SPIN 2004 Oct. 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

Optical Pumping Mechanism Spin exchange with optically pumped alkali metal rubidium vapor.

Optical Pumping Procedure cell optics Diode Laser Oven (160 o C) pickup coil RF drive coils Instrument Control Coils providing uniform magnetic field

x M xy M MzMz H0H0 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. Resonance condition:

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. T 1 – spin-lattice relaxation time; H 1 – magnetic component of RF field; H 0 – Holding magnetic field amplitude; – gyromagnetic ratio;

NMR Setup Schematic

NMR Setup for 3 He 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 meters Phase: degrees External RF radiation generator turned off NMR setup as a Receiver Voltage induced in the pick-up coils [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 : 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 S He to the water NMR signal height S w

Calibration Constant for Polarization Measurements (2) : amplitude of the water signal : amplitude of the Helium signal, : magnetic moments of protons in water and 3 He nucleus. Polarization of the He target proportional to magnetization.

Polarization Calculation The value of the water sample polarization is calculated from Boltzman statistics: T w : 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.

DPPH (Solid 2.2-Diphenil-1-Picrylhydrazyl) for Calibration of Polarization. UncertaintyAFP Polarization measurements7% 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, 1cm 3 powder) as material for calibration 10 turns of Pickup coils around DPPH Holding Field for 91kHz is less than 0.5G during AFP sweep

DPPH Signal X ChanelAbsorption Y ChanelDispersion

Water Signal

Summary NMR system constructed and calibrated for polarization measurements of the polarized 3 He Target with AFP method. Signal-to-noise ratio improved by making coils for NMR setup for polarization measurements. Measurements performed with DPPH and water