Use Of Ionization Chambers Research Articles

An investigation into the comparison between different dosimetric methods of measuring profiles and depth doses for dynamic wedges on a Varian 600C linear accelerator

Three dosimetric methods for commissioning the dynamic wedges on a Varian 600C linear accelerator operating at 4.7 MV were compared. The techniques involved the use of ionization chambers, X-ray verification film and solid state detectors. Ionization chambers gave the most accurate results, as expected, but data acquisition was very time consuming. Film dosimetry was found to have good spatial resolution for beam profiles, but problems were encountered with the acquisition of depth doses. Solid state detectors generally showed reasonable agreement with the ionization chambers.

Forward calorimetry in the upgraded UA1 experiment

The major improvement in the upgraded UA1 calorimetry at the S p pS is the general use of ionization chambers filled with tetramethylpentane (TMP) as a detection medium interspersed with uranium plates as absorber. To achieve overall uniformity of detection down to very small angles, an identical solution is proposed for the forward calorimetry. Forward calorimetry is essential for good total and missing energy measurement at high luminosity in view of the increasing rate of multiple collisions. Both designs for forward and very forward calorimeters are presented along with expected resolutions.

A clinical comparison of image quality and patient exposure reduction in panoramic radiography with heavy metal filtration

Laboratory and clinical studies with the use of rare earth intensifying screens and four different forms of heavy metal elements serving as additional beam filtration were performed for panoramic radiography to identify the most efficacious system. Balanced density images were evaluated for contrast indices, resolution, relative dose reduction, and subjective image quality. Clinical studies were performed with a standard calcium tungstate imaging system and the four most promising experimental imaging systems that showed improvement over the standard system. Dosimetric studies were performed with the use of ionization chambers and thermoluminescent dosimetry (TLD) dosimeters. Exposure reductions of 34% to 79%, depending on the anatomic site and the imaging system used, were achieved. Subjective image quality was evaluated and analyzed statistically. This study concluded that the use of a Kodak Lanex regular screen/T-Mat G film with either Lanex screen or yttrium added beam filtration results in reduced patient exposure in panoramic radiography while image quality is maintained or improved.

Part III preliminary surveillance of prospective site — Environmental considerations —

The environmental issues in the R-project are mainly considered from radiological safety point of view. Supposing a new experimental site for the program to be constructed in Toki Area, land and water surveys have been made since 1982 on the background radiation levels and radioactive material concentrations. Results of in-situ observations using instruments of various types are given and compared, such as TLD's (exposed for every three months), a pressurized ionization chamber, a NaI(Tl) detector in DBM mode, and a portable Ge detector. Also shown are the data from laboratory analyses of sampled materials in α- and γ-spectrometries, and neutron activation method. Tritium concentrations in river water samples have been quarterly measured with a liquid scintillation counter. These kinds of data will further be compiled to define the regional characteristics of the site environments. In relating to the expected radiation yields in the R-project, the importance of monitoring methods effective to pulsed radiation components is particularly emphasized. Possible use of ionization chamber and TLD's for this purpose is discussed in some detail with the preliminary application to the existing tokamak experiments on JIPP T-IIU.

Part III. Preliminary surveillance of prospective site — environmental considerations —

The environmental issues in the R-project are mainly considered from radiological safety point of view. Supposing a new experimental site for the program to be constructed in Toki Area, land and water surveys have been made since 1982 on the background radiation levels and radioactive material concentrations. Results of in-situ observations using instruments of various types are given and compared, such as TLD's (exposed for every three months), a pressurized ionization chamber, a NaI(Tl) detector in DBM mode, and a portable Ge detector. Also shown are the data from laboratory analyses of sampled materials in α- and γ-spectrometries, and neutron activation method. Tritium concentrations in river water samples have been quarterly measured with a liquid scintillation counter. These kinds of data will further be compiled to define the regional characteristics of the site environments. In relating to the expected radiation yields in the R-project, the importance of monitoring methods effective to pulsed radiation components is particularly emphasized. Possible use of ionization chamber and TLD's for this purpose is discussed in some detail with the preliminary application to the existing tokamak experiments on JIPP T-IIU.

A cautionary note on the use of ionization chambers for radiation dosimetry in different gas mixtures.

A cautionary note on the use of ionization chambers for radiation dosimetry in different gas mixtures.

