Performance of a prototype of an extrapolation minichamber in various radiation beams

An extrapolation minichamber was developed for measuring doses from weakly penetrating types of radiation. The chamber was tested at the radiotherapeutic dose level in a beam from a 90Sr+90Y check source, in a beam from a plane 90Sr+90Y ophthalmic applicator, and in several reference beams from an X-ray tube. Saturation, ion collection efficiency, stabilization time, extrapolation curves, linearity of chamber response vs. air kerma rate, and dependences of the response on the energy and irradiation angle were characterized. The results are satisfactory; they show that the chamber can be used in the dosimetry of 90Sr+90Y beta particles and low-energy X-ray beams.