Giant enhancement of the NMR resolution and sensitivity of the critical solutions of hyperpolarized fluids within closed carbon nanotubes

Abstract

We predict the effect of the nuclear spin density fluctuations on NMR spectra of critical solutions of spin-carrying atoms in closed carbon nanotubes (CNTs). The total effective dipolar coupling of nuclear spin-carrying of 129^Xe atoms is the sum of 2 terms i.e. g_0 of non-correlated 129^Xe atoms and g_1 depending on density fluctuations of Xe atoms. The coupling g_0 falls off to 0 as 1/V with increasing the volume V of CNTs, while the g_1 remains finite for long CNTs containing critical solution of Xe atoms. The g_1 is derived within the Landau-Ginzburg framework. When temperature T goes to critical temperature T_c, the g_1 is about 10 Hz for 129^Xe fluid in closed long tubes. To achieve the g_1>> g_0, 3 conditions should be met: (1) the large mobility of 129^Xe atoms, (2) the maximal isothermal compressibility of Xe nanofluid within CNTs that have to be (3) long and closed. We discuss 3 applications of such a behavior. First, when T goes to T_c, the FID from N magnetically equivalent 129^Xe atoms is broadened so wide that the FID splits into lattice of N equidistant resonances with finite spacing G=3g_1. Second, the absorption line shape of 129^Xe atoms in spin state I=N/2, m=N/2 has a single delta peak at frequency with the large shift N*G/2 from Larmor frequency W for N>>1. The dipolar field of nanofluid in the spin state I=N/2, m=-N/2 inverts the total magnetic field if N>1+2W/G. Third, we discuss the spontaneous superradiation of the nanofluid in course of depolarization I_x(t) in low-field resonator. At CP of the nanofluid, the I_x(t) causes the bursts of dissipated power ~(g_1)^2*N^3. In the opposite limiting case of the strong field resonator, the depolarization I_x(t) has the Dicke's power ~(W*N)^2. Far from the CP of Xe nanofluid, the dissipated power scales linear with N for fixed density of 129^Xe atoms.