Proton radioactivity from the highly neutron-deficient nuclide <sup>135</sup>Tb has been identified using a new double-sided silicon strip detector (DSSD) system at the Fragment Mass Analyser at Argonne National Laboratory. The decay occurs with an energy of Eρ=1179(7)keV and a half-life t<sub>1/2</sub>=940<sup>+320</sup>-<sub>220</sub><i>μ</i>s. <sup>135</sup>Tb was produced via the bombardment of a <sup>92</sup>Mo target with a 315MeV <sup>50</sup>Cr beam, and is the first proton emitter to be detected from a (p6n) evaporation channel in heavy ion fusion-evaporation reactions. Proton decay rate calculations suggest that this nuclide has a large prolate deformation, in agreement with the predictions of the Möller-Nix mass model and the experimental observations of the neighbouring odd-even lanthanide proton emitters <sup>131</sup>Eu and <sup>141</sup>Ho. An unsuccessful search for the potential proton emitters <sup>125,126</sup>Pm, using the (p6n) and (p5n) evaporation channels respectively, is also reported. The non-observation of <sup>126</sup>Pm is consistent with mass model Q<sub>P </sub>predictions, but the non-observation of proton emission from <sup>125</sup>Pm suggests a Q<sub>P</sub> value significantly higher than predictions (so that the decay occurs too quickly to be observable) or significantly lower (so that proton emission is not competitive with β decay), or places an upper limit on the production cross-section of this nucleus. The Q<sub>P</sub> predictions of the Möller-Nix and Liran-Zeldes mass models are compared with the currently available data set of experimentally-derived Q<sub>P</sub> values for proton-unbound nuclei in the region of observed proton radioactivity (51≤Z≤83). Both models are found to perform reasonably well and provide useful predictions in this extremely neutron-deficient region.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:659757 |
| Date | January 2006 |
| Creators | Munro, Peter |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15460 |
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