Steve P. G. Chappell

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.

Search for {sup 16}O+{sup 16}O+{sup 16}O structure in {sup 48}Cr

Two theoretical papers have suggested the existence of an {sup 16}O+{sup 16}O+{sup 16}O configuration in {sup 48}Cr. We report on three experimental searches for the ternary breakup of {sup 48}Cr to the {sup 16}O+{sup 16}O+{sup 16}O channel. No evidence is seen for the process. Upper limits for the cross section are reported. {copyright} {ital 1996 The American Physical Society.}

Two-dimensional alpha cluster structures in 28Si

Abstract A study has been made of the 12C(16O,12C12C) α reaction between the centre of mass energies of 28.3 to 36.8 MeV. A number of resonances in 28Si have been observed for final channels leading to the unbound 10.35, 11.09 and 14.82 MeV states in 16O. At two energies associated with previously observed resonances, the angular correlations of the exit channel particles have been analysed to measure the dominant angular momentum of the 28Si compound nucleus. Additional data were acquired at two off-resonance energies for comparison. Using an essentially model independent analysis, the values obtained were all in the region of 19–21 h , and are comparable with the grazing angular momentum in the entrance channel. The results are relevant to recent theoretical predictions of planar α-cluster structures in 28Si and are discussed in the context of the model predictions.

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.

Exotic molecular and halo states in

The two nuclei {sup 12}Be and {sup 14}Be have been studied using breakup reactions on p, {sup 12}C and {sup 208}Pb targets. The decay of {sup 12}Be into two helium clusters ({sup 6}He+{sup 6}He and {sup 4}He+{sup 8}He) was observed from a series of excited states between 10 and 25 MeV, with spins in the range 4{sup +} to 8{sup +}. The single neutron angular distributions for {sup 14}Be exhibit the narrow forward peak characteristic of a halo. The widths of these distributions in coincidence with {sup 12}Be fragments are {gamma}{sub L}=78{+-}6 and 80{+-}1 MeV/c for breakup on carbon and lead.

^{12,14}

The two nuclei {sup 12}Be and {sup 14}Be have been studied using breakup reactions on p, {sup 12}C and {sup 208}Pb targets. The decay of {sup 12}Be into two helium clusters ({sup 6}He+{sup 6}He and {sup 4}He+{sup 8}He) was observed from a series of excited states between 10 and 25 MeV, with spins in the range 4{sup +} to 8{sup +}. The single neutron angular distributions for {sup 14}Be exhibit the narrow forward peak characteristic of a halo. The widths of these distributions in coincidence with {sup 12}Be fragments are {gamma}{sub L}=78{+-}6 and 80{+-}1 MeV/c for breakup on carbon and lead.

Be

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.

Exotic molecular and halo states in

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.