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Bloch, Felix

magnetic nuclear describes solid

[blokh] (1905–83) Swiss–US physicist: invented nuclear magnetic resonance spectrometry.

Bloch was educated at Zürich and Leipzig, but following a short period of teaching in Germany moved to the USA in 1933. He spent the rest of his career at Stanford.

The theory of solid-state physics and of how electrons behave in solids was advanced by Bloch’s research. The Bloch wavefunction describes an electron which is moving freely in a solid and the term Bloch wall describes the boundary between two magnetic domains in a ferromagnetic material.

In 1946 Bloch introduced the nuclear magnetic resonance (NMR) technique, also developed independently by . Many types of atomic nucleus possess a magnetic moment and quantum mechanics indicated that the moment could only adopt one of a number of possible orientations with respect to an applied magnetic field. Each orientation requires a different energy and so transitions from one state to another can be accomplished if a photon of electromagnetic radiation (of radio frequencies) is absorbed. The magnetic moments of the proton and neutron were measured by this method and since then many complex molecules have been studied. The energy state of the nucleus gives information about its atomic neighbours in the molecule because of the effect of the surrounding electrons. Bloch shared the 1952 Nobel Prize for physics with Purcell, and the NMR method has since become a powerful analytical technique in chemistry.

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