Nucleon-induced excitation of collective bands in 12C

doi:10.1016/0375-9474(85)90072-7

Nuclear Physics A

Volume 445, Issue 2, 25 November 1985, Pages 304-332

https://doi.org/10.1016/0375-9474(85)90072-7 Get rights and content

Abstract

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.

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γ-ray emission in proton-induced nuclear reactions on natC and Mylar targets over the incident energy range, E<inf>p</inf> = 30 – 200 MeV. Astrophysical implications
2023, Nuclear Physics A
We have measured the γ-ray line production cross sections in proton-induced nuclear reactions on various target nuclei (¹²C, ¹⁶O, ²⁴Mg, ²⁸Si, ⁵⁶Fe) of chemical elements abundant in astrophysical sites (solar flares, the interstellar medium, cosmic compact objects) over the incident energy range of E_p = 30 – 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 separated sector cyclotron of iThemba LABS using a high-energy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the γ-ray energy spectra. In the current paper, we focus on γ-ray de-excitation lines produced in proton irradiations of $^{n a t}$ C and Mylar targets, in particular, on the prominent 4.439 and 6.129 MeV lines of ¹²C and ¹⁶O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays (LECRs) with the gas and dust of the inner galaxy. We report new γ-ray production experimental cross section data for ten nuclear γ-ray lines that we compare to previous low-energy data sets from the literature, to the predictions of the TALYS code of nuclear reactions and to a semi-empirical compilation. In the first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential (OMP) and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at E_γ = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results.
Coupled-channels optical model calculations with account of nuclear volume conservation
1999, Nuclear Physics A
A coupled-channel formalism based on the soft-rotator model is proposed which allows conservation of the nuclear volume for dynamically deformable nuclei. The extra coupling term due to the volume conservation contributes to a stronger coupling between levels of same spin and parity. The effect is demonstrated for the case of $n +^{12} C$ interaction leading to the O₂⁺ state located at 7.65 MeV for incident neutron energies of 20 to 40 MeV.
Nucleon interaction with 12C studied by the soft-rotator model and a limit on the charge-symmetry breaking in the nuclear mean field
1998, Nuclear Physics A
The soft-rotator model is extended to include the capability to calculate the proton-nucleus scattering, and is used for a consistent analysis of the collective nuclear structure, EM transition and the nucleon (both neutron and proton) interaction data of ¹²C. It is found that the model can describe these quantities to a good accuracy except for an anomalous behavior in the inelastic proton scattering to the first excited state at backward angles above the incident energy of 40 MeV. The difference in the neutron and proton real potential depths is used to infer the limit on the charge-symmetry breaking (CSB) in the nuclear mean field, which is found to be −5.7±16.6 MeV fm³, or (−0.6±1.8)% of the nuclear mean field of ¹²C. More precise neutron scattering data are highly desired because (1) the main source of the uncertainty for the CSB study came from the neutron interaction data, and (2) there is no neutron data corresponding to the anomaly in the proton inelastic scattering mentioned above.
Consistent description of collective level structure and neutron interaction data for 12C in the framework of the soft-rotator model
1997, Nuclear Physics A
We have measured the neutron elastic and inelastic scattering angular distributions of ¹²C at 28.2 MeV. This data, together with information from other works, was used to construct a neutron scattering data-base in the energy region from 20 to 40 MeV. Then, a systematic analysis of nuclear structure and neutron interaction data for ¹²C was carried out in the framework of the soft-rotator model. The model was firstly applied to analyse the low-lying collective level structure of the ¹²C nucleus successfully. The intrinsic wave function obtained in such an analysis was then used to construct the coupling potentials in the coupled-channels formalism to calculate the neutron total and scattering cross sections. The quadrupole deformation parameter obtained in the present analysis was 0.164, which was much smaller in the absolute sense than the value used in the rotation-vibration model employed frequently in the past, i.e. ≈0.6. When averaged over the β-vibration function, however, the present result yields an effective quadrupole strength of about the same scale as the previous studies due to softness of the ¹²C wave function with respect to β₂ degree of freedom. The soft-rotator model was found to be very successful in reproducing both the structure and neutron scattering data consistently for the first time in this mass region.
Calculated differential elastic and inelastic neutron scattering by 12C and 16O between 30 and 60 MeV
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Well-verified models for elastic and inelastic scattering of fast neutrons (and protons) from ¹²C and ¹⁶O are translated into a useful form for transport, dosimetry, and scintillator response calculations. The information presented here is complementary to published calculations (D. J. Brenner and R. E. Prael, Atomic Data and Nuclear Data Tables 41, 71, 1989) of secondary-particle production by incident neutrons in the energy region 15 ≤ E_n ≤ 60 MeV. Tables are given of Legendre expansion coefficients derived from fits to experimental cross sections at incident neutron energies E_n = 18-26 MeV and from fits to model predictions for 30- to 60-MeV neutrons.
Neutron elastic and inelastic scattering from Mg, Si, S, Ca, Cr, Fe and Ni AT E<inf>n</inf> = 21.6 MeV
1990, Nuclear Physics, Section A
The Studsvik high-resolution, low-background time-of-flight facility has been used to measure differential neutron elastic and inelastic scattering cross sections for Mg, Si, S, Ca, Cr, Fe and Ni at the neutron energy 21.6 MeV. The results have been analysed in terms of collective rotational, vibrational or rotation-vibrational models using the coupled-channels formalism. Optical model potential depths and geometrical parameters as well as nuclear deformation parameters were determined from fits to the measured data.

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^☆: This investigation was supported by PHS grant number 5-R01-CA25193 awarded by the National Cancer Institute and by National Science Foundation grant number PHY8108456.

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Nuclear Physics A

Abstract

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Cited by (26)

γ-ray emission in proton-induced nuclear reactions on <sup>nat</sup>C and Mylar targets over the incident energy range, E<inf>p</inf> = 30 – 200 MeV. Astrophysical implications

Coupled-channels optical model calculations with account of nuclear volume conservation

Nucleon interaction with <sup>12</sup>C studied by the soft-rotator model and a limit on the charge-symmetry breaking in the nuclear mean field

Consistent description of collective level structure and neutron interaction data for <sup>12</sup>C in the framework of the soft-rotator model

Calculated differential elastic and inelastic neutron scattering by <sup>12</sup>C and <sup>16</sup>O between 30 and 60 MeV

Neutron elastic and inelastic scattering from Mg, Si, S, Ca, Cr, Fe and Ni AT E<inf>n</inf> = 21.6 MeV

Nucleon-induced excitation of collective bands in 12C☆

Abstract

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Nucleon-induced excitation of collective bands in ¹²C☆