Feasibility of Surface Nuclear Magnetic Resonance With Absurdly Long Excitation Pulses

TY - JOUR

T1 - Feasibility of Surface Nuclear Magnetic Resonance With Absurdly Long Excitation Pulses

AU - Larsen, Jakob Juul

AU - Kass, M. Andy

AU - Grombacher, Denys

AU - Griffiths, Matthew P.

PY - 2024/10/28

Y1 - 2024/10/28

N2 - The common understanding in surface nuclear magnetic resonance (NMR) is that the excitation pulse should be kept much shorter than the NMR relaxation times for an effective excitation. We present analytic, numerical, and experimental evidence demonstrating that this need not be so, and surface NMR signals can be retrieved even for absurdly long excitation pulses. We solve the Bloch equations in the limit of infinitely long excitation and use this result to demonstrate that a measurable magnetization can be obtained with long excitation pulses. We perform numerical simulations of the Bloch equations incorporating effects of relaxation-during-pulse, and our results suggest that long excitation pulses can be used to increase the depth of investigation, but that the spatial resolution of long pulse excitation is low. Data collected in Kompedal, Denmark using up to 3 s long excitation pulses provide experimental proof for the feasibility of long pulse surface NMR.

AB - The common understanding in surface nuclear magnetic resonance (NMR) is that the excitation pulse should be kept much shorter than the NMR relaxation times for an effective excitation. We present analytic, numerical, and experimental evidence demonstrating that this need not be so, and surface NMR signals can be retrieved even for absurdly long excitation pulses. We solve the Bloch equations in the limit of infinitely long excitation and use this result to demonstrate that a measurable magnetization can be obtained with long excitation pulses. We perform numerical simulations of the Bloch equations incorporating effects of relaxation-during-pulse, and our results suggest that long excitation pulses can be used to increase the depth of investigation, but that the spatial resolution of long pulse excitation is low. Data collected in Kompedal, Denmark using up to 3 s long excitation pulses provide experimental proof for the feasibility of long pulse surface NMR.

KW - Bloch equations

KW - depth-of-investigation

KW - groundwater

KW - NMR physics

KW - NMR pulses

KW - surface NMR

UR - http://www.scopus.com/inward/record.url?scp=85206910657&partnerID=8YFLogxK

U2 - 10.1029/2024GL110826

DO - 10.1029/2024GL110826

M3 - Journal article

AN - SCOPUS:85206910657

SN - 0094-8276

VL - 51

JO - Geophysical Research Letters

JF - Geophysical Research Letters

IS - 20

M1 - e2024GL110826

ER -