  In this work, carbon $^{14}$C and Tritium were considered as possible
background source in the XENON1T experiment. The simulation results show that
if $^{14}$C is located in dust particles with a characteristic size of tens of
micrometers, then its beta spectrum is softened and can contribute to the
low-background part of the spectrum (up to 20 keV) of the XENON1T experiment.
In addition, it has been shown that the tritium spectrum is also significantly
distorted due to the threshold effect and the form in which tritium is living
in xenon. Comparison of the simulation results with experimental data allowed
us to estimate the activity level of $^{14}$C at about 1500 decays / t / year,
which gives the level of organic impurities containing $^{14}$C at the level of
2x10$^{-13}$ g/g. In the case of tritium background, spectrum distortions are
already caused by nanoparticles. Wherein the shape of the spectrum from tritium
sitting on the surface of the dust fits better into the experimental data than
the spectrum from pure tritium. In addition, since the dust absorbs part of the
decays, the total amount of tritium in xenon can be several times greater than
assuming a background from pure tritium in xenon (the factor strongly depends
on the size of the dust particles).
