  Measurements of the endpoint region of the tritium beta-decay spectrum
provides good possibility to determine neutrino mass. This, however, needs a
perfect monitoring of the spectrometer energy scale. A parallel measurement of
electron line of known energy - in particular the 83mKr conversion K-line - may
serve well to this purpose. The 83Rb decaying to 83mKr seems to be a very
suitable radioactive source due to its halflife of 86.2 day. In this work, we
determine the amount of 83Rb which is necessary for a successful monitoring.
