[en] Naphthylium ions generated by β tritium nuclear decay of 1,4-bitritionaphthalene were allowed to react in the gas phase with benzene. The reaction was studied at benzene pressures ranging from 5 to 60 torr, in the presence of a thermal radical scavenger [O₂]. The effect of the gaseous base [(CH₃)₃N] and of a noble gas [Ar] on the reaction were also investigated. The naphthylium ions react with benzene in the gas phase, yielding 1- and 2-phenylnaphthalenes, whose ratio markedly increases with the pressure of benzene and the concentration of the base. At the higher benzene pressures, and in the presence of the base, the isomeric composition of the products appears kinetically controlled and corresponds to a ratio 1:2 phenylnaphthalenes of 5.75. Moreover, this ratio reaches the value 7.33 in the presence of 400 torr of Argon. The mechanism of the gas phase naphthylation is discussed. (author)

[en] Short communications

[en] Tritiated napththylium ions, generated by spontaneous β-decay of [1,4-³H] naphthalene, have been allowed to react with benzene molecules in gaseous and liquid phase. The isomeric phenylnaphthalenes and fluoranthene have been found among the reaction products. The differences between the reactivity pattern of naphthylium ion in the two phases can be explained by the different efficiency of collisional stabilization of the excited reaction intermediates. (orig.)

[en] The degradation of a mixture of 18 different polycyclic aromatic hydrocarbons (PAHs) has been studied in acetonitrile solution by using γ-radiation at radiation doses of 100, 200 and 300 kGy. The mixture of radiolyzed PAHs was analyzed by liquid chromatography (HPLC) using a diode array detector. Radiolysis at 100 kGy total dose is already sufficient to cause the complete disappearance of all PAHs with the exception of fluorene and crysene which still survive in small amounts. They are known to be among the most radiation-resistant PAHs and can be completely eliminated from the radiolyzed solution by a treatment with ozone. Alternatively higher radiation dose (200 kGy) is needed to eliminate fluorene and crysene completely from the acetonitrile solution. PAHs can be degraded completely with an excess of ozone but the distribution of products is of course different from that obtained by radiolysis and radiolysis followed by ozonolysis. (author)

[en] The abiotic origin of some biologically active molecules and macromolecules have been reviewed. Particular emphasis has been dedicated to the formation of aminoacids and about the possible mechanisms for their asymmetric synthesis and accumulation. The phenomenon of racemization has been explained in detail and then applied in the context of the photo- and radioracemization. Apparent and true photo- and radioracemization have been distinguished. These phenomena play against the preservation of chirality of asymmetric molecules in meteorites and in space. This fact may explain why low enantiomeric excess have been found in meteorites and limited only to certain aminoacids quite uncommon in terrestrial environments. It can be hypothesized that chiral molecules are formed in space for instance under the CPL photolysis and then they are slowly and unselectively degraded and radioracemized by cosmic rays and other high energy radiations. However, the experiment on the radioracemization of certain terpenes has shown that the radioracemization rate is not so dramatically high to cause the complete racemization of the mixture even at very high radiation doses. The radioracemization reaction appears not selective at all, therefore the enantiomeric excess observed only in α-methyl amino acids in meteorites must be attributed to water-thermally driven methamorphism which is instead able to cause selective racemization on α-H amino acids but not on α-methyl amino acids

[en] Anthracite coal and oil bitumen were submitted to γ-radiation at a total dose of 1 MGy and the radiation-processed samples were studied by FT-IR spectroscopy, thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The coal samples were studied also by TGA coupled with FT-IR spectroscopy of the evolved gases. Thermal analysis has revealed a completely different behavior of the radiolyzed samples in comparison to the unirradiated samples. Both for coal and bitumen significantly less volatile fraction was released during the TGA and in both cases a significant increase in the amount of carbon coke produced at 800-900 deg C was observed. The radiation processed bitumen increased significantly its ethyl acetate insolubles content. These results were interpreted in terms of extensive crosslinking and coalification of the samples under the action of γ-radiation. The results of this study have been applied to the carbonization process of terrestrial sedimentary organic matter which is commonly attributed to the action of heat flux from the depth of the Earth but which may be also due to the action of natural radiation. Other application of the results of the present study is to the complex organic matter present on the surfaces of comets and meteorites. This complex matter was formed by exposure of simple precursors to a field of high energy radiation for millions or billions of years and is consequently transformed into coal-like and bitumen-like matter. The same arguments apply to the carbon grains present in the interstellar and circumstellar medium. (author)

[en] A relatively heavy petroleum fraction called distillate aromatic extract (DAE) which has been proposed to be the carrier of the emission bands of certain astronomical objects like protoplanetary nebulae (PPNe) and the so-called unidentified infrared bands (UIBs), has been radiolyzed with γ-radiation to a total dose of 1 MGy. The stability of DAE toward radiation was assessed by FT-IR and electronic spectroscopy. The gases produced during radiolysis have been identified by GC. They were essentially H₂ and CH₄. A certain degree of crosslinking has been verified on the radiation-processed material by measuring the hexane insoluble fraction of DAE, which increased dramatically after the radiation treatment. Further analyses were conducted using high performance liquid chromatography (HPLC) on the radiation processed sample in comparison to the pristine sample. (author)

[en] Three isomeric chiral terpenes, R(+)-limonene, S(-)-limonene and R(-)-α-phellandrene were γ-radiolyzed in sealed vials at room temperature with a total radiation dose of 317 kGy. The radiolyzed samples were analyzed by FT-IR, electronic absorption spectroscopy, liquid chromatography using a diode-array detector (HPLC-DAD) and by polarimetry. Despite a relatively high radiation dose used, all the chiral molecules selected have shown a low radioracemization rate. This fact and the role played by the impurities in the selective radio-degradation of one of the two enantiomers has been discussed in the context of the origin of chirality in prebiotic molecules and the chirality enhancement in a prebiotic world. The results were also discussed in the frame of the radiosterilization technique of chiral drugs, perfumes and food components. (author)

[en] Obsidians from occurrences located in Armenia have been analysed using neutron activation analysis, both instrumental and epithermal, in order to enhance the knowledge of characteristics of potential sources of raw material exploited during prehistory. An alternative characterization technique, the fission-track dating method, was also applied. Results contribute to increase the data-set for provenance studies of prehistoric obsidian artifacts in the Mediterranean and adjacent regions. (author)

[en] The sorptive behavior of tritiated water on natural, irradiated, chemically treated and heated at high temperatures Armenian zeolites was studied and their capacity for the separation and enrichment of tritiated water was evaluated. The distribution coefficients from the batch experiments were calculated for different zeolites and vary between 0.23 and 3.01. The influence of temperature, acidity, basicity, specific activity, electron and gamma-irradiation on sorption has been studied. (author)