<?xml version="1.0" encoding="utf-8"?><!DOCTYPE Zthes SYSTEM "http://zthes.z3950.org/xml/zthes-05.dtd">  <Zthes><term><termId>31303935</termId><termName>radon</termName><termType>PT</termType><termNote><![CDATA[ Radioactive chemical element having symbol Rn and atomic number 86. It is a colorless, odorless, tasteless inert gas. Radon is formed during the natural decay of radium. It is produced in rock and soil  and migrates to the surface, sometimes entering buildings through basement walls, resulting in low level exposure. Radon’s health risk is associated with the products of radon decay and not with the gas itself.  ]]></termNote><termCreatedDate>2026-03-30 20:21:44</termCreatedDate><relation><relationType>UF</relationType><termId>31303936</termId><termName>Rn</termName><termType>ND</termType></relation><relation><relationType>BT</relationType><termId>31298623</termId><termName>organic material</termName><termType>PT</termType></relation><relation><relationType>BT</relationType><termId>31319740</termId><termName>elements</termName><termType>PT</termType></relation><relation><relationType>RT</relationType><termId>31343599</termId><termName>radium</termName><termType>PT</termType></relation></term>  </Zthes>