The scattering of fermions on the superfluid bose-condensate

The influence of the fermionic impurity on the spectrum of the overcondensate excitations of the superfluid Bose system is being investigated. The scattering of the neutrons on the Bose condensate of the superfluid $^4$He and the mixture of the liquid $^3$He and $^4$He are considered. The analytical expression for the spectrum of the overcondensate excitations for these two systems has been found.