Absorption Cross Section

The absorption cross section σ as defined in this book is the sum of all the separate cross sections for processes that are possible resulting from a single photon absorption event at the wavelength of the absorbed photon.

Absorption cross section. Absorption cross sections for transitions starting at the ground state manifold are often obtained from absorption spectra measured e g. If the neutron is absorbed when approaching the nuclide the atomic nucleus moves up on the table of isotopes by one position. Another experimental quantity is the ionization efficiency.

This energy has to be released and the release can take place through any of several mechanisms. 6 of shaw et al 1992. Absorption cross section is a measure for the probability of an absorption process.

Cross section in nuclear or subatomic particle physics probability that a given atomic nucleus or subatomic particle will exhibit a specific reaction for example absorption scattering or fission in relation to a particular species of incident particle cross section is expressed in terms of area and its numerical value is chosen so that if the bombarding particle hits a circular area. Note that light in this context is described as consisting of particles i e photons. This sum is frequently called the total absorption cross section to emphasize the point.

Above the ionization threshold see chapter 8 the absolute photodissociation cross section can be obtained as the difference between the absolute total absorption cross section and the absolute photoionization cross section see for example for n 2 fig. With a white light source if the number density concentration of the ions is known. The cross sections for elements in the xcom database pertain to isolated neutral atoms and do not take into account molecular and solid state effects which modify the cross sections especially in the vicinity of absorption edges.

For instance 235 u becomes 236 u with the indicating the nucleus is highly energized. The spectral profile of emission cross sections can be obtained from fluorescence spectra if no reabsorption modifies the spectral shape and there is no spectral overlap. Relatively small cross sections such as those for delbruck scattering two photon compton scattering or photo.

Although the absorption cross section luminescence efficiency of lanthanides can be improved using organic ligands and energy transfer antenna effect the chelate molecules luminescence is quenched by pmma nonradiative transitions and efficient luminescence can be observed only for triplet state europium eu sup 3. A long table then appears which lists all the molecules that are currently available. In the context of sample absorption characteristics our use of the variable α for cross section should not be confused with another use as an absorption coefficient with units of cm 1 that is equal to nα in equation ref 6 73.