The α-decay of the Hoyle state in 12C: a new high-precision investigation

D Dell’aquila ,M Gulino,S Romano,G Santagati,G Spadaccini,L Acosta,A Ordine,I Indelicato,C Agodi,L Francalanza,M La Cognata,R G Pizzone ,L Lamia,M Cavallaro,S M R Puglia ,D Carbone,C Spitaleri,G G Rapisarda ,M Vigilante,G L Guardo ,F Cappuzzello,R Spartá ,G D’agata ,I Lombardo,G Verde,A Cvetinović ,S Cherubini,А Туміно

doi:10.1051/epjconf/201818401005

Abstract

The αdecay path of the Hoyle state in 12C (Ex = 7:654MeV) represents one ofthe most challenging questions of modern nuclear physics. Its knowledge can help in theunderstanding of cluster configurations in light nuclei and the possible existence of Bose-Einstein condensates in nuclei. In stars, it is involved in the so-called 3αprocess, wherethe 12C nucleosynthesis occurs. We studied the 14N(d; α2)12C(7:654) reaction at 10:5MeVincident energy to probe its direct decay component. We found, with a precision higherof a factor 5 than any other previous experiment, an almost total absence of direct decaysby-passing the ground state of 8Be. From our analysis, a new upper limit of such decayis found at 0:043% (95% C.L.). Astrophysical 3α process reaction rate calculations haveto be accordingly revised.

Highlights

The α-decay path of the Hoyle state in 12C (Ex = 7.654MeV) represents one of the most challenging questions of modern nuclear physics
9th European Summer School on Experimental Nuclear Astrophysics heavier nuclei consists in the so-called helium burning [1], where nuclei of helium are first transmuted into carbon and in heavier elements via subsequent radiative captures
Where ER is the Hoyle state energy of resonance, kB the Boltzmann constant and Γ the total level width. The latter is fully dominated by the α decay width, i.e. Γ = Γα + Γrad ≈ Γα, and so it results in a dynamical equilibrium 4He + 8Be 12C only broken by the small leakage to the 12C ground state given by the radiative decays

Summary

Introduction

The first of the two mechanisms is fully dominated by the Hoyle state process and by its sequential decay (SD) width, while in the second the 3α do not have energetically access to the intermediate resonances. In order to fully understand these processes, and the validity of the NACRE empirical rate formula, a precise knowledge of the decay pattern of the Hoyle state has to be experimentally achieved.

Results

Conclusion