16O(α, γ)20Ne capture γ-ray measurements on the excited Kπ = 0+ bands in 20Ne near 7 MeV

doi:10.1016/0375-9474(72)90741-5

Nuclear Physics A

Volume 197, Issue 1, 11 December 1972, Pages 1-16

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Abstract

Radiative widths have been measured for the E_α = 3074 keV (J^π = 0⁺), 3363 keV (J^π = 2⁺), 3872 keV (J^π = 2⁺) and 5368 keV (J^π = 4⁺z) resonances in the ¹⁶O(α,γ)²⁰Ne reaction, corresponding to level energies at 7191±3, 7420±1, 7826±3 and 9029±3 keV respectively. The radiative widths for decay to the 2⁺, first excited state and the 0⁺, ground state of ²⁰Ne are: 7191 → 1633 (4.35±0.75 meV), 7420 → 1633 (29±4 meV), 7420 → 0 (≦3.0±0.6 meV), 7826 → 1633 (11.7±1.6 meV), 7826 → 0 (57±7 meV) and 9029 → 1633 (340±42 meV). The following upper limits on the decay widths to the 4⁺, 4246 keV level were also obtained: 7420 → 4246 (< 2.2 meV), 7826 → 4246 (< 2 meV) and 9029 → 4246 (< 6.8 meV). The experimentally known interband electromagnetic matrix elements are compared with nuclear model predictions. The excitation energy region from 10.2 to 10.8 MeV in ²⁰Ne has been searched for a possible E_x → E(4⁺, 4246 keV) transition and an upper limit of ωγ < 0.6 eV can be placed on such a transition.

