Decoding 12C Hoyle State Radiative Decay & Carbon Formation
Dive into the radiative decay of 12C Hoyle state through charged-particle spectroscopy, understanding carbon formation pivotal for life's existence, and discovering the intriguing insights of nuclear astrophysics at the INPC 2025.
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Clarifying the radiative decay of 12C Hoyle state via charged-particle spectroscopy Luigi Redigolo Dip. di Fisica e Astronomia, Universit di Catania, Italy and INFN Sezionedi Catania, Italy 29thInternational Nuclear Physics Conference (INPC 2025)
Clarifying the radiative decay of 12C Hoyle state via charged-particle spectroscopy Luigi Redigolo Dip. di Fisica e Astronomia, Universit di Catania, Italy and INFN Sezione di Catania, Italy 29thInternational Nuclear Physics Conference (INPC 2025) Daejeon, South Korea, 29 May 2025
Talk outline Istituto Nazionale di Fisica Nucleare Sezione di Catania Sezione di Catania Introduction: C formation and triple-alpha process The Hoyle state of 12C and its decay modes Istituto Nazionale di Fisica Nucleare Discrepancies in recent determinations of the Hoyle state decay branching ratio The MORALIS experiment Charged particles spectroscopy and coincidence measurements Results and discussion Luigi Redigolo INPC 2025
Carbon formation Fundamental for the existence of life on Earth Mostly forged in stars during the three-alpha process 12C 8Be Ex ? The 12C nucleus is not formed in the Ground state, but in an excited state A direct capture would not justify the C abundance and the C/O ratio in the universe What is the history of this process?
The three process H. Bethe The formation of the 12C nucleus is extremely unlikely to happen from the simple collision of 3 particles T = 50x TSun would be required! 1939 C nucleosynthesis happens in the red giant phase E. J. pik 1951 It must be a sequential process 1952 4He + 4He 8Be 8Be + 4He 12C + D. Clayton, E. Salpeter But, at temperatures of T = 0.1 GK and = 105, there are only 0.5 8Be nuclei for one billion 4He! How can we justify the 12C abundance and the C/O ratio?
The Hoyle state In 1953, Fred Hoyle predicted the existence of a s-wave resonance to justify the observed C/O ratio and a viable mechanism for the 3 process. Hoyle state (0+) 7.65 MeV The existence of such a state was experimentally confirmed by W. Whaling (Caltech) during the same year. (2+) 4.44 MeV Ward Whaling (1923-2020) In 1956, H. Morinaga described the Hoyle state as a linear chain configuration of particles 12C (0+) - 0 MeV Haruiko Morinaga (1922-2018) First steps towards the understanding of the importance of clustering phenomena in nuclear astrophysics! J = 0+ verified by W. A. Fowler in 1957 Fred Hoyle (1915-2001)
The Hoyle state properties 12C excited states: crucial to highlight the presence and the characteristics of cluster phenomena, and their impact on the definition of various mechanisms. The structure of the12C nucleus and of its Hoyle state, with a pronounced cluster nature an open challenge in nowadays nuclear astrophysics studies Linear chain -cluster model Bent-arm Equilateral triangle Algebraic Cluster Model Microscopic models (Faddeev three-body formalism) Bose-Einstein condensate Microscopic models (GCM, RGM) Different models different 3 cluster structures for the Hoyle state THSR wavefunction But the12C nucleus needs to be formed in its ground state! How?
The Hoyle state decays A ground state12C nucleus can be formed only through a radiative decay of the Hoyle state. 12C 12C 8Be Ex = 7.65 MeV Ex = 7.65 MeV Ground state Radiative decay ~ 0.05 % Emission of two -rays (or e+ e- couple) and production of a ground state 12C nucleus Particle decay ~ 99.95% RD PD Emission (depicted as a two-step process) of an particle. The final products are 3 particles. Very rare, happens only around 1 in 104 times! It accounts for almost all the decays! The C abundance in the whole universe completely depends from the Branching ratio of the Radiative to the Particle decay! What is the real B.R. value?
The Hoyle state Branching ratio estimates Knowing the actual Branching ratio ?.?.= rad is thus fundamental for any tot estimate of the C production and C/O ratio in the universe. Commonly accepted value for the Branching ratio ?.?.=???? ?.? ?? ? The derived predictions are in line with experimental observations of C/Oratio ???? Up to 2020 T. Kib di et al., Phys. Rev. Letter 125, 2020 This value is ~50% higher and would imply a 33% increase in the 3 process rate. Dramatic impact on the C/O ratio and on C production processes. ?.?.=???? ?.? ?? ? ???? 2020 ?.?.=???? The B.R. value obtained from the presentcharged particle-coincidence experiment ?.?(?) ?? ? ???? 2024 The MORALIS experiment, 2023
The MORALIS experiment Performed at INFN-LNL (CN Accelerator) Year: 2023 Over 20 days of complessive beam time The low current makes possible to neglect spurious coincidences between the two telescopes Beam: 2H @ 2.7 MeV (~ 30nA) ? + ??? ?? + ???????? Target: Melamine (C3H6N6) + C Backing coincidence telescopes, @ 90 and 64.8
The MORALIS experiment Performed at INFN-LNL (CN Accelerator) Year: 2023 Over 20 days of complessive beam time The low current makes possible to neglect spurious coincidences between the two telescopes Beam: 2H @ 2.7 MeV (~ 30nA) ? + ??? ?? + ???????? Target: Melamine (C3H6N6) + C Backing Detectors: two anti-coincidence telescopes, @ 90 and 64.8 Excellent resolution and unitary coincidence efficiency to allow the reconstruction of the coincidence spectra! Dell Aquila et al., Sci. Rep. 14 (2024)
The experimental setup Ejectile spectrum 12C detector * (anti-coincidence telescope) 12C* ? Hoyle C3H6N6 target (tilted 65 ) 4.44 MeV Alpha detector (anti-coincidence telescope) The set-up allows to detect the particles emitted in coincidence with an excited 12C nucleus, and to measure their energy. Accelerated deuteron beam Forward telescope: Micro-positioning Z-stage + movable plate Accurate3D topological calibration unitary coincidence detection efficiency! First time in a coincidence experiment! *4.44 MeV peak used for calibration
Experimental results coincidence data BACKWARD DETECTOR Hoyle FORWARD DETECTOR Excludingoutliers data, it is possible to calculate a weightedbranchingratio value of ?.?.=???? ?.??(??) ?? ? ????? ????/????= 4.2(6) ?? ? In excellent agreement with the commonly accepted value!
BACKWARD DETECTOR ????? ?.??(??) ?? ? ????/????= 4.2(6) ?? ? Excludingoutliers data, it is possible to calculate a weightedbranchingratio value of FORWARD DETECTOR ?.?.=???? coincidence data the commonly accepted value! Hoyle In excellent agreement with Thanks for your attention!
