J. D. Malcolm

Absolute partial decay branching-ratios in 16O

The a-transfer reaction 126C(63Li, d)168O* has been performed at a 6Li bombarding energy of 42 MeV to populate excited states in 13C and 16O. Absolute branching ratios have been unambiguously determined for states in the excitation energy range 13.85 to 15.87 MeV and reduced widths are extracted.

Does a 4-? linear chain exist in 16O?

The12C(4He,8Be)8Be reaction has been measured with a beam energy ranging from 12.2 to 20.0 MeV. The ?-particles emitted in the decay of 8Be were detected in an array of four double sided silicon strip detectors. The excitation function for events in which the 8Be centre of mass angle ?cm = 90? provides evidence that the previously observed 6+ resonance at an excitation energy of 19.35 MeV in 16O is a 6+ doublet, with members at ~ 19.30 and 19.37 MeV.

Access to resonant states in 24Mg using the 12C(13C,4He+20Ne)n reaction

A study of the 12C(13C,20Ne+α)n reaction has been performed at 13C beam energies of 12.0, 13.5 and 20.0 MeV. The measurements were to explore the extent to which 24Mg excited states could be populated in a quasi-free 12C+12C→ 20Ne+α reaction in which the last neutron in the 13C beam acts as a spectator. Excited states in 24Mg are found at 13.25 (0.20) and 14.25 (0.20) MeV. These states are found to be produced from the neutron evaporation from the 25Mg compound nucleus. The kinematic region associated with the quasi-free condition is dominated by contaminants from the reactions associated with neutron decay of excited states in 21Ne populated in the 12C(13C,21Ne)α reaction.

Neutron decay of excited states in 21Ne populated in the 12C(13C,21Ne)4He reaction

The 12C(13C,α)21Ne reaction has been measured with a 13C beam energy of 20 MeV. States in 21Ne have been populated between 0 and 12 MeV with a resolution of ~350 keV (FWHM). A coincidence experiment has been performed in which either the bound 21Ne nucleus or the 20Ne nucleus produced via neutron decay is detected. This permitted the 21Ne states undergoing gamma decay and neutron decay to the ground and first excited states in 20Ne to be determined. The current measurements suggest several errors in the current compilation for 21Ne.

Disentangling unclear nuclear breakup channels of beryllium-9 using the three-axis Dalitz plot

The three-axis Dalitz plot has been applied to the breakup of a nucleus into unequal mass fragments for the first time. The Dalitz plot allows clear identification of the various breakup channels of 9Be → 2α + n process. The method has allowed the branching ratio for the 6.38 MeV level in9Be to be provisionally calculated when examining the 9Be(4He, α)ααn reaction. The effects of non-uniform angular distributions on the Dalitz plot must still be properly investigated along with the effects of contaminant reaction channels. It is proposed that this method could be used to determine the breakup branching ratio of a newly-measured level in this nucleus.

Breakup branches of Borromean beryllium-9

The breakup reaction 9Be(4He, 3α)n was measured using an array of four double-sided silicon strip detectors at beam energies of 22 and 26 MeV. Excited states in 9Be up to 12 MeV were populated and reconstructed through the measurement of the charged reaction products. It is proposed that limits on the spins and parities of the states can be derived from the way that they decay. Various breakup paths for excited states in 9Be have been explored including the 8Beg.s. + n, 8Be2+ + n and 5Heg.s. + 4He channels. By imposing the condition that the breakup proceeded via the 8Be ground state, clean excitation spectra for 9Be were reconstructed. The remaining two breakup channels were found to possess strongly-overlapping kinematic signatures and more sophisticated methods (referenced) are required to completely disentangle these other possibilities. Emphasis is placed on the development of the experimental analysis and the usefulness of Monte-Carlo simulations for this purpose.

Absolute decay width measurements in 16O

The reaction 126C(63Li, d)168O* at a 6Li bombarding energy of 42 MeV has been used to populate excited states in 16O. The deuteron ejectiles were measured using the high-resolution Munich Q3D spectrograph. A large-acceptance silicon-strip detector array was used to register the recoil and break-up products. This complete kinematic set-up has enabled absolute α-decay widths to be measured with high-resolution in the 13.9 to 15.9 MeV excitation energy regime in 16O; many for the first time. This energy region spans the 14.4 MeV four-α breakup threshold. Monte-Carlo simulations of the detector geometry and break-up processes yield detection efficiencies for the two dominant decay modes of 40% and 37% for the α+12C(g.s.) and a+12C(2+1) break-up channels respectively.

Simplicity from Complexity

The emergence of clustering in light nuclear systems is explored using the deformed harmonic oscillator as a starting point. The experimental evidence for various geometrical arrangements of clusters in carbon-12 is discussed.

Study of states in 14C via the 10Be(4He,4He)10Be reaction

A study of the 10Be(4He,4He)10Be reaction has been performed at 10Be beam energies of 25.0, 27.0, 29.0, 32.0, 34.0, 38.0, 40.0, 42.0, 44.0 and 46.0 MeV. The measurements were to explore possible molecular rotational bands in 14C. Three states at excitation energies of Ex = 18.8, 19.76 and 20.66 MeV have been measured and their spins have been determined to be 5−, 5− and 6+, respectively.

Evidence for a new {sup 12}C state at 13.3 MeV

The two reactions {sup 12}C({sup 4}He,{sup 4}He + {sup 4}He + {sup 4}He){sup 4}He and {sup 9}Be({sup 4}He, {sup 4}He + {sup 4}He + {sup 4}He)n were measured using an array of four double-sided strip detectors. Excited states in {sup 12}C were reconstructed filtered by the condition that the {alpha}-decay proceeded via the {sup 8}Be ground state. In both measurements, evidence was found for a new state at 13.3(0.2) MeV with a width 1.7(0.2) MeV. Angular correlation measurements from the {sup 12}C({sup 4}He, {sup 4}He + {sup 4}He + {sup 4}He){sup 4}He reaction indicates that the state may have J{sup {pi}}=4{sup +}.