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Scientific news from division 6

News 2008

From a water-equivalent material, a new extrapolation chamber was manufactured with the aid of which the absorbed dose to water can be determined in the phantom in the absence of a cavity. Thereby, the charging quantities generated at different plate distances are converted into the absorbed dose to water by means of Monte Carlo calculations. The conditions are selected in such a way that electron...

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The measurand in the dosimetry of brachytherapy sources is the absorbed dose rate to water, at a distance of 1 cm from the centre of activity of the radiation source, vertical to the source axis. With the aid of a water calorimeter, the desired measurand can be determined directly and with a small standard measurement uncertainty. As a first step, a water calorimeter already existing at PTB (type:...

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In the modelling of nanometric spectra, a cylinder of liquid water serves as a replacement for a DNA segment. This is why a procedure is required to rescale the nanometric spectra measured in gaseous media in such a way that they are equivalent to the nanometric spectra of a target of liquid water with nanometric dimensions. Such a scaling method is based on the ratio of the mean free path lengths...

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The uncertainties in the calculation of the ionization cluster generation by low-energy electrons in a material important to dosimetry depend to a very large extent on the quality of the ionization cross sections. To determine their influence, the ionization cluster generation by electrons in water was simulated with the aid of two different Monte Carlo programs (the Monte Carlo program of...

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The spectrometric determination of the energy dependence of the photon fluence is a substantial part of the characterization of the X-ray radiation fields realized in Department 6.6. For this purpose, the pulse height spectra of the radiation fields are measured and unfolded with an HPGe detector. In addition to the filtered spectra of the different spectra series, unfiltered spectra were recorded...

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Calorimetry and ionometry are two complementary methods for the realisation of the unit of absorbed dose to water at Co-60 gamma radiation. A comparison of the two methods yielded a significant difference of 1.4% ± 0.4%. The most probable cause of this is the literature values for the stopping power of electrons in graphite which are used for the conversion of the measured ionisation current of...

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Within the scope of a cooperation between Department 6.6 and the Loma Linda University Medical Center (LLUMC, San Bernardino, USA), the ionization cluster distribution for primary electrons was measured with the aid of an ion-counting nanodosimeter and compared with Monte Carlo simulations. The results show that due to the - compared to ions - very large scattering and wide angle distribution of...

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It is generally known that DNA is the radiation-sensitive target inside a cell and that the biological efficiency of ionizing radiation does not only depend on the absorbed dose but also on its track structure. For the calculation of such track structures, interaction cross sections between the DNA components and the electrons, which are in most cases released in large quantities as secondary...

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A digital data acquisition system developed by the ENEA (Ente per le Nuove tecnologie, l'Energia e l'Ambiente, Frascati) was put into operation and tested during utilization on the neutron reference fields of PTB's accelerator. Compared to the system used so far, spectrometric measurements can now be performed practically without quality losses for signal rates which are higher by up to a factor...

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Measurements of neutron scattering cross sections for lead, bismuth and tantalum in the energy range from 2 MeV to 4 MeV were carried out on PTB's time-of-flight spectrometer. The 15N(p,n) reaction was used for the production of monoenergetic neutrons. Differential and angle-integrated cross sections for the elastic and inelastic scattering could be determined with high precision and compared to...

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Ob ionisierende Strahlung, Umdrehungen, Durchflussmengen - alles, was sich in Impulsen ausdrückt, kann er zählen, und zwar schnell: der neu entwickelte Datenlogger der Physikalisch-Technischen Bundesanstalt (PTB). Dabei passt er mit seinen 9 cm x 6 cm x 2 cm in jede Hosentasche. An den kleinen Kasten können vier Geräte gleichzeitig angeschlossen werden und die vier schnellen unabhängigen Zähler...

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Most established X- and γ-ray methods for contraband and explosives detection in luggage and cargo depend critically on shape recognition and therefore on human operator skill. Furthermore, photon radiography only permits very limited differentiation among elements in the low-Z range and the latter can be rendered quasi undetectable by high-Z element shielding. In contrast, Fast-Neutron Resonance...

