Low Mass Francium and Emanation Isotopes of High AlphaStability

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Isotopes of francium with 126 or fewer neutrons have been looked for in bombardments of Th{sup 232} with 350 Mev protons from the 184-inch cyclotron. Fr{sup 212} with an apparent half-life of 19.3 minutes for branching decay by alpha emission (44%) to At{sup 208} and by orbital electron capture (56%) to Em{sup 212} has been found. Em{sup 212} is shown to be a 23-minute alpha-emitter. At{sup 208} decays primarily (99.5%) by orbital electron capture to Po{sup 208}, but shows 0.5% alpha-branching. The francium and emanation isotopes have alpha half-lives completely out of line with the predictions based on the previously ... continued below

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Hyde, E.K.; Ghiorso, A. & Seaborg, G.T. October 10, 1949.

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Isotopes of francium with 126 or fewer neutrons have been looked for in bombardments of Th{sup 232} with 350 Mev protons from the 184-inch cyclotron. Fr{sup 212} with an apparent half-life of 19.3 minutes for branching decay by alpha emission (44%) to At{sup 208} and by orbital electron capture (56%) to Em{sup 212} has been found. Em{sup 212} is shown to be a 23-minute alpha-emitter. At{sup 208} decays primarily (99.5%) by orbital electron capture to Po{sup 208}, but shows 0.5% alpha-branching. The francium and emanation isotopes have alpha half-lives completely out of line with the predictions based on the previously known isotopes of these elements. Their high alpha stability is believed to be due to a closed shell of 126 neutrons in analogy to the behavior of elements 83-85. The non-existence of long-lived francium in nature is discussed in the terms of this and other recent work on francium isotopes.

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  • Report No.: UCRL--469
  • Report No.: AECU-654
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.2172/932808 | External Link
  • Office of Scientific & Technical Information Report Number: 932808
  • Archival Resource Key: ark:/67531/metadc896324

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  • October 10, 1949

Added to The UNT Digital Library

  • Sept. 27, 2016, 1:39 a.m.

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  • Nov. 3, 2016, 8:12 p.m.

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Hyde, E.K.; Ghiorso, A. & Seaborg, G.T. Low Mass Francium and Emanation Isotopes of High AlphaStability, report, October 10, 1949; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc896324/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.