M. J. Leddy

The construction and operation of a hybrid gas-silicon detector for studies of cluster breakup reactions

A hybrid detector system has been constructed consisting of a gas filled ionization chamber and a large area silicon semiconductor strip detector within the same gas volume. The construction and operation of these detectors is described, together with a brief description of the electronics and data acquisition system used in cluster breakup studies. The techniques for software correction and gain matching of the detector energy signals are described and results are presented for the resolutions in energy, position and time. In a typical application, elements up to Ca are easily resolved and the positions of individual ions are measured with a resolution of <0.2 mm in the reaction plane, whilst energy resolutions approaching 200 keV can be obtained from the Si strip detector over a small area. Some spectra are presented for measurements of the breakup of Mg-24 into C-12 + C-12.

Association of the 12C+12C breakup states in 24Mg with the quasimolecular resonances.

A high resoution measurement of the [sup 12]C([sup 24]Mg,[sup 12]C[sup 12]C)[sup 12]C reaction shows that the [sup 24]Mg breakup states have widths in the region of 100 to 250 keV. The energies, widths, and spins of these states are seen to be consistent with those of the [sup 12]C +[sup 12]C quasimolecular resonances which occur in the same region of excitation in the [sup 24]Mg nucleus.

Comparison of resonances observed in the 12C(24Mg, 12C12C)12C and 12C(20Ne, 12C12C)8Be reactions

Abstract A study of the 12 C( 24 Mg, 12 C 12 C) 12 C reaction has revealed discrete states at excitation energies between 20 and 30 MeV in 24 Mg. Angular correlation analyses of some of the lower energy states confirms the report by earlier authors of monotonically increasing spin values consistent with a rotational sequence. Comparison with breakup observed in the 12 C( 20 Ne, 12 C 12 C) 8 Be reaction suggests that the same states in 24 Mg are populated, while the difference in laboratory cross sections in the two reactions is interpreted as evidence for the association of the breakup states with a prolate hyper-deformed configuration appearing in theoretical calculations for 24 Mg.

Reaction mechanism for the symmetric breakup of 24Mg following an interaction with 12C

Abstract Data on the yield of the symmetric breakup of 24 Mg as a function of beam energy are presented and compared with detailed calculations of the energy dependence. The 24 Mg states seen in symmetric breakup agree with previously observed breakup states having spin and parities J π = 4 + ,(6 + ),8 + . The data allow the variations of yield for individual states to be judged, as the beam energy is varied. The variation in the yield of the 4 + states is compared in detail with calculations assuming several possible compound nuclear or direct reaction mechanisms. It is concluded that a massive ( 12 C) transfer or a simple statistical compound process are unlikely mechanisms, but that each of several other mechanisms is consistent with the data.

The breakup of 24Mg into 16O and 8Be

The breakup of 24Mg into 16O and8Be fragments has been studied using the reactions 12C(24Mg, 16O8Be) 12C and 12C(20Ne, 16O8Be) 8Be. In the latter case, discrete states are observed near 24–28 MeV of excitation in 24Mg and the yield from this reaction is an order of magnitude greater than that of the former. This implies the excited configuration populated in 24Mg is favoured by the transfer of an alpha-particle and would therefore suggest an association with a 4-particle 4-hole configuration. This suggests a link with the octupole stabilised deformed minimum which appears in Nilsson-Strutinsky calculations of the potential energy surface in 24Mg, and also with the α - 16O - α structure predicted in cranked cluster model calculations. In the excitation spectrum no states appear above 31 MeV indicating a possible band termination in disagreement with recent results using the 16O+ 12C reaction. These results are discussed in terms of the Harvey model.

Can break-up reactions be used to probe high-lying inelastic channels in scattering?

The reaction has been studied to investigate a possible overlap with the scattering resonances observed in the and channels. Evidence for the break-up of was observed, but the yield was too low to be able to associate it with specific resonances.

Association of the C-12 + C-12 breakup states in Mg-24 with the quasimolecular resonances

A high resoution measurement of the [sup 12]C([sup 24]Mg,[sup 12]C[sup 12]C)[sup 12]C reaction shows that the [sup 24]Mg breakup states have widths in the region of 100 to 250 keV. The energies, widths, and spins of these states are seen to be consistent with those of the [sup 12]C +[sup 12]C quasimolecular resonances which occur in the same region of excitation in the [sup 24]Mg nucleus.

The breakup of24Mg into16O and8Be

The breakup of24Mg into16O and8Be fragments has been studied using the reactions12C(24Mg,16O8Be)12C and12C(20Ne,16O8Be)8Be. In the latter case, discrete states are observed near 24–28 MeV of excitation in24Mg and the yield from this reaction is an order of magnitude greater than that of the former. This implies the excited configuration populated in24Mg is favoured by the transfer of an alpha-particle and would therefore suggest an association with a 4-particle 4-hole configuration. This suggests a link with the octupole stabilised deformed minimum which appears in Nilsson-Strutinsky calculations of the potential energy surface in24Mg, and also with theα —16O —α structure predicted in cranked cluster model calculations. In the excitation spectrum no states appear above 31 MeV indicating a possible band termination in disagreement with recent results using the16O+12C reaction. These results are discussed in terms of the Harvey model.