spin 2004 oct. 14, 2004 w. kim, s.s. stepanyan, s. woo, m. rasulbaev, s. jin (kyungpook national...
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SPIN 2004Oct. 14, 2004
W. Kim, S.S. Stepanyan, S. Woo, M. Rasulbaev, S. Jin
(Kyungpook National University)S. Korea
Polarization Measurements of the Target with water and DPPH
3He
Optical Pumping Mechanism
Spin exchange with optically pumped alkali metal rubidium vapor.
Optical Pumping Procedure
cell
optics
Diode Laser
Oven (160 oC)
pickup coil
RF drive coils
Instrument Control
Coils providing uniform magnetic field
xMxy
M
MzH0
y
RF Coil
Nuclear Magnetic Resonance
If an RF field of frequency equal to Larmor frequency is applied orthogonal to H0 holding field , the particles can undergo reversal of their magnetic dipole moment orientation.
0 0H
Resonance condition:
02
Adiabatic Fast Passage
AFP sweep is produced sweeping main magnetic field through the resonance up and down the spin rotates an angle approaching 180° as the process is adiabatic.
01
1 1
1 1 dHH
T H dt
T1 – spin-lattice relaxation time;
H1 – magnetic component of RF field;
H0 – Holding magnetic field amplitude;
– gyromagnetic ratio;
NMR Setup Schematic
NMR Setup for 3He Target at KNU
Helmholtz coil system NMR Electronics
Optics Setup
Optics
NMR signal creation program
Laser control program
NMR measurement program
Test of the NMR Setup
Loop ~ NMR setup: 3 metersPhase: 40.00 degrees External RF radiation generator turned off
NMR setup as a Receiver
Vol
tage
indu
ced
in th
e pi
ck-u
p co
ils
[mV
]
Holding Magnetic Field [G]
Q-curve
Q-curve of pick-up coil circuit fitted with Lorentzian.
RF signal amplitude adjustments
Calibration Constant for Polarization Measurements (1)
S k M k n P
S : amplitude of the lock-in amplifier signal k : prop. Constant, taking a count gains, losses in the cables, …μ : magnetic moment of the sample.n : density of the spins .P : polarization of the sample
The signal induced in the pick-up coils by the AFP sweep and detected by the lock-in amplifier is proportional to the macroscopic magnetization M of the sample;
The ratio of the Helium NMR signal height SHe to the water NMR signal height Sw
He He He He He
w w p p w
S G n P
S G n P
Calibration Constant for Polarization Measurements (2)
1 with, pHe w
He w w p wHe w He He
S GP C C n P
n S G
: amplitude of the water signal : amplitude of the Helium signal , : magnetic moments of protons in water and 3He nucleus.
wS
HeS
p He
Polarization of the He target proportional to magnetization.
Polarization Calculation
9 9tanh tanh 7.4 10 0.074.102 2
pw
w w w
B h hP
kT kT kT
1181067.2 Ts
The value of the water sample polarization is calculated from Boltzman statistics:
Tw : water temp [K]
B : Resonance Holding field
ν (=91kHz) : RF field frequency
1 Amagat (amg) =
amplitude of the water signal extracted from the fit of the average NMR data.
31910689.2 cm
6wS V
22 3(6.67 0.05) 10 2482 2 Amagatspn cm
DPPH (Solid 2.2-Diphenil-1-Picrylhydrazyl) for Calibration of Polarization.
Uncertainty AFP Polarization measurements 7%
Helium density < 5%
Thermal signal < 1%
Amplitude measurement < 2.5%
Gains <1%
Experimental g-factor for DPPH : g=2.039±0.023 very close to electron
Used DPPH (5gr, 1cm3 powder) as material for calibration
10 turns of Pickup coils around DPPH
Holding Field for 91kHz is less than 0.5G during AFP sweep
BE g B h h
gB
91 0.5
h B
kHz B G
DPPH Signal
X ChanelAbsorption
Y ChanelDispersion
Water Signal
Summary
NMR system constructed and calibrated for polarization measurements of the polarized 3He Target with AFP method.
Signal-to-noise ratio improved by making coils for NMR setup for polarization measurements.
Measurements performed with DPPH and water