Ionisation measurements and the derivation of Wn in acetylene and carbon dioxide irradiated with neutrons

The use of ionisation chambers for neutron dosimetry requires a knowledge of Wn, the mean energy loss per ion pair. Experimental measurements of the ionisation in acetylene and carbon dioxide have been made for monoenergetic neutron beams of mean energies 0.236, 0.554, 1.12 and 1.72 MeV. The neutron fluences were measured with a De Pangher long counter calibrated at the National Physical Laboratory, and spectra determined by the time-of-flight technique. The measurements are compared with calculations based on the work of Dennis. Ionisation values were computed using a program which calculates kerma and uses different empirical models to describe the energy dependence of the W value of heavy ions. For acetylene agreement to better than +or-8% was obtained between the measured ionisation values and the calculated values based on these models. Larger discrepancies of up to 25% were observed between the measured and calculated ionisation in carbon dioxide.

Continuous radon concentration monitoring

The use of ionization chambers to continuously monitor the concentration of radon dissolved in ground water is described. In one case, air is bubbled through the water sample to strip the radon into the chamber. In a second operating mode, the sample water itself is flowed through the chamber. Support electronics systems are described for remote and urban applications.

Dose conversion factors for use with ionisation dosemeters for 6 to 35 MeV electron beams

Abstract The use of high-energy electrons in cancer therapy has created a need for sensitive and accurate dosimetric techniques which are applicable to the measurement of electron beams. The most logical first step is to extend the use of ionisation chambers in order to measure high-energy photon and particulate beams. This article deals with a comparative study of chemical and ionisation systems. The method and results of an investigation to determine conversion factors for use with commercial ionisation instruments are reported. Some incidental findings in the use of ionisation chambers in electron dosimetry are also presented. Using a variable volume, parallel-electrode chamber, experimental evidence was obtained to substantiate the Bragg-Gray cavity nature of the thimble chambers used in routine clinical dosimetry. The conversion factors obtained for a Baldwin-Farmer and Victoreen instrument show good agreement with the theoretically calculated values. The electron dose conversion factors reported by ...

X-ray Measurements near High-Power Klystrons

The intensity and quality of the x-radiation outside the lead shielding around ultrahigh-frequency and S-band klystrons were measured as a function of high voltage, pulse frequency, and microwave power output by use of ionization chambers. Independent 20 percent increases in each variable gave, respectively, 8-, 1.2-, and 1.5-fold increases in the intensity, and 36, 1, and 4 percent increases in the mean energy of the x-rays.

The use of ionization chambers for the absorbed dose calibration of high energy electron beam therapy units

A system is proposed for high-energy electron-beam calibration using small calibrated thimble ionization chambers. It is suggested that D = R. N. C F when D is the dose in rad., R the chamber reading, N the exposure factor for 60Co and C F is the overall conversion factor dependent upon the mean energy of the primary electrons at the point of measurements. Two sets of experimental data involving several different makes of chambers are compared with theoretical calculations and excellent agreement is found within experimental limits. A set of C F factors is proposed for different initial-energy electrons when a standard calibration phantom is used.

Measurement of Peak Voltage of Diagnostic X-Ray Generators

The measurement of the voltage of diagnostic X-ray generators, using the characteristic radiation emitted by scattering foils, is discussed, and a rigorous definition of the generator voltage which just equals that of the K-absorption edge is put forward. Previous methods of defining this voltage are shown to be either wrong or subject to random variations of up to 10%. Experimental evidence using a scintillation counter and multi-channel analyser is given in corroboration. The use of ionization chambers is also discussed and it is shown that reasonable accuracy (±1%) can be obtained using a single chamber to detect the characteristic radiation.The need for a differential filter of the same material as the scattering foil is considered, and evidence is presented to show that it can be replaced by a primary beam filter of aluminium of suitable thickness for the kilovoltage range under consideration.

Use of ionization chambers filled with a dielectric liquid in radiation dosimetry

The response to γ-rays and neutrons of an ionization chamber filled with hexane in function of various parameters (inter-electrode distance, collecting voltage, dose rate) has been studied in order to realize a dosimeter which would take advantage from the ionization in liquids. It has also been made a comparison with the response of the same chamber filled with air. From the results obtained, the employ of ionization chambers filled with a dielectric liquid seems particularly promising in dosimetry.

Measurement of Beam Current of Electron Accelerator by the Use of Ionization Chamber

Measurement of Beam Current of Electron Accelerator by the Use of Ionization Chamber