Boron, isotope ratio measurements

A precise quantitative determination of a natural boron sample (fix == 20/80) estimated at 0.1 mmol ( 1 mg) Is required with a 0.5% relative precision. Available spikes range typically from 90 to 99.9% °B, i.e. Ry = 10 to 1000 and a boron isotope ratio measurement can be performed with a relative precision e of 0.2%. Fig. 7 shows different interesting parameter combinations. 

Abundance sensitivity becomes critical when measuring extreme isotope ratios (>100 000) or when neighbouring elements are present in the sample at high concentrations. In ICP-MS this occurs for isotope ratio measurements of elements such as U and Th (extreme ratios) or boron isotope ratio measurements in the presence of high carbon contents (tailing of onto "B). Specially designed filters (electrostatic filter, quadrupole lenses) can increase the abundance sensitivity up to 2 x 10 (see Chapter 2, section 2.2.1 for further details). In the case of boron, a simple matrix separation can help. In the majority of isotope ratio measurements however abundance sensitivity effects are negligible. 

Isotopes in interstellar gas With the aid of the Hubble Space Telescope it has been possible for the first time to measure the boron isotopic ratio within diffuse clouds of the Milky Way. The interstellar ultraviolet radiation renders B ionized (B+) in the diffuse clouds therefore its spectrum is similar to that of the element Be, but at shorter wavelengths. The strongest resonance line lies in the ultraviolet, visible to Hubble spectrometers. The smaller mass of the 10B isotope shifts its line by 0.013 A (about 0.001%) toward longer wavelengths. Very detailed analysis of the line pair has shown in several clouds that today s interstellar abundance ratio is UB/ 10B = 3.4 0.7, which is consistent with the solar ratio 4.05. For the first time one can conclude that the solar ratio is not an abnormal one, but is shared by interstellar gas at a value larger than the ratio 2.5 that is produced by cosmic-ray collisions in the interstellar gas. Another source of11B is needed. 

Contamination affects isotope ratio measurements in a particularly negative way, when working with enriched isotopes or samples having a non-natural isotopic composition. In these cases, the contaminant always has a different isotope ratio than the sample and contamination causes the sample isotope ratio to change dramatically. In particular, ubiquitous elements such as boron and iron are highly susceptible to contamination and great care has to be taken to avoid this when such elements are measured. 

The cosmic-ray energy spectrum actually measured on Earth does not produce the boron isotopes in the correct ratio to match the solar-system value 1 LB/10B = 4.05. They instead produce the ratio 1 1B/10B = 2.5. For the likely resolution of this old problem, see 21B, below. 

Betti (1996) and co-workers used GD-MS for sample screening in isotopic measurements of zirconium, silicon, lithium, boron, uranium, and plutonium in nuclear samples. The results obtained from the GD-MS were compared with results from thermal ionization mass spectrometry (TIMS). For boron and lithium concentrations from //g/g to ng/g levels, isotopic ratios determined by GD-MS were comparable to TIMS in terms of accuracy and precision. Uranium isotopic ratios determined by GD-MS were also in good agreement with values measured by TIMS with regards to accuracy. Chartier et al. (1999) used GD-MS to analyze erbium and uranium in molybdenum-uranium fuel samples. The ratio of 166Er to 238U was then compared to numbers determined by thermal ionization mass spectrometry. The ratio of erbium to uranium was accurate to within 3% of the number determined by TIMS. 

While the ratio of the stable boron isotopes is such that it would seem to be relatively easy to measure compared to other stable isotope systems ( B/ °B 4, compared to 0.002005 and 0.011122), the chemical... 

Critical measurements are the exact spectra of the most common elements, hydrogen and helium, the fraction of antiparticles (antiprotons and positrons), isotopic ratios of elements such as neon and iron, the ratio of spallation products such as boron to primary nuclei such as carbon as a function of energy, the chemical composition near the knee, at about 5 x lO eV, and beyond, and the spectrum and nature of the particles beyond the ankle, at 3 x 10 eV, with special emphasis on the particles beyond the CZK cutoff, at 5 X 10 eV. 

In the center of the original core and then in the core with neptunium there were measured by several methods, the ratios of average fission cross-sections for 16 isotopes, including minor actinides, and of capture cross-sections in aurum, neptunium, uranium-238, the central reactivity coefficients with the use of samples, the sodium void effect of reactivity, the efficiency of a mock-up of the central control rod with enriched and natural boron carbide, ad well as the fission reaction rate distributions with height. 

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