Linearity testing and dead-time determination for MC-ICP-MS ion counters using the IRMM-072 series of uranium isotope reference materials

Abstract

The IRMM-072 series of reference materials is applied to perform linearity testing and dead time determinations for the ion counters on two MC-ICP-MS mass spectrometers at the IAEA.

U–Th–Pb geochronology and simultaneous analysis of multiple isotope systems in geological samples by LA-MC-ICP-MS

“…Furthermore, Hoffmann et al (2005) 33 observed that the nonlinearity starts at count rates as low as 10 cps, much lower than that of the 10 4 to 10 5 cps threshold reported by Richter et al (2001). 31 Richter et al (2009, 2016) 30,39 reported insignicant non-linearity in the responses of SEMs on the same ion counters (MasCom) used by Zhang et al (2015). 34 These studies highlight the importance of detailed characterization of each ion counter on a new system.…”

“…Applications using SEMs in ion counting mode, however, suffer from variability in detection efficiency, which is associated with time and ion beam size. 7,30,32 In order to obtain high accuracy and precision chronological data using LA-MC-ICP-MS systems with ion counters, it is necessary to characterize each detector in detail so that corrections can be applied (e.g. cross-calibration of the relative yield between ion counters and/or Faraday cups, dead time and non-linearity).…”

“…This parameter is a feature of both the detector itself and the ion counting electronics, which depend on the pulse ampliers. 30 Dead time is corrected by applying the equation I t ¼ I 0 /(1 À I 0 s), where I t is the count rate corrected for dead time losses, I 0 is the count rate obtained with no dead time correction applied (i.e., dead time $0 ns) and s is the apparent dead time of the detection system. 31 Several methods have been developed to determine the dead time (e.g., ref.…”

“…The dead time for each ion counter on an MC-ICP-MS was recently ascertained by measuring isotopic ratios in U series solutions (IRMM-072) and Ba, Lu and W solutions in static mode, which makes the procedure independent of plasma instability and therefore is an ideal method for MC-ICP-MS instruments. 7,30 The reason for the non-linear response of ion counters is still not well understood. A non-linear response results in relatively more pulses counted at higher beam intensities, 31,33 perhaps due to a memory effect.…”

“…Some aspects of MIC systems, such as non-linear behavior, dri in counting efficiency depending on the count rate, and the difficulty in determining the IC dead time, can limit their precision. 7,30…”