ASTM E2426-10(2019)

Standard Practice for Pulse Counting System Dead Time Determination by Measuring Isotopic Ratios with SIMS

SIGNIFICANCE AND USE
5.1 Electron multipliers are commonly used in pulse-counting mode to detect ions from magnetic sector mass spectrometers. The electronics used to amplify, detect and count pulses from the electron multipliers always have a characteristic time interval after the detection of a pulse, during which no other pulses can be counted. This characteristic time interval is known as the “dead time.” The dead time has the effect of reducing the measured count rate compared with the “true” count rate.  
5.2 In order to measure count rates accurately over the entire dynamic range of a pulse counting detector, such as an electron multiplier, the dead time of the entire pulse counting system must be well known. Accurate count rate measurement forms the basis of isotopic ratio measurements as well as elemental abundance determinations.  
5.3 The procedure described herein has been successfully used to determine the dead time of counting systems on SIMS instruments.6 The accurate determination of the dead time by this method has been a key component of precision isotopic ratio measurements made by SIMS.
SCOPE
1.1 This practice provides the Secondary Ion Mass Spectrometry (SIMS) analyst with a method for determining the dead time of the pulse-counting detection systems on the instrument. This practice also allows the analyst to determine whether the apparent dead time is independent of count rate.  
1.2 This practice is applicable to most types of mass spectrometers that have pulse-counting detectors.  
1.3 This practice does not describe methods for precise or accurate isotopic ratio measurements.  
1.4 This practice does not describe methods for the proper operation of pulse counting systems and detectors for mass spectrometry.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Dec-2018
• ICS: 71.040.50 - Physicochemical methods of analysis
• Technical Committee: E42 - Surface Analysis
• Drafting Committee: E42.06 - SIMS

Relations

• Replaces: ASTM E2426-10 - Standard Practice for Pulse Counting System Dead Time Determination by Measuring Isotopic Ratios with SIMS
• Effective Date: 01-Jan-2019
• Refers: ASTM E673-03 - Standard Terminology Relating to Surface Analysis (Withdrawn 2012)
• Effective Date: 01-Dec-2003
• Refers: ASTM E673-02a - Standard Terminology Relating to Surface Analysis
• Effective Date: 10-Dec-2002
• Refers: ASTM E673-01 - Standard Terminology Relating to Surface Analysis
• Effective Date: 10-Nov-2001
• Refers: ASTM E673-98E1 - Standard Terminology Relating to Surface Analysis
• Effective Date: 10-Nov-2001

Overview

ASTM E2426-10(2019) is an international standard developed by ASTM, outlining a practice to determine dead time in pulse counting systems used for isotopic ratio measurements via Secondary Ion Mass Spectrometry (SIMS). Electron multipliers in magnetic sector mass spectrometers utilize pulse-counting detection electronics, which experience a brief interval-known as "dead time"-after each ion detection during which additional pulses cannot be counted. Correctly characterizing this dead time is essential for achieving accurate ion count rates over the operational range of instrument detection, which in turn underpins reliable isotopic ratio analysis and elemental abundance determinations.

Key Topics

• Pulse Counting System Dead Time:
  Dead time refers to the short period after a pulse event during which a detection system cannot register subsequent pulses. This can lead to underestimation of true count rates.

• SIMS Instrument Application:
  This standard is especially tailored for SIMS mass spectrometers but is broadly applicable to other systems with pulse-counting detectors.

• Isotopic Ratio Measurement:
  The method relies on measuring isotope ratios in elements with at least three naturally occurring isotopes, with one being significantly more abundant to improve accuracy.

• System Characterization:
  The standard provides a framework to verify whether the detected dead time remains independent of count rate, an important factor for high-precision measurements.

Applications

The practice outlined in ASTM E2426-10(2019) is crucial for:

• Calibration of Mass Spectrometers:
  Ensuring accurate pulse-counting detector performance in mass spectrometry instruments used for precise scientific research or industrial analysis.

• High-Precision Isotope Analysis:
  Establishing the foundational measurements necessary for advanced applications in geochemistry, materials science, and microelectronics by ensuring that isotopic ratios are reliably quantified.

• Quality Assurance and Instrument Validation:
  Essential for laboratories and quality control departments to routinely verify instrument performance, avoid systematic errors, and support traceable measurements.

• Comparison Across Instrument Platforms:
  Facilitates standardized comparison of isotopic data between different instruments and laboratories by providing a uniform approach to dead time determination.

Common industries and fields of use include:

• Surface analysis laboratories
• Environmental and geological analysis
• Semiconductor manufacturing
• Material characterization and forensic science

Related Standards

For comprehensive implementation and context, the following standards are referenced or related:

• ASTM E673: Terminology Relating to Surface Analysis (withdrawn, referenced for historical definitions).
• ISO 21270: Surface Chemical Analysis-X-ray Photoelectron and Auger Electron Spectrometers-Linearity of Intensity Scale, providing complementary terminology and definitions for counting system measurements.

When working with pulse-counting detectors for SIMS or other mass spectrometry applications, adherence to these standards ensures accurate dead time determination and, ultimately, more reliable data in isotopic and elemental analysis.

Summary

ASTM E2426-10(2019) establishes a standardized practice for evaluating and correcting dead time effects in pulse counting systems, notably in SIMS instruments, thereby supporting accurate isotopic ratio measurement. Understanding and applying this standard is integral for scientists and technical professionals aiming for precision and reliability in mass spectrometric data across a broad spectrum of scientific and industrial fields.

