Nuclear reactions with radioactive, isomer beams: Coulomb excitation of 18Fg.s. and its Jπ=5+ isomer 18Fm using a large position-sensitive NaI array
✍ Scribed by J.A. Zimmerman; F.D. Becchetti; H.C. Griffin; D.A. Roberts; M.Y. Lee; T.W. O’Donnell; J.A. Brown; R.M. Ronningen; T. Glasmacher; R.W. Ibbotson; H. Scheit; B. Pritychenko; D.W. Anthony; P.A. Lofy; M. Steiner
- Publisher
- Elsevier Science
- Year
- 2007
- Tongue
- English
- Weight
- 254 KB
- Volume
- 579
- Category
- Article
- ISSN
- 0168-9002
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✦ Synopsis
Intermediate-energy projectile Coulomb excitation of the unstable nucleus 18 F g.s. and its short-lived E x ¼ 1.1 MeV (J p ¼ 5 + ) isomeric state (t 1/2 ¼ 162 ns) 18 F m have been studied at 30 MeV per nucleon. Radioactive beams of 18 F g.s. and 18 F m nuclei were produced by nucleon transfer on a carbon production target and delivered to a secondary 197 Au target for Coulomb excitation. Photons emitted in the vicinity of the 197 Au target were detected in a large-solid-angle position-sensitive NaI(Tl) array, which allowed for the identification of the beam and target excited states populated by intermediate-energy Coulomb excitation. Two possible 18 F ground-state excitations were identified, and B(Elm) values were deduced. Upper limits were established for reduced transition probabilities B(E1m) and B(E2m) of several predicted transitions from the 18 F m isomeric state, 5 + -4 + , 4 À , 3 + , and compared with values inferred from g-decay lifetimes. An indication of an enhanced in-flight isomer decay, possibly due to the Coulomb interaction with the target is observed and discussed. The special detector configurations and analytical techniques needed for these types of measurements are described together with suggested improvements.