Radiative Stopping Power
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Radiative stopping power (Srad) is due to radiative interactions and is mostly based on Bremsstrahlung production alone. Different from collision (ionization) stopping power, only light charged particles (electrons and positrons) experience appreciable energy losses through these interactions. This type of radiative stopping power results from charged particle Coulomb interaction with nuclei of the absorber. Energy spent in radiative collisions is carried away from the charged-particle track by the photons.

The radiative stopping power can be evaluated easily by the mass radiative stopping power Srad (in MeV · cm2/g), which is one type of the mass stopping powers. Srad is given by,

           mass radiative stopping power ----------------------- [4431a]

where, Na -- The number of atoms per unit mass (Na = N/m)
           σrad -- The total cross section for bremsstrahlung production
           Ei -- The initial total energy of the light charged particle, given by Ei = EKi + mec2
           EKi -- The initial kinetic energy of the light charged particle

Inserting σrad for non-relativistic particles Srad can by re-written by,

           mass radiative stopping power ------------------------- [4431b]

where Brad is a slowly varying function of Z and Ei. The mass radiative stopping power Srad is proportional to (NAZ2/A), that indicates a proportionality with the atomic number Z of the matter and the initial total energy Ei of the light charged particle as shown in Figure 4431.

Mass radiative and collision stopping powers for electrons in water (H2O), aluminum (Al) and lead (Pb) shown with red and green curves, respectively, against the electron kinetic energy.

Figure 4431. Mass radiative and collision stopping powers for electrons in water (H2O), aluminum (Al)
and lead (Pb) shown with red and green curves, respectively, against the electron kinetic energy. Adapted from NIST.

 

 

 

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