A DBLA measurement of the lifetime of the first excited level in 18O and a critical comparison of lifetime results by different methods

doi:10.1016/0375-9474(82)90333-5

Nuclear Physics A

Volume 377, Issue 1, 15 March 1982, Pages 268-280

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Abstract

An accurate measurement of the lifetime of the 1.982 MeV level in ¹⁸O has been obtained by bombarding ⁴He and ¹H implanted targets with beams of 34 and 47 MeV ¹⁸O ions. The mean lifetime determined by fitting the Doppler-broadened γ-ray lineshapes with experimentally determined stopping powers was 2.80 ± 0.07 ps. A detailed comparison of the mean lifetime values obtained by different techniques for this level and several other sd shell transitions suggest that recent Coulomb excitation B(E2; 0⁺ → 2⁺) values for ¹⁸O are ≈ 10% too small.

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Energy levels of light nuclei A = 18-19
1995, Nuclear Physics, Section A
Lifetime measurements of levels in 34Ar: Isoscalar and isovector matrix elements for E2 analogue transitions
1985, Nuclear Physics, Section A
Mean lifetimes have been measured for the low-lying levels in ³⁴Ar(T_z = − 1) excited by the bombardment of ³He-implanted Au targets with a beam of 80 MeV ³²S. The lifetimes determined by fitting Doppler-broadened γ-ray lineshapes are as follows (E_x in keV, τ in fs): 2091, 460 ± 60; 3288, 280 ± 50; 3871, > 270 and 4128, 1301⁺¹⁷⁰₋₁₃₀. The resulting transition matrix elements for the 2⁺₁ → 0⁺₁ and 2⁺₂ → 0⁺₁ transitions are compared with those for the analogue transitions in ³⁴S (T_z = + 1) and ³⁴Cl(T_z = 0) to determine the isoscalar and isovector components. The component values are compared with theoretical calculations and with values of the ratio of neutron to proton matrix elements determined by inelastic scattering with strongly interacting probes.
Accurate measurements of E2 lifetimes using the coincidence recoil-distance method
1984, Nuclear Physics, Section A
Mean lives of four E2 transitions in the (2s, 1d) shell have been measured using the recoil-distance method (RDM), γ-rays de-exciting the level of interest were detected in coincidence with particles detected in an annular detector at a backward angle thereby reducing the background and producing a beam of recoiling nuclei of well-defined energy and recoil direction. Lifetimes measured were: $^{22} Ne, 1.275 MeV level (2^{+} → 0^{+}), 5.16±0.13 ps;^{26} Mg, 3.588 MeV level (0^{+} → 2^{+}), 9.29±0.23 ps;^{30} Si, 3.788 MeV level (0^{+} → 2^{+}), 12.00±0.70 ps;^{38} Ar, 3.377 MeV level (0^{+} → 2^{+}), 34.5±1.5 ps$ . The present measurements are compared to those of previous investigators. For the ²²Ne level, averaged results from four different measurement techniques are compared and found to be in good agreement. The experimental results are compared to shell-model calculations.
Lifetimes of levels in 25Na and 26, 27Mg excited via the 26Mg bombardment of 3H
1983, Nuclear Physics, Section A
Lifetimes have been measured for nine levels in ²⁵Na, the first two excited states of ²⁷Mg, and the First excited state of ²⁶Mg by bombarding a Ti³H target with 40 MeV ²⁶Mg ions. Mean lifetimes were determined by fitting the Doppler-broadened γ-ray lineshapes with lineshapes calculated using experimentally-measured stopping powers. The ²⁵Na results are compared to predictions of recent shell-model calculations.
Elastic and inelastic scattering of 120 MeV 18O from 208Pb and the spin alignment of the 2+ state of 18O
1983, Nuclear Physics, Section A
The elastic and inelastic scattering of ¹⁸O ions at 120 MeV from a target of ²⁰⁸Pb have been studied. Cross sections for excitation of the 2⁺ state at 1.982 MeV in ¹⁸O and of the 3⁻ state at 2.61 MeV in ²⁰⁸Pb were measured. In addition, the populations of the m-substates for the ¹⁸O excitation were deduced from the Doppler-broadened line shapes. The data were subjected to a coupled-channels analysis using either Woods-Saxon or folding-model potentials. In addition, the ¹⁸O excitation was found to be described very well by use of a semi-microscopic model. The analyses consistently indicated the presence of a positive static hexadecapole moment of several e · fm⁴ for the 2⁺ state of ¹⁸O. The m-substate population distributions were found to be better fitted if a vector spin-orbit coupling was introduced for the 2⁺ state of ¹⁸O with a sign opposite to that for the nucleon-nucleus case.
Quadrupole moment of the first excited state of 32S
1982, Nuclear Physics, Section A
The static quadrupole moment and B(E2; 0⁺ → 2⁺) value for the first excited state of ³²S were measured using the reorientation effect in Coulomb excitation of ³²S projectiles. Silicon surface barrier detectors were used to detect ³²S ions scattered from ²⁰⁸Pb at mean laboratory angles of 90° and 174°, for bombarding energies in the range 122 to 160 MeV. The results for constructive (destructive) interference from the second 2⁺ state in ³²S are QP_2⁺ = −16.0±2.2 (−13.3±2.2) e·fd² and B(E2; 0⁺ → 2⁺) = 292±17 (307±17) e²·fm⁴

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Nuclear Physics A

Abstract

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Cited by (15)

Energy levels of light nuclei A = 18-19

Lifetime measurements of levels in <sup>34</sup>Ar: Isoscalar and isovector matrix elements for E2 analogue transitions

Accurate measurements of E2 lifetimes using the coincidence recoil-distance method

Lifetimes of levels in <sup>25</sup>Na and <sup>26, 27</sup>Mg excited via the <sup>26</sup>Mg bombardment of <sup>3</sup>H

Elastic and inelastic scattering of 120 MeV <sup>18</sup>O from <sup>208</sup>Pb and the spin alignment of the 2<sup>+</sup> state of <sup>18</sup>O

Quadrupole moment of the first excited state of <sup>32</sup>S