The Farmer type ionization chambers are intended for the absolute dosimetry of photon and electron beams at therapy level dose rates. Furthermore, these chambers are suitable for dosimetry in proton fields and for depth dose measurements and field profile analysis. When calibrated accordingly, these chambers can be used to measure the quantities absorbed dose to water, absorbed dose to air, air kerma, or exposure in air, depending on the type and quality of radiation and the relevant code of practice. The FC65-G ionization chamber is intended for reference dosimetry and calibrations, while the FC65-P ionization chamber is intended for daily checks of treatment machines and for any other use in frequent routine application.

The chamber is designed preferably for the energy ranges of photons and electrons at medical accelerators. It can also be employed in X-ray beams with generating potentials from 70 kV and for gamma radiation of 137Cs and 60Co. The energy range of proton beams with available beam quality correction factors is between 50 and 250 MeV.