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The synthesis of nuclei in diverse cosmic scenarios is reviewed, with a summary of the basic concepts involved before a discussion of the current status in each case is made. We review the physics of the early universe, the proton to neutron ratio influence in the observed helium abundance, reaction networks, the formation of elements up to beryllium, the inhomogeneous Big Bang model, and the Big Bang nucleosynthesis constraints on cosmological models. Attention is paid to element production in stars, together with the details of the pp chain, the pp reaction, $^{3}$ He formation and destruction, electron capture on $^{7}$ Be, the importance of $^{8}$ B formation and its relation to solar neutrinos, and neutrino oscillations. Nucleosynthesis in massive stars is also reviewed, with focus on the CNO cycle and its hot companion cycle, the rp-process, triple- $α$ capture, and red giants and AGB stars. The stellar burning of carbon, neon, oxygen, and silicon is presented in a separate section, as well as the slow and rapid nucleon capture processes and the importance of medium modifications due to electrons also for pycnonuclear reactions. The nucleosynthesis in cataclysmic events such as in novae, X-ray bursters and in core-collapse supernovae, the role of neutrinos, and the supernova radioactivity and light-curve is further discussed, as well as the structure of neutron stars and its equation of state. A brief review of the element composition found in cosmic rays is made in the end.
A compilation of charged-particle induced thermonuclear reaction rates
1999, Nuclear Physics A
Low-energy cross section data for 86 charged-particle induced reactions involving light (1 ⩽ Z ⩽ 14), mostly stable, nuclei are compiled. The corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 10⁶ K to 10¹⁰ K are calculated. These evaluations assume either that the target nuclei are in their ground state, or that the target states are thermally populated following a Maxwell-Boltzmann distribution, except in some cases involving isomeric states.
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Radiative decays of unbound levels in 20Ne
1980, Nuclear Physics, Section A
Nine levels in the range 8.7 to 12.5 MeV in ²⁰Ne have been investigated with the ¹⁶O(α, γ)²⁰Ne and ¹⁶O(α, α')¹⁶O^∗(6.13 MeV) reactions using a differentially pumped windowless gas target. Three of the levels have not been observed previously in these reactions, and new information has been obtained for most of the others. In particular, the 11.27 MeV 1⁻ level is shown to have T = 1, a result of relevance to a proposed parity violation experiment, and the analogue of the 1.97 MeV (3⁻ T = 1) level in ²⁰F is shown to lie at 12.25 MeV in ²⁰Ne rather than at 12.39 MeV as proposed previously. In addition, the 12.25 MeV level has a width Γ < 1 keV, in contrast to the value Γ ∼ 5 keV reported in other work. The electromagnetic transition rates for positive parity T = 1 states in ²⁰Ne are compared with shell-model calculations.
Measurements of the radiative widths of the first T = 1, 2+ state of 20Ne and their relationship to analog β-decays
1977, Nuclear Physics, Section A
The radiative widths for decays of the ²⁰Ne T = 1, 2⁺ (10.27 MeV) state were measured by resonance α-capture in the reaction ¹⁶O(α, γ)²⁰Ne. A special windowless gas-cell target yielded a low-background spectrum enabling six γ-branches to be observed with a Ge(Li) detector. The six branches correspond to decays from the 10.27 MeV level to the following levels: 2⁺(7.83 MeV), 2⁺(7.42 MeV), 3⁻(5.62 MeV), 2⁻(4.97 MeV), 2⁺(1.63 MeV) and 0⁺(g.s.). The branching ratios and radiative widths Γ_γ to these levels are: 7.83 MeV [(0.22 ± 0.06)%, 0.008 ± 0.002 eV], 7.42 MeV [(6.9 ± 0.4)%, 0.31 ± 0.04 eV], 5.62 MeV [(2.1 ± 0.2)%, 0.097 ± 0.014 eV], 4.97 MeV [(1.3 ± 0.1)%, 0.060 ± 0.008 eV], 1.63 MeV [(88.9 ± 0.5)%, 4.08 ± 0.43 eV] and 0.0 MeV [(0.64 ± 0.14)%, 0.029 ± 0.008 eV]. The radiative widths to the 1.63 MeV and 7.42 MeV levels are used to determine the CVC predictions of the weak magnetism form factors and their effects on certain β-decay observables are evaluated.
The radiative width of the lowest T = 1 state of 20Ne and fundamental β-decay studies
1976, Nuclear Physics, Section A
Ge(Li) detector observations of the ¹⁶O(α, γ)²⁰Ne reaction and a measurement of the stopping cross section for 6.93 MeV α-particles in anodized tantalum (Ta₂O₅) targets are combined with previous β-delayed γ- and α-observations of ²⁰Ne(10.27 MeV, T = 1) decay to obtain the partial decay widths. The values obtained are Γ_γ = 4.08 ± 0.33 eV for the 8.64 MeV γ-transition to the first excited state, and γ_α = 116 ± 20 eV for the isospin forbidden α-decay to ¹⁶O. The γ-decay is discussed in relation to model calculations, to a test of the conserved vector current hypothesis and to possible second-class-current effects in the analogous β^± decays of ²⁰Na and ²⁰F. The small α-decay width is used to set an isospin impurity limit of less than about 1 % for ²⁰Ne(10.27 MeV, T = 1).
A cryo-pumped gas target for the study of radiative capture reactions
1976, Nuclear Instruments and Methods

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^†: Permanent address: Chalk River Nuclear Laboratories, AECL, Chalk River, Ontario, Canada.

^††: Permanent Address: Central Research Institute for Physics, Budapest, Hungary.

^†††: Present address: Physics Department, University of Guelph, Guelph, Ontario, Canada.

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Nuclear Physics A

Abstract

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A compilation of charged-particle induced thermonuclear reaction rates

Radiative decays of unbound levels in <sup>20</sup>Ne

Measurements of the radiative widths of the first T = 1, 2<sup>+</sup> state of <sup>20</sup>Ne and their relationship to analog β-decays

The radiative width of the lowest T = 1 state of <sup>20</sup>Ne and fundamental β-decay studies

A cryo-pumped gas target for the study of radiative capture reactions