neutron spectrometry

Neutron spectrometry

A generic term applied to experiments in which neutrons are used as the probe for measuring excited states of nuclides and for determining the properties of these states. The term neutron spectroscopy is also used. The strength of the interaction between a neutron and a target nuclide can vary rapidly as a function of the energy of the incident neutron, and it is different for every nuclide. At particular neutron energies the interaction strength for a specific nuclide can be very strong; these narrow energy regions of strong interactions are called resonances (see illustration). The strength of the interaction, expressing the probability that an interaction of a given kind will take place, can be considered as the effective cross-sectional area &sgr; presented by a nucleus to an incident neutron.

Energy-level diagram for the product nucleus ^AZ* with mass number A and charge number Z

Neutron spectroscopy can be carried out by two different techniques (or a combination): (1) by the use of a time-pulsed neutron source which emits neutrons of many energies simultaneously, combined with the time-of-flight technique to measure the velocities of the neutrons; this time-of-flight technique can be used for neutron measurements from 10^-3 eV to about 200 MeV; (2) by the use of a beam of nearly monoenergetic neutrons whose energy can be varied in small steps approximately equal to the energy spread of the neutron beam; however, useful “monoenergetic” neutron sources are not available from about 10 eV to about 10 keV.

Neutron spectroscopy has yielded a mass of valuable information on nuclear systematics for almost all nuclides. The distribution of the spacings between nuclear levels and the average of these spacings have provided valuable tests for various nuclear theories. The properties of these levels, that is, the probabilities that they decay by neutron or gamma-ray emission, or by fission, and the averages and distribution of these probabilities have stimulated much theoretical effort.

In addition, knowledge of neutron cross sections is fundamental for the optimum design of thermal fission power reactors and fast neutron breeder reactors, as well as fusion power reactors now in the conceptual stage. Cross sections are needed for nuclear fuel materials such as ²³⁵U or ²³⁹Pu, for fertile materials such as ²³⁸U, for structural materials such as iron and chromium, for coolants such as sodium, for moderators such as beryllium, and for shielding materials such as concrete. See Nuclear structure

neutron spectrometry

[′nü‚trän spek′träm·ə·trē] (nuclear physics) A method of observing excited states of nuclei in which neutrons are used to bombard a target, causing nuclei to be transmuted into excited states by various nuclear reactions; the resultant excited states are determined by observing resonances in the reaction cross sections or by observing spectra of emitted particles or gamma rays. Also known as neutron spectroscopy.

单词	neutron spectrometry
释义	neutron spectrometry Neutron spectrometry A generic term applied to experiments in which neutrons are used as the probe for measuring excited states of nuclides and for determining the properties of these states. The term neutron spectroscopy is also used. The strength of the interaction between a neutron and a target nuclide can vary rapidly as a function of the energy of the incident neutron, and it is different for every nuclide. At particular neutron energies the interaction strength for a specific nuclide can be very strong; these narrow energy regions of strong interactions are called resonances (see illustration). The strength of the interaction, expressing the probability that an interaction of a given kind will take place, can be considered as the effective cross-sectional area &sgr; presented by a nucleus to an incident neutron. Energy-level diagram for the product nucleus ^AZ* with mass number A and charge number Z Neutron spectroscopy can be carried out by two different techniques (or a combination): (1) by the use of a time-pulsed neutron source which emits neutrons of many energies simultaneously, combined with the time-of-flight technique to measure the velocities of the neutrons; this time-of-flight technique can be used for neutron measurements from 10^-3 eV to about 200 MeV; (2) by the use of a beam of nearly monoenergetic neutrons whose energy can be varied in small steps approximately equal to the energy spread of the neutron beam; however, useful “monoenergetic” neutron sources are not available from about 10 eV to about 10 keV. Neutron spectroscopy has yielded a mass of valuable information on nuclear systematics for almost all nuclides. The distribution of the spacings between nuclear levels and the average of these spacings have provided valuable tests for various nuclear theories. The properties of these levels, that is, the probabilities that they decay by neutron or gamma-ray emission, or by fission, and the averages and distribution of these probabilities have stimulated much theoretical effort. In addition, knowledge of neutron cross sections is fundamental for the optimum design of thermal fission power reactors and fast neutron breeder reactors, as well as fusion power reactors now in the conceptual stage. Cross sections are needed for nuclear fuel materials such as ²³⁵U or ²³⁹Pu, for fertile materials such as ²³⁸U, for structural materials such as iron and chromium, for coolants such as sodium, for moderators such as beryllium, and for shielding materials such as concrete. See Nuclear structure neutron spectrometry [′nü‚trän spek′träm·ə·trē] (nuclear physics) A method of observing excited states of nuclei in which neutrons are used to bombard a target, causing nuclei to be transmuted into excited states by various nuclear reactions; the resultant excited states are determined by observing resonances in the reaction cross sections or by observing spectra of emitted particles or gamma rays. Also known as neutron spectroscopy.
随便看	lockheed martin space systems company lockheed martin space systems company - missiles and space operation lockheed martin stennis operations lockheed martin tactical aircraft systems lockheed martin tactical defense systems lockheed martin tactical systems lockheed martin technical operations lockheed martin technology services lockheed martin technology services group lockheed martin transportation and security solutions lockheed martin utility services lockheed martin vought systems lockheed missiles and space company lockheed missile systems division lockheed palo alto research laboratory lockheed q-star single engine observation aircraft/sail plane lockheed sanders, inc. lockheed skunkworks lockheed spurious emission detector lockheed, sunnyvale lockheed u-2 lock her away lock her in lock her out lock her up