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

Importancia y uso:

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.

Subcomité:

E42.06

Volúmen:

03.06

Número ICS:

71.040.50 (Physicochemical methods of analysis)

Palabras clave:

dead time; isotopic ratios; pulse counting; SIMS;