Recent Precision Mass Measurements at Princeton

  • Lincoln G. Smith


A description of the principles of operation and essential elements of the rf spectrometer was presented in 1967(1). Further details of procedures, a discussion of precision, and measurements of sixteen doublets yielding the mass excesses of H, D, 14N, 16O, 35C1 and 37C1 were given in a recent paper (2). It has been shown: (a)that, with the technique of visual peak matching, the standard “setting” error of a single reading is about 1/2500 of the half-width of a peak; and (b) that the frequency ratio (f2/fl) may easily be determined within a few parts in 1010 so that no calibration uncertainty arises from equating this to the mass ratio (M1/M2) for the highest precision attainable. Thus, in the absence of other, greater sources of error, masses should be determinable for resolutions achieved (2–4x105) from the mean of ten readings with an accuracy between 3 and 6 parts in 1010. After elimination of a number of purely instrumental sources of error, the primary known remaining sources that limit precision are small electric fields that do not shift with the applied voltages in inverse proportion to the two masses being compared. Their presence is readily shown by the study of wide “calibration” doublets for which the differences in mass numbers are one or two units. Considerable progress in neutralizing the effects of these fields has been made by applying small adjustable d.c. voltages in series with the high voltage applied to the ion source and with the lesser voltages applied to one of each pair of external deflectors and to each internal deflector as explained in reference (2).


Mass Excess Electric Field Effect Small Electric Field Instrumental Source Main Lens 
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Copyright information

© Plenum Publishing Company Ltd 1972

Authors and Affiliations

  • Lincoln G. Smith
    • 1
  1. 1.Joseph Henry LaboratoriesPrinceton UniversityUSA

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