N. Michielsen

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.

Influence of the type of CD case on the track density distribution in CDs exposed to thoron.

A novel approach for retrospective thoron (Rn-220) measurements in buildings was recently proposed. It employs CDs/DVDs as detectors, in which the alpha-tracks formed by thorons progeny Po-212 are analyzed. Compact disks and DVDs that had been stored in their cases are suitable, because the case provides a fixed and reproducible geometry of the Po-212 source. Since the measurement and calibration procedures involve analysis of different pieces of the disk, it is important to test the homogeneity of the track density over the disk area. This report presents results of such a study, in which disks in different containers were exposed to thoron. In almost all disks, the track density was inhomogeneous, increasing significantly near the holes in the container through which thoron could enter. However, as demonstrated, in disks regularly used and randomly rotated in their containers, the track density is expected to homogenize. It is concluded that the homogeneity of the tracks should be tested in disks exposed to thoron in homes and should be estimated or compensated in calibration exposures.

A new thoron atmosphere reference measurement system.

A new thoron reference ((220)Rn) in air measurement system is developed at the LNE-LNHB with the collaboration of the IRSN. This measurement system is based on a reference volume with an alpha detector which is able to directly measure thoron and its decay products at atmospheric pressure. In order to improve the spectrum quality of the thoron progenies, we have applied an electric field to catch the decay products on the detector surface. The developed system is a portative device which can be used to measure reference thoron atmosphere such as the BACCARA chamber at IRSN (Picolo et al., 1999). As this system also allows the measurement of radon ((222)Rn) in air, it was validated using the radon primary standards made at the LNE-LNHB. This thoron measurement system will be used, at IRSN, as a reference instrument in order to calibrate the thoron activity concentration in the BACCARA facility.

Measurement of the unattached radon decay products with an annular diffusion channel battery

Publisher Summary This chapter describes a new method to determine the size distribution of short-lived radon decay products of nanometer size. To eliminate certain problems induced by the instruments classically used, a new device has been built. It consists of five Annular Diffusion Channels of different lengths equipped with a reference filter; they operate in parallel. During sampling, the nanometer-range particles are partly trapped by diffusion onto the inner channel walls, whereas the others are collected on downstream filtering membranes. A prototype ADC battery to measure size distribution of short-lived radon decay products in nanometer form was designed to have a better selectivity than current devices. From activity data measured in each unit, the size distribution of nanometer size radon daughters can be reconstructed through a non-linear inversion method, EVE. The size range of concern is within 0.3 and 5 nm and corresponds to diffusion coefficients in the range 0.2–22 mm 2 s −1 .

What we can learn from measurements of air electric conductivity in 222 Rn-rich atmosphere: Air Electric Conductivity

Electric conductivity of air is an important characteristic of the electric properties of an atmosphere. Testing instruments to measure electric conductivity ranging from ~10-13 to 10-9 S m-1 in natural conditions found in the Earth atmosphere is not an easy task. One possibility is to use stratospheric balloon flights; another (and a simpler one) is to look for terrestrial environments with significant radioactive decay. In this paper we present measurements carried out with different types of Conductivity Sensors in two 222Rn-rich environments, i.e. in the Roselend underground tunnel (French Alps) and in the IRSN BACCARA chamber. The concept of the Conductivity Sensor is based on the classical time relaxation method. New elements in our design include isolation of the sensor sensitive part (electrode) from the external electric field and sensor miniaturization. This greatly extends the application domain of the sensor and permits to measure air electric conductivity when the external electric field is high and varies from few tens of V m-1 to up to few tens of kV m-1. This is suitable to propose the instrument for a planetary mission. Two-fold objectives were attained as the outcome of these tests and their analysis. First was directly related to the performances of the Conductivity Sensors and the efficiency of the Conductivity Sensor design to shield the external electric field. Second objective aimed at understanding the decay mechanisms of 222Rn and its progeny in atmosphere and the impact of the enclosed space on the efficiency of gas ionization. This article is protected by copyright. All rights reserved.

Development of a primary thoron activity standard for the calibration of thoron measurement instruments

The LNHB and IRSN are working on a reference atmosphere for thoron ((220)Rn) instrument calibration. The LNHB, as the national metrology institute for activity measurement in France, has to create a new thoron reference standard in order to estimate with accuracy the thoron concentration of a reference atmosphere. The measurement system presented in this paper is based on a reference volume using an alpha detector, which is able to measure thoron and its decay products to define the thoron concentration of a thoron reference atmosphere. This paper presents the first results with this new system using a well-known radon ((222)Rn) atmosphere and a thoron ((220)Rn) atmosphere.

Determination of 218Po nanometer size distribution in a controlled environment by two new systems

Publisher Summary This chapter focuses on the determination of 218 Po nanometer size distribution in a controlled environment by two new systems. An intercomparison with two new diffusion battery systems based on a new technique using an Annular Diffusion Channel for one Laboratory and a Cylindrical Diffusion Tube for the other, was carried out under controlled conditions in a large radon chamber. However, it can be observed that the experimental penetration data obtained from the two diffusion batteries is always slightly lower when radon concentration and relative humidity are both high. The estimated distributions using three different deconvolution algorithms do not clearly show a difference in the size distribution indicating a low sensitivity of these inversion systems. Therefore, it would be interesting to carry out a set of measurements in more extreme conditions, such as in the range from 10 to 90% for relative humidity and from 2 to 80 kBqm −3 to analyze the influence of radon concentration level and relative humidity to the 218 Po nanometer size distribution.