ISO_NWIPs-for-Ballot

ISO/NP

Although all nuclei have a charge, for some nuclear species this charge spins on the nucleus axis. The 292 effect of spinning of the nuclear charge results in the generation of a magnetic moment along the axis. 293 The nuclear moment of this spinning charge, i.e. the nuclear spin ( I ), will have a value of 1/2, 1, 3/2 … 294 n /2 (where n is an integer). A nucleus for which I = 0 means that there is no spin. In quantum mechanics, 295 for a spin I , the number of directions that are possible for the nucleus in a uniform external magnetic 296 field is defined by the expression 2 I + 1. Accordingly, when a nucleus is placed in a magnetic field, the 297 nuclear moment (arising from the spins of the protons and neutrons) is oriented in (2 I + 1) different 298 energy levels. Since I = 1/2 for 1 H and 13 C, there are two energy levels for these nuclei. 299 When a nucleus with gyromagnetic ratio γ is placed in an external magnetic field H 0 , the relationship 300 between the transitions between the energy levels and the applied radio frequency v is given by 301 Formula (1). 302 π2 0 H (1) 303 where 304 is the electromagnetic wave frequency ; 305 is the gyromagnetic ratio; 306 307 H 0 is the external magnetic field. 308 309 When there is resonance (transition between energy states) caused by applying radio waves at 310 frequency , the absorption of radio waves at that frequency (NMR signals) can be observed. Since the 311 absorption coefficient (transition probability) for a nucleus is a constant, and does not depend on the 312 environment, the intensity of the acquired NMR signal is basically proportional to the number of nuclei. 313 The spins that have been shifted to the higher energy level by the transition return to a thermal 314 equilibrium state after a certain period of time. This process is called “relaxation”, and the "relaxation 315 rate" is a measure of the kinetics of the return of magnetisation to its equilibrium value. 316 When a molecule is placed in a magnetic field, the electrons in the molecule shield the nucleus from the 317 external magnetic field. The nuclei within the molecule will be shielded to different extents in each 318 different environment, so the resonant frequency of nuclei will be different in each different 319 environment, which is observed as separate signals. The position of the signal is expressed as the 320 chemical shift, delta ( . 321 Since the resonant frequency changes in proportion to the magnetic field, the chemical shift x is defined 322 by Formula (2), and is a quantity that is independent of the strength of the magnetic field. 323 324 R R R s ＋ v v v x (2) 325 where 326 x is the chemical shift; 327 s is the resonance frequency of the sample nuclei; 328 R is the resonance frequency of the reference nuclei; 329

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