RESUMEN
The separation methods for soil samples applied at PSI are based on extraction chromatography and ion exchange. After sample leaching, the actinides are pre-concentrated via precipitation using oxalic acid. Besides the classical separation methods applying the extraction chromatographic resins U/TEVA (for U, Th), TRU (Pu, Am), new methods were recently implemented to increase the radiochemical recovery of particularly trivalent Am and Cm. These methods do not require initial reduction of Pu(IV) to Pu(III) but stabilize Pu on the tetravalent oxidation state using a mixture of NaNO(2)/H(2)O(2) in strong acidic medium. The Pu-fraction is then fixed along with Th onto Dowex AG 1-X2 anion exchanger resin. Th is eluted via complexation with 10M HCl, Pu via reduction with HI. The fractions of Am+Cm and U are loaded onto DGA resin. This resin shows extraordinary high distribution coefficients (k'-values) exceeding 10(4) (for Am) in strong nitric acid medium. The separation between U and Am is obtained quantitatively by decreasing the HNO(3) concentration from 3 to 0.25 M (stripping of the U-fraction) while Am can be easily eluted thereafter using 0.25 M HCl as complexation compound.
Asunto(s)
Elementos de Series Actinoides/aislamiento & purificación , Contaminantes Radiactivos del Suelo/aislamiento & purificación , Americio/aislamiento & purificación , Cromatografía , Curio/aislamiento & purificación , Resinas de Intercambio Iónico , Plutonio/aislamiento & purificaciónRESUMEN
Rapid and simple methods are applied at the PSI radioanalytical laboratory for determining anthropogenic actinides in waste and nuclear reactor waters (U, Pu, Am, Cm) as well as for analysis of naturally occurring alpha-emitters in continental river and ground water. Anion exchange chromatography followed by alpha-spectrometry as well as alpha/beta-LSC is applied for the reactor coolant waters. To avoid alpha-spectrum interference between 238Pu and 241Am at 5.5 MeV, the Pu-fraction is purified using anion exchange resin. Prior to the separation of the Pu-fraction, all actinides (U, Pu, Am, Cm) are adsorbed batch-wise under stirring onto Actinide Resin and subsequent decomposition of the reagent. The residue is then re-dissolved in a sulfate buffer solution for electrolytic deposition. In tabular water samples isotopes of Ra and Po are analyzed additionally via sorption onto manganese coated discs (Ra) and deposition on silver discs (Po). For counting times of 1 day and use of 0.1-1l sample aliquots, detection limits of a few mBql(-1) can be obtained easily.
Asunto(s)
Elementos de Series Actinoides/análisis , Monitoreo del Ambiente/métodos , Residuos Industriales/análisis , Reactores Nucleares , Ríos/química , Contaminantes Radiactivos del Agua/análisis , Partículas alfa , Resinas de Intercambio Aniónico , Cromatografía por Intercambio Iónico , Radioisótopos/análisisRESUMEN
Three analytical techniques are presented which are used at PSI for determination of U and Th isotopes (234U, 235U, 238U, 228Th, 230Th, 232Th) in different materials, i.e. environmental samples (soils, minerals) and dental ceramics as well as in urine for in vitro monitoring of potentially exposed workers. Depending on the sample quantity available and/or required detection limits the measurements are performed either directly via gamma spectrometry or via alpha particle counting with preceding separation chemistry. The separation methods applied are based on either extraction chromatography or on sorption of U and Th on actinide selective resin. Following sample digestion, chemical yield spike additions (232U, 225Th or 225Th), chemical purification and electro-depositional source preparation, alpha particle measurement is carried out using low-level alpha spectrometry. This technique allows detection limits of less than 0.2 mBq per counting source if the assay lasts over a few days and is therefore suitable for determination of trace quantities of short-lived 225Th that can be hardly detected by means of mass spectrometric techniques.
Asunto(s)
Monitoreo de Radiación/métodos , Radioisótopos/análisis , Torio/análisis , Torio/aislamiento & purificación , Humanos , Exposición Profesional , Radiometría/métodos , Contaminantes Radiactivos del Suelo/análisis , Uranio/análisis , Uranio/aislamiento & purificaciónRESUMEN
A neurogenic disorder of acquired speech, aphasia not only is a speech disorder but also implies restriction in communicative independence. In line with the WHO's principle of attending to the consequences of disease as well, speech rehabilitation has to deal not only with aphasia in terms of speech disorder (i.e., impairment) but also with aphasia in terms of communicative ability disorder (i.e., disability) as well as with aphasia in terms of psychosocial interference (i.e., handicap). Current speech therapy orientations can be assigned to these three dimensions and the need for these three levels of approach can be assessed accordingly in light of the course of the condition. Given the speech disorder's frequently limited amenability to therapeutic intervention, a psycholinguistics-communication oriented speech rehabilitation as well as counselling and psychologically focussed measures are increasingly relevant to enable a more appropriate response to reduced communicative independence and ensuing psychosocial handicaps.