Non-equilibrium thermodynamics of cross-relaxation

✍ Scribed by R. Lenk

• Publisher: Elsevier Science
• Year: 1979
• Tongue: English
• Weight: 405 KB
• Volume: 63
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(79)87048-7

✦ Synopsis

There are many nuclei. isotopicaliy or chemicaIIy dilute in solids which can revea1 vaiuabie structural tiormation-Because of their low abundance and sometimes because of their smzdl gyromagnetic ratio y, they frequentry give undetectabIe NMR sigmds. In order to increase the sensitivity of the detection of rare spins, many double-irradiation techniques have been developed [I-5] _ AII these techniques are able to enhance the weak NMR signals by repeatedly transferred polarization from a more abundant species with a high 7 to the iow abundztnce (rare) species; in other words, a gain of sensitivity can be obtained by utilizing the "reservoir" of abundant spins_ This domain can be treated thermodynamically_ In this context let us imagine a thermodynamic system with a heat bath "'3" and two subsystems-The first subsystem is created by the abundant spins "I" and the second by the rare spins '27, as schematically presented in fig_ I_ A disturbance of the thermodynamic equihirium in the whofe system "I f S + B" by cooling of the subsystem "I" using the appropriate methods [Sj. is followed by a cross-relaxation process_ As will be shown in the pzsent paper, this situation can be handIed by using the methods of &ssical or quantum-statistical non-equilibrium thermodynamics_ In these investigations transfer of nuclear poiarization is achieved, using the cross-relaxation 'Y + "I", which is characterized by the cross-relation time (T,)s,. Note that the "I" subsystem has a Iarge hear 5 Now Sk0 LaboI;ltoIre de PhylroIogie VigitaIe_