Irradiation and measuring conditions

A typical irradiation time is 10-15 s. Longer irradiation times increase the possible contribution of long-lived activities. 

The neutron flux, which depends e.g. on the deuteron beam intensity and 

9 10 n/cm. s in the installation described by Hoste et al. (185). Usually a deuteron intensity of 1 mA is used with this installation (186). 

In general a ca. 2 s delay is necessary for pneumatic transfer of the samples. If the samples are etched after the irradiation (see below) a ca. 12 s delay is required. 

According to Sterlinski (191) the measuring time leading to the highest sensitivity is ca. 2 half-lives or ca. 14 s. 

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The irradiation and measurement conditions for the analyses are given in the Table 4.2. 

The effect depends not only on the irradiation and measuring conditions, but also on the quality of the measuring electronics. 

The solvent extraction experiments coupled with DSC and FTIR data show that the degree of cure of these mixtures, under identical irradiation and bake conditions, is dependent on the concentration and nature (% acrylonitrile) of the rubber modifier. The sol fractions for PCI cured epoxy films with three different rubber modifiers (5), ETBN-13 (27% CN), ETBN-8 (17% CN) and ETBN-15 (KMTCN) at a range of concentrations are shown in Figure 2. The data show that a decrease in extent of cure occurs with increased rubber concentration and that this decrease (ETBN-13 > ETBN-8 > ETBN-15) may be correlated to the percent acrylonitrile in the rubber modifier. This is supported by the FT-IR spectra of two of these mixtures (IV and VI) as shown in Figure 3 and the quantitative measure of the extent of cure as a function of irradiation time for mixtures V (30% TBN-13) and VIII (30% ETBN-15) as compared to mixture IX (no rubber) silicon in Figure 4 (8). 

This expression is readily simplified when standards of known composition are irradiated and counted with the samples. If the irradiation and decay conditions are kept constant and all measurements are made with a constant neutron flux and detector geometry, the concentration by weight of element X becomes the simple ratio ... 

Therefore, two methods are routinely employed (1) a comparator standard with known elemental content is irradiated and measured under the same conditions as the sample, or... 

In the early 1970s, Simonits proposed the development of a standardization method using universal fc-factors. In this method, the essential information for a gamma ray emitted by any nuclide produced by neutron activation would be contained in a universal constant, the ko factor, and all factors depending on the specific irradiation and counting conditions would be calculated by models. The inventors of the ko method envisioned that for each sample analyzed at least one neutron flux monitor would be co-irradiated and counted, and all other parameters of the models would be measured once and only remeasmed when irradiation conditions changed. Thus, multielement analysis could be performed with the same amount of work needed for single-element analysis. 

The method described was used by Petit et al. (37) for the determination of boron in industrial zirconium. Although somewhat different from those used by Petit et al. (37), the irradiation, etching and measuring conditions described in 2.4.1.1. can be used. 

The method described was developed by Mortier et al. (38) for the determination of boron in doped zirconium (100, 20, 1 and 0.5 pig/g of boron), in undoped zirconium and in zircaloy. The conditions given can be used for all these materials. For the 100 and 20 f g/g samples, however, shorter irradiation and measuring times may be used and an instrumental determination is feasible if 6 MeV protons are used. Table IV-3 summarises the most important nuclear reactions of zirconium and its impurities or alloying elements with protons. For low boron concentrations Be must be separated chemically from the radionuclides produced. 

The conditions for the determination of nitrogen in niobium and tantalum (42)(45)(46) using the N(p,n) 0 reaction are similar to those described under 2.3 except for the irradiation (12 MeV protons, 0.5 lA for Nb and 3 to 4 /.A for Ta) and measuring conditions (No lead absorber needed, detector with 5 % relative detection efficiency). 