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After an extensive testing phase, the dosimetry system NAVIDOS, developed by PTB and Christian Albrechts University in Kiel, was installed by Lufthansa Technik in August 2008 on a Lufthansa Airbus A340-300 and put into operation on August 15, 2008. The aim of the measurements is to investigate the influences which solar activity, for example, or the change of the magnetic field of the Earth have...

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In cooperation with Nuclitec GmbH (formerly QSA Global GmbH), PTB is currently developing a measuring set-up for the characterisation of large-area photon reference sources for the calibration of surface contamination monitors. With the measuring procedures to be developed, the photon flux, the activity and the activity distribution of different sources are to be determined according to ISO...

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As radon measurement is currently becoming increasingly important in society (e.g. in the fields of health care, energy-saving measures and medical radioprotection), the setting up of a Low Level Radon Reference Chamber (LL-RRC) has been tested within the scope of a feasibility study. According to the present results, the unit can be realised with an uncertainty of 5 % (k=2) for this range of...

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Ir-192 and Co-60 brachytherapy sources show - in spite of their rotationally symmetric structure - a radial anisotropy of their radiation field vertical to the central axis of the sources which cannot be completely neglected. Since the beginning of the year 2008, this anisotropy has also been determined in the calibration of the sources and stated in the calibration certificate.

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Towards the end of this year, a copy of the PTB measuring system for dosimetry by means of alanine and electron spin resonance will be installed at the Belgian Xios Hoogeschool Limburg within the scope of a cooperation. This procedure is aimed at implementing a quality assurance system for dosimetry for modern radiation therapy forms such as IMRT for Belgium.

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At PTB, a new monitor for the measurement of pulsed neutron radiation has been developed, based on the detection of β- radiation from activity reactions on silver. PTB has applied for a patent for this development.

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The uncertainty of measurements made with an extended-range Bonner sphere spectrometer in high-energy neutron fields has been analysed by means of Bayesian methods. It was shown that the spectrum below approx. 1 MeV is well determined whereas the information from the measurements is not sufficient to determine the high-energy end of the spectrum with low uncertainty.

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With three new electron accelerators, PTB has expanded its measurement capabilites for dosimetry in radiation therapy. On 11th July 2008, Prof. Dr. Ernst O. Göbel and State Secretary Jochen Homann from the Federal Ministry of Economics and Technology officially dedicated, at the PTB site in Braunschweig, the Richard Glocker Building, which houses the accelerators.

The core tasks of the facility...

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During nuclear fission, the radionuclides Sr-89 and Sr-90 are generated with relatively high fission yield. After release, they can get into the environment and - due to the chemical similarity of strontium with calcium - into the human food chain and be stored in the bones. This is why Sr-90 with its effective half-life of 17.5 years is dose-relevant in particular for children (e. g. milk). As...

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From 22 to 26 September, PTB hosted the "5th International Conference on Radionuclide Metrology-Low-Level Radioactivity Measurement Techniques (ICRM-LLRMT)". The focal point of this conference was measuring, analysis and calibration methods for the exact determination of the smallest quantities of radionuclides, as well as international comparison measurements aimed at improving the quality of...

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For the purpose of comparisons, the "Unit of Activity" Working Group sent radioactive solutions of the nuclides Ce-139 and Y-88 to the international reference system SIR at the BIPM and has thus met its obligations emanating from the Mutual Recognition Arrangement (MRA). At the same time, these two nuclides are important for the testing and further development of computing models in the field of...

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In a cooperation with the National Institute of Standards and Technology (NIST) and the Nederlands Meetinstituut (NMi), the primary standards for the realization of the unit of the absorbed dose to water of beta brachytherapy sources were compared. The object of the comparison was the determination of the absorbed dose to water in the near field of a 106Ru planar source. Similar types of sources...

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A workshop on "Source Preparation in Radionuclide Metrology" was held at the PTB in the framework of the Virtual European Radionuclide Metrology Institute (VERMI). The event gave participants from the NPL, LNE-LNHB, IRMM and PTB the opportunity to exchange their experience in theory and in practice.

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