Secondary Logo

Journal Logo

Institutional members access full text with Ovid®

NORM Contamination—Now You See It, Now You Don’t

Krieger, Kenneth*

doi: 10.1097/01.HP.0000165875.69525.d0
Articles: Operational Topic

Contamination from naturally occurring radioactive material on the inside of piping or tanks in refineries can usually be easily detected from the outside by external gamma measurements with simple count rate meters or more complicated gamma spectroscopy instruments. Usually, such contamination is from radium in equilibrium with its progeny. A number of different gamma rays are emitted by this mix. However, due to certain processes or circumstances, a significant amount of NORM can be present without the characteristic gamma signature of radium and its progeny. The process of cracking low molecular weight hydrocarbon gases from crude oil allows radon through but leaves radium behind. The radon enters the process piping and decays, depositing its short-lived decay products or progeny. When the short-lived progeny decay, all that is left are alpha and beta emitters. When this occurs, measurements taken on the outside of piping indicate no elevated levels of gamma radiation; however, elevated levels of alpha and beta radiation can be detected on the inside of the piping. 210Pb is usually the only gamma emitter detected on the inside of the piping and, its gamma ray energy is such that little if any penetrates the walls of the piping. Since one of the release criterion for piping material is an external dose rate of less than 50 μR h−1, it is possible that a survey from the outside of the piping can be negative when, in fact, thee can be appreciable contamination on the inside of the piping.

* Earth Tech Inc., 8005 Outer Circle Drive, Brooks City-Base, San Antonio, TX, 78235.

Some NORM contamination on the inside of refinery tanks or piping can be difficult to detect or evaluate from the outside.

©2005Health Physics Society