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Scientific news from division 6

News 2013

Fundamentals of metrology

For dose measurement in clinical practice, ionization chambers are used which are calibrated to indicate the absorbed dose to water in a 60Co radiation field. If such a dosemeter is used in a high-energy photon or electron field of a clinical linac, the change in the response of the dosemeter has to be taken into account by applying a radiation quality correction factor kQ. For seven types of...

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In radiotherapy, one differentiates between external radiotherapy and internal radiotherapy - the latter being called brachytherapy. In brachytherapy (Greek "brachys" = short, close), the tumour is irradiated directly by implanting small radioactive sources (so-called "seeds") into the patient. The seeds are placed inside or close to the tumour. The advantage of this form of therapy is that...

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In radiotherapy, one increasingly relies on irradiation with small fields and with fields that can be adapted to the tumour profile such as, e.g., in intensity-modulated radiotherapy (IMRT). This poses particular challenges to dosimetry, since methods have to be developed to be able to measure the dose distribution of these fields with high spatial resolution. Due to their simple handling and the...

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The number of CT examinations has more than doubled in Germany since 1996. In 2010, 61 % of the collective effective dose of the population could be attributed to X-ray examinations for CT imaging. This statistic shows how important CT dosimetry has become.

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The XENON Dark Matter Project is an experiment which takes place in the Gran Sasso underground laboratory and is geared to searching for WIMPs (Weakly Interacting Massive Particles), a variant of Dark Matter. Determining precisely the emission rate of a neutron source used in this experiment could clarify discrepancies.

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Metrology of economy

Currents from ionization chambers lie in the range from less than a femtoampere up to a few nanoamperes and the most reliable way of determining them is to measure the charge. Such an instrument capable of measuring the charge with several measuring ranges and an input bias current of less than 0.3 fA is not commercially available and has therefore now been developed. For quality assurance...

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Metrology of society

Radon trägt nach neuesten Erkenntnissen gleichauf mit der Medizin am stärksten zur Strahlenbelastung der Bevölkerung bei. Im Hinblick auf die geplante EU-weite Absenkung der Referenzwerte, ausgelöst durch die Neubewertung des Radons seitens der International Commission on Radiological Protection (ICRP), ist in der PTB eine neuartige Anlage zur Kalibrierung von Radon-Messgeräten entwickelt worden,...

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Neutron resonance radiography is a technique to measure the distribution of certain light elements (C, N, O, H) in large-volume samples. WINBUGS, a program using Bayesian Monte Carlo methods, was used for the reconstruction of the element distribution from experimental and simulated data sets and has been successfully tested with the aid of radiographic experiments and simulations.

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In medicine, the use of medical linacs is constantly increasing to treat tumours by means of radiotherapy. Due to the high photon energy they generate, an intense scattering radiation field occurs also outside of the primary beam. This scattering radiation field, which leads to an additional, undesired exposure rate, was determined by means of special ionization chambers and personal dosemeters at...

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Within the scope of the European Metrology Research Programme (EMRP), PTB is coordinating the research project "BioQuaRT: Biologically weighted Quantities in Radiotherapy". Together with partners from 6 countries and with funds amounting to 3.5 million euros over a period of 3 years, the project is aimed at advancing the development of a metrological basis for the consistent quantification...

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The neutron monitor AGREM, developed at PTB, has been tested in different pulsed radiation fields and compared with other neutron monitors. Whereas commercial monitors exhibited a saturation behaviour with increasing dose in the pulse, the indication of PTB's monitor increased, in all cases, in a linear manner with the dose.

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At the request of the Ministry of the Environment, Energy and Climate Protection of Lower Saxony, measurements were carried out in the centre of the town of Gorleben. Data from measurement hut No. 5, which is located approx. 2 km from the transport cask storage facility, have shown that exclusively neutrons from cosmic radiation contribute to the ambient dose equivalent.

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International affairs

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