Boron natural abundance plus#

It was shown that the mass discrimination in the mass spectrometers used is dependent on the magnitude of the isotopic ratio. more » These results are in very close agreement with recent work and differ significantly from the present internationally accepted values.

Boron natural abundance plus#

Specimens of commercial silver of diverse ages possess abundance ratios within the limits of the determinations and thus the calculated atomic weights are: chemical scale (O = 16) 107.8740 plus or minus 0.0033 physical scale (O/sup 16/ = 16) 107.9037 plus or minus 0.0026 unified scale (C/sup 12/ figures are the 95% confidence limits for the random errors added to estimates of possible systematic errors. « lessĪn examination of the isotopic abundance ratio in natural silver by means of the mass spectrometer resulted in a value of 1.0733 plus or minus 0.0043 for the absolute isotopic abundance ratio Ag/sup 107//Ag/sup 109/.

The ratio B/ sup 11//B/sup 10/ was determined to be 4.05 plus or minus 0.10, a value which substantiates those obtained by several recent investigators. Fragmentation of hydrogens from the methyl borate molecule in the mass spectrometer necessitates complex corrections to make it possible to obtain the absolute abundance ratio of the isotopes. Any natural variation which exists in these samples must be less than 1.5%. The composition of the boron in the samples investigated was found to be constant within the limits of experi mental error. The samples were prepared from material obtained from a variety of geological environments in the hope that they would reflect the extent of natural variation in the isotopic composition of boron. Boron isotope analyses were conducted on twelve samples of more » methyl borate in a 12-inch, 60 deg, single- focusing mass spectrometer. In order to avoid such reactions, methyl borate, the methanol ester of boric acid, was chosen for the mass- spectrometric analyses in this investigation. Boron trifluoride is unsuitable for this purpose because it is capable of reacting with many of the components of a mass spectrometer. This controversy seems to stem, in part, from the fact that several investigators have used boron trifluoride as a radium for massspectrometric analysis. The atomic weight of boron and the possible existence of natural variations in its isotopic composition are both matters of active controversy. These values yield for the absorption cross section of the B/sup 10/ isotope at the reference velocity 3840 plus or minus 11 barns as deduced from the natural boron results, and 3837 plus or minus 9 barns from the enriched sample. The deduced values for the boron absorption cross section at the reference neutron velocity of 2200 m/sec are for natural boron sigma /sub a/ = 760.8 plus or minus 1.9 barns and for the enriched boron sigma /sub a/ = 3703 plus or minus 8.9 barns. This quantity remains a constant over the entire energy range covered and its mean value for natural boron is K = (1.674 more » plus or minus 0.0041) barns m/ mu sec and for the enriched boron K = (8.15 plus or minus 0.019) barns m/ mu sec. From the accurate total cross-section values obtained, the ratio of the boron absorption cross section to the reciprocal of neutron velocity was calculated. Samples of natural boron with an isotopic abundance of (19.81 plus or minus 0.02) per cent B/sup 10/ atoms, and boron enriched up to (96.515 plus or minus 0.013) per cent were used for these measurements. The total cross section of B/sub 2/O/sub 3/ was measured from 0.006 to 0.082 ev with the BR-1 slow-chopper.