Choosing optimal exposure times for XRF core‐scanning: Suggestions based on the analysis of geological reference materials

Abstract

X‐ray fluorescence (XRF) core‐scanning is a fast and nondestructive technique to assess elemental variations of unprocessed sediments. However, although the exposure time of XRF‐scanning directly affects the scanning counts and total measurement time, only a few studies have considered the influence of exposure time during the scan. How to select an optimal exposure time to achieve reliable results and reduce the total measurement time is an important issue. To address this question, six geological reference materials from the Geological Survey of Japan (JLK‐1, JMS‐1, JMS‐2, JSD‐1, JSD‐2, and JSD‐3) were scanned by the Itrax‐XRF core scanner using the Mo‐ and the Cr‐tube with different exposure times to allow a comparison of scanning counts with absolute concentrations. The regression lines and correlation coefficients of elements that are generally used in paleoenvironmental studies were examined for the different exposure times and X‐ray tubes. The results show that for those elements with relatively high concentrations or high detectability, the correlation coefficients are higher than 0.90 for all exposure times. In contrast, for the low detectability or low concentration elements, the correlation coefficients are relatively low, and improve little with increased exposure time. Therefore, we suggest that the influence of different exposure times is insignificant for the accuracy of the measurements. Thus, caution must be taken when interpreting the results of elements with low detectability, even when the exposure times are long and scanning counts are reasonably high.

Practical guidelines and recent advances in the Itrax XRF core-scanning procedure

“…With 100 seconds exposure time, the correlation coefficients between scanning intensities and reference concentrations of laboratory-prepared reference resins are all higher than 0.97 for pollution related elements such as Cr, Mn, Ni, Cu, Zn, and Pb. Moreover, as suggested by Huang et al (2016) from the experience of sediment reference standards, the strong linear relationship between scanning intensities and reference concentrations of resins remains similar even with exposure time as brief as 1 second. Thus, this method provides a fast and inexpensive method to quantitatively assess multiple element concentrations in the resins, and can be used as an environmental monitoring tool for large geographic areas in order to understand the variations of environmental contaminants across a landscape.…”

Signal-to-noise ratios, instrument parameters and repeatability of Itrax XRF core scan measurements of floodplain sediments

“…The 10 th percentile of the distribution, which avoids outliers at the tail of the SNR distribution, could be used to determine whether particular values of tube voltage, current and exposure time are likely to deliver measurements above the LOQ for the majority of the element profile. Although Huang et al (2016) concluded that increasing Itrax XRF exposure time gives insignificant improvements in accuracy, Figure 4 demonstrates that for elements such as Rb and Zr increasing exposure time can substantially increase the proportion of measurements with SNRs greater than the LOQ.…”

Tsunami Elemental Signatures in the Samoan Islands: A Case Study

“…The scanner was fitted with a Mo-tube and a magnetic susceptibility meter, with XRF scans performed on each core at 30 kV and 55 mA using 10 s exposure time and sampled at 500 μm step size. In comparison, Itrax analysis of the Little Pigeon Bay cores were carried out using similar settings at the University of Auckland [8], with a negligible difference of 4 s exposure time between the two datasets [20].…”