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

Abstract

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.