| Fundamentals of metrology |
| Generation of defined pulsed photon radiation fields now possible |
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In dosimetry for radiation protection in pulsed fields of ionising radiation, problems occur when the use of electronic radiation protection dosemeters is prescribed. As a reaction, PTB has set up the world's first facility for the generation of pulsed X-ray radiation in which the physical parameters of the radiation pulse can be adjusted. This pulsed X-ray facility was developed in close cooperation with Siemens on the basis of a modern medical standard product. This facility will for the first time enable the testing of dosemeters for measurements in pulsed radiation fields. |
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| Stroboscopic Imaging with Thermal-Neutrons |
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A multi-frame gated optical imaging system for time-resolved neutron radiography was developed. It will be used for energy selective imaging in pulsed beams (e.g.Bragg edge radiography) or as a stroboscopic imaging system for thermal-neutron radiography of dynamic processes. First results of its evaluation at the ANTARES facility of the Munich research reactor FRM 2 are presented. |
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| Retrospective determination of the statistical contribution to the uncertainty of Monte Carlo simulated nanodosimetric distributions |
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When deterministic dosimetric quantities, such as the depth-dose profile, are calculated using Monte-Carlo methods, additional auxiliary counters have to be scored in the simulation to allow the determination of the statistical uncertainty contribution. On the contrary, in the Monte-Carlo simulation of stochastic quantities, like e.g. nanodosimetric ionisation cluster size distributions, the statistical uncertainty contribution can be derived from the simulation results by an alternative and less CPU-intensive approach. |
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| Absolute Determination of the Activity of 228Th |
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At PTB, activity measurements on 228Th solutions have for the first time been carried out by means of liquid scintillation counting and used within the scope of the comparison in the International Reference System (SIR). |
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| PTB’s thermal neutron reference field at the Research Reactor FRG-1 of GKSS ceases to exist |
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In 2008 - after an operating time of more than 50 years - it was decided to decommission the research reactor FRG-1 of the GKSS 2010 (GKSS News of October 2008). The reactor was officially closed down on June 28, 2010. The reactor was decommissioned in view of the restructuring of neutron research in Germany, focussed on the FRM II in Munich. |
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| Activity determination and decay data of 113mCd |
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The activity of 113mCd was determined with two liquid scintillation counting methods with small uncertainties. By combining the procedure with measurement results from gamma spectrometry, the photon emission probability of the 264 keV transition could - for the first time - be exactly determined. The half-life of the isotope, too, was redetermined with improved uncertainty. |
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| In the focus of attention: thoron |
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Whether in Asia, Europe or Latin America: An ever increasing number of geological and epidemiological studies are turning their attention to the short-lived radon isotope Rn-220 (half life T½ = 55 s) - also called "thoron" - which has so far hardly received any consideration. At present, the newly developed detector systems used can be traceably calibrated only at PTB: Since 2010, the primary standard for the thoron activity concentration - the thoron emanation measuring set-up (TEM) - has been available to customers and is almost continuously booked up. |
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| Setting-up of a Low-Level Radon Reference Chamber |
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In order to calibrate measurement devices for the activity concentration of Rn-222 in air below 1000 Bq/m3, a low-level radon reference chamber is currently being set up: It covers a traceable volume (0.5 m3) for the generation of the reference atmosphere, a device for the transfer of defined activities and the development of a high-sensitivity transfer standard. |
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| Homogeneity of thoron fields |
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In a cooperation with the Bundesamt für Strahlenschutz (Federal Office for Radiation Protection), mathematical simulations (method: Finite Elements based on the measurement of the turbulent transport processes) of a thoron distribution were compared with measurements of the associated thoron activity concentration in the thoron progenies chamber. |
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| Investigations on the energy resolution of spectrometers |
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By means of deconvolution procedures it is possible to resolve structures in a spectrum which are finer than the instrument resolution of the spectrometer. A new procedure now allows this property (which is called "super-resolution") to be determined quantitatively for the first time for a scintillation spectrometer which is used for plasma diagnosis. This procedure is also of significance for other applications. |
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| Calorimetric determination of kQ factors for ionization chambers in photon radiation fields of small size |
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The ionization chambers used in dosimetry for radiation therapy are usually calibrated at 60Co radiation in the measurand absorbed dose to water. If used at other radiation qualities, e.g. at higher photon energies, the change of the response of the ionization chamber is taken into account by means of the energy-dependent kQ factor. Both - the calibration factor and the kQ factor - relate to a field size of 10 cm x 10 cm. Modern irradiation devices, e.g. medical linacs for IMRT, tomotherapy or cyberknife devices use, however, considerably smaller radiation fields. For dosimetry under these radiation conditions, it must be ensured that the original kQ factors of the ionization chambers used are still valid. With the aid of a water calorimeter, the energy-dependent kQ factors of ionization chambers of the type NE2561 for 6 MVx and 10 MVx photon radiation were determined up to field sizes of 3 cm x 3 cm. Within the achieved standard measurement uncertainty of approx. 0.4 %, no change of the kQ factors with the field size was observed. |
