Development of 222Rn Emanation Sources with Integrated Quasi 2π Active Monitoring

Abstract

In this work, a novel approach for the standardization of low-level 222Rn emanation is presented. The technique is based on the integration of a 222Rn source, directly, with an α-particle detector, which allows the residual 222Rn to be continuously monitored. Preparation of the device entails thermal physical vapor deposition of 226RaCl2 directly onto the surface of a commercially available ion implanted Si-diode detector, resulting in a thin-layer geometry. This enables continuous collection of well resolved α-particle spectra of the nuclei, decaying within the deposited layer, with a detection efficiency of approximately 0.5 in a quasi 2π geometry. The continuously sampled α-particle spectra are used to derive the emanation by statistical inversion. It is possible to achieve this with high temporal resolution due to the small background and the high counting efficiency of the presented technique. The emanation derived in this way exhibits a dependence on the relative humidity of up to 15% in the range from 20% rH to 90% rH. Traceability to the SI is provided by employing defined solid-angle α-particle spectrometry to characterize the counting efficiency of the modified detectors. The presented technique is demonstrated to apply to a range covering the release of at least 1 to 210 222Rn atoms per second, and it results in SI-traceable emanation values with a combined standard uncertainty not exceeding 2%. This provides a pathway for the realization of reference atmospheres covering typical environmental 222Rn levels and thus drastically improves the realization and the dissemination of the derived unit of the activity concentration concerning 222Rn in air.

Metrology infrastructure for radon metrology at the environmental level

“…Since the mechanism causing the release of radon consists of a combination of two processes, on the one hand the recoil of the nuclei resulting from alpha decay and on the other hand the diffusion processes, the amount of radon released usually correlates with environmental parameters, such as relative humidity and temperature, since these influence the effective diffusion coefficient. To investigate these dependencies, novel sources have been developed at PTB with the metrological possibility of continuous determination of the emanation [8]. Thus, it can be shown that at low penetration depth of the ionimplanted 226 Ra, there is no measurable dependence of the emanation on the ambient humidity and only a small dependence on the temperature [9].…”

Beyond the State of Art: New Metrology Infrastructure for Radon Measurements at the Environmental Level

“…Since the mechanism that causes the release of radon consists of a combination of two processes, on the one hand the recoil of the nuclei as a result of alpha decay and on the other hand the diffusion processes, the amount of radon released usually correlates with environmental parameters, such as relative humidity and temperature, since these influence the effective diffusion coefficient. In order to investigate these dependencies, novel sources were developed at PTB with the metrological possibility of continuous determination of the emanation [8]. Thus, it could be shown that at low penetration depth of the ionimplanted 226 Ra there is no measurable dependence of the emanation on the ambient humidity and only a small dependence on the temperature [9].…”

Environmental Radioactivity Monitoring and Measurements: Radon and Thoron

“…Implementing large-scale radon monitoring networks to provide concentration data for environmental sciences and ensuring their comparability requires calibration techniques for radon monitors in this concentration range, which is one of the tasks of the EU traceRadon project. Mertes et al [ 8 ] presented a novel approach to standardizing low-level radon emanation. The technique was based on integrating the radon source directly with an -particle detector to facilitate the continuous monitoring of radon residues.…”