For the upgrade of existing dosimetric early warning networks in Europe spectrometric detectors based on CeBr3, LaBr3, SrI2, and CdZnTe are investigated as possible substitutes for the current ...detector generation which is mainly based on gas filled detectors. The additional information on the nuclide vector which can be derived from the spectra of γ-radiation is highly useful for an appropriate response in case of a nuclear or radiological accident.
The measured γ-spectra will be converted into ambient dose equivalent H*(10) using a method where the spectrum is subdivided into multiple energy bands. For each band the conversion coefficients from count rate to dose rate is determined. The derivation of these conversion coefficients is explained in this work. Both experimental and simulative approaches are investigated using quasi-mono-energetic γ-sources and synthetic spectra from Monte-Carlo simulations to determine the conversion coefficients for each detector type. Finally, precision of the obtained characterization is checked by irradiation of the detectors in different well-known photon fields with traceable dose rates.
•Spectro-dosimeters can replace existing dosimeters of early warning networks.•They can be characterized experimentally and with Monte-Carlo simulations.•Precision is similar or even better than that of a conventional dosemeter.•Potential to serve as advanced dosimetric secondary standards in the future.
Data on risk factors for etiologic subtypes of ischemic stroke are still scant. The aim of this study was to characterize stroke subtypes regarding risk factor profile, outcome, and current treatment ...strategies.
We analyzed data from 5017 patients with acute ischemic stroke (42.4% women, aged 65.9+/-14.1 years) who were enrolled in a large multicenter hospital-based stroke data bank. Standardized data assessment and stroke subtype classification were used by all centers.
Sex and age distribution, major risk factors and comorbidities, recurrent stroke, treatment strategies, and outcome were all unevenly distributed among stroke subtypes (P<0.001, respectively). Cardioembolism, the most frequent etiology of stroke (25.6%), was particularly common in the elderly (those aged >70 years) and associated with an adverse outcome, a low rate of early stroke recurrence, and frequent use of thrombolytic therapy and intravenous anticoagulation. Large-artery atherosclerosis (20.9%), the most common cause of stroke in middle-aged patients (those aged 45 to 70 years), showed the highest male preponderance, highest rate of early stroke recurrence, and highest prevalence of previous transient ischemic attack, current smoking, and daily alcohol consumption among all subtypes. The highest prevalence of hypertension, diabetes mellitus, hypercholesterolemia, and obesity was found in small-vessel disease (20.5%), which, in turn, was associated with the lowest stroke severity and mortality.
Our results foster the concept of ischemic stroke as a polyetiologic disease with marked differences between subtypes regarding risk factors and outcome. Therefore, studies involving risk factors of ischemic stroke should differentiate between etiologic stroke subtypes.
A new generation of dosemeters, based on the scintillators LaBr3, CeBr3 and SrI2, read out with conventional photomultipliers, to be used in the field of environmental gamma-radiation monitoring, was ...investigated. The main features of these new instruments and especially their outdoor performance, studied by long-term investigations under real weather conditions, are presented. The systems were tested at the reference sites for environmental radiation of the Physikalisch-Technische Bundesanstalt. The measurements are compared with that of well characterized classical dose rate reference instruments to demonstrate the suitability of new spectrometers for environmental dose rate monitoring even in adverse weather conditions. Their potential to replace the (mainly Geiger Müller based) dose rate meters operated in about 5000 European early waning network stations as well as in environmental radiation monitoring in general is shown.
•A new generation of dosemeters, based on the scintillators was investigated.•Their suitability for environmental dose rate monitoring is demonstrated.•Their potential to replace dose rate meters is shown.•With an adopted evaluation software they can have almost ideal dosimetric properties.