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| Neutron Activation of Molybdenum Isotopes |
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The effective cross sections for neutron activation of diverse molybdenum (Mo) isotopes were measured in the neutron energy range between 7 MeV and 15 MeV. |
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| Nanodosimetric measurements with deuterons |
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The stopping power of a substance depends on the type charge state and energy of the ionizing particle being stopped. The stopping power is identical for different ions of the same charge and identical velocities. The first moment of the frequency distribution of the size of ionization clusters - the mean ionization cluster size M1(Q) - is proportional to the stopping power. Therefore, M1(Q) should also be identical for ions which are isotopes (i.e. with a different mass number A, but an identical atomic number Z) if the charge state and the particle velocity are the same. The comparison of the mean ionization cluster size M1(Q) for the measured frequency distribution of the ionization cluster size for primary proton and deuteron beams of different particle velocities shows - for both gases - a comparable dependence on the particle velocity. Compared to the values for protons, the measurement data for deuterons are, however, shifted systematically towards smaller values. |
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| Simulation of nanodosimetric ionization cluster size distributions with Geant4-DNA |
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As a result of the Geant4-DNA project, a second Monte Carlo program for nanodosimetric simulation calculations is now available in addition to the track structure program developed at PTB. For a series of beam qualities, the parameters of the nanodosimetric track structure were calculated by means of the two programs and compared with each other. |
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| Verification of Monte Carlo simulations for dosimetry in radiation therapy |
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Monte Carlo calculations enable the simulation of electron and photon transport through matter. Based on the simulations, among others, the (mean) energy can be determined which is deposited within a certain volume during the passage of the particles. In the field of radiation therapy, the correctness of such Monte Carlo simulations is particularly important, since they provide the possibility of determining the dose for treatment planning more accurately. |
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| Digital Data Acquisition for Spectrometry with a High-resolution Diamond Detector |
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Commercially available detectors made of monocrystalline diamond offer the potential for applications in fusion research. With a newly developed fast current amplifier combined with a digital data acquisition system, it is possible to perform measurements at extremely high neutron fluence rates. Measurements with monoenergetic neutrons and high-energy charged particles confirm that this measuring system is suitable for high-resolution spectrometry. |
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| Total electron-scattering cross sections of pyrimidine |
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The total electron-scattering cross sections of pyrimidine, the core constituent of two of the four DNA nucleic bases, were determined experimentally in the energy range between 20 eV and 1 keV. |
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| Differential Elastic Electron-Scattering Cross Sections of Trimethyl Phosphate |
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The cross sections for elastic electron scattering in trimethyl phosphate were determined experimentally for electron energies between 20 eV and 1 keV and compared with theoretical calculations. Hence, the elastic electron scattering cross sections are now known for both constituents of the DNA backbone. |
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| First more realistic simulation of the ionization cluster generation in DNA segments |
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Total, differential elastic and double differential inelastic electron scattering cross sections of tetrahydrofuran have been measured at PTB and were included in the PTB Monte-Carlo program for track structure simulation. First simulation results based on these cross sections indicate that previous the biological damage to DNA is overestimated when the cross sections of water are used instead. |
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| Neutron source strength of a 228Th gamma testing source for the BOREXINO experiment |
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For the BOREXINO experiment in the Laboratori Nazionali del Gran Sasso (LNGS), a 228Th gamma testing source is required which may show only a very low neutron emission. Such a source, prepared by the Max Planck Institute for Nuclear Physics, Heidelberg, and by other partners, was investigated at PTB. The measurement of the neutron source strength has shown that it meets the condition for being used at the LNGS. |
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| Metrology for economy |
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| Metrology for society |
| Quality Assurance for Radiation Therapy in Belgium Based on Alanine/ESR dosimetry |
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In Belgium, a project started this year for quality assurance in radiotherapy, the so-called BeldART project (Belgian dosimetry audits in radiotherapy). The dosimetry measurement system employed by the Belgian group located at the NUTEC centre of the XIOS Hogeschool in Diepenbeek, Belgium, is based on the detection of radiation-induced free radicals in alanine by electron spin resonance (ESR). Methods and software were adapted to the special requirements within the framework of a collaboration with the PTB. Parts of the measurement system used were developed at PTB, e.g. the probe holder for the spectrometer and the software for the data evaluation.
