X-ray targets
From MedPhysWiki
- In comparison with the range R of electrons of a given kinetic energy KE in the target material, targets are divided into two main groups: thin and thick.
- A thin target has a thickness much smaller than R, while the thickness of a thick target is on the order of R.
- For thin target radiation, the energy radiated is proportional to the product (KE)Z, where Z is the target atomic number. The intensity versus photon energy (photon spectrum) is constant from 0 to KE, and 0 for all energies above KE.
- A thick target may be considered as consisting of a large number of superimposed thin targets. The intensity I(hν) of a thick target spectrum is expressed as:
I(hν)=CZ(KE−hν),
where
C is a proportionality constant and hν is the photon energy.
- X-rays are used in diagnostic radiology for diagnosis of disease and in radiation oncology (radiotherapy) for treatment of disease.
- X-rays produced by electrons with kinetic energies between 10 keV and 100 keV are called superficial x-rays, with electron kinetic energies between 100 keV and 500 keV orthovoltage x-rays, and with electron kinetic energies above 1 MeV megavoltage x-rays.
- Superficial and orthovoltage x-rays are produced with x-ray tubes (machines), while megavoltage x-rays are most commonly produced with linacs and sometimes with betatrons and microtrons.
- Typical thin and thick target bremsstrahlung spectra originating from 100 keV electrons striking a thin and thick target, respectively, are shown in Fig. 5.1.
