*2.1.1 222Rn determination by solid-surface barrier detector*

One of the ways of determining 222Rn activity it is through alpha spectrometry by counting alpha emitting progenies of 222Rn.

A known quantity of radon air is drawn by two filters in a cylindrical system, whereby one filter keeps the radon progeny and particular matter, the other filter receives radon. On the second filter, ingrowth of radon takes place, the second filter faces the surface barrier detector, and therefore, alpha spectra are produced.

In a simple method, positively charged progenies are collected onto a metal surface that is placed inside chamber's negative potential. For example, the positively charged 218Po particles gathered on a metal surface are counted by a surface barrier detector.

The advantage of using a surface-barrier detector is high resolution, low background, ability to distinguish the signals of 222Rn progenies and 222Rn due to the fact that they have varying alpha energies [17].


#### **Table 1.**

*Radon chamber.*