After the Chernobyl nuclear power plant accident in 1986, all Member States of the European Union have installed area dose rate monitoring networks so that radiological incidents can be detected ...quickly. However, the different technical approaches and procedures led to inconsistencies in the area dose rate data. In the last 15 years, the working group 'Environmental Radiation Monitoring' of the European Radiation Dosimetry Group (EURADOS) has performed six pan-European intercomparison exercises for detector systems operated in national dosimetric early warning networks. These intercomparisons aimed at the harmonisation of area dose rate measurements of radiation monitoring stations in Europe. The intercomparisons revealed differences in technical properties of the dose rate monitoring systems as well as in the calibration and measuring methods that led to deviations of measured dose rate values by a factor of 5 or more under the same measuring conditions. As a result of the intercomparisons, the accuracy of dose rate measurements could be improved considerably. Further progress in metrologically correct measurements of area dose rates in the natural environment and necessary steps towards a metrologically sound pan-European system for environmental radiation monitoring will be discussed.
For measuring the quantity ambient dose equivalent, H*(10), various passive photon and neutron dosemeters have been newly developed and are used in particular for the monitoring of nuclear facilities ...in the radiation field of the natural ambient radiation. Since 2005, the Physikalisch-Technische Bundesanstalt (PTB) has been performing intercomparisons to study fundamental properties and the long-term behaviour of area dosemeters under real environmental conditions, i.e. the accuracy of photon and neutron measurements performed in the complex natural radiation field. Measuring bodies from four European countries were the participants, including Germany. The goal was, on the one hand, quality assurance for existing passive dosemeters and measurement procedures and, on the other hand, the experimental investigation of whether the requirements of the appropriate standards and guidelines are met in practical use.
The responses of electronic dose rate meters were investigated in a large volume radon chamber at PTB in a wide range of radon activity concentrations. The measurements were conducted under ...controlled laboratory conditions and measured dose rate data are compared with Monte-Carlo simulations. Consequences concerning environmental monitoring are described. A further result is that the direct measurement of the dose rates produced by radon progeny in air is hardly possible in radon atmospheres with high activity concentrations, because the major contribution of measured dose rates is produced by radon progeny on the housing of the dose rate instruments. The latter effect largely depends on the ability of surfaces to absorb radon progeny. The Monte-Carlo simulations revealed quantitative results on the height of the single contributions to the total dose rate measured in the radon chamber. When environmental dose rate measurements are performed, the plate-out on detectors can be neglected.
PTB operates an Underground laboratory for DOsimetry and spectrometry (UDO) in the Asse salt mine at a depth of 490 m below the ground. The ambient dose equivalent rate at UDO is only 2 nSv h−1. ...Therefore, UDO is well suited for dosimetry at low dose rates as well as for other low-level measurements. UDO provides the only photon calibration facility worldwide for calibrations at low dose rates (comparable to those in the natural environment and even below), which are traceable to primary standards. Photon fields are generated by using radioactive sources of the following nuclides: 241Am, 57Co, 137Cs, 60Co and 226Ra. The dose rates and mean photon energy values at the reference point of this calibration facility were calculated analytically after performing calibration measurements using a secondary standard. This procedure ensures for the traceability of the reference dose rate values to PTB's primary standards. The mean photon energy of each spectrum was calculated with respect to the different quantities air kerma and ambient dose equivalent, respectively. The assessment of the uncertainties of the basic properties of the photon calibration fields will be described.
To investigate muon-induced nuclear reactions leading to the production of radionuclides, targets made of C
9H
12, SiO
2, Al
2O
3, Al, S, CaCO
3, Fe, Ni, Cu, Gd, Yb and Tl were irradiated with 100 ...and 190 GeV muons in the NA54 experimental setup at CERN. The radionuclide concentrations were measured with accelerator mass spectrometry and γ-spectroscopy. Results are presented for the corresponding partial formation cross-sections. Several of the long-lived and short-lived radionuclides studied are also produced by fast cosmic ray muons in the atmosphere and at depths underground. Because of their importance to earth sciences investigations, calculations of the depth dependence of production rates by fast cosmic ray muons have been made.
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