Gamma irradiation absorption

Similar to pure polyglycoHc acid and pure polylactic acid, the 90 10 glycolide lactide copolymer is also weakened by gamma irradiation. The normal in vivo absorption time of about 70 days for fibrous material can be decreased to less than about 28 days by simple exposure to gamma radiation in excess of 50 kGy (5 Mrads) (35). 

Polydioxanone (PDS) is completely elirninated from the body upon absorption. The mechanism of polydioxanone degradation is similar to that observed for other synthetic bioabsorbable polymers. Polydioxanone degradation in vitro was affected by gamma irradiation dosage but not substantially by the presence of enzymes (39). The strength loss and absorption of braided PDS, but not monofilament PDS, implanted in infected wounds, however, was significantly greater than in noninfected wounds. 

Ito and Matsuda studied the y-radiolysis of 2-methyltetrahydrofuran (MTHF) solutions of diphenyl sulfone and dibenzothiophene-S,S-dioxide (DBTSD) at 77 K. They found that the radical anions of these sulfone compounds are formed and have intense absorption bands at 1030 nm and 850 nm, respectively. The blue glassy solution of y-irradiated diphenyl sulfone has absorption bands at both 1030 nm and 360 nm while the absorption spectrum of the benzenesulfonyl radical formed by UV irradiation of diphenyl sulfone solution at 77 K showed only a peak at 382 nm. Gamma-irradiated phenyl methyl sulfone solution showed an absorption band only at 385 nm. Consequently the appearance of the absorption bands in 800-1030 nm of diphenyl sulfone and DBTSD may suggest that the unpaired electron is delocalized on two phenyl rings. The same authors studied the radiolysis of MTHF solutions of disulfones (diphenyl and dihexyl disulfones). They found a blue coloring of the solution by the y-radiolysis of diphenyl disulfone and dihexyl disulfone due to absorption peaks at 695 nm and 690 nm respectively, besides smaller absorptions at 300-400 nm. Comparing these results to the previous observation, that phenyl methyl sulfone solution absorbs only at 398 nm, results in the conclusion that the absorption band at 690 nm is due to the linked two sulfone moieties. The authors found that substituents on the phenyl ring lead to shifts in the absorption maxima of the... 

Comparison of this luminescence intensity in different samples reveals that any correlation is absent any impurity concentration. Thus it was supposed that the mostly probable luminescence center is Ti, which presence is quite natural in Ti bearing benitoite. The wide occurrence of Ti " minor impurities in minerals was detected by EPR. Like the other d ions (V, Mo ), Ti ions occur often in minerals as electron center (Marfunin 1979). It may be realized in benitoite, which does have some natural exposure to gamma rays in its natural setting. There could be radiation centers, such as, for example, Ti + gamma ray + electron donor Ti + electron hole. Benitoite color does not change with gamma irradiation to quite high doses (Rossman 1997) but luminescence is much more sensitive compared to optical absorption and can occur from centers at such low concentration that they do not impact the color of a benitoite. 

Allyl Free Radicals. Ayscough and Evans (3) have recently studied, by ESR measurements, the types of allylic free radicals produced by gamma-irradiation of several monomeric olefins. In irradiated polyethylene the allyl free radical is quite stable, persisting for several months at room temperature (31). The presence of these allyl free radicals is most noticeable in the case of high density polyethylene, and this type of free radical is undoubtedly the cause of the slow oxidation of polyethylene at room temperature, which lasts for 40 or more days after irradiation (10). Williams and Dole (40) could observe little if any oxidation of low density polyethylene when it was exposed to air after irradiation. By oxidation we mean formation of carbonyl groups as detected by infrared absorption studies at 1725 cm"1. Parenthetically, it should be noted that adding an oxygen. molecule to a free radical produces initially another type of free radical, a peroxy free radical, but in this paper we shall not discuss free radicals of this or any other types except those of hydrocarbons. 

Figure 2. Changes in infrared absorption following gamma-irradiation of Mylar film (4, 12). Absorption maxima of—OH and —COOH near 2.82 and 3.05 microns, respectively...

The very rapid oxidation of phenols by solvent radical cations can be expected to yield phenol radical cations as the first products. These species are short-lived, except in highly acidic solutions, and were not observed in the microsecond pnlse radiolysis experiments described above. They were detected, however, in frozen matrices and with nanosecond pulse radiolysis Gamma irradiation of phenols in w-butyl chloride or in l,l,2-trichloro-l,2,2-trifluoroethane (Freon 113) at 77 K produced phenol radical cations, which were detected by their optical absorption and ESR spectra . Annealing to 133 K resulted in deprotonation of the radical cations to yield phenoxyl radicals. Pulse radiolysis of p-methoxyphenol and its 2,6-di-fert-butyl derivative in w-butyl chloride at room temperature produced both the phenol radical cations and the phenoxyl radicals. The phenol radical cations were formed very rapidly k = 1.5 x 10 ° M s ) and decayed in a first-order process k = 2.2 x 10 s ) to yield the phenoxyl radicals. The phenoxyl radicals were partially formed in this slower process and partially in a fast process. The fast process of phenoxyl formation probably involves proton transfer to the solvent along with the electron transfer. When the p-methoxy group was replaced with alkyl or H, the stability of the phenol radical cation was lower and the species observed at short times were more predominantly phenoxyl radicals. 

