Assay methods for U-238, Th-232, and Pb-210 in lead and calibration of Bi-210 bremsstrahlung emission from lead

TL;DR

This paper presents advanced assay methods for measuring U-238, Th-232, and Pb-210 in lead, including isotope dilution ICP-MS, alpha spectroscopy, and bremsstrahlung radiation detection, with applications to ten lead samples.

Contribution

It introduces novel combined chemical and radiation measurement techniques for precise quantification of radionuclides in lead samples.

Findings

U-238 and Th-232 levels are below detection limits in tested samples.

Pb-210 concentrations vary from 0.1 to 75 Bq/kg across samples.

New bremsstrahlung measurement method correlates with Pb-210 levels.

Abstract

Assay methods for measuring 238U, 232Th, and 210Pb concentrations in refined lead are presented. The 238U and 232Th concentrations are determined using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) after anion exchange column separation of dissolved lead samples. The 210Pb concentration is inferred through {\alpha}-spectroscopy of a daughter isotope, 210Po, after chemical precipitation separation on dissolved lead samples. Subsequent to the 210Po {\alpha}-spectroscopy assay, a method for evaluating 210Pb concentrations in solid lead samples was developed via measurement of bremsstrahlung radiation from \b{eta}-decay of a daughter isotope, 210Bi, by employing a 14-crystal array of high purity germanium (HPGe) detectors. Ten sources of refined lead were assayed. The 238U concentrations were <34 microBq/kg and the 232Th concentrations ranged <0.6-15 microBq/kg, as determined by the ICP-MS assay method. The 210Pb concentrations ranged from ~0.1-75 Bq/kg, as inferred by the 210Po {\alpha}-spectroscopy assay method.