Physics
Physics Basics
Equipements
Flattening Filter
- To compensate for the lack of scatter at the edge of the field by deliberately designing a profile that increases toward the edges.
Radiation Detectors
All detectors make use of ionization and excitation processes.
Gas Ionization detectors
- ionization chambers
- Geiger-Mueller(G-M) counters
- Proportional counters
Basic parts!
- A chamber with fixed volume of gas
- gas can be air, methane
- chamber=probe
- Two electrodes ( positive and negative )
- When photons pass through the chamber ==> ion pairs produced ==> ionization current produced
- Because chamber is polarized ==> ions travel to the oppposite charged electrode
- Some ions recombine
- Collection efficiency is the fraction of charges actually collected
- Above 300volts —> ionization chamber region ( efficiency almost 100% )
Photons
Maximum Depth Dose
Try to imagine what happens when electron hit surface of any thing :
- At a very first layer —> Photon excite an electron
- This electron travels through its path which has a known range according to the energy it has acquired from the photon
- This electron range is the the depth of Dmax
- Let's say it has the energy of the photon
- As the electron travels though it's path, it excite secondary electrons…
- Until the end of the range of the primary electron, it reaches to it's equilibrium
- Electron equilibrium happens in a point/level in which energy loss is compensated by energy gained.
See Dmax
Electron
page revision: 13, last edited: 25 Nov 2011 16:51