Consequences of and potential reasons for inadequate dead time measurements in isotope ratio mass spectrometry

Re-evaluation of the ages of 40Ar/39Ar sanidine standards and supereruptions in the western U.S. using a Noblesse multi-collector mass spectrometer

“…An IC detector should measure a constant ratio of two isotopes regardless of signal size, provided the detectors respond linearly to input ions and the dead time correction is appropriate. We did not determine the dead time experimentally, but instead employed the isotope ratio approach (e.g., Nelms et al, 2001;Nygren et al, 2011) to evaluate if the instrument dead time setting in the IC0 and IC1 collectors is at an optimum value, and to determine at what signal sizes the instrument dead time setting is no longer appropriate. We measured atmospheric Ar in single collector mode over a range of signal sizes from 50,000 to 875,000 cps (Fig.…”

Atomic spectrometry update. Advances in atomic spectrometry and related techniques

“…Compensation for detector dead-time is another important factor which has been found to be voltage dependent for an electron multiplier, 197 with only a 2 ns disparity between actual and used dead-time giving rise to significant non-linearity. The method of averaging a number of ratios collected over the course of a measurement in SIMS has been shown to cause a positive bias, 198 and the authors propose the use of Beale's estimator when the bias from the summed counts is unacceptably large.…”

Measurement of the molar mass of the 28Si-enriched silicon crystal (AVO28) with HR-ICP-MS

“…In the AVO28 crystal, the abundance of 28 Si is extremely high (>99.99%), and the isotope ratio of n( 28 Si)/n( 29 Si) is over 200 000, 13 which is almost impossible to measure directly by mass spectrometry by now. To solve this problem, a novel approach called 'virtual element' isotope dilution mass spectrometry (VE-IDMS) was developed by the Physikalisch-Technische Bundesanstalt (PTB, Germany).…”

“…[6][7][8] Considering the continuity of mass metrology, the relative uncertainty of N A must not exceed 2 Â 10 À8 . 9 To enable the silicon crystal experiment, a highly 28 Si-enriched (AVO28) crystal was grown and two 28 Si spheres with perfect shape were manufactured under the organization of the International Avogadro Coordination (IAC). 10 Then the Avogadro constant can be obtained using eqn (1), in which each parameter of the silicon sphere needs to be determined accurately.…”

“…Initially, the molar mass of the AVO28 crystal was measured by gas mass spectrometry and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), but a large discrepancy was found between their measurement results. 12 The natural Si contamination in the enriched 28 Si material, which was difficult to correct on-line when using gas mass spectrometry, was thought to be the main reason. However, inuences from natural Si contamination and the instrumental memory effect can be eliminated by the matrix matching method when using MC-ICP-MS.…”