Untitled

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

“…Here, the two decay rates Γ extracted from traces a and c in Fig. 1 yield D = 1.54 × 10 −3 cm 2 /s at X = 2.8%, in good agreement with published values [5,14]. The RMS sequence appears to be a lot more robust than the CPMG sequence against dipolar effects.…”

“…Mono-exponential decays of the echo amplitudes are observed. At high magnetisations (traces b and d), the echo shapes are strongly altered and the much faster decay is no longer exponential, as previously reported [5,10]. Since 180…”

“…The quadratic dependence of Γ CPMG on τ and G has been checked in a previous series of experiments, in which it was demonstrated that D can be accurately measured with this method in our apparatus [5]. Here, the two decay rates Γ extracted from traces a and c in Fig.…”

“…We also demonstrated that it is possible to achieve dynamic stabilisation of transverse precession in laser-polarised He mixtures using a series of MS cycles to periodically refocus the dipolar interactions. In this paper, we report preliminary results that establish the potential of multiple-echo MS-based NMR sequences for spin diffusion measurements at high magnetisation densities, and confirm the fact that conventional spin echo techniques completely fail to achieve this goal [5].…”

“…The decay of the average transverse magnetisation is thus expected to remain dominated by dipolar-induced instabilities at high magnetisation densities. Indeed, early attempts to generate single Hahn spin echoes and Carr-Purcell spin echo trains in highly polarised 3 He-4 He dilute mixtures have led to the observation of multiple echoes [8] and of non-exponential decay [5], respectively. (traces a and c), spin echoes have the shapes that are expected given the sample geometry and the gradient strengths.…”