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

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Presentation transcript:

Possible Shears Bands in 204 At and 206 Fr Evan Seyfried

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

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 S. Frauendorf, Nuc. Phys. A 601 (1997) 41-55

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

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

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

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

Data Shears Bands 206 Fr 204 At Shell Model States

Level Schemes

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

ħω (MeV) J (ħ)

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

Future Direction Evidence for shears bands, floating above expected odd-odd shell model states in both 204 At and 206 Fr (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

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

Nilsson Diagrams

Data Level Schemes:

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 S. Chmel, S. Frauendorf, and H. Hubel, Phys. Rev. C 75, (2007)