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H M Kramer

Publications and source records attributed to H M Kramer.

11 recordsLinked to original sources
PubMed2004

Calibration of dosemeters used in mammography with different X ray qualities: EUROMET project no. 526.

The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrated.

Calibration↗
PubMed2002

The role of de-excitation electrons in measurements with graphite extrapolation chambers.

A method is described for determining the absorbed dose to graphite formedium energy x-rays (50-300 kV). The experimental arrangement consists of an extrapolation chamber which is part of a cylindrical graphite phantom of 30 cm diameter and 13 cm depth. The method presented is an extension of the so-called two-component model. In this model the absorbed dose to graphite is derived from the absorbed dose to the air of the cavity formed by the measuring volume. Considering separately the contributions of the absorbed dose to air in the cavity from electrons produced in Compton and photoelectric interactions this dose can be converted to the absorbed dose to graphite in the limit of zero plate separation. The extension of the two-component model proposed in this paper consists of taking into account the energy transferred to de-excitation electrons, i.e. Auger electrons, which are produced as a consequence of a photoelectric interaction or a Compton scattering process. For the system considered, these electrons have energies in the range between about 200 eV and 3 keV and hence a range in air at atmospheric pressure of 0.2 mm or less. As the amount of energy transferred to the de-excitation electrons is different per unit mass in air and in graphite, there is a region, about 0.2 mm thick, of disturbed electronic equilibrium at the graphite-to-air interface. By means of the extension proposed, the x-ray tube voltage range over which a graphite extrapolation chamber can be used is lowered from 100 kV in the case of the two-component model down to at least 50 kV.

Computer Simulation↗
PubMed2001

Mixed high energy photon and electron radiation fields for calibrating radiation protection dosemeters.

According to ISO 4037-3, calibrations of radiation protection dosemeters with photon radiation of energies above 3 MeV are performed under conditions of charged particle equilibrium. No information is provided concerning how to determine the response of dosemeters to radiation fields in the more general case when these conditions are not fulfilled. This paper deals with the production of mixed high energy photon and electron fields characterised by a lack or an excess of charged particles relative to conditions of equilibrium and describes a new procedure for the dosimetry in such fields. Through variation of the charged particle fluence fraction with respect to a nearly constant photon fluence, Hp(10) and H'(10) values varied by up to a factor of 1.74. The above mentioned basic study was utilised in the recent IAEA intercomparison (Co-ordinated Research Project 1996-1998) and EURADOS 'trial performance test' (1996-1998) for individual monitoring of photon radiation in testing response characteristics of individual dosemeters in non-charged particle equilibrium conditions.

Air Pollution, Radioactive↗
PubMed2001

Response of radiation protection dosemeters in mixed high-energy photon and electron radiation fields.

The response of radiation protection dosemeters in terms of the phantom-related operational quantities Hp(10) and H'(10.0 degrees) was measured for personal and area monitoring systems in mixed high-energy electron and photon radiation fields with energies up to 7 MeV. Using mixed radiation fields composed of different fractions of charged particle and photon fluence, three conditions were produced at the point of measurement: charged particle equilibrium (CPE) (a), a lack (b) and an excess (c) of charged particles relative to the conditions of CPE. Personal and area dosemeters of different types were investigated under conditions (a)-(c). A large variability of the response of the different dosemeter types was observed. The results are presented and discussed.

Air Pollution, Radioactive↗
PubMed2000

Experimental determination of practical peak voltage.

In diagnostic radiology the practical peak voltage was initially derived by postulating that, for a given combination of X-ray tube and contrast geometry, a constant X-ray tube voltage should produce the same low level contrast as an arbitrarily pulsating X-ray tube voltage. It has been shown previously that the practical peak voltage can be properly defined as a weighted average of the X-ray tube voltage. Up to now the concept of practical peak voltage was based entirely on the results of calculations. The present paper describes the experimental investigations for measuring and comparing the contrast-equivalent X-ray tube voltage and practical peak voltage derived from an invasive measurement of the time-dependent X-ray tube voltage. Within the experimental uncertainties, the results demonstrate the mutual equivalence of the practical peak voltage and the contrast-equivalent X-ray tube voltage.

Algorithms↗
PubMed1998

The practical peak voltage of diagnostic X-ray generators.

A new quantity termed the "practical peak voltage" is proposed. This quantity is derived by equating the low level contrast in an exposure made with an X-ray tube connected to a generator delivering any arbitrary wave form, to the contrast produced by the same X-ray tube connected to a constant potential generator. Out of the great number of possible contrast configurations one is selected as being suitable for diagnostic radiology. By means of an eigenvalue problem a direct link is established between the electrical quantity X-ray tube voltage and the practical peak voltage which was initially defined through the properties of the X-ray field. It is shown that the spread in total X-ray tube filtration as encountered in medical diagnostic radiology can influence the result of a measurement of the practical peak voltage only marginally.

Electricity↗
PubMed1984

Arrhythmias in mitral valve prolapse. Effect of selection bias.

To assess the contribution of bias in subject selection to the prevalence of arrhythmias in cases of mitral valve prolapse (MVP), we compared ambulatory arrhythmias in 63 patients with MVP and 28 symptom-matched control subjects. All subjects were in sinus rhythm. Mean 24-hour heart rate of the prolapse population was lower than that of the control group (76 v 82 beats per minute). Mean atrial premature complex (APC) density per 1,000 beats (0.9 v 0.7 for patients with MVP and control subjects, respectively) and mean ventricular premature complex (VPC) density per 1,000 total beats (1.2 v 1.5) did not differ between groups. Small differences between groups in APC and VPC complexity did not reach statistical significance. Our findings suggest that, compared with similarly symptomatic controls, patients with MVP do not have as high an excess prevalence of arrhythmias as previously believed.

Adult↗