The 23Na(p, γ)24Mg reaction and the giant dipole resonance in 24Mg

doi:10.1016/0375-9474(68)90399-0

Nuclear Physics A

Volume 116, Issue 3, 19 August 1968, Pages 682-694

https://doi.org/10.1016/0375-9474(68)90399-0 Get rights and content

Abstract

The ²³Na(p, γ)²⁴Mg reaction has been studied over the region of excitation corresponding to the giant dipole resonance. Gamma rays to the ground state and to the first and to the second plus third excited states have been observed. The (p, γ₀) cross section is on the average smaller than it is in other doubly even nuclei in this region. The (p, γ₁) cross section is considerably larger than the (p, γ₀) and clearly follows a giant-resonance shape. A part of the giant resonance built upon the second and/or third excited states is also observed. A fluctuation analysis finds the coherence width to be about 75 keV. The angular distributions of both γ₀ and γ₁ show the usual small energy variation that has come to be associated with the giant resonance.

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The coupled channels approach in the shell model intermediate coupling is presented. The problems of orthonormalization of the solutions, fulfillment of boundary conditions, agreement of the effective two-body intercation with the nuclear average field and continuum discretization are considered. It is shown that in light and medium nuclei the description of the structure and decay characteristics of multipole giant resonances can be reduced to the solution of a compact algebraical system of equations. The model is applied to the description of the photonuclear reactions on the ²⁴Mg, ²⁸Si and ³²S nuclei. The origin of the gross and intermediate structure of the dipole giant resonance (DGR) as well as the partial decay channels of the DGR are studied. It is found that the ²⁴Mg DGR splitting results from the nuclear shape deformation.
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We have studied the Giant Dipole Resonance (GDR) built on the excited states of ¹¹²Sn formed in the fusion of ¹⁹F with ⁹³Nb. The excitation energy of the compound nucleus ¹¹²Sn was 130 and 152 MeV. High-energy γ-rays were detected in a 7-element BaF₂ cluster and 4 NaI(Tl) scintillators. Coincidences with the evaporation residues detected in two parallel-plate avalanchecounters ensured that the γ-rays were associated with fusion events. In order to study the characteristics of the GDR, we have performed analyses of the γ-ray spectra within the statistical model, using a continuous evolution of the GDR centroid energy with the mass and the temperature of the emitting nucleus, and a nuclear temperature dependent level density parameter. The theoretical prescriptions concerning the evolution of the GDR width with excitation energy have been tested. We show that, in order to reproduce the γ-spectra, the increase of the width must be more rapid than the two theoretical predictions. The width has to reach large values, of the order of 15 to 20 MeV above 100 MeV of excitation energy. These values are greater than the saturation value of about 12 MeV which has been published following the analyses using constant parameters. On this condition, the shape of the spectra can be reproduced with or without a saturation of the width. It is therefore not possible to say if the increase of the width is due to angular momentum effects or to collisional effects.
Partial photonucleon cross sections and the 24Mg giant dipole resonance
1988, Nuclear Physics, Section A
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The photodisintegration of 24Mg
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The giant dipole resonance (GDR) of ²⁴Mg was studied by measuring two different types of decay spectra: (a) prompt de-excitation γ-rays emitted following photodisintegration, and (b) those of charged photoparticles. Energy-integrated (γ, n) and (γ, p) cross sections to specific residual states and also partial (γ, p) and (γ, α) cross sections are presented. The observed decay properties are discussed with reference to the 1p1h model, and the isospin purity of the GDR is assessed. Detailed comparison with theoretical models, however, indicates that the existing calculations fail to describe correctly both the deduced 1p1h composition and structure of the GDR.

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^☆: Work performed under the auspices of the U.S. Atomic Energy Commission.

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Nuclear Physics A

Abstract

References (18)

Nucl. Phys.

Nucl. Phys.

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The 23Na(p, γ)24Mg reaction and the giant dipole resonance in 24Mg☆

Abstract

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Phys. Lett.

Ann. of Phys.

The ²³Na(p, γ)²⁴Mg reaction and the giant dipole resonance in ²⁴Mg☆