S. Boag

Digital pulsed NMR spectrometer for nuclear spin-polarized 3He and other hyperpolarized gases

We describe here a simple low frequency (<200 kHz) pulsed digital NMR spectrometer suitable for a number of applications where the monitoring of nuclear spin-polarized (hyperpolarized) gases is required. The device is implemented using a digital I/O card and passive duplexer and details of the necessary hardware are presented along with a description of the excitation pulse and digital filtering techniques used. Furthermore we discuss the use of a modified function to describe the free induction decay of the gas that is used to account for the change in lineshape due to magnetic field gradients found across the polarized gas. We present data obtained using the spectrometer including measurements of polarization, destruction per pulse and spin up and relaxation time constants and have shown a low destruction per pulse of only 0.014%, resulting in only a 1 part in 10 000 correction for our system.

Measurement of laser heating in spin exchange optical pumping by NMR diffusion sensitization gradients

This paper details pulsed gradient NMR measurements of the H3e diffusion coefficient in sealed cells during spin exchange optical pumping. The potential of ultra low field magnetic resonance imgaing (MRI) and NMR for noninvasive measurement of cell pressure is demonstrated. Diffusion sensitization gradients allow measurement of the H3e diffusion coefficient from which the pressure and/or temperature of the gas can be determined during optical pumping. The pressure measurements were compared with neutron time of flight transmission measurements. Good agreement was observed between the temperature/pressure measurements and predictions based on Chapman–Enskog theory. The technique had sufficient sensitivity to observe the diffusion coefficient increasing with temperature in a sealed cell. With this method, evidence for laser heating of the H3e during optical pumping was found. The results show that NMR diffusion measurements allow noninvasive measurement of the cell temperature and/or pressure in an optical ...

Low magnetic field manipulation of 3He spins using digital methods

Simple methods for manipulating 3He spins at low magnetic fields using low cost digital I/O cards are presented. A brief overview of a digital NMR spectrometer is given along with practical information on the implementation and an assessment of the losses per pulse. Through the use of coils with different quality factors the effects of radiation damping are investigated and assessed in the context of the sample polarisation using neutron transmission measurements. The hardware is further used to synthesize an adiabatic swept pulse which is used to reverse the 3He spin direction, allowing the selection of a particular neutron spin.