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| Characterisation of the radiation fields of commercial radiation therapy instruments |
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For the two clinical accelerators "Elekta Precise" which are available at PTB, the radiation fields of the photon qualities of 6 MV and 10 MV were successfully simulated and experimentally verified. For 25 MV, 15 MV, 8 MV and 4 MV the preparations are underway. Thus, the radiation fields for the calibration of dosimeters are exactly known. |
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| The half-life of 79Se |
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Within the scope of a cooperation of several institutes, the half-life of the long-lived isotope 79Se could be determined with a clearly improved uncertainty. PTB has contributed in particular by activity measurements performed with the aid of liquid scintillation counting. |
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| Completion of the world’s largest accelerator facility for dosimetry in radiation therapy |
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After a construction period of two years and a test phase of approx. one year, the world’s largest electron accelerator facility for dosimetry in radiation therapy has started normal operation. On a useful area of approx. 1000 m2, three accelerators cover all experimental requirements of dosimetry. The photon radiation fields of clinical practice can be realized as well as well-defined electron beams for basic research. The facility is equipped in such a way that both the number and the kinetic energy of the electrons hitting the respective experiment, can be determined with utmost accuracy, i. e. with relative measurement uncertainties below 10-3. |
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| Energy Dependence of the Response of Storage Foils |
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Besides surgery and chemotherapy, radiation therapy is a method which is frequently used to treat cancer. Today, it is used with at least half of all cancer patients. By using modern irradiation methods, patients can be treated in such a way that practically only the tumour tissue is irradiated with the desired dose and surrounding healthy tissue is mostly spared. |
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| First Calibration of a Secondary Standard for 192Ir Radiation in the Unit of Absorbed Dose Rate to Water |
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The German Standardisation Committee "Radiology" has decided to use, as a matter of principle, the measurand "absorbed dose to water" for calibrations of the dosimetric systems employed in radiation therapy. In a special field of radiation therapy - i.e. in brachytherapy - dosimetry is, however, currently still based on the characterisation of radiation sources using the measurand "air kerma". Within the scope of a European research project, a well-type ionisation chamber – similar to those used to measure the dose rate of medical radiation sources in hospitals – has been calibrated in the unit absorbed dose rate to water for the first time.
All in all, this leads to lower uncertainties for planning and determining the dose to be applied to a patient. |
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| Renewal of the measuring devices: relocation of radon metrology |
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Radon metrology at PTB moves to another location: After 20 years of successful work in the setting-up, investigation and development of new procedures, the laboratory area so far used is becoming too small. The extension of radon metrology in the past few years from radon-222 to radon-220 (thoron) and, recently, to the sector of low-level measurements, has brought about an increase in measuring devices.
In the basement of the new building - the renovated Elster Geitel Building - a new radon standard chamber RNK-II with a volume of approx. 21 m3 and a partly renewed thoron progenies chamber TFK-II with a volume of approx. 6 m3 have been established.
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| First success in the INS project "Pulsed Radiation in Radiation Protection" |
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Within the scope of the programme "Innovation with Standards (INS)", funded by the German Association for Electrical, Electronic and Information Technologies (Deutsche Kommission Elektrotechnik Elektronik und Informationstechnik) of DIN and VDE (DKE), the project "Pulsed Radiation in Radiation Protection" has been approved. The aim of this project is to develop an innovative concept for the standardization and testing of radiation protection dosemeters for the field of pulsed radiation and to prepare an international standard from it. |
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| Characterization of a Miniature X-ray Tube with the Medipix2 Detector |
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The use of a miniature X-ray device for intra- or post-operative irradiation has increasingly established itself as an alternative to the radioactive sources used today in brachytherapy, the so-called "seeds". An advantage is that the local irradiation is electrically regulated and is limited in time. Thus, no radioactive sources must remain permanently in the body, as is usually the case in brachytherapy with LDR (low dose rate) seeds. The dose applied by means of a miniature X-ray facility strongly decreases with distance so that the tumour tissue situated directly at the applicator surface receives a high dose, whereas the healthy tissue situated further away is spared. |
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| Preliminary Study for the Construction of a Direct-reading Dosimeter for Astronauts |
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In 2007, the European Space Agency (ESA) started developing a direct-reading dosimeter for astronauts. PTB was involved in a preliminary study dedicated to the conceptual construction of a dosimetric system in the International Space Station (ISS). |
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| International affairs |
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| Additional information |
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