Understanding Photodivision and Electrodivision in Electron Beam Oncology

[lavster]

Im reading a paper about use of electron beams in oncology and it says:

"The mechanism of neutron production in the region of electron beam energies under consideration is determined by photodivision of nuclei by bremsstrahlung photons and the small contribution of electrodivision by electrons".

what is photodivision and electrodivision? is this just fission induced by photons and electrons respectively? or is it a different process altogether?

thanks

 

[Bob S]

Usually, electron-beam oncology is by production of bremsstrahlung (photon) radiation, by stopping the electron beam in a high-Z (usually tungsten) target. High-Z collimators (also tungsten) are used to control the size and shape of the irradiated area. Tungsten is especially useful for a collimator because of its high density.

All elements have a photo-neutron cross section (γ,n) for producing free electrons. With few exceptions, the High-Z materials like tungsten have a lower threshold (6 to 8 MeV) and a higher "giant dipole resonance" peak neutron production cross section, sometimes over 1 barn per atom. This photo-neutron production greatly increases with electron-beam energies over 8-10 MeV, and effectively limits the electron beam energy used for electron-beam oncology. Usually, the direct electroproduction of neutrons is much smaller, when compared to the electron-bremsstrahlung-photoproduction channel..

See thumbnail of neutron yields vs. electron beam energy in thick bremsstrahlung targets. Note that only uranium has a higher photoneutron yield than tungsten.
From http://www.google.com/url?sa=t&sour...puG6CQ&usg=AFQjCNFDwgclxNI5B5_Li3phSoXsuzy69g

Bob S

 

[lavster]

excellent - thanks! :)