NORM Contamination: Alpha/Beta but Little Gamma Radiation
K.V. Krieger (Earth Tech Inc.)
Naturally occurring radioactive material (NORM) contamination usually can be easily detected on the outside of piping or tanks in refineries by taking external gamma measurements with simple count rate meters or more complicated gamma spectroscopy instruments, as radium and progeny emit many gamma rays when in equilibrium. However, due to special processes and certain circumstances, a significant amount of NORM may be present without the characteristic gamma signature of radium and its progeny. It was found that during the process of cracking ethane and methane from crude oil, radium is not deposited, while the daughters are deposited. 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 may be detected on the inside of the piping. When analyzing the contents on the interior of the pipe for gamma radiation, the contents contain only lead-210 (210Pb). This indicates that all parents have decayed or that 210Pb was the only NORM that was deposited. During the cracking process, the heat involved is believed to cause radon to enter the process while allowing radium to pass through the system. As one of the release criteria for piping material is an external dose rate of less than 50 microroentgens per hour (μR hr–1), how much of this NORM-contaminated material has been released as noncontaminated throughout the years?