Experimental search for the singlet metastable deuteron in the radiative n-p capture

We performed an experimental search for the bound state singlet deuteron predicted in some microscopic calculations. The predicted energy of this level is in vicinity of the deuteron disintegration threshold. This state should manifest itself in two-photon transition following thermal neutron capture by protons. The experiment consists in the search for the second gamma-ray in the cascade through a high statistics measurement of γ-ray spectra after thermal neutron capture by hydrogen nuclei. The upper limit 15 μb is obtained for the cross section of the singlet deuteron production with the bound energy in the range 25–125 keV.