Ion recombination in ionization chambers is usually considered as a side effect, which influences the accuracy of the determination of the absorbed dose. This is generally true for volume recombination, but not always for initial recombination, i.e. the recombination which occurs between the ions created in the same track of a single ionizing particle or resulting from a single ionization event...

The percentage depth dose in the build-up region and the surface dose for the 6-MV photon beam from a Varian Clinac 23EX medical linear accelerator was investigated for square field sizes of 5 × 5, 10 × 10, 15 × 15 and 20 × 20 cm(2)using the EGS4nrc Monte Carlo (MC) simulation package. The depth dose was found to change rapidly in the build-up region, and the percentage surface dose increased p...

Response of a micro volume (0.01 ml) ionization chamber has been studied with pulsed proton beams which are used for clinical purposes and has been compared with those of some JARP ionization chambers (0.6 ml). All chambers used had been calibrated by standard 60Co beams at the Electrotechnical Laboratory (ETL) and exposure calibration factors, Nx, were obtained on advance. Two methods are used...

The Delta(4) diode array phantom (Scandidos, Uppsala, Sweden) was evaluated for verification of segmental intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) on an Elekta linear accelerator (Crawley UK). The device was tested for angular sensitivity by irradiating it from 36 different gantry angles, and the responses of the device to various step-and-shoot s...

Several national and international protocols have been established for the dosimetry of x-ray beams used in radiotherapy. For the very low energy x-rays (0.035 mm1.0 mm Al HVL) only two codes are available: the UK IPEMB Code of Practice and the German standard, DIN 6809 Part 4. The measurement of very low energy x-ray beams is normally performed with parallel plate ionization chambers calibrate...

We present studies of Heliumand Argon-filled ionization chambers exposed to intense neutron fluxes from PuBe neutron sources (En = 1− 10 MeV). The sources emit about 10 neutrons per second. The number of ion pairs in the chamber gas volume per incident neutron is derived. While limited in precision because of a large gamma ray background from the PuBe sources, our results are consistent with th...

A high energy particle beamline is described which is capable of transporting a high intensity electron beam to potentially occupied areas. Ionization chamber measurements of electron beam intensity are described together with the ion chamber calibration and necessary corrections. The results of the measurements are compared with a Monte Carlo calculation of the electron intensity. (Submitted t...

An X-ray calorimeter has been used to determine the to ta l energy t ransported by bremsstrahlung beams with maximum photon energies between 18.2 and 170 Mev. The measurements from two experiments have been used to calibrate an aluminum ionization chamber for routine determinations of to ta l beam energy. The calibrations are compared with calibrations of the same chamber made with a scintillat...