Decay of nuclear magnetization by bounded diffusion in a constant field gradient
| Autor: | Pabitra N. Sen, Thomas M. de Swiet |
|---|---|
| Rok vydání: | 1994 |
| Předmět: | |
| Zdroj: | The Journal of Chemical Physics. 100:5597-5604 |
| ISSN: | 1089-7690 0021-9606 |
| DOI: | 10.1063/1.467127 |
| Popis: | Transverse magnetization of spins diffusing in a bounded region in the presence of a constant field gradient is studied. We investigate the breakdown at short times of the much used formula for the Hahn echo amplitude in a constant gradient in unbounded space: M(2τ)/M(0)=exp(−2D0g2τ3/3). Here D0 is the diffusion constant in unbounded space and g is the field gradient multiplied by the gyromagnetic ratio. We find that this formula is replaced by M(2τ)/M(0)=exp[−2Deffg2τ3/3 +O(D5/20g4τ13/2S/V)] with an effective diffusion coefficient Deff(2τ) =D0[1−α√D0τ(S/V) +...], where α is a constant and S/V is the surface to volume ratio of the bounded region. Breakdown is complex but we find that the interplay between a natural length scale lc=(g/D0)−1/3 and the geometry of the region governs the problem. The long‐time behavior of the free induction decay and echo amplitude are then considered where pure exp[−const t] decay is expected. We consider some simple geometries and find in addition to the well‐known result, ... |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|