Tz. Kokalova

New Measurement of the Direct 3α Decay from the 12C Hoyle State

Excited states in certain atomic nuclei possess an unusual structure, where the dominant degrees of freedom are those of α clusters rather than individual nucleons. It has been proposed that the diffuse 3α system of the ^{12}C Hoyle state may behave like a Bose-Einstein condensate, where the α clusters maintain their bosonic identities. By measuring the decay of the Hoyle state into three α particles, we obtained an upper limit for the rare direct 3α decay branch of 0.047%. This value is now at a level comparable with theoretical predictions and could be a sensitive probe of the structure of this state.

Structure of neutron-rich Be and C isotopes

The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2−, and 3/2−, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C.

Gas-like state ofαclusters around aO16core inMg24

We have studied gas-like states of {alpha} clusters around an {sup 16}O core in {sup 24}Mg based on a microscopic {alpha}-cluster model. The 0{sup +} states below the {sup 16}O+{alpha}+{alpha} threshold, which are candidates for the resonance solution judging from the energy convergence behavior, are strongly excited by an isoscalar monopole (E0) operator from the ground state, which could be observed as an experimental signature of well-developed {alpha} gas-like states in the excited states. These states have significant overlaps with the THSR (Tohsaki-Horiuchi-Schuck-Roepke) wave functions with large spatial extension.

ALPHA-CLUSTER STATES POPULATED IN 24Mg + 12C

Charged particle and γ-decays in light α-like nuclei are investigated for 24Mg +12C. Various theoretical predictions for the occurence of superdeformed and hyperdeformed bands associated with resonance structures with low spin are presented. The inverse kinematics reaction 24Mg +12C is studied at Elab(24Mg) = 130 MeV. Exclusive data were collected with the Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the VIVITRON Tandem facility at Strasbourg. Specific structures with large deformation were selectively populated in binary reactions and their associated γ-decays studied. Coincident events from α-transfer channels were selected by choosing the excitation energy or the entry point via the two-body Q-values. The analysis of the binary reaction channels is presented with a particular emphasis on 20Ne-γ and 16O-γ coincidences.

Characterization of the proposed 4-α cluster state candidate in O 16

CITATION: Li, K. C. W., et al. 2017. Characterization of the proposed 4−α cluster state candidate in ¹⁶O. Physical Review C, 95(3):1-6, doi:10.1103/PhysRevC.95.031302.

Reaction mechanisms in 24Mg+12C and 32S+24Mg

The occurence of “exotic” shapes in light N = Z α‐like nuclei is investigated for 24Mg+12C and 32S+24Mg. Various approaches of superdeformed and hyperdeformed bands associated with quasimolecular resonant structures with low spin are presented. For both reactions, exclusive data were collected with the Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the VIVITRON Tandem facility of Strasbourg. Specific structures with large deformation were selectively populated in binary reactions and their associated γ‐decays studied. The analysis of the binary and ternary reaction channels is discussed.

Structure studies of excited states of 17C and 16C

The structure of excited states of 17 C has been studied using the three-neutron transfer reaction 14 C( 12 C, 9 C) 17 C at 231 MeV. Thirteen states above the neutron threshold up to 16.3 MeV excitation energy are observed. The large negative reaction Q-value of Q 0 = -46.930 MeV leads to a strong mismatch between entrance and exit channels. In this case the population of stretched configurations is strongly favoured. The lowest-lying 9/2 + state could be identified at 3.10 MeV, in excellent agreement with shell model calculations. Further tentative assignments could be given for several other states. A striking agreement is observed between excitation energies of 17 C and those states of 16 C populated in the 13 C( 12 C, 9 C) 16 C reaction, when the level schemes of both nuclei are aligned along the 9/2 + state at 3.10 MeV in 17 C and the [9/2 + ⊗ 1/2 - ]5 - state at 8.92 MeV in 16 C. Deviations between E x ( 17 C) and the difference E x ( 16 C) - 5.82 stay within the range of +0.14/ - 0.17 MeV for ten pairs of states of these isotopes.

Binary reaction decays from 24Mg + 12C

Charged-particle and

BAND STRUCTURES IN 12Be: EXPERIMENTAL RESULTS

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High multiplicity α-particle breakup measurements to study α-condensate states

decays in