Experimental measurements of break-up reactions to study alpha clustering in carbon-12 and beryllium-9

Smith, Robin (2017). Experimental measurements of break-up reactions to study alpha clustering in carbon-12 and beryllium-9. University of Birmingham. Ph.D.

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Abstract

Due to the high binding energy of the α-particle, this object can preform in heavier atomic nuclei. This work explores α-clustering in \(^9\)Be and \(^12\)C by measuring their nuclear break-up. For \(^9\)Be, it has been proposed that the two α-particles of the unstable \(^8\)Be nucleus are bound together by a covalently shared neutron. This thesis reports the observation of a state in \(^9\)Be at 3.8 MeV through the \(^9\)Be(\(^4\)He,α)ααn reaction. By comparing its reduced width with that of a potential mirror analogue in \(^9\)B, its angular momentum was shown to be J < 7/2. This is consistent with a hitherto unmeasured 3/2\(^+\) molecular binding configuration state. The \(^12\)C nucleus is thought to consist of three α-clusters and its famous Hoyle state has been shown to possess an unusually large volume. Due to its low density, this state may behave like a Bose-Einstein condensate, where the fermonic structures of the constituent α-particles are no longer important. By precisely measuring the decay of the Hoyle state into three α-particles, through the \(^12\)C(\(^4\)He,α)3α reaction, an upper limit for the direct 3α decay branch of 0.047% was obtained. This lies below predictions for the decay of a condensate state, casting doubt on this interpretation.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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