Preparation of Mn-fiber standards for the efficiency calibration of the delayed coincidence counting system (RaDeCC)

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• 作者：Jan C. Scholten ; Mai Khanh Pham ; Oxana Blinova ; Matthew A. Charette ; Henrieta Dulaiova ; Mats Eriksson
• 关键词：dium isotopes ; Mn-fiber standards ; RaDeCC system ; Efficiency determination
• 刊名：Marine Chemistry
• 出版年：2010
• 出版时间：20 August 2010
• 年：2010
• 卷：121
• 期：1-4
• 页码：206-214
• 全文大小：1316 K

文摘

Precise measurements of the short-lived radium isotopes ²²³Ra and ²²⁴Ra by means of the delayed coincidence counting system (RaDeCC) rely on an efficiency calibration of this system using Mn-fiber standards for which radium activities are exactly known. We prepared seventeen different standards by placing Mn-fibers in seawater spiked with various amounts of ²²⁷Ac (with ²²³Ra in radioactive equilibrium), ²²⁸Th (in radioactive equilibrium with ²³²Th and ²²⁴Ra) and ²²⁶Ra. We tested for quantitative adsorption of ²²⁷Ac and ²²⁸Th on the Mn-fibers by: (1) measuring ²²⁷Ac and ²³²Th in the residual solutions after preparing the Mn-fiber standards and (2) monitoring their ²²³Ra and ²²⁴Ra activities over a period of  100 days. In the residual solutions, the activities of ²²⁷Ac and ²³²Th were ≤ 1.0 % and ≤ 5.3 % , respectively, of the activities initially added to the Mn-fibers. Our results indicate that Milli-Q water washing of the Mn-fibers is the major source of our observed losses of thorium. Measurements of ²²⁷Ac standards over 1 1/2 years indicate a significant decrease of measurable ²²³Ra with time prohibiting the long-term use of ²²⁷Ac Mn-fiber standards. We found the ²²⁴Ra efficiency to be independent of the range of ²²⁷Ac, ²²⁸Th and ²²⁶Ra activities on the Mn-fibers standards used. The efficiency determination for ²²³Ra, however, may be biased in the case of relatively high ²²⁴Ra activities due to insufficient correction of chance of coincidence. Thus we suggest using a single ²²⁷Ac Mn-fiber standard for the efficient determination of ²²³Ra.