Experimental search for the bound-state singlet deuteron in the radiative $n\text{−}p$ capture

We performed an experimental search for the bound-state singlet deuteron predicted in some microscopic calculations. The predicted energy of this metastable level is in the vicinity of the deuteron disintegration threshold. This state should manifest itself in a 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 $\gamma$-ray spectra after cold neutron capture by hydrogen nuclei. The upper limit $2\mu \mathrm{b}(2\sigma$ level) is obtained for the cross section of the singlet deuteron production with the binding energy in the range 10–125 keV.

Figure 1

Part of the $\gamma$-ray spectrum (50–2400 keV) of the coaxial HPGe detector measured with the polyethylene target.

Figure 2

Part of the $\gamma$-ray spectrum (2100–2210 keV) of the coaxial HPGe detector measured with the polyethylene target.

Figure 3

Part of the $\gamma$-ray spectrum (2100–2210 keV) of the low-energy HPGe detector measured with the polyethylene target.

Figure 4

Part of the $\gamma$-ray spectrum (2100–2210 keV) of the coaxial HPGe detector measured with the water target.