An inter-laboratory comparison of low-level measurements in ground-level aerosol monitoring

A new apparatus for on-site calibration of gamma dose rate monitors

In order to carry out on-site calibrations of environmental gamma dose rate monitors, a new irradiation apparatus was developed in this study. The apparatus mainly consists of a piece of ¹³⁷Cs source, a set of beam attenuators, and 3 built-in laser rangefinders, and it can be remotely controlled by using a laptop through WiFi network. With an activity of 4.6 × 10⁸ Bq of ¹³⁷Cs source, the reference air kerma rate could be adjusted from 0.26 μGy h^-1 to 140 μGy h^-1 by changing the calibration distance from 0.5 m to 5 m and using different beam attenuators (or none), and both the reproducibility and the homogeneity of reference radiation were better than 97%. The overall uncertainty of the calibration was estimated to be 6.5% (k = 2). Both the laboratory and field experiments confirmed that the calibration method met the requirements of ISO 4037-1. As the advantages of portability and simplicity, it is considered that the new irradiation apparatus is applicable to stationary gamma radiation monitors for on-site calibration.

Qualification of a precision pattern dispenser

In order to automate sample preparation processes, a precision pattern dispenser was designed to reproducibly dispense radioactive solutions at pre-defined positions. It is composed of an automatic liquid sample handling unit coupled to an XYZ table. Qualification tests were conducted to evaluate the performance of the instrument and to assess the compliance with the requirements, in particular trueness (< 2%) and repeatability (< 1%). The instrument allows preparing sources in different source holders and on air filters, in a fast and accurate way.

Application of modern anticoincidence (AC) system in HPGe γ-spectrometry for the detection limit lowering of the radionuclides in air filters

The use of active and passive shields can substantially reduce the Minimum Detectable Activity (MDA) of the γ-ray counting systems, rejecting events induced by cosmic-rays or by environmental radioactivity. However, the size and geometry of the samples lead to limitations in the background reduction in routine measurements. The Minimum Detectable Activity (MDA) values for low energy of γ-ray emitting radionuclides (<200 keV) deposited in three typical air filter geometries have been compared for anticoincidence and single HPGe detector mode of γ-spectrometry systems. The relative increase in the Figure Of Merit (FOM) values from to 10-37% has been achieved for AC counting mode for radionuclides of ²¹⁰Pb, ²³⁴Th, ²³⁵U and ²²⁶Ra deposited on the three kinds of air filters.