Carr-Purcell-Meiboom-Gill spin echo pulse sequence

Spin-spin relaxation times T2 are determined by the Carr-Purcell-Meiboom-Gill spin echo pulse sequence and provide information about slower molecular motions (66,67). 

Another way to detect slow motions is by deuteron transverse spin relaxation experiments using a modified Carr-Purcell-Meiboom-Gill spin echo pulse sequence [42-44]. Information about the dynamics of liquid crystals can be retrieved from the frequency dispersion (see Fig. 2) and the anisotropy of relaxation rates. 

Carr-Purcell-Meiboom-Gill spin echo pulse sequence 599... 

Values of the spin-spin relaxation-time (Tz) for individual spectral lines may be measured by Fourier transformation of the echoes produced by a Carr-Purcell-Meiboom-Gill type of pulse sequence,174 but only in a simple manner, if there is no homonuclear spin-coupling present.175 Refocusing of the dispersing magnetization-vector by... 

Harbridge, J.R., Eaton, S.S., and Eaton, G.R. 2003. Comparison of electron spin relaxation times measured by Carr-Purcell-Meiboom-Gill and two-pulse spin-echo sequences. J. Magn. Reson. 164 44-53. 

In electron spin echo relaxation studies, the two-pulse echo amplitude, as a fiinction of tire pulse separation time T, gives a measure of the phase memory relaxation time from which can be extracted if Jj-effects are taken into consideration. Problems may arise from spectral diflfrision due to incomplete excitation of the EPR spectrum. In this case some of the transverse magnetization may leak into adjacent parts of the spectrum that have not been excited by the MW pulses. Spectral diflfrision effects can be suppressed by using the Carr-Purcell-Meiboom-Gill pulse sequence, which is also well known in NMR. The experiment involves using a sequence of n-pulses separated by 2r and can be denoted as [7i/2-(x-7i-T-echo) J. A series of echoes separated by lx is generated and the decay in their amplitudes is characterized by Ty. ... 

Measurement of a true T2 can be obtained using a spin-echo pulse sequence, such as the Carr-Purcell-Meiboom-Gill (CPMG) sequence, which minimizes the loss of phase coherence caused by inhomogeneities (Kemp, 1986). 

T2 measurements usually employ either Carr-Purcell-Meiboom-Gill (CPMG) [7, 8] spin-echo pulse sequences or experiments that measure spin relaxation (Tlp) in the rotating frame. The time delay between successive 180° pulses in the CPMG pulse sequence is typically set to 1 ms or shorter to minimize the effects of evolution under the heteronuc-lear scalar coupling between 1H and 15N spins [3]. 

CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence to odd-half-integer quadrupolar spin systems. It was found that QCPMG (controlled CPMG) can be one order of magnitude more sensitive than quadrupolar echo MAS experiments. Assisted by numerical simulation, the QCPMG MAS experiments can be used to determine the quadrupolar as well as chemical shift tensors. ... 

Fig. 25. Free-induction decay (FID) after a 90° pulse at t=0 and a series of Carr/Purcell/ Meiboom/Gill (CPMG) spin echoes in linear polyethylene (M, =92,300) at 150 °C. The 180° pulses of the CPMG sequence are indicated by vertical lines. The homogeneity of the external magnetic flux density is demonstrated by an FID of water at 30 °C. The data demonstrate the existence of strong internal field gradients arising from voids [152]...

Multipulse techniques, widely used in magnetic resonance, are also very common in NQR spectroscopy. They are effectively used for increasing sensitivity, reducing the duration of the experiment, and for measuring relaxation times in the sample. In NQR such well-known sequences as spin-echo, Carr-Purcell (CP), Meiboom-Gill-modified CP, spinlocking sequence and phase-alternated pulse sequence are widely used. There is a large practical... 

Figures 2.13, 9.1, and 9.2 demonstrate the formation of an echo following a tt pulse. Application of additional tt pulses can be used to form a train of echoes. It is clear that the dephasing of magnetizations following an echo is of the same form as the initial dephasing during the FID and that application of a second tt pulse at 3T causes a second echo at 4t, etc. The envelope formed by the echo peaks decays according to the real T2, rather than T2, and Fourier transform of each echo provides a set of partially relaxed spectra, from which T2 of each line may be determined. (Carr and Purcell first recognized the value of such a long sequence of TT pulses,104 and their names are usually used to depict the method, but the technique that we described for the spin echo in Chapter 2 and that discussed here include a refinement by Meiboom and Gill,105 as discussed later.)...

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