将以下内容翻译为英语，并严格按照分子式形式排版：
这里判定的主要镭源来自煤矿燃烧后的粉尘，通常等同 226 Ra的量为 0.3 pCi/g，来源于燃煤产物的一次风和二次风的混合物。
Radioactive Ra mainly comes from the dust of the coal after combustion, in general, equals the quantity of 226 Ra is 0.3 pCi/g, deriving from a mixture of primary air and secondary air of the products of combustion.
user
The primary source of radioactivity here is from the dust produced after coal combustion, typically equivalent to 0.3 pCi/g of 226Ra, originating from a mixture of primary and secondary air in the combustion products.
assistant