  This paper is dedicated to the simulation of the so-called trapping-effect
observed in the Troitsk nu-mass experiment. The effect is caused by the
magnetic trapping of decay electrons in the windowless gaseous tritium source
and the gradual evaporation of those electrons. As a result, alongside regular
tritium beta-spectrum electrons, we see additional electrons that are initially
trapped in the source and escape it with changed energy. The spectrum of
evaporated electrons is quite peculiar (almost flat for monochromatic initial
electrons) and could not be directly measured in the experiment. So one has to
rely on simulations. Also, it is possible that the same effect could be
observed in other cases of magnetic traps.
