Introduction

Radiofrequency Quadrupolar NMR Stark Spectroscopy: Steady State Response Calibration and Tensorial Mapping

“…In particular, prior work at 77 K corresponded to T 1 ( 69 Ga) ∼ 15 s, in contrast to our room-temperature value of ∼0.3 s. Similarly large disparities of the time constants for development and decay of steady state coherences are likewise expected, and may have prevented their observation. We also note that steady state coherences may be expected in the related field of nuclear acoustic resonance (NAR), which utilizes coherent acoustic waves to modulate quadrupolar and other spin interactions. Thus, as for rf E fields, resonant acoustic excitation drives spin transitions with Δ m = ±1 or ±2, yielding M z ss < M 0 at steady state.…”

“…Abragam presented straightforward derivation [pp 138−141 and 417−420 of ref ] of the expression valid under these circumstances: M z s s / M 0 = false( 1 + f I W T 1 false) − 1 where W is the transition probability per unit time between spin levels m and m ± 2, T 1 is the spin−lattice relaxation time, and f I is a spin-dependent, unitless prefactor, equal to 8/5 for spins I = 3/2, or f I = (8 I ( I + 1) − 6) /(5 I (2 I − 1)) for an arbitrary spin I . [See p 299 of ref .] It is noteworthy that, although multiexponential spin−lattice relaxation is known for quadrupolar mechanisms with inequivalent rates for Δ m = ±1 and ±2 transitions, , an effective single-exponential constant ( T 1 ) is justified for the case of cubic crystals (such as GaAs).…”

Fissile and Non-Fissile Material Detection using Nuclear Acoustic Resonance Signatures: Final Report

“…NAR coupling mechanisms occur because acoustic energy can couple to the material's nuclear spin system via various electric and magnetic interactions. [4] This includes the dynamic electric quadrupole interaction, in which the acoustic wave dramatically couples to the electric quadrupole moments of the nuclear spins; the magnetic dipole (or Alpher-Rubin) interaction [6], in which the acoustic waves couple to the magnetic moments of the nuclear spins; the hexadecapole interaction, in which the acoustic wave couples to the electric hexadecapole (16-pole) moments of the nuclear spins; and magnetic dipole-dipole interaction, in which acoustic wave couple to the materials via magnetic interactions among nuclear spins themselves. These various mechanisms couple to different multipole moments of the nuclear spins, each one leading to a different set of values for the observing interaction intensities, angular dependence, and line widths and line shapes.…”

“…Thus, NAR cannot only be used as a detection tool, but it also has the potential to be used in the laboratory to characterize intact materials imbedded in an apparatus. [4].…”