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No abstract available

[en] Replacement batteries for the widely used 'Farmer-Baldwin Sub-standard x-ray Dosemeter' (Farmer 1955), manufactured by Baldwin Industrial Controls, of Dartford, Kent, have become expensive and difficult to obtain, resulting in a number of such units being unnecessarily taken out of service. This note describes how the relatively simple addition of a DC-DC inverter can drastically reduce the maintenance costs of the instrument (MK2 version) by powering it from three commonly available 1.5 V cells, type U2 (IEC type R20). The function of the various controls on the instrument is not affected in any way. (author)

[en] Former measurements of ionization current produced in moist air by X rays led to propose a variation curve for W (mean energy expended in air per ion pair formed) as a function of the amount of water vapor in air. This curve is used here to predict the ionization current for a cavity chamber exposed to γ rays. The predictions are in agreement with measurements recently made in two other laboratories

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[en] A cavity theory is used to relate the dose deposited in the cavity sensitive volume of the detector) to that in the surrounding medium which may be of different atomic number or composition. Burlin proposed a general cavity theory to include all cavity sizes. The Burlin theory ignores all secondary-electron scattering effects which results in large discrepancies in dose to the cavity compared with the experimental results in high atomic number media. Kearsley proposed a new general cavity theory which includes secondary-electron scattering at the cavity boundary. The Kearsley theory showed excellent agreement with experimental results for ⁶⁰Co γ-rays ut poor correlation for 10 MV x-rays. The Kearsley theory has numerous parameters and the magnitude of the input parameters is arbitrary; therefore the dose to the cavity depends on the choice of parameters. We have developed new cavity theory which includes secondary-electron backscattering from the medium into the cavity. The strengths of this proposed theory are that it contains few parameters and a methodical way of determining the magnitude of the parameters experimentally. The proposed theory gives better agreement with experimental results in lithium fluoride thermoluminescence dosimeters or ⁶⁰Co γ-rays and 10 MV x-rays in aluminium, copper and lead than do the Burlin and Kearsley cavity theories. (author)

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[en] The principal items of the agenda were relating to: progress reports from the Laboratories, comparison between absorbed dose calibration standards and between exposition calibration standards (national calibration standards, humidity corrections for cavity chambers, quality of the radiation to be used in the comparisons), measurements in various fields (protection, industrial radiations and very high dose rates), physical quantities and unities and comparison between activity, power and exposition measurements. In appendix, description is given of the calorimeters used by some national Laboratories for measuring absorbed doses, together with two reports of air-walled chambers

[en] The fast neutron therapy facility at the University of Washington has been in routine clinical use for 25 years. 50.5 MeV protons produce neutrons in a beryllium target mounted on an isocentric gantry. Beam shaping is accomplished with a 40-leaf collimator. Dosimetry measurements for treatment planning and calibration are performed with tissue equivalent ion chambers. A layered phantom of alternating Solid Water and Plastic Water slabs has been developed for rapid dose verification measurements. The neutron field in the room has been used for radiation testing of electronic components.

[en] Analysis of the charge collected at several voltages (0.11, 0.19, 0.32, 0.39, 0.41) in the dose rate range studied reveals that the ion collection efficiency results obtained by the two-voltage and extrapolation methods agree with those derived by using single-voltage data, empirically deduced constant and ion chamber dimensions in the Boag theory for a cylindrical chamber and pulsed radiation. This reiterates that, when a fixed voltage ionometric system is used for dose calibrations at therapy levels, the problem of charge recombination loss can be handled satisfactorily. In a saturation condition, linear behaviour between the collection efficiency and the dose rate can be used to correct the measured dose. (author)