The existence of the dineutron was predicted over 70 years ago. At present, a
number of experimental works confirm this assumption. By virtue of the
principle of isotopic invariance, a singlet deuteron must also exist. The
possibility of describing the neutron-proton interaction in the state at low
energies as the excitation of a quasi-stationary level (singlet deuteron) lying
below the deuteron decay threshold is discussed. The position, neutron and
radiative widths of the level are determined by the scattering length, the
effective radius, and the cross section for the radiative capture of neutrons
by protons. Experiments to search for this level are discussed. The discovery
of the singlet deuteron would be confirmation of the existence of the
dineutron