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To evaluate the relative gain of the 10 13 Ω current 403 amplifier prior to sample analyses, we repeated the measurements of the 238 U/ 235 U 404 ratios in a uranium solution with Faraday cups connected to 10 13 and 10 11 Ω 405 amplifiers. The relative gain of the 10 13 Ω amplifier was calculated as 406 ( 238 U11/ 235 U13)/( 238 U11/ 235 U11), where the subscript indicates the resistors of the Faraday 407 cup amplifiers. We also developed approaches to correct for the effects of baseline, 408 memory, tailing, hydride, and mass biases. Using the new static measurement method, 409 we repeatedly measured 234 U/ 238 U and 238 U/ 235 U ratios for the international uranium 410 standards HU-1 and SRM950a, as well as for the national uranium standards 411 GBW04412 and GBW04428. Our results (presented with ±2σ) show that the 412 international standards HU-1 (n=10) and SRM950a (n=10) have 234 U/ 238 U atomic 413 ratios of (54.90±0.03) ×10 -6 and (53.88±0.

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