Keywords: dead time, pulse counting, SIMS, isotopic ratio measurement, mass spectrometry, ASTM E2426, electron multipliers, instrument calibration

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2426 − 10 (Reapproved 2019)
Standard Practice for
Pulse Counting System Dead Time Determination by
Measuring Isotopic Ratios with SIMS
This standard is issued under the fixed designation E2426; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ISO Standard:
ISO 21270 Surface chemical analysis -- X-ray photoelectron
1.1 This practice provides the Secondary Ion Mass Spec-
and Auger electron spectrometers -- Linearity of intensity
trometry (SIMS) analyst with a method for determining the
scale; and references 1, 2, 10, 13 and 14 therein.
dead time of the pulse-counting detection systems on the
instrument. This practice also allows the analyst to determine
3. Terminology
whether the apparent dead time is independent of count rate.
3.1 Definitions:
1.2 This practice is applicable to most types of mass 3.1.1 See Terminology E673 for definitions of terms used in
spectrometers that have pulse-counting detectors. SIMS.
3.1.2 See Terminology ISO 21270 for definitions of terms
1.3 This practice does not describe methods for precise or
related to counting system measurements.
accurate isotopic ratio measurements.
m2 m1
3.1.3 isotopic ratio, n—written as X/ X, for an element
1.4 This practice does not describe methods for the proper
X with isotopes m1 and m2, refers to the ratios of their atomic
operation of pulse counting systems and detectors for mass
abundances. When it is a value measured in a mass spectrom-
spectrometry.
eter it refers to the ratio of the signal intensities for the two
species.
1.5 This standard does not purport to address all of the
m2 m2
3.1.3.1 Discussion—Thenotation∆ Xorδ Xreferstothe
safety concerns, if any, associated with its use. It is the
fractional deviation of the measured isotopic ratio from the
responsibility of the user of this standard to establish appro-
m2
standard ratio or reference. In this practice, ∆ X will refer to
priate safety, health, and environmental practices and deter-
the fractional deviation of the measured ratio, uncorrected for
mine the applicability of regulatory limitations prior to use.
m2
mass-fractionation (see 3.1.4) and δ X will refer to the
1.6 This international standard was developed in accor-
fractional deviation of the measured ratio that has been
dance with internationally recognized principles on standard-
corrected for mass-fractionation. An example for magnesium
ization established in the Decision on Principles for the
(Mg) is:
Development of International Standards, Guides and Recom-
25 24
mendations issued by the World Trade Organization Technical Mg/ Mg
~ !
Meas
∆ Mg 5 21 (1)
25 24
Barriers to Trade (TBT) Committee.
~ Mg/ Mg!
Ref
where:
2. Referenced Documents
25 24 5
( Mg/ Mg) = 0.12663.
Ref
2.1 ASTM Standard:
3.1.4 mass-fractionation, n—sometimes called “mass-bias,”
E673 Terminology Relating to SurfaceAnalysis (Withdrawn
referstothetotalmass-dependent,intra-isotopevariationinion
2012)
intensity observed in the measured isotopic ratios for a given
elementcomparedwiththereferenceratios.Itcanbeexpressed
as the fractional deviation per unit mass.
3.1.4.1 Discussion—The mass of an isotope i of element X
This practice is under the jurisdiction of ASTM Committee E42 on Surface
mi
Analysis and is the direct responsibility of Subcommittee E42.06 on SIMS.
( X) shall be represented by the notation m, where “i”isan
i
Current edition approved Jan. 1, 2019. Published January 2019. Originally
integer.
approved in 2005. Last previous edition approved in 2010 as E2426–10. DOI:
10.1520/E2426–10R19.
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from International Organization for Standardization (ISO), ISO
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Standards volume information, refer to the standard’s Document Summary page on Geneva, Switzerland, http://www.iso.org.
the ASTM website. Catanzaro, E. J., Murphy, T. J., Garner, E. L., and Shields, W. R., “Absolute
The last approved version of this historical standard is referenced on IsotopicAbundanceRatiosandAtomicWeightofMagnesium,” Journal of Research
www.astm.org. of the National Bureau of Standards, Vol 70a, 1966, pp. 453–458.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2426 − 10 (2019)
4. Summary of Practice retriggerable (non-paralyzable, or non-extendable), or a com-
bination of the two. In a retriggerable system the length of the
4.1 This practice describes a method whereby the overall
discriminator output pulse is increased if a pulse arrives at the
effective dead time of a pulse counting system can be deter-
discriminator input before the output has returned to its
mined by measuring isotopic ratios of an element having at
quiescentstate.Somesystemshaveanadditionalrecoverytime
least 3 isotopes. One of the isotopes should be approximately
after the output has returned to its quiescent state during which
afactorof10moreabundantthantheotherssothatafirstorder
they will not react to input pulses. This time just adds to the
estimate of the dead time can be calculated that will be close to
system dead time. In such a system the dead time is given by:
the true value. The efficacy of the method is increased if the
2τC
True
sample is flat and uniform, such as a silver (Si) wafer or a C 5 C e (2)
Meas True
polished metal block so that the count rate of the isotopes
where:
varies minimally during the individual measurements.
C = the measured count rate,
Meas
C = the true count rate, and
True
5. Significance and Use
τ = the dead time.
5.1 Electron multipliers are commonly used in pulse-
7.1.1.1 In a non-retriggerable system a pulse is simply
counting mode to detect ions from magnetic sector mass
ignored if it arrives before the discriminator output has
spe
...