Stringent upper limit on the direct 3α decay of the Hoyle state in 12C

SMITH, Robin, GAI, Moshe, AHMED, Mohammad, FREER, Martin, FYNBO, Hans, SCHWEITZER, Deran and STERN, Sarah (2020). Stringent upper limit on the direct 3α decay of the Hoyle state in 12C. Physical Review C: Nuclear Physics, 101, 021302(R).

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We investigate an implication of the most recent observation of a second Jπ=2+ state in 12C, which was measured using the 12C(γ,α)8Be(g.s.) reaction. In addition to the dissociation of 12C to an α-particle and 8Be in its ground state, a small fraction of events (2%) were identified as direct decays and decays to excited states in 8Be. This allowed a limit on the direct 3α partial decay width to be determined as Γ3α<32(4) keV. Since this 2+ state is predicted by all theoretical models to be a collective excitation of the Hoyle state, the 3α partial width of the Hoyle state is calculable from the ratio of 3α decay penetrabilities of the Hoyle and 2+ states. This was calculated by using the semiclassical Wenzel-Kramers-Brillouin approach and we deduce a stringent upper limit for the direct decay branching ratio of the Hoyle state of Γ3α Γ <5.7×10−6, over an order of magnitude lower than previously reported. This result places the direct measurement of this rare decay mode beyond current experimental capabilities.

Item Type: Article
Uncontrolled Keywords: Materials and Engineering Research Institute; Department of Engineering and Mathematics; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; Nuclear & Particles Physics
Identification Number:
Page Range: 021302(R)
SWORD Depositor: Symplectic Elements
Depositing User: Symplectic Elements
Date Deposited: 05 Feb 2020 10:10
Last Modified: 18 Mar 2021 02:17

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