TTigh pressure mass spectrometry has recently provided much detailed kinetic data (5, 12, 13, 14, 15, 17, 22, 24, 26, 29) concerning ionic reactions heretofore unobtainable by other means. This information has led to increased understanding of primary reaction processes and the fate of ionic intermediates formed in these processes but under conditions distinctly different from those which prevail in irradiated gases near room temperature and near atmospheric pressure. Conclusive identification and measurements of the rate constants of ionic reactions under the latter conditions remain as both significant and formidable problems. 

Figures 7.5 and 7.6 give the measured spectral reflectances and transmittances of fabrics. It is clear from Figure 7.5 that color (6,white 7,black 1,yellow) has a significant effect in reflecting solar irradiance, and also we see why these colors can be discriminated in the visible spectral region of 0.6 pm. However, in the spectral range relevant to fire conditions, color has less of an effect. Also, the reflectance of dirty (5a) or wet (5b) fabrics drop to <0.1. Hence, for practical purposes in fire analyses, where no other information is available, it is reasonable to take the reflectance to be zero, or the absorptivity as equal to 1. This is allowable since only thin fabrics (Figure 7.6) show transmittance levels of 0.2 or less and decrease to near zero after 2 pm.

The y particle is emitted virtually instantaneously on the capture of the neutron, and is known as a prompt y - it can be used analytically, in a technique known as prompt gamma neutron activation analysis (PGNAA), but only if such y s can be measured in the reactor during irradiation. Under the conditions normally used it would be lost within the nuclear reactor. In this reaction, no other prompt particle is emitted. The isotope of sodium formed (24Na) is radioactively unstable, decaying by beta emission to the element magnesium (the product nucleus in Figure 2.13), as follows ... 

We wanted to be able to correct measurements of dielectric loss (conductance) and dielectric constant of polymerizing styrene solutions for whatever contribution arose from the dead polystyrene present in the solutions. What better way to make polystyrene that was free of all catalyst fragments and polar groups than to irradiate pure, dry styrene Using the same exhaustive drying technique that we were developing for our a-methylstyrene studies, we prepared a batch of pure, dry styrene. This was then to be irradiated under such conditions that approximately 15% conversion to polymer would occur. 

UV-B spectral global irradiance and total ozone direct sun measurements carried out at Lisbon during 1990 with a MARK 11 Brewer ozone spectrophotometer and with clear-sky conditions were used for comparison at several zenith angles, total ozone and aerosol conditions. However, because aerosol optical depth measurements were not available at this time it was decided to use T5oo=0.0 for the model input. The results of the Model/Brewer ratios for global spectral irradiances are shown in Figure 5. The results are similar and consistent with the earlier LOWTRAN 7 (6) comparison, where the ratio approaches to unity as the wavelength increases,... 

The time series of local noon UV (290-325 nm) irradiance measurements from January 1st 1992 to December 31st 1998 are plotted in Figures 1 and 2. The main factors determining the two distributions and the differences between them are total ozone, latitude and meteorological conditions [3, 4],... 

To avoid difficulties related to the growth of pressure in a sealed vessels as well as temperature measurement, the esterification reaction of acetic acid with propanol was carried out in an open vessel under reflux conditions. It was found that ester concentrations during the course of the reaction were comparable under both conventional and microwave conditions [20]. In a similar reaction (i.e., the esterification of trimethylben-zoic acid with propanol), the kinetic parameters of the reaction under the Arrhenius law were estimated for conventional conditions. Then ester concentrations were calculated theoretically and compared with the results obtained for the reaction under microwave conditions. It was found that the theoretical values correlated well with the experimental results so microwave irradiation did not influence the rate of the reaction [21]. 

The stability under irradiation of the calix[4]arene-bis(tm-octylbenzo-crown-6) (BOBCalixC6)-based solvent system (mixture composed of calix[4]arene, an aromatic fluoro-propanol as modifier, and trioctylamine in aliphatic diluent) was tested under chemical and radiolytic conditions representative of the alkaline-side process (265). After y-irradiation doses as high as 0.16 MGy, no significant loss of BOBCalixC6 was measured (less than 10%). 

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