Standardization of Rn-222 concentration using the multi-electrode proportional counter.

Standardization of the concentration of gaseous 222Rn based on a multi-electrode proportional counter (MEPC) is under development as a primary standard in Japan. In this study, the concept and evaluation of its performance are reported. The latter consists of a preliminary result for the uncertainty budget associated with the measurement of the MEPC and compensation of the electric field distortion in the MEPC. Moreover, an ionization-chamber-based gas circulation system was added for the calibration of radon monitors in the air.

Simulation of a well-type HPGe detector for samples both in the hole and on top of the endcap.

A well-type HPGe detector model with the existence of a particular dead area in the HPGe crystal was developed for use in Monte Carlo simulation codes to better model gamma-ray efficiency characteristics. Dissimilarities of counting efficiencies between simulation and calibration were successfully minimized for the case of point and volume sources. Simulations using the resulting model are applicable to the activity measurement of samples both in the hole and on top of the endcap of the well-type HPGe detector.

A practical evaluation of measurement uncertainty in gamma-ray efficiency curve determination through an analytical approach.

An example of uncertainty evaluation of an efficiency curve is reported. In the applied method, the efficiency curve is determined through the weighted least square method based on measured efficiencies employing a mixed-radionuclide standard source. The variance-covariance matrix of the efficiencies is determined by evaluating the uncertainties of the counting, the calibrated radioactivities, the correction factors for true coincidence summing, and the inadequacy of the fitting function. The proposed method can be a basis to develop a more general procedure.