Detection and Quantification Capabilities for 85Kr with the NIST Low-Level Gas Counting System: Impacts of Instrumental and Environmental Backgrounds

Published

April 1, 2001

Author(s)

Lloyd A. Currie, George A. Klouda

Abstract

Among the most important, conservative geochemical tracers are the long-lived isotopes of krypton, ⁸¹Kr and ⁸⁵Kr. Following a very brief review of the metrology and applications of these two radionuclides, we focus on the low-level measurement the 10.8 year fission product ⁸⁵Kr, in connection with its use for studying atmospheric transport and short term (decadal) atmosphere-ocean exchange and mixing. A special challenge for the study of ⁸⁵Kr in the environment is to reduce detection/quantification limits to mBq levels, to minimize the need to take costly (large) atmospheric and marine samples for geochemical studies, where current radioactivity concentrations (northern, mid-latitudes) are about 1.4 Bq m^-3 (troposphere) and 0.08 Bq 1000 kg^-1 (surface ocean water). A second challenge is to design a measurement protocol that takes into account not only the effect of instrumental background on detection/quantification limits, but also the effects of environmental background levels and their variability. Tests of these capabilities were performed theoretically, based on performance characteristics of the NIST low-level gas counting system, and experimentally, using quantitative dilutions of a ⁸⁵Kr reference sample and a contemporary atmospheric sample. Recent enhancements to the NIST system, including a high purity 5 cc quartz counter and an active (NaI) shield, have resulted in a background reduction by more than an order of magnitude to 0.02 cpm and the ability to quantify ambient ⁸⁵Kr in 1.5 L air or 25 L seawater with 2000 min paired sample-background counting periods.

Citation

Journal of Radioanalytical and Nuclear Chemistry

Volume

248

Issue

No. 1

Pub Type

Journals

Keywords

atmospheric transport and circulation, conservative radionuclide tracers, detection/quantification limits, environmental ⁸⁵Kr, environmental backgrounds, instrumental backgrounds, low-level gas counting, marine transport and circulation

Citation

Currie, L. and Klouda, G. (2001), Detection and Quantification Capabilities for ⁸⁵Kr with the NIST Low-Level Gas Counting System: Impacts of Instrumental and Environmental Backgrounds, Journal of Radioanalytical and Nuclear Chemistry (Accessed October 15, 2024)