Hamill, Guarino, and Ronayne (II) gamma irradiated 0.18 mole % benzyl chloride in glassy 2-methyltetrahydrofuran (MTHF) at liquid nitrogen temperature and obtained a maximum ultraviolet absorption band at 320 m/x in agreement with Porter and Strachan, see Table I. They also irradiated 1.0 mole % allyl chloride, allyl bromide and allyl alcohol in 3-methylpentane (3-MP) and in all cases observed a maximum absorption band at 228 m/x which they attributed to the allyl free radical. They also irradiated 3-chloro-1-butene and 3-chlorocyclohexene in 3-MP and determined the wavelengths of the absorption band maxima of the 1-methyl allyl and 2-cyclohexen-l-yl free radicals given in Table I. 

Tn an earlier paper (13) p-nitrosodimethylaniline (RNO) was postu-lated to be an efficient scavenger of the OH radical at pH 9 in cobalt-60 gamma irradiated, air saturated, aqueous solutions. It was also postulated to be specific for the OH radical in these solutions since evidence was presented that neither HOL> nor 02 destroyed the chromophoric group at 440 n.m., the absorption maximum of RNO in the visible region of the spectrum for neutral and basic solutions. Relative rate constants for the reaction of OH with RNO and other molecules were reported to be in good relative agreement with those reported by others who used both the pulse radiolysis method and indirect competition techniques. 

OPTICAL ABSORPTION AND DEFECTS IN GAMMA-IRRADIATED ROCHELLE SALT CRYSTALS. //ENGLISH TRANSLATION OF IZV. AKAD. NAUk SSSR, SER. FIZ. 33 111 287-1969.//... 

IR spectroscopic analysis showed that the treatment of polyacrylonitrile films and fibres by gamma-irradiation led to cleavage of the polymer chains forming carbonyl-containing functional groups, the composition of which depended on the treatment conditions. The presence of terminal methyl groups in the treated polymer was detected in its IR spectra only in the presence of residual basic solvent. The occurrence of conformational changes was revealed by the behaviour of the absorption bands. 12 refs. 

Figure 11.1 shows a collection of FTIR spectra through the thickness of a shelf-aged, EtO-sterilized cup where bulk oxidation was evident. Gamma irradiation of the UHMWPE was ruled out by examination of the transvinylene region of the ETIR spectra. The absorption at 1718 cm i is attributed to ketones. In this case, the oxidation was associated with poor consolidation of the UHMWPE, rather than the result of the sterilization process itself. These results suggest that prosthetic UHMWPE needs stabilization, as the totality of commercial polyolefines. Biocompatible stabilizers, such as vitamin E (an a-tocopherol), are easily available on the market and already employed in a number of different applications (Costa et al. 1998b, Costa et al. 2000). 

Figure 6. The absorption spectra of in ultraviolet region for the initial and irradiated polymers 1- PP 2-PVA 3-PMMA (The solid line -initial samples the dashed line- gamma-irradiated samples common losses)...

The absorption of PVA in spectral range 190-300 nm is due to carbonyl chromophoric groups, which are obtained as a result of oxidation process with participation of atmospheric oxygen [76], The small increase in transmission in the spectral range of 185-193 nm, as indicated by the dependence of Aae =f(R, ) is in the case of PMMA due to the dynamic and concurrent processes of destruction and scission of the polymer macro-chains rmder the influence of gamma-irradiation ( - the spectral index of common loses of absorption and scattering forgiven sample) [76],... 

Figure 2. Absorption spectrum of silver particles produced by "push-pull" reduction, where each silver atom undergoes several reduction-reoxidation cycles before it is finally reduced. The initiation of reduction occurs by gamma irradiation. The solution contained I.O IO" M AgC104 and l.OTO" M sotfium polyphosphate." ...

J.S. Mitchell, Increase in ultra-violet absorption of cytoplasm after therapeutic X- and gamma-irradiation. Nature 146, 272-273 (1940)... 

Both flie design and operation of commercial nuclear power plants are planned with the safety of the public foremost in mind. Therefore, plants rely on multiple barriers to protect the public from flie highly radioactive fuel and the multitude of radioactively hot materials created in the core. While the fuel itself is obviously radioactive, normally nonradioactive materials can also become hot by neutron absorption and gamma irradiation while inside the core. 

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