Consequences of and Potential Reasons for Inadequate Dead Time Measurements in Isotope Ratio Mass Spectrometry

Precise and accurate determination of the dead time of a pulse counting system is critical for correct isotope ratio determinations. In this paper, potential problems in the determination of dead time are investigated as well as the consequences of using an erroneous value when correcting for dead time. It is shown how the voltage setting of a SEM can affect the dead time of the system. This can be due to an increased pulse height distribution giving after-pulsing effects, which are not corrected for by a detector dead time model. This hypothesis is supported by pulse height measurements of the output signal of the SEM. Output signals of the amplifier and SEM of an Element2 are also studied and the different nature of these signals (extending vs non-extending) and the consequences of this in the correction of dead time count losses are discussed. It is also found that the dead time values determined via isotope ratio measurements can differ with up to 2.7 ns under optimised instrumental settings, and it is also shown that a relatively small difference (2 ns) in the actual dead time of the system and the value used to correct for dead time results in apparent non-linearity of the system which has been reported by other authors.

NYGREN Ulrika;  RAMEBÄCK Henrik;  VESTERLUND Anna;  BERGLUND Michael; 

2011-02-09

ELSEVIER SCIENCE BV

JRC56928

1387-3806,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC56928,   

10.1016/j.ijms.2010.11.018,