MONITORING FOR LEAD CONTAMINATION

Abstract

One of the first accomplishments of the Sub-committee on Low-Level Contamination of Materials and Reagents of the National Research Council, National Academy of Sciences, has been a study of the radioactive contamination of commercial lead. Twelve lead samples, ten from current commercial production and two “aged” specimens, showed a wide range of contamination levels. Yet, several of the commercial samples were comparable to the best aged leads available for low-level gamma shielding. The contaminant was identified as 210Pb. Good correlation was observed in the measurements at three laboratories. The radioactive contamination in lead is caused by 210Pb which occurs in lead derived from ores geologically associated with uranium. Since the decay products have a high ratio of alpha to gamma radiation and since alpha counting is considerably less complex than gamma counting, the alpha technique is definitely indicated. 210Pb concentrations of 1 to 100 pCi/g could be measured by means of the 210Po daughter. Therefore, lead samples may be monitored by alpha counting. A similar rationale is applicable to the beta radiation from 210Pb and its daughters. Therefore, beta counting must be considered as an alternate possible monitoring technique. Commercially available alpha and beta counters and techniques have been investigated to determine which of these would be applicable to a monitoring system, what counting times are required and what methods are most suitable. Apparatus on hand has been tested, and some apparatus was borrowed and purchased for evaluation. The results indicate that standard commercial equipment will provide adequate monitoring for lead contamination and so make practical the supply and acquisition of very-low activity lead.