  The problem of possible application of an ultracold neutron (UCN) trap as a
detector of dark matter particles with long-range radius of forces has been
considered. Transmission of small recoil energy in scattering is a
characteristic of long-range forces. The main advantage of the ultracold
neutron technique lies in possibility of detecting recoil energy as small as
$10^{-7}$ eV. Here are presented constraints on the interaction potential
parameters: $U(r)=a r^{-1} e^{-r/\lambda}$ for dark matter particles and
neutrons, as well as on the density value of long-range dark matter on the
Earth. The possible mechanism of accumulation of long-range dark matter on the
Earth surface is considered and the factor of density increase on the Earth
surface is evaluated. The results of the first experiment on search of
astronomical day variation of ultracold neutron storage time are under
discussion.
