Spin-1 Polarized Target NMR Analysis

The UNH nuclear physics group produces polarized targets that are essential for the study of nucleon spin structure. The polarization of the material must be known to excellent precision to limit systematic uncertainties. Nuclear magnetic resonance (NMR) is used to determine the polarization of the target. The polarization is extracted by comparing the NMR lineshape to that of a reference signal where the polarization is known. Typically, the calibration is determined by measuring the lineshape at thermal equilibrium (TE) where Boltzmann statistics describe the equilibrium polarization. However, the signal to noise at equilibrium is extremely small which makes this calibration challenging. Maintaining the low temperature (1 K) and magnetic field (5 T) required for the TE over extended periods of time is a difficult experimental demand.

Alternative approaches exist to calibrate NMR measurements by directly extracting the polarization from analysis of the NMR lineshape (See for example O. Hamada etal., C. Dulya et al., or W.  F.  Kielhorn).  These approaches rely on the ratio of peaks and plateaus in a spin-1 NMR lineshape, and can use complex mathematical fits and functions to describe the data. These techniques work well during a steady state but can fail to model the polarization accurately during the dynamic nuclear polarization  process,  especially when the polarization is changing rapidly. 

I will discuss a novel method for fitting and determining polarization from a ND3 signal. This new approach exploits the expected mathematical symmetry of specific magnetic sub-level transitions, and potentially allows for the spin transition lines that make up an NMR signal to be determined even during rapid changes in polarization. It is also generalizable to other spin-1 systems, and has been shown to work well during steady states. I will present a comparison of this new approach to existing techniques and also discuss potential drawbacks and limitations.