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Recent Progress in Nuclear Physics Studies through Spins and Nuclear Moments

Recent Progress in Nuclear Physics Studies through Spins and Nuclear Moments. P.F. Mantica Chemistry and NSCL Michigan State University East Lansing, MI 48824 mantica@msu.edu. SPIN2006. October 3, 2006. Outline of Talk. Nuclear spin polarization from intermediate energy reacitons

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Recent Progress in Nuclear Physics Studies through Spins and Nuclear Moments

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  1. Recent Progress in Nuclear Physics Studies through Spins and Nuclear Moments P.F. Mantica Chemistry and NSCL Michigan State University East Lansing, MI 48824 mantica@msu.edu SPIN2006 October 3, 2006

  2. Outline of Talk • Nuclear spin polarization from intermediate energy reacitons • Nucleon removal reactions • Nucleon pick-up reactions • Ground state magnetic moments of mirror nuclei • 35K-35S and nuclei with small Sp values • 57Cu-57Ni and shell breaking of doubly-magic 56Ni • Excited-state g factors in even-even nuclei • Application of transient field to fast beams • Shape transition in the neutron-rich sulfur isotopes

  3. Magnetic Moments and Nuclear Structure Since the electromagnetic interaction has a simple and well-known structure, the study of nuclear moments is an effective means for testing nuclear wave functions. Nuclear magnetic dipole moment: m = <I,M=I|mz|I,M=I> For a nucleon in a shell-model orbit: 2d5/2 2d5/2 1g7/2 1g7/2 50 50 1g9/2 1g9/2 2p1/2 2p1/2 1f5/2 1f5/2 2p3/2 2p3/2 28 28 1f7/2 1f7/2 20 20 1d3/2 1d3/2 2s1/2 2s1/2 1d5/2 1d5/2 8 8 1p1/2 1p1/2 1p3/2 1p3/2 2 2 1s1/2 1s1/2 protons neutrons

  4. Magnetic Moments and Mirror Nuclei Isospin,T, is a quantum number that arises from the identical treatment of protons and neutrons due to the charge independence of nuclear forces. The z-component of isospin,Tz = (N – Z)/2, is a measure of the neutron–proton asymmetry in the nucleus. If isospin is a good quantum number The summed moments of mirror nuclei, those nuclei that differ simply by exchange of protons and neutrons, can be directly related to the expectation value of the isoscalar magnetic moment.

  5. Isoscalar Spin Expectation Values:T = 1/2 Mirror Partners 17N-17Ne 1.5 1.0 Spin expectation value 0.0 -1.0

  6. Known Ground-State Moments 57Cu, Tz = -1/2 35K, Tz = -3/2

  7. Spin Polarization via Fragmentation(nucleon removal) • Fragments collected off the central beam axis. • Polarization as large as 20% for 12B fragments at wings of momentum distribution. • In initial experiments no spin polarization detected at the peak of the momentum yield curve. • Provides a means for measuring ground state dipole moments of exotic nuclei. Asahi et al., Phys. Lett. B251, 488 (1990)

  8. Details of the Kinematical Model When Q = 0 When Q 0

  9. Nucleon Pick-up Reactions outgoing projectile part target nucleon <p/A>F/<p/A>beam 18O (E = 80 MeV/nucleon) From momentum conservation, the data to the left are consistent with the nucleon picked up with the Fermi momentum 230 MeV/c oriented along the direction of the projectile motion Souliotis et al., Phys. Rev. C46, 1383 (1992) Pfaff et al., Phys. Rev. C51, 1348 (1995)

  10. 37K Spin Polarization 150 MeV/A 36Ar on Be target Reaction: 36Ar + p  37K 37K fragments implanted into a KBr crystal T1/2 (37K) = 1.23 s Qb+EC (37K) = 6.1 MeV Polarization monitored by pulsed magnetic field method Maximum polarization observed when separator tuned just off the peak production of 37K Groh et al., PRL 90, 202502 (2003)

  11. Spin Polarization via Nucleon Pickup outgoing projectile part target nucleon At the peak of the momentum distribution, <pF> = p0, <pPF> = pbeam, and <pt> = pFermi spin polarization is positive Lz increases linearly with K

  12. Coupled Cyclotron Facility Layout • Experimental apparatus: • 4π-Array (N2), • 92-inch chamber (N3), • S800 magnetic spectrograph (S3) • segmented Ge-array for -ray Doppler shift correction • Si-strip-CsI array for high efficiency charged particle coincidence experiments • Superconducting “sweeper” magnet for n-coincidences at 0 degrees • Modular neutron array (MONA) for high-efficiency neutron detection • Gas stopping and Penning trap

  13. Dipole Magnet for Nuclear Moment Measurements • A small dipole magnet will be located in the S1 vault for nuclear moment measurements. • magnet gap = 10 cm – capability for catcher cooling • Bmax = 5000 Gauss – improved PMT performance at • optional vacuum chamber high B fields Mantica et al., NIM A422, 498 (1999)

  14. Nuclear Magnetic Resonance • Energy of magnetic substates E = mIgNB • Energy difference between adjacent substates E = gNB • Typical transition energy E = (1)(5e-27 J/T)(0.1 T) E = 5e-26 J radiofrequency region! Measure β angular distributions:

  15. Science Motivation for m(35K) • Highest mass mirror pair for T=3/2 nuclei • Test of isospin symmetry in heavier nuclei • Proton separation energy of 35K only ~78 keV • Nuclide lies very near proton drip line • Systematic variation of T=3/2 mirror moments Sp = 140 keV Minamisono et al., PRL 69, 2058 (1992)

