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| Fundamentals of metrology |
| Determination of the activity and photon emission probabilities of antimony-124 |
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Within the scope of the international EUROMET Project 907, PTB's "Unit of Activity" Working Group successfully met the challenge of realizing the unit of activity of 124Sb and determining 41 photon emission probabilities. At the same time, this project gave the impetus to the establish-ment of new procedures and the updating of existing ones. |
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| Determination of the half-life of the primordial isotope samarium-147 |
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In cooperation with the Technical University of Munich, PTB determined the half-life of the long-lived radionuclide samarium-147, which is important for geochronology. The uncertainty could be significantly reduced as compared to earlier measurements. |
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| Calorimetric determination of the absorbed dose to water in the near field of 192Ir brachytherapy sources |
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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: GammaMed 12i; initial activity: approx. 370 GBq) was modified for use with 192Ir brachytherapy sources so that the absorbed dose rate to water in the near field of the source could be determined at a minimum distance of 24.35 mm. Thereby, a relative standard measurement uncertainty of smaller than 1 % could be achieved. |
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| First measurements of the absorbed dose to water for interstitial brachytherapy |
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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 transport phenomena need not be taken into account in the Monte Carlo calculations. |
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| Digital data acquisition system for spectrometry with scintillation detectors |
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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 of 10. |
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| Initiative for the improvement of the data set for electron transport in water |
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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 Department 6.6 and GEANT4-DNA). This work was performed in cooperation with Mrs. Marion Bug (Centre for Medical Radiation Physics, University of Wollongong) and represents the first step of an extensive initiative which will allow the data set for the electron transport in water to be improved and these data to be made available to the scientific community. |
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| Particle track reconstruction in the measurement of the ionization clusters distribution with the aid of an ion-counting nanodosimeter |
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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 the primary electrons, the particle track reconstruction plays an important part in data analysis. It is, therefore, important to upgrade the ion-counting nanodosimeter with a suitable system for the detection of the particle track structure and the triggering of the electrons. |
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| Double differential inelastic electron scattering cross sections of DNA components |
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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 particles in the tissue during the passage of ionizing radiation, are indispensable. In view of this fact, the double differential inelastic electron scattering cross sections were experimentally determined as a function of the scattering angle and of the secondary electron energy of tetrahydrofuran (C4H8O), which has a structure that is almost identical to deoxyribose. |
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| Experimental testing of the scalability of track structures of ionizing radiation in nanometric volumes |
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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 of the ionizing particles in the respective medium.
At the PTB accelerator facilities, nanometric spectra were measured in monoenergetic proton and alpha particle beams in the energy range from 0.1 MeV to 20 MeV. C3H8 and N2 served as target gases.
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| Spectrometry of X-ray radiation fields |
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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 for all anode voltages occurring in the spectra series. These unfiltered spectra allow - by subsequent numerical filtering with any filters desired – any desired X-ray spectra to be generated. |
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| Determination of the mass-energy absorption coefficients of air in the hard X-ray region |
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From the results of several comparison measurements carried out on the free-air ionisation chamber PK100 by means of the cryogenic radiometer SYRES I which was further developed for the hard X-ray region by Working Group 7.13 "X-ray Radiometry", the mass energy absorption coefficient of air for photons having energies between 10 keV and 90 keV has been experimentally determined. |
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| Comparison of the ionometric and the calorimetric determination of the absorbed dose to water at Co-60 gamma radiation |
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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 the graphite cavity ionisation chamber into the absorbed dose rate to water. |
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| Metrology for economy |
| Measurement of cross sections for the elastic and inelastic scattering of neutrons on lead, bismuth and tantalum in the energy range from 2 MeV to 4 MeV using the 15N(p,n) reaction as neutron source |
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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 other data. Above 3 MeV, there are significant deviations from the inelastic scattering cross sections calculated from photoemission cross sections for the lowest excited states.
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| Metrology for society |
| Thoron progeny chamber commissioned for calibration |
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Within the scope of a biennial third-party project, the thoron progeny chamber was fully equipped and is now available for the realisation of the unit Bq/m3 of 220,222radon and 220,222radon progenies. |
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| Now published: "Modern routine methods and quick procedures for the determination of Sr-89 and Sr-90 in environmental monitoring" |
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During nuclear fission, the radionuclides Sr-89 (T½ = 50.5 d) and Sr-90 (T½ = 28.4 a) 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 the dose coefficients of the nuclides are different, an assessment of a radiation exposure of persons requires an exact distinction between the activity concentrations of Sr-89 and Sr-90. |
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| Results of the periodic comparison measurements of beta extremity dosimeters from 2002 to 2007 |
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At various working places involving ionising radiation, e.g. in medicine and industry, finger ring dosimeters are used to check whether the legal dose limits are not exceeded. The dosimeters for the measurement of beta radiation have been submitted to a yearly quality check by PTB for 6 years. All types of dosimeters used in Germany have passed these checks up to now. |
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| Richard Glocker Building dedicated |
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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 encompass the providing of standards of the unit "gray" for the absorbed dose to water, as well as the testing, improving and developing of dosimeters and dosimetric procedures for clinical practice. The focus of the dosimetric fundamental research is the investigation of the interaction between radiation and various materials, including biological systems.
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| NAVIDOS has started its measuring operation on a Lufthansa Airbus A340 since August 15, 2008 |
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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 on the area dose rate at flight altitudes. In addition, the measurements serve to ensure the quality of the dose determination for the flying personnel. |
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| Photon reference sources for the calibration of surface contamination monitors |
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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 standard 8769. |
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| Feasibility study for a low-level radon reference chamber concluded |
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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 activity concentration. |
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| Chamber-to-chamber variation of the energy dependence of the response of ionization chambers |
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For 10 ionization chambers of the type PTW 30013 and 10 of the type PTW 31013, individual responses in the high-energy photon radiation fields of PTB’s linear accelerator were determined relative to the response in the 60Co radiation field. The variation in the obtained kQ factors of all chambers amounts to less than 0.3 % (related to the mean value of all kQ factors). The tests carried out offer some potential for further improvement of the data contained in the DIN 6800-2 standard. |
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| Determination of the radial anisotropy of the radiation field of 192Ir and 60CO brachytherapy sources |
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192Ir and 60Co 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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| PTB Alanine Dosimetry System for Quality Assurance in Belgium |
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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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| Neutron monitor for pulsed radiation |
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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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| Energy-Selective Neutron Imaging for Detection of Contraband in Luggage and Cargo |
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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 Radiography (FNRR) is one of the most promising methods for fully automatic detection and identification of contraband concealed in luggage and cargo. This is related to the fact that neutrons probe the nuclear properties of the absorber and exhibit highly characteristic structure in their various interaction cross sections with different isotopes and at diverse neutron energies.
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| Bayesian analysis of spectrometric measurements in high-energy neutron fields |
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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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| International affairs |
| VERMI Workshop on "Source Preparation in Radionuclide Metrology" |
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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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| PTB hosted the 5th International ICRM-LLRMT Conference |
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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 radioactivity measurements. |
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| Determination of the activity of 139Ce and 88Y within the scope of international comparison measurements |
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For the purpose of comparisons, the "Unit of Activity" Working Group sent radioactive solutions of the nuclides 139Ce and 88Y 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 liquid scintillation counting according to the CIEMAT/NIST and TDCR method; they support the new and further development of these measurement methods at PTB. |
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| International comparison of the primary standards for the realization of the unit of absorbed dose to water of beta-brachytherapy sources |
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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 are used in eye tumor radiation therapy. The comparison showed an agreement of the results within the scope of the uncertainties. |
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| Additional information |
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