Spin-parity assignments of excited states in 12C

doi:10.1016/0375-9474(73)90064-X

Nuclear Physics A

Volume 201, Issue 2, 5 February 1973, Pages 247-263

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Abstract

The reaction ¹²C(α, α')¹²C^∗(3α) is observed by using 90 MeV a-particles in ionographic matter. The energies of the three α-particles from the break-up of ¹²C^∗ are plotted in Dalitz diagrams. The density distributions for the three α-particles in the diagrams are calculated by assuming the spins and parities for the states in ¹²C^∗(3α). The spin-parities for the states are assigned by comparing the observed density distributions with those calculated.

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Energy levels of light nuclei A = 12
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The 3α-cluster structure of excited states in ¹²C is investigated by taking into account the correct boundary condition for three-body resonant states. In this study, we adopt the Complex Scaling Method (CSM), which enables us to obtain the resonant states that can be described as square integrable states with the same boundary conditions as those of the bound states, and calculate not only resonance energies but also the total decay widths of the 3α system. We compare the calculated resonance parameters to the experimental data and also to the previous 3α model results obtained with a bound state approximation. Our results well explain the many observed levels and give an assurance for the presence of the second $2^{+}$ state, which is expected by the 3α model calculations with the approximations of bound state or two-body scattering. As for the negative-parity states, it is considered that the calculated $4^{-}$ state is assigned to the observed $E_{x} = 13.4 MeV$ state. Through the calculation of channel amplitudes, the obtained third $0^{+}$ state is found to have a s-wave dominant and a more dilute structure compared to the second $0^{+}$ state.
Radiative capture in the light heavy-ion systems 6Li+6Li and 6Li+7Li at E<inf>c.m.</inf> = 1-8 MeV
1991, Nuclear Physics, Section A
The heavy-ion radiative-capture reactions ⁶Li(⁶Li, γ)¹²C and ⁷Li(⁶Li, γ)¹³C have been studied. Utilizing a large-volume NaI(Tl) γ-spectrometer, the γ-transitions to the ground state and the three lowest excited states of ¹²C in the former case and the transitions γ₀, γ₁, $γ 23$ , γ₄ and $γ 567$ in the latter case could be resolved. The evaluation of absolute cross sections which range from 0.3 to 210 nb/sr relies on the thoroughly investigated response function of the spectrometer. Excitation functions at 125° as well as three-point angular distributions at several energies were measured. The results are compared with statistical model calculations. The latter make use of a smooth angular momentum cutoff in the entrance channel, isospin mixing in the compound nucleus, and giant resonances built upon excited states for γ-strenght distributions. All data are described by these model calculations. In addition to these statistical features a broad resonance (gL ∼ 0.8 MeV) is observed for th γ₁-transition in ⁶Li(⁶Li, γ)¹²C at E_x ∼ 30.3 MeV.
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1991, Nuclear Physics, Section A
The expectation spectra obtained by the Monte Carlo simulation of those reaction mechanisms which are known to occur in the interactions of light nuclei have been compared with the experimental distributions of various physical variables obtained from a complete measurement, in 4π geometry, of the ¹²C(n, n3α) reaction. By the use of this method, contributions of various reaction channels, including the three-body nα⁸Be and the four-body nααα simultaneous breakup, have been extracted. The present study has also shown that the Monte Carlo simulation of the sequential reaction mechanism alone may be successfully used in modelling the four-body n3α final state. This is true for any variable or correlation of variables and for any specific experimental condition, provided the known ¹²C excitation spectra with given branching ratios to the transition via ⁸Be_g.s. are used as input data for the Monte Carlo simulation.
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1985, Nuclear Physics, Section A
Detailed differential elastic and inelastic neutron scattering data for ¹² C at E_n = 20–26 MeV are presented and analyzed in terms of a deformed optical potential and rotation-vibration interaction in a coupled-channel formalism. All well-established states in ¹²C up to 15 MeV excitation energy are observed in the experiment. Additional neutron scattering, total and reaction cross-section data for 20 < E_n < 100 MeV are incorporated into the analysis to determine more precisely the energy dependence of the deformed potential well parameters. A newly developed formalism for the treatment of radius, diffuseness and potential depth oscillations of a nucleus with a deformed equilibrium shape is compared with both (p, p′) and (n, n′) data. The resulting model provides an improved description of earlier (p,p') data and confirms K^π assignments for some excited bands in ¹²C.
Transition densities between the 0<inf>1</inf>+, 2<inf>1</inf>+, 4<inf>1</inf>+, 0<inf>2</inf>+, 2<inf>2</inf>+, 1<inf>1</inf>- and 3<inf>1</inf>- states in 12C derived from the three-alpha resonating-group wave functions
1981, Nuclear Physics, Section A
All the multipole transition densities between the seven T = 0 states in ¹²C are calculated with the use of the microscopic 3α resonating-group wave functions which are obtained by dynamically solving the 3α relative motion with the total antisymmetrization taken into account exactly. The observed elastic and inelastic electron scattering form factors for the transition to the 2₁⁺, 4₁⁺, 0₂⁺, 1₁⁻and 3₁⁻ states are well reproduced with no additional effective charge. The existence of a deformed intrinsic state for the 0₁⁺, 2₁⁺and 4₁⁺states is deduced by the analysis of the transition densities between them which are derived by the weak-coupling-type 3α wave functions; the intrinsic density distribution is illustrated. The monopole density distribution of the 0₂⁺, 2₂⁺ and 1₁⁻, states is found to be much longer ranged than that of the 0₁⁺, 2₁⁺ and 4₁⁺ states; the 3₁⁻ state case is intermediate. On the basis of the transition densities between the 0₁⁺, 2₁⁺, 0₂⁺ and 2₂⁺ states, analysis is made of the transition between the shell-like states and the molecule-like states with a large spatial-structure change. Specific, effective nucleon-nucleon interactions are folded into the transition densities here obtained. The evident dependence of the radial shape of the folded nucleon-¹²C form factors on the choice of the interactions and the multi-step form factors for the excitation of the 0₂⁺, 1₁⁻ and 3₁⁻ states are discussed.

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Nuclear Physics A

Abstract

References (7)

Nucl. Phys.

Compt. Rend.

Rev. Mod Phys.

Nucl. Phys.

Rev. Mod. Phys.

Cited by (23)

Energy levels of light nuclei A = 12

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Radiative capture in the light heavy-ion systems <sup>6</sup>Li+<sup>6</sup>Li and <sup>6</sup>Li+<sup>7</sup>Li at E<inf>c.m.</inf> = 1-8 MeV

Monte Carlo analysis of the four-body final state in the neutron-induced <sup>12</sup>C breakup

Nucleon-induced excitation of collective bands in <sup>12</sup>C