First observation of a 5- Resonance in 12C; evidence for triangular D3h symmetry

[摘要] This thesis reports a measurement of the break-up reaction \(^1\)\(^2\)C(\(^4\)He, \(^1\)\(^2\)C*)\(^4\)He performed at the Birmingham MC40 cyclotron facility at a beam energy of 40 MeV. An array of four double-sided silicon-strip detectors was used to detect the final-state products of the reaction. Results from previous measurements of this reaction have shown that various excited states in \(^1\)\(^2\)C can be populated. In the present study the 13.3 MeV and the 22.4 MeV resonances were, in particular, populated. The latter has been seen for the first time.The analysis for both resonances was performed using the angular correlations technique from which their spin and parity were determined with values of J\(^p\)=4\(^+\) and J\(^p\)=5\(^-\), respectively. Monte-Carlo simulations were performed both before and after the experiment in order to have the optimal detector-array efficiency and normalise the results of the angular correlations analysis. The results have been compared to predictions of the algebraic cluster model, for which the J\(^p\)=4\(^+\) is thought to be related to a rotational band based on the Hoyle state and the J\(^p\)=5\(^-\) resonance is part of the ground-state band. This latter state provides strong evidence for triangular D\(_3\)\(_h\) symmetry corresponding to an equilateral triangle structure, observed here for the first time in a nucleus.

[发布机构] University:University of Birmingham;Department:School of Physics and Astronomy

[关键词] Q Science;QC Physics