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E Schüle

Publications and source records attributed to E Schüle.

7 recordsLinked to original sources
PubMed2006

Determination of the recombination correction factor kS for some specific plane-parallel and cylindrical ionization chambers in pulsed photon and electron beams.

It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.

Biophysics↗
PubMed2004

Air density correction in ionization dosimetry.

Air density must be taken into account when ionization dosimetry is performed with unsealed ionization chambers. The German dosimetry protocol DIN 6800-2 states an air density correction factor for which current barometric pressure and temperature and their reference values must be known. It also states that differences between air density and the attendant reference value, as well as changes in ionization chamber sensitivity, can be determined using a radioactive check source. Both methods have advantages and drawbacks which the paper discusses in detail. Barometric pressure at a given height above sea level can be determined by using a suitable barometer, or data downloaded from airport or weather service internet sites. The main focus of the paper is to show how barometric data from measurement or from the internet are correctly processed. Therefore the paper also provides all the requisite equations and terminological explanations. Computed and measured barometric pressure readings are compared, and long-term experience with air density correction factors obtained using both methods is described.

Air↗
PubMed2002

The use of plane-parallel chambers in electron dosimetry without any cross-calibration.

Current dosimetry protocols from AAPM, DIN and IAEA recommend a cross-calibration for plane-parallel chambers against a calibrated thimble chamber for electron dosimetry. The rationale for this is the assumed chamber-to-chamber variation of plane-parallel chambers and the large uncertainty in the wall perturbation factor (p(wall)60Co)pp at 60Co for plane-parallel chambers. We have confirmed the results of other authors that chamber-to-chamber variation of the investigated chambers of types Roos, Markus, Advanced Markus and Farmer is less than 0.3%. Starting with a calibration factor for absorbed dose to water and on the basis of the three dosimetry protocols AAPM TG-51, DIN 6800-2 (slightly modified) and IAEA TRS-398, values for (p(wall)60Co)Roos of 1.024 +/- 0.005, (p(wall)60Co)Markus of 1.016 +/- 0.005 and (p(wall)60Co)Advanced Markus of 1.014 +/- 0.005 have been determined. In future this will permit electron dosimetry with the above-listed plane-parallel chambers having a calibration factor N(D, w)60Co without the necessity for cross-calibration against a thimble chamber.

Calibration↗
PubMed2001

Electron dosimetry based on the absorbed dose to water concept: a comparison of the AAPM TG-51 and DIN 6800-2 protocols.

The dosimetry protocols DIN 6800-2 and AAPM TG-51, both based on the absorbed dose to water concept, are compared in their theoretical background and in their application to electron dosimetry. The agreement and disagreement in correction factors and energy parameters used in both protocols will be shown and discussed. Measurements with three different types of ionization chambers were performed and evaluated according to both protocols. As a result the perturbation correction factor P(60Co)wall for the Roos chamber was determined to 1.024 +/- 0.5%.

Algorithms↗
PubMed2000

[Veterinary service and supervision of equine competitions].

Because of the growing interest in animal health and welfare in breeding and sport--specially in the horse--the regulation of the German Riding Association (FN) was updated. The result--the LPO 2000--refer more functions to the veterinarian. At first the permanent presence of the vet is necessary, at second he controls the correct, new installed vaccination against influenza-virus. The functions of vet-check, general horse-control and doping are wide up in number and consultation. For this the veterinarian must decree about much experience and good preparation. The organisations of the veterinarians of the countries and the FN work together to develop the knowledge and competence in horse-sport for a better protection.

Animal Husbandry↗
PubMed1981

[Investigations on contrast values in mammography (author's transl)].

Measurements of the spectral distribution of x-rays using a Si(Li)-detector form the basis for an investigation into contrast values provided by molybdenum and tungsten tubes in mammography. In order to evaluate contrast, the intensity of the characteristic radiation and of the brems rays were related to anode kV and thickness of section; the spectral intensity was then calculated for small calcium inclusions in soft tissues. For average tissue thickness (4 cm.) and an anode working at 30 kV, the molybdenum tube with a molybdenum filter is significantly better than a tungsten tube. With increasing size of breast, hardening of the radiation also increases, until for practical purposes contrast is determined by the brems rays alone. At this stage there is only little difference between the molybdenum and tungsten spectrum, and in the resultant contrast.

Humans↗