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Scientific news from division 6

News 2012

Fundamentals of metrology

Die Untersuchung von Umweltparametern auf der Marsoberfläche ist Ziel der "Mars Scientific Laboratory"-Mission (MSL), die von der NASA am 26. November 2011 von Cape Canaveral (Florida, USA) aus gestartet wurde. MSL ist ein neues Gefährt namens "Curiosity" (deutsch "Neugierde"), das zehn wissenschaftliche Instrumente an Bord hat, mit denen die chemische und geologische Zusammensetzung der dortigen...

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To guarantee the worldwide uniformity of dosimetry and the international recognition of PTB calibrations, PTB participated in the key BIPM-organized comparison BIPM.RI(I)-K6, in which the primary standards of PTB and of the BIPM for the realization of the unit "absorbed dose to water" were compared in high-energy photon fields on accelerators. The measurements for this comparison - for which the...

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Activity determinations were carried out on several solutions of the isotope Lu-177 which is used in nuclear medicine. Some measurements were realized within the scope of an international comparison in which PTB achieved the smallest measurement uncertainty. In addition, nuclide data such as photon emission probabilities and the half-life were determined.

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At the research accelerator for dosimetry in radiation therapy, an experiment for the absolute verification of Monte Carlo radiation transport calculations is carried out within the scope of a doctoral thesis. For this purpose, the electron energy must be determined as exactly as possible. For determination of the electron energy, a system based on the principle of magnetic spectrometry was...

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The international working group, consisting of 9 members, for the elaboration of an ICRU Report with regard to the topic of radon measurements met at PTB in April 2012. This report is to provide worldwide harmonized quality standards for radon measurements (Rn-222 and Rn-220, and their respective progeny) as well as for the handling of exposure determinations, up to a harmonized dosimetry system....

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PTB’s thoron emanation measuring facility (TEM) provides the only possibility worldwide to calibrate Rn-220 measuring instruments. The appurtenant emanation sources have been investigated with regard to their long-term stability for the first time. This investigation has shown significant trends whose origins cannot be clearly attributed yet.

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In order to calibrate measuring devices for the determination of the Rn-222 activity concentration in air in the range below 1000 Bq/m3 in a traceable way, a low-level radon reference chamber was set up. This chamber consists of a traced-back volume for the generation of the reference atmosphere, a facility for the generation and transfer of defined activity, and a highly sensitive transfer...

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To check the reliability of the dosimetry system based on alanine/ESR, a blind test was carried out with the support of the BIPM. At a standard uncertainty of approx. 0.4 %, the doses determined are only 0.12 % higher than was expected after a key comparison of the primary standards.

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Detectors made of synthetic single-crystal diamonds are suited as high-resolution neutron spectrometers for use in extreme neutron fluxes like the ones present in fusion facilities. In a measuring campaign at PTB’s ion accelerator facility, a procedure was tested which allows the response functions of the detector to be determined in the energy range relevant for fusion diagnostics, i. e. from 6...

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The joint research project "ACCIS", which was supported by BMBF, investigates a screening system for medium-sized freight units which is based on neutron- and gamma-radiation. With the two (neutron- and gamma-) imaging systems completed, a significant intermediate milestone has been attained.

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A device used to generate supersonic molecular beams from temperature-stable liquids has been developed for an apparatus serving to determine the absolute cross sections for the fragmentation of DNA constituents after electron or ion bombardment.

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Measured electron scattering cross sections of the DNA component pyrimidine have been implemented in the Monte Carlo code PTra. Track structure simulations show that the number of ionizations of pyrimidine significantly increases compared to water, which is conventionally used as a surrogate of DNA.

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The SNO+ detector is to be used to investigate diverse aspects of neutrino physics. The detector consists of a liquid scintillator tank of 12 m in diameter in which the neutrino-induced events are detected by approx. 10,000 photomultipliers. For the liquid scintillator, linear alkylbenzene (LAB) is used as a solvent, and 2,5-Diphenyloxazole (PPO) is used as primary scintillator. Within the scope...

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Metrology of economy

The FATAL (A modelling framework for Fault-Tolerant Asynchronous Logic) project is aimed at developing a simulation model for asynchronous logic which takes the impacts of radiation effects on the circuit into account. On the basis of this model, it shall in future be possible to develop asynchronous logic which is resistant to radiation effects.

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Metrology of society

Forty-eight participants from Germany, Austria, France and Switzerland gathered at the 7th LSC user meeting to obtain information and exchange their experiences on the latest developments in the field of liquid scintillation counting for activity measurements.

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Sophisticated radiochemical investigations have allowed Ca-41 to be extracted from nuclear material. The number of Ca-41 atomic nuclei contained in the material obtained was determined by means of thermal ionization mass spectrometry (TIMS). At PTB, the activity of the radionuclide was measured for the first time using the TDCR method. The half-life of the long-lived isotope Ca-41 was determined...

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Within the scope of the European Metrology Research Programme (EMRP) (www.emrponline.eu), the new 3-year project for dosimetry in radiotherapy "Metrology for radiotherapy using complex fields" was launched on 1 June 2012. Nine national metrology institutes, a university and 15 cooperation partners from industry, from hospitals and from research institutes are taking part in this project. The...

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In practical radiation protection, large-area sources with a known surface emission rate, a known activity and a good uniformity are required for the calibration of contamination monitors. At PTB, a procedure has now been developed to calibrate and comprehensively characterize also photon-emitting large-area sources. PTB is thus the only metrology institute worldwide which is able to calibrate...

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Within the scope of a comparison measurement between the DAkkS-accredited BfS laboratory and PTB, two radon-222 progeny atmospheres were compared by means of a transfer standard. The comparison took place in PTB’s new radon reference chamber and provided a good agreement within the accuracy required for accreditation.

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The multi-wire impulse ionization chamber, which has been developed as a transfer standard, has been calibrated in the large radon reference chamber with a primary standard and is now available to PTB for calibration operation.

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The International Commission on Radiological Protection (ICRP) has drastically lowered its recommended annual dose limit for the eye lens. Detailed calculations carried out at PTB show that there is a need for action with regard to the selection of suitable dosemeters, especially in the case of beta-radiation.

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The underground laboratory for dosimetry and spectrometry (UDO), which was operated by PTB at the Asse II mine for nearly 20 years, had to be closed down. It was possible to set up and commission a new underground laboratory (UDO II) at the 430 m level below ground in the Braunschweig-Lüneburg salt mine of the "european salt company" (esco) in Grasleben near Helmstedt.

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International affairs

The project aims to further international standardization in the field of pulsed radiation. To this end, PTB elaborated a draft for the international Technical Specification "ISO 18090-1 Radiological protection – Characteristics of reference pulsed radiation – Part 1: Photon radiation" which was internationally accepted.

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