| 219Rn is a kind of radioactive gas, which can break away from its absorbing mediuminto the atmosphere.219Rn and its daughter nuclides come into being aerosol easily,when the aerosol is breathed into the human body, it can produce internalexposure.There are plenty of219Rn at some place such as high enriched uraniumstorage and spent fuel cooling pool, people have paid more attention to theradioprotection of219Rn and its daughters. Some natural radioactivity nuclides forexample227Ac and223Ra can be applied as a tracer in the field of science researchsuch as Groundwater Transference, Isotopic Oceanography, besides,227Ac is requiredto monitor in the investigation of naturally occurring radioactive material (NORM).For measuring these nuclides, we can measure their daughter219Rn, and it is veryconvenient for sample preparation. To accomplish all of these works, a standard219Rnsource is needed.219Rn is a daughter of227Ac, which decays with a half-life of21.8years, and is the most suitable nuclide of actinide to prepare a219Rn standard source.Comparing with the method to preparing227Ac by the neutron irradiation of226Ra in anuclear reactor, the cost of render separation of227Ac from the ore is more lower.Therefore the first task of developing the standard radioactive219Rn source isextraction and purification of227Ac and determination of its radioactivity andradiochemical purity.In this paper, based on the difference of adsorption performance on ion exchangeresin of the main radionuclides of uranium series, thorium series, and actinide indifferent kind of acid and acidity, we established an efficient and fast method forseparating and collecting227Ac from uranium ore, and a process to determine itsradioactivity and radiochemical purity by γ-ray Spectrometry and emanation method. The experimental results show that U, Th, Ra, Pa can be removed from the matrix bychromatography, while if the uranium ore is high-grade, it is necessary to add aextraction separation step before ion exchange chromatography. By trackingmeasurement of the growth of219Rn and the decay of211Pb, we found that thecorresponding half-life calculated from the fitting equation of211Pb measurement datais36.5min which is close to the literature half-life value of211Pb, i.e.36.1min, and themeasurement curve of219Rn growth fits well with the theoretical growth curve.Boththe growth and the decay of counting rate are successful identifications for theconclusion that the parent nuclide of this source is227Ac. Radioactivity andradiochemical purity of the source have been determined by γ-spectrometry andemanation method. The activity of the source is1093±8Bq, and the content of maininterference of nuclide is lower0.5%by γ-spectrometry, which is close to the1034±120Bq,0.4%by emanation method. It shows that the process designed byourselves is feasible.The separation process and measuring method reserched in this paper will make thesynthesis of227Ac become convenient and cheap. When the requirement of chemicalpurity is not very high, we can use this method to replace the method of neutronirradiation of226Ra. Besides227Ac obtaind form the experiment mainly used todevelop a standard219Rn source, which is absorbed on the specially selectedion-exchange agent, and can remain stable over a wide humidity range of air (40%~90%). The219Rn source made by227Ac obtaind form the experiment can be used tothe research of radiation dosimetry of219Rn, as well as calibration of219Rn measuringequipment. However, there is no standard219Rn source around the world yet. The aimof this work is to extract high radioactive purity227Ac and use it to develop standard219Rn source, which is of great scientific significance and practical value. |
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