Capture Cross Section
The absorption neutron cross-section of an isotope of a chemical element is the effective cross sectional area that an atom of that isotope presents to absorption, and is a measure of the probability of neutron capture. It is usually measured in barns (b).
Absorption cross section is often highly dependent on neutron energy. Two of the most commonly specified measures are the cross-section for thermal neutron absorption, and resonance integral which considers the contribution of absorption peaks at certain neutron energies specific to a particular nuclide, usually above the thermal range, but encountered as neutron moderation slows the neutron down from an original high energy.
The thermal energy of the nucleus also has an effect; as temperatures rise, Doppler broadening increases the chance of catching a resonance peak. In particular, the increase in uranium-238's ability to absorb neutrons at higher temperatures (and to do so without fissioning) is a negative feedback mechanism that helps keep nuclear reactors under control.
Read more about this topic: Neutron Capture
Famous quotes containing the words capture, cross and/or section:
“Writing prejudicial, off-putting reviews is a precise exercise in applied black magic. The reviewer can draw free- floating disagreeable associations to a book by implying that the book is completely unimportant without saying exactly why, and carefully avoiding any clear images that could capture the reader’s full attention.”
—William Burroughs (b. 1914)
“In ancient times—’twas no great loss—
They hung the thief upon the cross:
But now, alas!—I say’t with grief—
They hang the cross upon the thief.”
—Anonymous. “On a Nomination to the Legion of Honour,” from Aubrey Stewart’s English Epigrams and Epitaphs (1897)
“Personally I think we’re over-specialized. Why it’s getting so we have experts who concentrate only on the lower section of a specimen’s left ear.”
—Martin Berkeley, and Jack Arnold. Prof. Clete Ferguson (John Agar)