Nuclear spin

nuclear spin indicates the total angular momentum of an atomic nucleus . Investigations of nuclear spin are important to understand the structure of atomic nuclei. Above all however they are used to the chemical analysis and for medical investigations.

Nuclear spin becomes by the spin of the core components (neutrons and protonswith in each case spin 1/2) and their angular momentum determines. Since the angular momentum is always integral, applies: Nuclear spin is integral, if the number of the core components is altogether straight, otherwise half-integral. Cores with straight lines of neutron and straight lines proton number have a nuclear spin of 0, there itself the neutronsand/or. Protons apparent in each case to pairs with antiparallel spin align. This does not apply to cores with odd neutron and proton number, since the partnerless neutron and proton remaining in each case are in from each other independent bowls. The spin depends additionally on the internal excitation state of the core.

WithNuclear spin does not concern it a spin in the closer sense, there the atomic nucleus in accordance with the standard model differently than e.g. the electron an internal structure possesses. The consequence is that the magnetic moment can be aligned even antiparallelly to the spin, approximately with the isotope 17 O.A similar discrepancy gives it also with the neutron, which a magnetic moment possesses, although it is electrically neutral.

Table of contents

applications

medicine

the Magnetresonanztomografie or nuclear spin tomography uses the circumstance that init detaches outside magnetic field the energy of the core of the fact whether the spin (and the associated magnetic moment) is aligned parallel or antiparallelly to this field. In the case of magnetic fields of 5 Tesla arises as a result of it a fragmentation of the energy levels of the initial state of the core in the order of magnitude of10,-25 J, according to a photon frequency in the order of magnitude of 100 MHz (corresponds to a radio frequency within the range of the very high frequency). Appropriate one electromagnetic radiation can be absorbed by the atomic nuclei. Without the nuclear spin resonance radiation of this frequency in the sample material is only slightly absorbed.

Kernspintomographen inmedical employment measure mostly the distribution of hydrogen - atomic nuclei (protons) in the body. Differently than when X-raying thereby changes in the fabric can be made well visible mostly. In order to make three-dimensional sectional views possible, inhomogenous magnetic fields are used, so that only in each case in a small part of the taken upFabric the resonance condition is fulfilled.

structural analysis

with the chemical structural analysis by nuclear spin resonance (English. nuclear magnetic resonance, NMR) are observed however the effects, which have the surrounding electrons and neighbouring atoms on nuclear spin. For example free electrons in the proximity can do an additionalMagnetic field produce, which strengthens or weakens the outside field accordingly. Thus the frequencies shift, with which the resonance condition is fulfilled.

Web on the left of

 

  > German to English > de.wikipedia.org (Machine translated into English)