ABSOLUTE ISOTOPIC ABUNDANCE RATIOS AND THE ATOMIC WEIGHT OF A REFERENCE SAMPLE OF POTASSIUM.

Abstract

Solid sample, thermal ionization, mass spectrometry has been used to obtain absolute values for the isotopic abundance ratios of a reference sample of potassium. Standards of known isotopic composition, prepared by gravimetrically mixing nearly isotopically and chemically pure separated isotopes of **3**9K and **4**1K, were used for calibration. The absolute isotopic abundance ratios are **3**9K/**4**1K equals 13. 8566 plus or minus 0. 0063 and **4**0K/**4**1K equals 0. 0017343 plus or minus 0. 0000061 which yield atom percent compositions of **3**9K equals 93. 2581 plus or minus 0. 0029. **4**0K equals 0. 01167 plus or minus 0. 00004, and **4**1K equals 6. 7302 plus or minus 0. 0029. The calculated atomic weight for potassium is 39. 098304 plus or minus 0. 000058. The indicated uncertainties are overall limits of error which are the sum of the uncertainty components for ratio determinations and the components covering the effects of known sources of possible systematic error.