{"doi":"10.1103/physrev.94.630","title":"Effects of Diffusion on Free Precession in Nuclear Magnetic Resonance Experiments","abstract":"Nuclear resonance techniques involving free precession are examined, and, in particular, a convenient variation of Hahn's spin-echo method is described. This variation employs a combination of pulses of different intensity or duration (\"90-degree\" and \"180-degree\" pulses). Measurements of the transverse relaxation time ${T}_{2}$ in fluids are often severely compromised by molecular diffusion. Hahn's analysis of the effect of diffusion is reformulated and extended, and a new scheme for measuring ${T}_{2}$ is described which, as predicted by the extended theory, largely circumvents the diffusion effect. On the other hand, the free precession technique, applied in a different way, permits a direct measurement of the molecular self-diffusion constant in suitable fluids. A measurement of the self-diffusion constant of water at 25\\ifmmode^\\circ\\else\\textdegree\\fi{}C is described which yields $D=2.5(\\ifmmode\\pm\\else\\textpm\\fi{}0.3)\\ifmmode\\times\\else\\texttimes\\fi{}{10}^{\\ensuremath{-}5}$ ${\\mathrm{cm}}^{2}$/sec, in good agreement with previous determinations. An analysis of the effect of convection on free precession is also given. A null method for measuring the longitudinal relaxation time ${T}_{1}$, based on the unequal-pulse technique, is described.","journal":"Physical Review","year":1954,"id":2842,"datarank":33.46727845089024,"base_score":8.764209507142004,"endowment":8.764209507142004,"self_citation_contribution":1.3146314260713008,"citation_network_contribution":32.15264702481894,"self_endowment_contribution":1.3146314260713008,"citer_contribution":32.15264702481894,"corpus_percentile":99.0,"corpus_rank":1949,"citation_count":6400,"citer_count":198,"citers_with_citation_signal":198,"citers_with_endowment":198,"datacite_reuse_total":0,"is_dataset":false,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"1954-05-01","authors":[{"id":32150,"name":"E. M. Purcell","orcid":null,"position":1,"is_corresponding":false},{"id":32151,"name":"Edward M. Purcell","orcid":null,"position":2,"is_corresponding":false},{"id":32149,"name":"H. Y. Carr","orcid":null,"position":0,"is_corresponding":true}],"reference_count":8,"raw_metadata":{"citation_network_status":"fetched"},"created_at":"2026-03-01T18:20:47.508186Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}