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Possible Shears Bands in 204 At and 206 Fr

Possible Shears Bands in 204 At and 206 Fr. Evan Seyfried. N=120. S. Frauendorf, Z. Phys. A 358, 163–167 (1997). Motivation. Shears bands known along Z = 82 Pb nuclei Predicted along N = 120 series of nuclides. S. Frauendorf, Nuc. Phys. A 601 (1997) 41-55. Background.

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Possible Shears Bands in 204 At and 206 Fr

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  1. Possible Shears Bands in 204At and 206Fr Evan Seyfried

  2. N=120 S. Frauendorf, Z. Phys. A 358, 163–167 (1997) Motivation • Shears bands known along Z=82 Pb nuclei • Predicted along N=120 series of nuclides

  3. S. Frauendorf, Nuc. Phys. A 601 (1997) 41-55 Background • Quick Shears Band Review High-j, proton-particle / high-j, neutron-hole interaction: Perpendicular at lowest energies  Off-axis total angular momentum Large magnetic dipole moment develops Magnetic Rotation: Tilted Axis Cranking (TAC) model: Quantized precession of the magnetic dipole moment, μ┴) about the total angular momentum ( J ) Closing of Shears  Shows I(I+1) rotation-like behavior in near-spherical nuclei

  4. Experiment • Argonne National Lab • ATLAS accelerator, GAMMASPHERE • Fusion-evaporation reaction • 30Si + 181Ta  211Fr* • Beam Energy: 152 MeV • 15E6 γ-γ coincidences • 20 hrs beam time • Nuclei of interest produced: 204At  α3n 206Fr  5n

  5. W. Reviol, D.G. Sarantites, et. al., Nuclear Instruments and Methods in Physics Research A 541 (2005) 478-500 Experiment WashU’s HERCULES • High-efficiency Evaporation-Residue Counter Under Lots of Elastic Scattering (ratio σE-R/σfission ~ 1/200) • 64 thin fast-plastic scintillators in 4 concentric rings

  6. Data Projection of Coincidence Matrix X-rays used for Isotopic ID

  7. Data Francium (86 keV) & Astatine (79 keV) X-ray gates Fr 205Fr 206Fr 207Fr At 203At 204At

  8. Data Shears Bands 206Fr Shell Model States 204At Shell Model States

  9. Level Schemes

  10. Why Shears? • Characteristic low-energy energy-level spacing • Band sits high in energy above the shell model states • Possible alignment:

  11. J (ħ) ħω (MeV)

  12. Fr Shears Bands from light Pb and Bi to the N=119 isotones Rn At Po J (ħ) Bi ħω (MeV) Pb

  13. Future Direction • Evidence for shears bands, floating above expected odd-odd shell model states in both 204At and 206Fr (N=119 isotones) • More evidence needed, but we consider them possible shears bands 1. Longer run to find linking transitions to shell model states • Angular correlation for M1 confirmation • Confirm configurations for the band 2. Lifetime measurement to determine B(M1)’s

  14. Thanks to: • U.S. Naval Academy: D.J. Hartley • Washington University: W. Reviol, D.G. Sarantites, C.J. Chiara, O.L. Pechanaya • CSNSM: K. Hauschild, A. Lopez-Martens • Argonne: M.P. Carpenter, R.V.F. Janssens, D. Seweryniak, S. Zhu Sponsored by grants from the NSF and DOE

  15. Nilsson Diagrams

  16. Data • Level Schemes:

  17. S. Chmel, S. Frauendorf, and H. Hubel, Phys. Rev. C 75, 044309 (2007) Shears Bands • Demonstrates back-bending seen in shears bands in the light-Pb nuclei • B(M1)/B(E2) values limited to >___ (μ┴)2/(eb)2 • Longer data run needed to observe B(E2) values • S. Chmel, et. al. report same problem with light Pb nuclei • Lifetime measurements required to get B(M1) values

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