  16. Isoscalar Spin Expectation Values:T = 1/2,3/2 Mirror Partners 17N-17Ne 1.5 1.0 Spin expectation value 0.0 -1.0

  17. Magnetic Moment of 35K • rf sweeps between 520 and 620 kHz • based on previous measurement of g(35K) = 0.24(2)* • H0 = 3012 G • FM = ±10 kHz, H1 ~ 2 G *Schafer et al., PRC 57, 2205 (1998) 35K in KBr g(35K) = 0.261±0.004 The 35K-35S mirror pair is the heaviest T=3/2 system studied to date. The isoscalar spin expectation value <s> = -0.284±0.040 agrees well with T=1/2 systematics nL = 600±10 kHz Mertzimekis et al., PRC 73, 024318 (2006)

  18. Isoscalar Spin Expectation Values:T = 1/2,3/2 Mirror Partners 1.5 1.0 Spin expectation value 17N-17Ne 0.0 35S-35K -1.0

  19. Buck-Perez Plot for T = 3/2 Nuclides Plot of gp v. gn extracted for mirror moments shows linear trend with slope a and intercept b T = 1/2 Theory T = 3/2 a and b results are similar, even though T=3/2 nuclei near the proton drip line Buck, Merchant, and Perez, PRC 63, 037301 (2001)

  20. Science Motivation for m(57Cu) Copper-57 = Nickel-56 + proton • Highest mass mirror pair for T=1/2 nuclei • Test of isospin symmetry in heavier nuclei • Single-proton configuration outside “doubly-magic” 56Ni • Excellent test case for comparison with shell-model predictions • Systematic variation of Cu magnetic moments shows unexpected behavior Golovko et al., Phys. Rev. C70 014312 (2004).

  21. 57Cu Results Resonance Curve m(57Cu) = 2.00 ±0.05 mN Cu magnetic moments The new m(57Cu) shows a positive deviation from the systematic trend of the heavier Cu magnetic moments, however, the value is still significantly smaller than theoretical estimates. Minamisono et al., PRL 96, 102501 (2006).

  22. Breaking of 56Ni core? Spin expectation values The 57Cu-57Ni mirror pair is the heaviest T=1/2 system studied to date. The isoscalar spin expectation value: <s> = -0.78±0.031 deviates significantly from predictions that expect 56Ni to have double-magic character Small magnetic moment of 57Cu ground state and negative spin expectation value for the A=57, T=1/2 mirror pair suggests that 56Ni is not a good doubly-magic core in 57Cu

  23. Neutron-Rich S Isotopes: Rapidly Changing Structure 38S 38S 40S 40S Sulfur isotopes are in a region of changing structure for 20<N<28 gfactors can give information on proton and neutron contribution to the wavefunction of the first excited 2+ state

  24. proton & neutron: g different in sign and magnitude Extreme single particle result: Sensitivity of g factors • Protons in sd shell,with Z=16 subshell closure at stability • Single-particle structure influenced by shell gaps: n f7/2 gap, p s1/2-d3/2 gap - 1.3 p3/2 - 0.55 f7/2 +0.08 d3/2 sd shell s1/2 +5.59 +1.92 d5/2 p n

  25. High velocity transient field technique 20 MeV/u ~5 MeV/u 40 MeV/u Projectiles: 38S: 105 pps E(2+)=1292 keV t(2+)= 4.9 ps 40S 104 pps E(2+)= 903 keV t(2+)= 20 ps 355 mg/cm2 Au target for intermediate-energy Coulomb excitation (with spin alignment) 110 mg/cm2 Fe target, at room temperature. Magnetized by external electromagnet No B applied B applied Excited-state spin precesses while traversing the magnetized foil g-rays Dq  gBTF

  26. Transient field endstation

  27. 38,40S results Doppler corrected spectra (q=40o). Correction performed event-by-event using particle energy measured in phoswich detector. Gamma-ray angular distribution in projectile frame, corrected for Lorentz boost.

  28. g(2+) results: 38,40S (radioactive) (stable) Using BTF parametrizationand Dq from double ratios,g factors were extracted. g(2+; 38S) = +0.13(5) g(2+; 40S) = -0.02(6) Davies et al., PRL 96, 112503 (2006).

  29. Summary • Beta-NMR spectroscopy at the NSCL • Spin polarization observed for proton pick-up reactions at fragmentation energies • New data for spin expectation values of T=3/2 and T=1/2 nuclides • Transient field method on fast fragments • Fast-fragment g(2+) measurements successfully performed at the NSCL • Lifetimes as short as 1-2 ps are accessible • TF measurements with rates as low as 104 particles per second • Other areas under development • TDPAD on high-spin isomers near 68Ni • Development of NQR methods at the NSCL

  30. Collaborators • Polarization via Nucleon Pickup • A.D. Davies, D.E. Groh, S.N. Liddick, T.J. Mertzimekis, J.S. Pinter, W.F. Rogers, A.E. Stuchbery, and B.E. Tomlin • Magnetic Moment of 35K • A.D. Davies, D.E. Groh, S.N. Liddick, T.J. Mertzimekis, and B.E. Tomlin • Magnetic Moment of 57Cu • A.D. Davies, M. Hass, T. J. Mertzimekis, K. Minamisono, J. Pereira, W.F. Rogers, J. Stoker, B. Tomlin, and R. R. Weerasiri • g(2+) of 38,40S • A. Becerril, C.M. Campbell, J.M. Cook, P.M. Davidson, A.D. Davies, D.C. Dinca, A. Gade, S.N. Liddick, T.J. Mertzimekis, W.F. Mueller, A. Stuchbery, J.R. Terry, B.E. Tomlin, A.N. Wilson, K. Yoneda, and H. Zwahlen Supported in part by NSF PHY-01-10253 and NSF PHY-99-83810

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