Postirradiation method

One weakness of postirradiation methods, i.e., analysis of the ablation properties and surface analysis, as tools for studying the ablation mechanisms of polymers is the possibility that reactions after irradiation cause the observed effect. These results are therefore only indirectly related to the abla-... 

Each type of dosimeter requires a specific procedure to ensure accurate and reproducible results, such as postirradiation heat treatment. Others need to be stabilized for a certain time (up to 24 h with some) before readings of absorbance are taken. The absorbance reading can be done by conventional spectrophotometry or other, more involved methods. 

A number of studies concerned with the effect of irradiation upon intermediary metabolism in carrots have been conducted. One such study utilizing the methods of Ap Rees and Beevers (1,2) involved measuring the relative radiation susceptibility of the pentose phosphate (PP) and the Embden-Meyerhof (EM) systems in the postirradiation period. 

Y. Ohnishi, M. Itoh, K. Mizuno, H. Gokan, and S. Fujiwara, Postirradiation polymerization of e beam negative resists Theoretical analysis and method of inhibition, J. Vac. Sci. Technol. 19, 1141 (1981). 

Ohnishi, M. Suzuki, K. Saigo, Y. Saotome, and H. Gokan, Postirradiation polymerization of e beam negative resists Theoretical analysis and method of inhibition, Proc. SPIE 539, 62 (1985). " R.R. Kunz, M.W. Horn, R.B. Goodman, P.A. Bianconi, D.A. Smith, J.R. Eshelman, G.M. Wallraff, R.D. Miller, and E.J. Ginsberg, Surface imaged silicon polymers for 193 nm excimer laser lithogra phy, Proc. SPIE 1672, 385 (1992). 

In a study from our laboratoiy (Chatteijee et al., 1996), a novel P postlabeling method was employed to detect UVB-induced DNA lesions in the epidermis and its prevention by GTP. This study showed that epidermal DNA from UVB-exposed mice at 24h contain up to five DNA lesions. Quantitation of these lesions showed that their formation increased in a UVB dose-dependent manner. Treatment of DNA samples with the bacteriophage DNA repair enzyme T4 endonuclease V confirmed that four of these lesions are pyrimidine dimers. While some of these lesions were repaired 18h after UVB irradiation, 30% of them persisted even 48h postirradiation. Topical application of GTP... 

In some extremely demanding cases, pre-irradiation chemical concentrations are carried out together with postirradiation separations, combining the advantages and the drawbacks of both techniques. This method, referred to as PC-RAA, can provide the highest possible sensitivity of trace element analysis among the AA techniques. 

Several other valuable publications have recently appeared on the use of RNAA for trace elements in metals, e.g., the analysis of Na and K in W-Ti alloys by Kim et al. (1998) and trace elements in ancient gold objects by Olariu et al. (1999). Postirradiation RNAA methods separating a single element have the advantages that low detection limits as well as high analytical accuracy can be achieved when results are corrected for chemical losses and all possible interferences are taken into consideration. 

Dang et al. (2000) increased the sensitivity of NAA for Th by separating the indicator radionuclide, Pa, using co-predpitations with manganese dioxide and barium sulfate and determined Th in total diet samples. A similar postirradiation procedure was coupled to the following pre-irradiation separation and concentration of Th (PC-RNAA) by H5llriegl et al. (2005) to increase the sensitivity of the method for the determination of urinary Th excretions. The pre-concentration procedure consisted of phosphate and caldum oxalate coprecipitations. The detection limit of Th in the urine sample was about 10 pg (0.04 jiBq). 

Silicon. It is assumed that Si is an essential element for humans. A postirradiation RNAA method of sufficiently high sensitivity for biological studies has been reported by Kucera and Zeisler (2005). The postirradiation separation consists of ffision, followed by sequential evaporation of Cl, Br, and the distillation of Si as Sip4 that is absorbed in a boric acid and ammonium molybdate-containing solution. The beta radiation emitted by Si produced with thermal neutrons via the Si(n,y) Si reaction was measured by liquid scintillation counting (LSC). Detection limits as low as 0.5 pg/g could be achieved. 

In order to resolve the present inconsistencies in serum and blood vanadium determination, Byrne and Versieck [81] reported a totally postirradiation radiochemical neutron activation analysis method. Their procedure was as follows After irradiating the sample for up to 12 min at a nuclear reactor neutron flux of 4 x 10 n/cm -sec the sample was transferred to a 100-mL, long-necked, silica Kjeldahl flask containing 3 mL 18 M H2SO4, 20 ji,g V carrier, and a weighed aliquot of... 

---