Fast radiochemical extraction of carbon in photoactivation analysis of pure boron

The problem under consideration was stimulated by the investigation of a possible violation of the Pauli exclusion principle during the early stage of the Universe formation, i.e. in the period of nucleosynthesis. The experiments were carried out at the 30 MeV microtron in the IPP by the photoactivation technique and aimed at searching of chemically boron-like carbon nuclei in the samples of pure boron. Preliminary tests of different samples of pure boron for impurity content performed by the photo- and thermal neutron activation, chemical, mass- and optical spectroscopy analyses have showed that unfortunately the carbon content in the samples is rather high and is at a level (37) x 10-2 wt. %. Besides there are also chlorine and fluorine (approx. 10-2 wt. %) in the samples and metallic impurities with a total level of about 0.1 wt. %. That is why the non-destructive activation variant of the determination of carbon nuclei content in boron is impossible and therefore we developed a special radiochemical procedure for pure boron extraction from the samples in the form of B2O3 or H3BO3. The procedure contains two stages: (i) alloying of the irradiated sample in a mixture KNO3 + KOH followed by decomposition of carbonates and distillation away of 11CO2; (ii) extraction of metals by sodium diethyldithiocarbonate. The alloying technique is based on a fast decomposition of the irradiated sample in the mixture of KNO3 + KOH (6:1) at the temperature of 600 degC during 5 min, dissolving of the cooled mixture in water (10 ml) and subsequent distillation off of the 11CO2 from boiling acidic solution of HCl (30 ml) during 5 min. The extracted carbon dioxide is absorbed in 12M KOH whose β+ activity was measured by the (gamma-gamma)-coincidence spectrometer to check the efficiency of the extraction. The measurement showed that during 5 min, 94% of the carbon atoms is extracted from the solution. For fast extraction of metals a sodium diethyldicarbonate was used. Hydrochloric acid was added to the solution followed by citric acid and carbonate. As a result, metallic complexes were formed and then a chloroform was added. The activity of the water phase after extraction, which contains the purified boron acid, was measured with (gamma-gamma) spectrometer. The time needed for extraction of the metals is about 20 min. (author)