Radiative decays of unbound levels in 20Ne

doi:10.1016/0375-9474(80)90143-8

Nuclear Physics A

Volume 334, Issue 1, 28 January 1980, Pages 109-126

https://doi.org/10.1016/0375-9474(80)90143-8 Get rights and content

Abstract

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.

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Separation of the 1+/1- parity doublet in 20Ne
2015, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
The $(J, T) = (1, 1)$ parity doublet in ²⁰Ne at 11.26 MeV is a good candidate to study parity violation in nuclei. However, its energy splitting is known with insufficient accuracy for quantitative estimates of parity violating effects. To improve on this unsatisfactory situation, nuclear resonance fluorescence experiments using linearly and circularly polarized γ-ray beams were used to determine the energy difference of the parity doublet $Δ E = E (1^{-}) - E (1^{+}) = - 3.2 {(\pm 0.7)}_{stat} {(_{- 1.2}^{+ 0.6})}_{sys} keV$ and the ratio of their integrated cross sections $I_{s, 0}^{(+)} / I_{s, 0}^{(-)} = 29 {(\pm 3)}_{stat} {(_{- 7}^{+ 14})}_{sys}$ . Shell-model calculations predict a parity-violating matrix element having a value in the range 0.46–0.83 eV for the parity doublet. The small energy difference of the parity doublet makes ²⁰Ne an excellent candidate to study parity violation in nuclear excitations.
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.
Adopted values complemented with lower and upper limits of the rates are presented in tabular form. Analytical approximations to the adopted rates, as well as to the inverse/direct rate ratios, are provided.
Energy levels of light nuclei, A = 20
1998, Nuclear Physics A
Gamma-ray decaying states at high excitation in 20Ne
1987, Nuclear Physics, Section A
A search has been made for high-lying states in ²⁰Ne which decay by γ-ray emission. The states were populated via the ¹²C(¹²C, α)²⁰Ne reaction at a beam energy of 37.1 MeV. A technique which allowed the measurement of γ-ray emission probabilities down to less than 1% was employed. In addition to previously known γ-ray emitting states, states at 11.89, 12.01, 12.10, 12.17 and 12.38 MeV were found to have observable γ-ray decay modes.
Measurement of a highly retarded α-particle decay in 20Ne
1984, Nuclear Physics, Section A
The partial widths for α-particle and γ-ray decay of the second 2⁺ T = 1 level in ²⁰Ne at 12.22 MeV have been measured. The reaction ¹⁹F(³He, d)²⁰Ne was employed, with deuterons detected in singles and in coincidence with γ-rays from the decay of the 12.22 MeV level. The coincidence efficiency was determined using the 100% γ-decay of the 10.89 MeV 3⁺ T = 1 level. The ratio of the γ-decay width to the total width of the 12.22 MeV level was measured to be 0.88 ±0.05, which combined with a recent 16^O(α, γ)²⁰Ne measurement yields a very small α-particle width of 0.32±0.06 eV. This result is also of relevance to the radiative decay of the 18.43 MeV 2⁺ T = 2 level in ²⁰Ne, and confirms a large discrepancy between the measured γ-decay width of the 2⁺ T = 2 level and the predictions of the shell model.
Evidence for isovector parity mixing in the 11.264 MeV 1+ T = 1 state in 20Ne
1983, Nuclear Physics, Section A
A search has been carried out for the 1⁺ T = 1 level at 11.264 MeV in ²⁰Ne formed as a parity-forbidden resonance in the ¹⁶O(α,γ)²⁰Ne reaction. The yield of 11.26 MeV γ-rays was measured as a function of α-particle energy over an interval of 8 keV centred on the expected resonance energy of the 1⁺ T = 1 level. An energy and intensity standard was provided by the nearby 1⁻ T = 1 resonance at an excitation energy of 11.275 MeV in ²⁰Ne. A significant improvement in the fit to the measured yield curve was obtained by including a sharp resonance at the expected energy of the 1⁺ T = 1 level. From the analysis it is concluded that the 1⁺ T = 1 level has been observed with 90% confidence. The resonance strength extracted from the fit implies a parity-forbidden a-particle width of 42(+-20)× 10⁻⁶ eV for the 1⁺ T = 1 level. The corresponding parity non-conserving matrix element linking the 1⁺ T = 1 level with the 1⁺ T = 0 state at 11.23 MeV therefore lies within the, range 0.8 eV ⩽ 〈V_PNC^ΔT = 1〉 ⩽ 2.6 eV.

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^†: Present address: CEGB Computing Centre, 85 Park Street, London SEI.

^††: Present address: Lawrence Berkeley Laboratory Berkeley, California 94720, USA.

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Nuclear Physics A

Abstract

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Separation of the 1<sup>+</sup>/1<sup>-</sup> parity doublet in <sup>20</sup>Ne

A compilation of charged-particle induced thermonuclear reaction rates

Energy levels of light nuclei, A = 20

Gamma-ray decaying states at high excitation in <sup>20</sup>Ne

Measurement of a highly retarded α-particle decay in <sup>20</sup>Ne

Evidence for isovector parity mixing in the 11.264 MeV 1<sup>+</sup> T = 1 state in <sup>20</sup>Ne