Alpha structure of ¹⁶O at high excitation energies by ³He+¹³C nuclear reactions

¹ Dipartimento di Fisica e Astronomia ”Ettore Majorana”, Università di Catania, Via S. Sofia, Catania, 95123, Italy
² Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Via S. Sofia, Catania, 95123, Italy
³ Dipartimento di Fisica ”E. Pancini”, University of Naples Federico II, Via Cintia, Naples, 80126, Italy
⁴ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Via Cintia, Naples, 80126, Italy
⁵ Dipartimento di Fisica e Astronomia, University of Padova, Via Marzolo, Padua, 30020, Italy
⁶ Dipartimento di Fisica, University of Firenze, Via G. Sansone, Sesto Fiorentino (FI), 50019, Italy
⁷ Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, Via G. Sansone, Sesto Fiorentino (FI), 50019, Italy
⁸ Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Via Marzolo, Padua, 30020, Italy
⁹ Istituto Nazionale di Fisica Nucleare, Lab. Nazionali di Legnaro, Via dell’Universit‘a, Legnaro (PD), 35020, Italy

^* e-mail: luigi.redigolo@ct.infn.it

Published online: 28 October 2024

Abstract

This work investigates high energy states in the self-conjugate ¹⁶O nucleus, through the analysis of ¹³C(³He,α)¹²C reactions in the 1.4 2.2 MeV bombarding energy range. The cross-section of the decay channel in which an α particle is emitted in coincidence with a ¹²C residual nucleus in the Hoyle state, leading to four α particles in the final channel, has been measured thanks to a low-threshold and high-resolution array. The occurrence of two low-spin resonant states is highlighted by the analysis of angular distributions, with J^π = 2⁺ and 3⁻, at respective energies of ≃ 24.1 and 24.5 MeV. In this energy window, the observed branching ratios for the transition involving the emission of the Hoyle state appear to be way larger than calculations based on the barrier penetration alone, pointing out to the possible occurrence of largely clustered high-energy states in ¹⁶O.