G. Butterweck

Characteristics of the Neutron Irradiation Facilities of the PSI Calibration Laboratory

The neutron radiation fields of the Calibration Laboratory at Paul Scherrer Institute (PSI) are traceable to the national standards of the Physikalisch‐Technische Bundesanstalt (PTB) in Germany. A Berthold LB6411 neutron dose rate meter for neutron radiation is used as a secondary standard. Recently, a thorough characterization of the neutron irradiation fields of the 241Am‐Be and 252Cf sources by means of reference measurements and a detailed MCNPX simulation of the irradiation facility has been initiated. In this work, the characteristics of the neutron radiation fields are summarized and presented together with model equations and an uncertainty analysis. MCNPX results are shown for the 241Am‐Be source. A comparison of measured and simulated data shows an excellent agreement. From the simulation, valuable information about the neutron fields like the contribution of scattered neutrons in the fields and the energy spectra could be obtained.

Intercomparison exercise of calibration facilities for radon gas activity concentration

Publisher Summary International intercalibration and intercomparison exercises are used as an important tool to provide confidence in the capability of national metrology institutes and calibration laboratories. The quality systems of national institutes provide the basis for running intercomparisons, in this case, in the field of the radon activity concentration in air. Interchange of an electronic radon measuring instrument (intercomparison device) that demonstrated ruggedness during shipping in the past, was considered a convenient means for a relative comparison of radon reference atmospheres. Practical problems of measuring technique led to a restriction to the quantity of the radon activity concentration in the case of most radiation protection measurements. This leads to higher uncertainties in exposure and dose calculations, as well as in the risk estimations of epidemiology. Improvements in metrology and the extension of calibration capabilities worldwide to radon progeny measurement are therefore be of great practical importance.

Investigation of the stability of commercial neutron probes.

At the Paul Scherrer Institutes Calibration Laboratory, neutron reference fields are provided for the calibration of ambient and personal dose equivalent (rate) metres and passive dosemeters. To ensure traceability to the standards of the Physikalisch-Technische Bundesanstalt (PTB) in Germany, the neutron fields are characterised by means of a PTB-calibrated Berthold LB6411 neutron probe which is used as a secondary standard. The LB6411 detector suffers from an unstable, increasing dose rate reading in the order of up to +5 % (according to the manufacturers, this is due to a charging effect in the (3)He proportional counter). In a calibration, this instability is usually corrected for based on the reading obtained with a test source. In this work, the instability was investigated by means of measurements under irradiation with ambient dose equivalent rates up to 24 mSv h(-1) for up to 20 h and compared with the behaviour of an LB6419 and a Thermo Wendi-2 probe. The reading of the instruments was found to reach a plateau, e.g. it becomes stable after ∼90 min during irradiation with 10 mSv h(-1) neutrons. The plateau is reached faster for higher dose rates. This supports the interpretation as a charging effect in the proportional counter. The effect could also be duplicated in an irradiation with photons from a (137)Cs source. The decay time of the accumulated charge was found to be very long, i.e. the instrument showed a stable reproducible reading for up to 6 h after the plateau was reached. From these observations, a conditioning procedure was derived which ensures a stable operation of the instrument after an irradiation of the instrument preceding its use in the reference measurements.

In-vivo measurement of deposition and absorption of unattached radon progeny

Publisher Summary Exposure to airborne radon progeny in the domestic environment yields the largest source of exposure to ionizing radiation of the general public. The radiation protection principle of overestimating the risk rather than underestimating it has limitations when applied to sources of natural radiation. As the exposure to radon progeny concerns the total population of a country, a consensus has to be found between the justified wish of the people for protection against health risks and the financial expenditure and administrative effort necessary for protective actions. The choice of an action level for radon exposure plays an important part in the decision for remedial actions against elevated radon concentrations. Scientific research has the assignment to supply the fundamental knowledge for this choice. The present results together with literature data on the absorption of aerosol attached radon progeny show that the unattached fraction is absorbed at a faster rate into blood than the attached radon progeny. This results in the equivalent dose to the lung for a typical home being reduced by about 15%.