Answer to Question #1847 Submitted to "Ask the Experts"

Q

With respect to radon, what does the term "plated out" mean?

A

This answer assumes that the "radon" being referred to is ²²²Rn. Nevertheless, the answer would not be materially different if we were considering ²²⁰Rn (thoron). Radon is a noble gas. When it decays, it produces four short-lived decay products: ²¹⁸Po, ²¹⁴Pb, ²¹⁴Bi and ²¹⁴Po. All of these are solids. For the most part, these decay products attach themselves to airborne particulates. When the particulates are deposited on surfaces such as walls and floors, we say that the associated radon decay products are plating out. The magnitude of the plate-out depends, among other things, on the nature of the air currents and the types of surfaces that are available. For example, surfaces with a static charge are particularly effective at accumulating radon decay products. It should be mentioned that the "unattached" radon decay products (those not attached to airborne particulates) are also subject to plating out. The radon itself, being an unreactive noble gas, does not plate out on surfaces. Instead, it remains in the air. Paul Frame, CHP, PhD