Analysis after Irradiation

SEM pictures were taken after irradiation at both wavelengths with fluences below and above the threshold of ablation after various numbers of pulses. After irradiation at both wavelengths with fluences below the threshold of ablation, no changes of the surface morphology could be detected. A totally different behavior was observed for the higher energies. After 308-nm irradiation with 30 mj cm 2 roughening of the surface was detected. The microstructures reached a maximum intensity after about ten pulses (Fig. 11a) and got less pronounced with successive pulses, as shown for 60 pulses in Fig. 1 lb. 

The microstructures which appear as holes in the pictures have a diameter of about 1 /tm. In the case of 248-nm irradiation the surface appeared different. A well-pronounced nap structure is detected (Fig. 12 a) with growing nap sizes. After 250 pulses (shown in Fig. 12b) the naps reach a size of about 5 /im. On the top of the naps additional material is detected, which grows in some cases to tree-like structures (shown in Fig. 12c). It can also be seen that this material did not cover the surface completely. 

After more than five pulses the trend changes and the contact angle increases drastically, although the SEM pictures show the development of more 

FT-Raman Spectroscopy. In order to get information about the observed chemical changes of the surface, FT-Raman spectroscopy was used to examine the surface after laser irradiation. Due to the high penetration depth of the Nd YAG laser beam of the spectrometer we were well aware that possible information would mainly consist of bulk properties. But nevertheless the spectra are valuable because there is also a large possibility of decomposition, especially of the triazene chromophore in the bulk. Raman spectroscopy was used, as compared to IR spectroscopy, because of the less complex band structure of the polymer and the larger Raman cross section of the N=N-N chromophore. Measurements with normal Raman spectroscopy were not possible, due to a high fluorescence background with the use of visible excitation light. 

After irradiation with 10,000 pulses with 10 mj cm-2 at 308 nm (b), an increase of the bands corresponding to the polymer is detected, whereas the background decreases slightly. No new bands could be detected and the peak ratios remain constant. 

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VOLATILE PRODUCTS ANALYSIS AFTER IRRADIATION OF POLYETHYLENE [272]... 

Holzbecker and Ryan [825] determined these elements in seawater by neutron activation analysis after coprecipitation with lead phosphate. Lead phosphate gives no intense activities on irradiation, so it is a suitable matrix for trace metal determinations by neutron activation analysis. Precipitation of lead phosphate also brings down quantitatively the insoluble phosphates of silver (I), cadmium (II), chromium (III), copper (II), manganese (II), thorium (IV), uranium (VI), and zirconium (IV). Detection limits for each of these are given, and thorium and uranium determinations are described in detail. Gamma activity from 204Pb makes a useful internal standard to correct for geometry differences between samples, which for the lowest detection limits are counted close to the detector. 

The analysis of acid present before irradiation was determined to be 2 x 10 6 mmol for a one micrometer films on a 2 inch wafer. This is a significant fraction of total acid present after irradiation. For a 0.5 mJ/cm2 dose, this is nearly 30% of the total acid content. However, the acid present before exposure is not significant for t-BOC thermolysis. No carbonyl infrared absorbance change was noted following softbake. 

Studies performed at RCRM have shown that hematopoietic and immune systems reconstitution after irradiation depends greatly on the functional abilities of the stem cells. Subset analysis and expression of CD34-i- antigens on bone marrow and peripheral blood cells were studied in Chernobyl accident clean-up workers including patients with leukemia and myelodysplasia and patients exposed to the natural levels of irradiation (table 2). 

The mechanism of the decay reaction of the methyl free radicals at —196° is not known however, the y-ray irradiation of polypropylene at — 196°C. produces only methane and no ethane (36), as demonstrated by gas analysis after warming to room temperature after irradiation. It may be that the methyl free radicals abstract hydrogen atoms on warming to room temperature or that hot methyl radicals are produced during the radiolysis with sufficient excess energy to abstract hydrogen atoms at liquid nitrogen temperature. 

Soxhlet Extraction Analysis. Powdered samples of GMC were degassed and sealed under vacuum into pyrex tubes, and irradiated at room temperature (25-30 °C) in a Cobalt-60 Gammacell. The dose rate determined by Fricke dosimetry was 0.24 Mrad/hr. Doses up to 20 Mrad were utilized. After irradiation, the tubes were opened and the samples placed in cellulose thimbles. A Soxhlet extraction was performed with methylethyl ketone at 76 1°C for 18-20 hrs. The insoluble material was dried to constant weight and the gel fraction calculated from initial weight. 

Only three new amino acids were found (by automatic amino acid analysis) in poly-D,L-alanine after irradiation in 0.1% solution in the absence of O2 with doses to 5 Mrads. All were in yields less than G = 0.02. The first was eluted before aspartic acid and was therefore acidic the second was eluted in the position of aspartic acid, and the third in the position of glycine. We have not been able to confirm the identities of these products by TLC because of the low yields. The products found by amino acid analysis could not account for the discrepancy between amide-like ammonia formed (G = 0.66) and alanine destroyed (G = 1.9). Aspartic acid is formed when alanine is irradiated in solution 26), and it is likely that the carboxylation reaction proposed by these authors also accounts for the observed aspartic acid formation in PDLA. 

The utility of Ge(Li) detectors in activation analysis is best illustrated by their applications to trace element analyses in complex matrices such as rocks, meteorites, and biological materials. Immediately after irradiation of materials of these types the principal activities are due to 24Na and 42K, since sodium and potassium are major matrix components and have favorable activation properties. In order to determine trace element... 

In another case in which a number of exemplary control experiments were done, Markwell and Fox (1980) crosslinked the outer membranes of enveloped viruses with methyl 3-(p-azidophenyl)dithio]propionimidate. Virus (4 mg protein/ml) was reacted with the imidate (0.1 to 0.5 mM) at 0°C for 30 min at pH 8.5. The reaction was quenched with 50 mM ammonium acetate, 50 mM NEM (30 min, 25 °C), and the vims recovered by centrifugation. After irradiation the crosslinked polypeptides were examined in a two-dimensional SDS-polyacrylamide gel. One complication was that the crosslinking pattern had to be compared with a native pattern of disulfide linkages, and a reagent with a different cleavable crosslink may have been a better choice. As mentioned above, the analysis was simplified by the use of surface labeling. 

Absorption at 650 nm was found to increase in around 1 ps in accord with the decay of the absorption at 515 nm after irradiation with a 360-nm laser pulse (fiyhm 180 fs). The absorption bands at 515 and 650 nm were assigned to S i - Sn transitions of the open-ring form (or some intermediate produced from the excited state of the open-ring form) and the closed-ring form, respectively. By taking into account the pulse duration and the time constant of formation of 1.1 ps, this kinetic analysis reproduced the decay and the rise profile. This result clearly indicates that the photocyclization of the dithienylethene took place in 1 ps. 

To determine the photoinduced structure, the orange crystals that were formed after irradiation of benzene solutions of 6-phenoxy-5,12-naphthacenequinone were used.46 It turned out that the elemental composition of the photoinduced form coincided with the ana-quinone composition. In addition, the interaction of 6-phenoxy-5,12-naphthacenequinone with ammonia and aniline in benzene resulted in the formation of compounds that were identified as derivatives of ana-naphthace-nequinone by the counter synthesis. The ana structure of the photoinduced form was supported by the similarity of the absorption spectrum of the ana form to the spectra of unsubstituted and 5-bromo derivatives of 6,12-naphthacenequinone46 as well as by the analysis of the IR spectra of initial and photoinduced forms of 6-phenoxy-5,12-naphthacenequinone. 4... 

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