Dictionary:Capture cross section

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1. The atomic capture cross section for neutrons is the effective area within which a neutron has to pass to be captured by an atomic nucleus. It is a probabilistic value dependent on the nature and energy of the particle as well as the nature of the capturing nucleus. Atomic capture cross section is often measured in barns (1 barn=10–28 m2). 2. The macroscopic capture cross section, Σ, is the effective cross-sectional area per unit volume for capture of neutrons; it depends on the number of atoms present as well as their atomic capture cross sections. The unit of measure for Σ is cm2/cm3=103 cu, where cu=capture unit (q.v.). 3. The rate of absorption of thermal neutrons with a velocity V is VΣ.