Positron Radioactivities of O14, Ne18, Si26, and S30

G. Frick, A. Gallmann, D. E. Alburger, D. H. Wilkinson, and J. P. Coffin
Phys. Rev. 132, 2169 – Published 1 December 1963
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Abstract

A Siegbahn-Slätis intermediate-image spectrometer has been used to measure the positron spectra of the isotopes O14, Ne18, Si26, and S30 produced by a He3 beam from a 5.5-MeV Van de Graaff accelerator. O14 was formed in the C12(He3, n)O14 reaction and it emits a positron group of Emax=(4.085±0.030) MeV to the ground state of N14 and another group having Emax=(1.821±0.007) MeV to the 2.3-MeV level. The branching ratios are (0.65±0.05)% (logft=7.23±0.04) and (99.35±0.05)% (logft=3.49±0.01), respectively. The measured half-life of O14 is 71.3±0.1 sec. Ne18 was formed in the O16(He3, n)Ne18 reaction and we find Emax=(3.416±0.009) MeV to the ground state of F18, and T½=1.47±0.10 sec. From a study of the beta and gamma rays of Ne18 by means of scintillation detectors we find a second positron branch feeding the 1.04-MeV level of F18. The branching ratios obtained from these measuremtns are (91±3)% (logft=3.02±0.02) to the ground state and (9±3)% (logft=3.47±0.13) to the 1.04-MeV level. The isotope Si26, produced by the Mg24(He3, n)Si26 reaction, decays with two branches to Al26. The more energetic branch feeds the 0.229-MeV isomeric state of Al26 and has Emax=3.828±0.013 MeV from a magnetic spectrometer measurement, while the second branch is masked by other positron activities. We find T½=2.1±0.1 sec for Si26. The second position branch of Si26 has been confirmed by observation of (0.820±0.010) MeV gamma rays in coincidence with positrons. Branching ratios of Si26, measured with scintillation detectors, are (664+1)% (logft=3.520.02+0.04) for the branch to the 0.229 MeV level of Al26 and (341+4)% (logft=3.360.05+0.02) for the branch to the 1.059-MeV level. S30 was produced by the Si28(He3, n)S30 reaction and it decays with a half-life of 1.4±0.1 sec and with positron branches of Emax=(5.085±0.026) MeV to the ground state of P30 and Emax=(4.422±0.022) MeV to the 0.684-MeV level. The branching ratios, obtained by analyzing the positron spectrum, are (20±1)% (logft=4.39±0.03) and (8015+1)% (logft=3.490.03+0.09) respectively. Positron-gamma coincidence measurements have confirmed the decay scheme. Some comments are made on the abnormal value of the matrix element in the decay of O14 to the ground state of N14 and the results on the pure Fermi transitions observed in each of the isotopes are discussed.

  • Received 22 July 1963

DOI:https://doi.org/10.1103/PhysRev.132.2169

©1963 American Physical Society

Authors & Affiliations

G. Frick, A. Gallmann, D. E. Alburger*, D. H. Wilkinson, and J. P. Coffin

  • Institut de Recherches Nucléaires, Strasbourg, France

  • *Permanent address: Brookhaven National Laboratory, Upton, New York.
  • Permanent address: Nuclear Physics Laboratory, Oxford, England.

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Vol. 132, Iss. 5 — December 1963

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