Methode der massenspektroskopischen Dispersionsbestimmung

Even in the most carefully built mass-spectrograph, one cannot rely on the ideal massscale when measuring isotopic weights with highest precision, as is necessary for the calculation of nuclear binding energies. Instead, the actual mass-scale in the neighbourhood of a “line” of unknown mass (line on a photographic plate or peak of a curve recording voltage, etc.) has to be ascertained with the help of neighbouring lines of known masses simultaneously recorded and measured (dispersion lines). The approximation of the mass-scale and the evaluation of the unknown line can be done in a clear and general way by the use of Lagrange′s method of interpolation (§ 1 and 2). — However, Lagrange′s approximation without any further assumption would not be sufficient if one has at one′s disposal only a few dispersion lines widely separated, as is the case especially in the range of light masses. Here one has to make partial use of the knowledge of the ideal mass-scale; this is outlined in detail for the special cases of one and of two dispersion lines. In certain cases one will have to use up to three dispersion lines (§ 3). — Furthermore, it is not sufficient to ascertain the mass-scale with the help of a set of dispersion lines in a certain range of the plate (or of the voltage, etc.) at a particular value of the field strength of the deflecting magnet (or of a similar parameter) in order to evaluate an unknown line which subsequently has been brought into this range by varying the field strength; because the dispersion of an apparatus depends always slightly on the field strength (f. i. on account of the unavoidable saturation phenomena of the iron). The order of magnitude of this effect has been estimated from experiments (§ 4). — Finally, there is given an account of the ideal mass-scales of all existing mass-spectrographs, including recent precision mass-spectrometers and a discussion of the methods of evaluation used up to the present time (§ 5 and 6).