2.7.1.2 - Adsorption on Active Carbon 'PicoRad'

Introduction

Active carbon in metal boxes is generally used for the analysis of Radon in air by adsorption and subsequent measurement by γ-spectrometry through the daughter nuclides ²¹⁴Pb and ²¹⁴Bi. In a special arrangement (PicoRad^TM, provided e.g. by FCI Consulting & Instruments) (fig. 39), active carbon can be used for adsorption of Rn and further desorption into an organic cocktail, which is then measured by LS [Passo et al. 1989].

A polyethylene vial is equipped with an air transparent cartridge containing 1.2 g of granulated active carbon and 2 g of silica gel. After exposition to air, organic scintillation cocktail is carefully added to the bottom of the vial, into which Radon is then desorbed.

Materials and Equipment

• PicoRad^TM (e.g. FCI Consulting & Instruments)

• Organic cocktail

• PSD LS counter

Procedure

1. The Radon sampler is de-caped and exposed to air for 2 to 3 days.

2. 10 mL of organic cocktail are carefully pipetted in such a way that the active carbon is not moistened.

3. The vial is closed and stored for 4 to 20 h before α/β-PSD measurement. 

Evaluation

The Radon activity concentration C_Rn is calculated from the known exposition time for Radon adsorption, transport and desorption time (without moisture correction) according to

R_M = Measured rate (cpm)

R₀= Background (cpm)

f_k = Calibration factor = 1.2919 (Bq/m³) / cpm

(for evaluation with a+b measurement, Triathler)

f_k = Calibration factor = 2.2548 (Bq/m³) / cpm

(for evaluation in a-channel, Triathler)

f(x₁) = 1.28157_*e^-0.008675*x1 – 1.3637xe^-0,1426*x1

x₁ = Storage after cocktail addition (hours)

g(x₂) = 1 - e^{-0.04506*x 2}

x₂ = Exposition time (hours)

h(x₃) = e^{-0.008675*x 3}

x₃ = Storage after exposition (hours)

[Frenzel 2006]

Detection Limit (MDA): 15 Bq/m³

Total analysis uncertainty: 15 %

Frenzel E. 2006: Measurement, evaluation and calculation of the activity concentration of Rn-222 in air with PicoRad vials following the pattern of the method of “MPA- Dortmund – Henke, Rox and Weinberg, Application Note FCI Frenzel Consulting & Instruments

Passo C. J. and Floeckner J. M. 1989: The LSC approach to Radon counting in air and Water; in: H. Ross et al., “Liquid Scintillation and Organic Scintillators”, pp 375-384, Lewis Publishers 1989, Chelsea