Formation of Long-Lived Nuclear Molecules in (p, ²He) Nuclear Reactions on ¹⁵⁹Tb and ¹⁸¹Ta

This paper deals with the study of long-lived nuclear molecules, consisting of heavy nuclei — products of the (p, 2He) nuclear reactions on 159Tb and 181Ta — and 2He in a bound state. The lighter nucleus 2He is localised within the potential well of a heavy one, but both of them keep their identity and constitute an equivalent nucleus of the atom, which does not recognise the complex structure of such a nuclear molecule. We identified this unique configuration based on processing results of instrumental gamma-ray spectra of Tb and Ta foil samples irradiated with protons of energies below the thresholds of the corresponding (p, 2p) nuclear reaction. Then we experimentally determined the half-lives of 2He decaying by positron emission and electron capture for the Fermi and Gamow–Teller transitions and calculated the phase space factors as well as the binding energy and the radius of 2He to be equal 402 keV and 10.2 fm, respectively.