this work. Additional information is provided by this method (CXRF) and measurement sensitivity is improved. INTRODUCTION X-ray fluorescence spectrometry has been recognized as an indispensable and powerful elemental analysis technique for many years [1-3]. XRF measurement techniques have focused primarily on detecting individual X-rays. According to previous work [4-7], the main problem for sensitivity improvement of in vivo lead in bone measurement is the background from back-scattered source photons. With the objective of improving measurement sensitivity, the authors are applying and investigating the use of Coincidence X-Ray Fluorescence (CXRF) spectrometry in the measurement of lead in bone. Coincidence spectrometry has been applied previously to various fields, such as radioisotope standardization [8, 9] and gamma-gamma or particle-gamma coincidence measurements [10, 11], to improve measurement sensitivity and to better understand the physical processes involved. The fundamental idea of coincidence spectrometry is to detect multiple events that are correlated in time of emission, which has the effect of minimizing the background. Suppose two detectors are available for a radiation detection experiment. For events that are not emitted at the same time, the singles counting rate in the two detectors is N1 and N2, respectively. For coincidence measurement, a very short time window, τ (often of nanosecond magnitude), is applied for the measurement. If two events, one from each detector, are detected within that time window, a coincidence event is scored. This is illustrated in Figure 1, where only events of case A will be scored. Of all the coincidence events scored, there will be some events caused by chance or Copyright ©JCPDS International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume 47. 91