Development of a motorized system for the characterization of the RQR reference x-ray beams at the KFSHRC's SSDL using an extrapolation chamber.

An extrapolation chamber of type Böhm 23392, used for the dosimetry of RQR beam qualities at the Secondary Standard Dosimetry Laboratory of King Faisal Specialist Hospital, is presented. A computer-based motorized system consisting of a stepping motor coupled to the chamber's built-in micrometer screw was designed to expedite the measurements process, giving a linear relationship between the number of motor steps and the chamber depth with a Coefficient of Determination (COD) equal to 0.9990. The extrapolation chamber along with the motorized system was used to determine the extrapolation curves. The slope of the extrapolation curves, measured for the eight RQR beam qualities with a relative uncertainty between 0.17% and 0.58%, varies linearly with the beam quality expressed in terms of HVL, with a COD between 0.9995 and 1.0000.

Establishment of ISO 4037-1 X-ray Narrow-Spectrum Series at SSDL of Algiers.

The aim of this work was to develop some X-ray qualities recommended by the International Standardization Organization (ISO) in its standard ISO 4037-1. X-ray qualities corresponding to narrow-spectrum series were established, determined their characteristics and found good agreement with those of reference X-ray beam qualities [difference between first half-value layer (HVL1) < 5% for all qualities]. Acceptable results have also been obtained for second half-value layer (HVL2). The production of X-ray spectra corresponding to developed X-ray qualities with Monte Carlo code PENELOPE (PENetration and Energy Loss Of Positrons and Electrons) was simulated. The characteristics [HVL1, HVL2, homogeneity coefficient (HC) and mean energy (Emean)] of simulated spectra have been calculated and compared to those of measured spectra at Physikalisch-Technische Bundesanstalt taken as reference spectra. The obtained results showed a good agreement between simulated and measured spectra (differences in HVL1, HVL2, HC and Emean were 1.7, 1.44, 0.44 and 1.3%, respectively). The comparison between simulated and measured spectra by calculating the conversion coefficients from air kerma to the personal dose equivalent, hpk(10), and to the ambient dose equivalent, hk*(10), was supplemented. The comparison between the calculated quantities (hpk(10) and hk*(10)) for the two X-ray spectra series showed a good agreement (the maximum difference was <0.4% for hpk(10) and <0.3% for hk*(10)). Furthermore, the percentage depth dose produced in water by simulated and measured spectra was investigated and a good agreement was found between the obtained curves. The established X-ray qualities have been fully characterised (measurement and Monte Carlo simulation). These X-ray beams can be used for calibration of radiation protection instruments and for reference irradiations.

Effect of background and transport dose on the results of the personal dose equivalent Hp(10) measurements in photon fields obtained during the intercomparison 2013 of the African region.

As part of the intercomparison on the measurement of personal dose equivalent Hp(10), jointly organised by the International Atomic Energy Agency and the Algerian Secondary Standard Dosimetry Laboratory, for the African region, up to 12 dosemeters were added to the packages of the 28 participants to evaluate the background and transport dose (BGTD), received by the dosemeters before and after their irradiation at the SSDL (environmental irradiations, scanning process at the airports, etc.). Out of the 28 participants, only 17 reported the corresponding BGTD measured values, which lied between 0.03 and 0.8 mSv. The mean measured value of BG was (0.25±0.14) mSv, which is significantly high compared with the lowest dose value used in the intercomparison exercise. The BGTD correction shifted the overall results of the intercomparison from an overestimation of dose (∼8 % before applying BGT dose correction) to an underestimation of dose (-9 % after correction). The measurement protocol and the detailed analysis of the results and applied corrections are discussed in this paper.

Intercomparison 2013 on measurements of the personal dose equivalent Hp(10) in photon fields in the African region.

An intercomparison exercise on the measurement of personal dose equivalent Hp(10) was jointly organised by the International Atomic Energy Agency and the Nuclear Research Centre of Algiers through its Secondary Standard Dosimetry Laboratory in the African region. This intercomparison exercise was aimed at verifying the performance of the individual monitoring services of the participants in order to assess their capabilities to measure the quantity Hp(10) in photon (gamma and X ray) fields helping them to comply with dose limitation requirements. The scope of this intercomparison was aimed at passive dosemeters, which determine the personal dose equivalent in photon radiation fields, mainly for thermoluminescence and optically stimulated luminescence dosemeters. Twenty-seven countries from the Africa region and from outside Africa participated in this exercise. The intercomparison protocol, including the preparation of the dosemeters and the irradiation procedures, is described and the results are presented, analysed and discussed.

Optimum parameters of TLD100 powder used for radiotherapy beams calibration check.

External audit of the absorbed dose determination from radiotherapy machines is performed using Lithium fluoride (LiF) TLD-100. Optimal parameters needed to obtain highly accurate dosage from LiF powder was investigated, including the setup of the Harshaw 4000 reader. A linear correspondence between the thermoluminescent signal and the mass of the powder was observed, demonstrating that the dose can be evaluated with small samples of powder. The reproducibility of the thermoluminescence dosimeter (TLD) readings obtained with up to 10 samples from 1 capsule containing 160 mg of powder was around 1.5% (1 standard deviation [SD]). The time required for the manual evaluation of TLDs can be improved by 3 readings without loss of accuracy. Better reproducibility is achieved if the capsules are evaluated 7 days after irradiation using a nitrogen flow of 300 cc/min.

Calibration of plane parallel ionization chambers: a new service for secondary standard dosimetry laboratories?

This paper presents the results of calibration of PTW Markus and NACP ionization chambers following the procedures outlined in the TRS 381 International Atomic Energy Agency code of practice. According to this dosimetry protocol, calibration of plane parallel chambers follows 2 methods. The first method uses a high-energy electron beam and consists of comparing the plane parallel chamber with a cylindrical chamber whose N(D,air) calibration factor, traceable to cobalt-60 (60Co), is known, while the second method applies to a 60Co gamma beam whose air kerma rate is known at the calibration point. As the second method is generally applied in Secondary Standard Dosimetry Laboratories, the consistency of calibrations free in-air and in a water phantom has been studied. A close agreement is shown between the 2 methods (the calibration factors differ by at most 0.98%). These results lead to the conclusion that either of the 2 calibration methods can be used, provided that the correction factors given by the TRS 381 code of practice are applied.