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Recent%20Progress%20in%20Nuclear%20Physics%20Studies%20through%20Spins%20and%20Nuclear%20Moments

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Title: Recent%20Progress%20in%20Nuclear%20Physics%20Studies%20through%20Spins%20and%20Nuclear%20Moments


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_at_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 ltI,MImzI,MIgt 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 neutronproton
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
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
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 QbEC (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
At the peak of the momentum distribution, ltpFgt
p0, ltpPFgt pbeam, and ltptgt pFermi spin
polarization is positive
Lz increases linearly with K
12
Coupled Cyclotron Facility Layout
  • Experimental apparatus
  • 4p-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 ß angular distributions
15
Science Motivation for m(35K)
  • Highest mass mirror pair for T3/2 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 T3/2 mirror moments

Sp 140 keV
Minamisono et al., PRL 69, 2058 (1992)
16
Isoscalar Spin Expectation Values T 1/2,3/2
Mirror Partners
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) 0.2610.004
The 35K-35S mirror pair is the heaviest T3/2
system studied to date. The isoscalar spin
expectation value ltsgt -0.2840.040 agrees
well with T1/2 systematics
nL 60010 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 T3/2
nuclei near the proton drip line
Buck, Merchant, and Perez, PRC 63, 037301 (2001)
20
Science Motivation for m(57Cu)
  • Highest mass mirror pair for T1/2 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 T1/2
system studied to date. The isoscalar spin
expectation value ltsgt -0.780.031 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 A57,
T1/2 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 20ltNlt28
g factors can give information on proton and
neutron contribution to the wavefunction of the
first excited 2 state
24
Sensitivity of g factors
  • Protons in sd shell, with Z16 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
  • proton neutron g different in sign and
    magnitude
  • Extreme single particle result

0.08
d3/2
sd shell
s1/2
5.59
1.92
d5/2
p
n
25
High velocity transient field technique
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 (q40o). 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
g (2 38S) 0.13(5)
Using BTF parametrization and Dq from double
ratios, g factors were extracted.
g (2 40S) -0.02(6)
gp(theory) gn(theory) g(theory) g(experiment)
38S 0.298 -0.301 -0.0026 0.13(5)
40S 0.276 -0.241 0.035 -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 T3/2 and
    T1/2 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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