recent progress in nuclear physics studies through spins and nuclear moments
DESCRIPTION
Recent Progress in Nuclear Physics Studies through Spins and Nuclear Moments. P.F. Mantica Chemistry and NSCL Michigan State University East Lansing, MI 48824 [email protected]. SPIN2006. October 3, 2006. Outline of Talk. Nuclear spin polarization from intermediate energy reacitons - PowerPoint PPT PresentationTRANSCRIPT
Recent Progress in Nuclear Physics Studies through Spins and Nuclear Moments
P.F. ManticaChemistry and NSCLMichigan State UniversityEast Lansing, MI [email protected]
SPIN2006October 3, 2006
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
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:
= <I,M=I|z|I,M=I>
For a nucleon in a shell-model orbit:
neutron823proton585
01
21
121
..
gg
jgggj
s
ssp
1s1/2
1p3/2
1p1/2
1d5/2
2s1/2
1d3/2
1f7/2
1f5/2
28
2028
502p3/2
2p1/2
1g9/2
1g7/2
2d5/2
protons1s1/2
1p3/2
1p1/2
1d5/2
2s1/2
1d3/2
1f7/2
28
2028
50 1g9/2
1g7/2
2d5/2
neutrons
1f5/22p3/2
2p1/2
Magnetic Moments and Mirror Nuclei
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.
JiJi
ii 30
JiT
z iTT,T,Jz
012
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.
38.0)()( JTTTT zz
Isoscalar Spin Expectation Values:T = 1/2 Mirror Partners
17N-17Ne
Spin
exp
ecta
tion
val
ue
1.0
-1.0
0.0
1.5
Known Ground-State Moments
35K, Tz = -3/2
57Cu, Tz = -1/2
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)
Details of the Kinematical Model
y
z x
Beam
k = (k , k , k )x y z
R = (X, Y, Z)
TargetProjectile
-k / pfx
L
defProjectile- rest fram e
Target
sincos RkRk xyz
LP z /When = 0
Rkyz
00 ppatP
When 0
defLx pk 0
00 ppatP
Nucleon Pick-up Reactions
Pfaff et al., Phys. Rev. C51, 1348 (1995)Souliotis et al., Phys. Rev. C46, 1383 (1992)
18O (E = 80 MeV/nucleon) tPFF ppp outgoing projectile
parttarget
nucleon
0.960
0.965
0.970
0.975
0.980
0.985
19O 18N 17C
AlTa
<p/A
> F/<
p/A>
beam
Fermi
P
PPF
FF
F pApA
AAp 1
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
37K Spin Polarization150 MeV/A 36Ar on Be target
Reaction:
36Ar + p 37K
37K fragments implanted into a KBr crystal
T1/2 (37K) = 1.23 sQ+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)
Spin Polarization via Nucleon Pickup
tPFF ppp outgoing projectile
parttarget
nucleonAt the peak of the momentum distribution,<pF> = p0, <pPF> = pbeam, and <pt> = pFermispin polarization is positive
Lz increases linearly with K
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
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)
Nuclear Magnetic Resonance
• Energy of magnetic substates
E = mIgNB• Energy difference
between adjacent substates
E = gNB• Typical transition
energyE = (1)(5e-27 J/T)(0.1 T)
E = 5e-26 Jradiofrequency region!
Measure β angular distributions:θcos1)θ( 1PAW
Science Motivation for (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
Minamisono et al., PRL 69, 2058 (1992)
Sp = 140 keV
Isoscalar Spin Expectation Values:T = 1/2,3/2 Mirror Partners
17N-17Ne
Spin
exp
ecta
tion
val
ue
1.0
-1.0
0.0
1.5
Magnetic Moment of 35K
L = 600±10 kHz
35K in KBr
g(35K) = 0.261±0.004
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)
Mertzimekis et al., PRC 73, 024318 (2006)
The 35K-35S mirror pair is the heaviest T=3/2 system studied to date. The isoscalar spin expectation value
<> = -0.284±0.040 agrees well with T=1/2 systematics
Isoscalar Spin Expectation Values:T = 1/2,3/2 Mirror Partners
17N-17Ne 35S-35K
Spin
exp
ecta
tion
val
ue
1.0
-1.0
0.0
1.5
Buck-Perez Plot for T = 3/2 Nuclides
Buck, Merchant, and Perez, PRC 63, 037301 (2001)
Plot of gp v. gn extracted for mirror moments shows linear trend with slope and intercept
nn
pp
gGgG
000.1199.1
102.0001.1096.0122.1
np gg
016.0052.1010.0148.1
T = 1/2
T = 3/2
Theory
and results are similar, even though T=3/2 nuclei near the proton drip line
Science Motivation for (57Cu)
• Highest mass mirror pair for T=1/2 nucleiTest 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).
Copper-57 = Nickel-56 + proton
57Cu Results
Minamisono et al., PRL 96, 102501 (2006).
The new (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.
Cu magnetic moments
Resonance Curve
(57Cu) = 2.00 ±0.05 N
Breaking of 56Ni core?The 57Cu-57Ni mirror pair is the heaviest T=1/2 system studied to date. The isoscalar spin expectation value:
<> = -0.78±0.031 deviates significantly from predictions that expect 56Ni to have double-magic character
Spin expectation values
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
Sulfur isotopes are in a region of changing structure for 20<N<28
g factors can give information on proton and neutron contribution to the wavefunction of the first excited 2+ state
Neutron-Rich S Isotopes: Rapidly Changing Structure
38S
40S
38S
40S
Sensitivity of g factors
• proton & neutron: g different in sign and magnitude
• Extreme single particle result:
826.3,0:586.5,1:
12)( 2
1
s
s
s
ggnggp
gggjg
d5/2
s1/2
d3/2
f7/2
sd shell+0.08
+5.59
+1.92
- 0.55
p3/2- 1.3
• Protons in sd shell,with Z=16 subshell closure at stability
• Single-particle structure influenced by shell gaps: f7/2 gap, s1/2-d3/2 gap
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
40 MeV/u
20 MeV/u
~5 MeV/uProjectiles:
38S: 105 pps E(2+)=1292 keV (2+)= 4.9 ps
40S 104 pps E(2+)= 903 keV (2+)= 20 ps
-rays
gBTF
No B applied B appliedExcited-state spin precesses while traversing the magnetized foil
High velocity transient field technique
Transient field endstation
Doppler corrected spectra (=40o). Correction performed event-by-event using particle energy measured in phoswich detector.
Gamma-ray angular distribution in projectile frame, corrected for Lorentz boost.
nucnuc
lab dd
2
2
)cos1(1
38,40S results
g (2+ ; 38S) = +0.13(5)g (2+ ; 40S) = -0.02(6)
Using BTF parametrizationand from double ratios,g factors were extracted.
(radioactive)
(stable)
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)
g(2+) results: 38,40S
Davies et al., PRL 96, 112503 (2006).
SummaryBeta-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 secondOther areas under development
• TDPAD on high-spin isomers near 68Ni• Development of NQR methods at the NSCL
CollaboratorsPolarization 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. TomlinMagnetic 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