A cryogenically pumped, windowless gas target has been used to study the radiative alpha-capture reaction on <sup>16</sup>O and <sup>12</sup>C targets, giving information on the electromagnetic decay properties of various unbound states in <sup>20</sup>Ne and <sup>16</sup>O. Several states in <sup>20</sup>Ne have been observed in this reaction for the first time. The first five unit-isospin, natural parity states in <sup>20</sup>Ne have been observed. The isospin assignment of the 11.27 MeV (1<sup>-</sup>)) state has been made definite by the observation of a strong Ml decay to the 8.85 MeV (1<sup>-</sup>)state, and the analogue of the 1.97 MeV state in <sup>20</sup>F has been identified with the <sup>20</sup>Ne state at 12.25 MeV. Angular distribution measurements have shown the spin of this state to be 3<sup>-</sup>), and the total width has been shown to be less than 1 keV, contradicting previous reports. The 12.22 MeV (2<sup>+</sup>)state has been resolved clearly as an individual resonance for the first time. The electromagnetic transition rates for the lower T=l states in <sup>20</sup>Ne are compared with shell model calculations. Five zero-isospin capture resonances in <sup>20</sup>Ne have been studied, the gamma-decay of the 8.70 MeV (1<sup>-</sup>), 9.11 MeV (3<sup>-</sup>) and 11.92 MeV (4<sup>+</sup>) states being observed for the first time. A remeasurement has been made of the enhanced E2 decay strength of the 8<sup>+</sup> member of the ground state rotational band, giving <sup>ω</sup>=l31 <sup>±</sup>18 meV, in agreement with a previous less accurate value. This result is compared with shell model calculations. A study of the capture reaction on <sup>12</sup>C has been performed in the beam energy range 5.22 MeV < Eα < 9.53 MeV. No new capture resonances have been found but the known inelastic resonances have been seen. The 11.10 MeV (4<sup>+</sup>) state has been studied and the strength for the decay to the 6.13 MeV (3<sup>-</sup>) state has been shown to be only half of a previous result. The 12.05 MeV (0<sup>+</sup>) state has not been observed, but a limit has been placed on its strength.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:258414 |
| Date | January 1980 |
| Creators | Hurst, Michael John |
| Contributors | Allen, K. W. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:f643792e-98ec-44d5-ad8e-c6d8ab1801db |
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