Standardization of63Ni by 4πβ Liquid Scintillation Spectrometry With3H-Standard Efficiency Tracing.
The low energy (Eβmax= 66.945 keV ± 0.004 keV)β-emitter63Ni has become increasingly important in the field of radionuclidic metrology. In addition to having a lowβ-endpoint energy, the relatively long half-life (101.1 a ± 1.4 a) makes it an appealing standard for such applications. This paper describes the recent preparation and calibration of a new solution Standard Reference Material of63Ni, SRM 4226C, released by the National Institute of Standards and Technology. The massic activityCAfor these standards was determined using 4πβliquid scintillation (LS) spectrometry with3H-standard efficiency tracing using the CIEMAT/NIST method, and is certified as 50.53 kBq ·g-1± 0.46 Bq · g-1at the reference time of 1200 EST August 15, 1995. The uncertainty given is the expanded (coverage factork= 2 and thus a 2 standard deviation estimate) uncertainty based on the evaluation of 28 different uncertainty components. These components were evaluated on the basis of an exhaustive number (976) of LS counting measurements investigating over 15 variables. Through the study of these variables it was found that LS cocktail water mass fraction and ion concentration play important roles in cocktail stability and consistency of counting results. The results of all of these experiments are discussed.
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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BE
Zimmerman
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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R
Collé
CIEMAT/NIST Method; beta-counting; liquid scintillation; nickel-63; radioactivity; standards