Question

A beam of 1 MeV neutrons of intensity 5 x108 neutrons/cm2-sec strikes a thin ? target of mass of 0.041grams . The area of the target is 0.5 cm2 and is 0.05 cm thick. The beam has a crosssectional area of 0.1 cm2. At 1 MeV, the total cross-section of ? is 2.6 b.

calculate the (a) macroscopic total cross-section of C-12 at 1MeV; (b) collision density in the target.

Answer 1

Answer:

In contrast to the neutron flux, the neutron intensity is the number of neutrons crossing through some arbitrary cross-sectional unit area in a single direction per unit time (a surface is perpendicular to the direction of the beam). The neutron intensity is a vector quantity.

Collision among gas particles

n is the number density of the target particles (SI units: m−3). If the particles in the gas interact by a force with a larger range than their physical size, then the cross section is a larger effective area that may depend on a variety of variables such as the energy of the particles.

The influence of the target density on the charge-changing—ionization and electron capture—cross sections when fast ions penetrate through solid targets is considered. It is shown that, with the target density increasing, electron-capture cross sections decrease and ionization cross sections increase, resulting in a higher mean charge of exit ions after a solid target compared to a gas target