International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry最新文献

The study of the radio degradation of DNA is one of a number of phenomena being investigated to develop methods for identifying irradiated foods. The specific behaviour under radiation of the mitochondrial DNA from beef liver gives the possibility of detecting if the product has been irradiated or not. An identification method could finally be developed. The appraisal of the mitochondrial supercoiled DNA fraction constitutes an unambiguous detection test for beef liver irradiation. A total of 120 different samples were irradiated at 5 different doses. The dose limit of detection is lower than 2 kGy. No effects due to storage conditions were observed.

Protection effect of aromatic (naphthalene, phenanthrene) and hydroaromatic (tetralin, octahydrophenanthrene) compounds in irradiated liquid alkane has been investigated as a model experiment for the radiolysis of polymers. Liquid n-hexadecane has been selected as the model linear amorphous polymer and the protection effect has been studied by analyzing the radiolysis products. In the presence of additives, degradation of n-hexadecane, reduction of radiolysis products, including H₂ evolution, and selective degradation of the additive have been observed. Energy transfer (excitation and charge) to the additive reduces the solvent excitation which is the precursor of the radiolysis products. The additive reacts with the solvent molecules according to its reactivity to form adduct compounds. Mass analysis shows that these adduct compounds have a smaller number of double bonds in their aromatic rings due to hydrogenation. Aromatic compounds are more reactive than hydroaromatic compounds towards n-hexadecane and their adducts consume more hydrogen than those of the hydroaromatic compounds, and therefore aromatic compounds reduce gas formation more effectively than hydroaromatic compounds. From the effect of aromatic compounds, it is concluded that hexadecene is produced neither by H₂ elimination from the lowest excited state of n-hexadecane nor by disproportionation of n-hexadecyl radicals, but is mainly produced directly from the decomposition of the excited cations of n-hexadecane.

Radiation-induced radicals in sulfite-doped calcite and aragonite were characterized by ESR. Among the many ESR signals produced, only four signals are dependent on the SO^2-₃ concentration; an axial signal (g_⊥=2.0038 and g|=2.0024) in calcite, and an orthorhombic signal (g₁=2.0042, g_2=2.0038 and g₃=2.0025), an isotropic signal (g=2.0034) and an isotropic signal (g=2.0060) in aragonite. The former two signals exhibit hyperfine structures arising from ^33S$\text{(I=}\text{3}\text{2}\text{, 0.75\%}$ natural abundance), and are attributed to SO^-₃ radicals. The isotropic signal at g=2.0034 in aragonite is considered to be due to rotating SO^-₃ radicals. Rotating or tumbling molecules (probably SO^-₂) produced by thermal decomposition of SO^2-₃ seem to be responsible for the isotropic signal at f=2.0060.

Electron impact cross sections for various electronic excited states and for ionization of water vapor are represented by analytic forms that cover non-relativistic as well as relativistic energy region. This inelastic cross section set may serve as a convenient input for electron transport calculations relevant in several fields. With this cross section input an electron energy deposition study has been carried out using a Monte Carlo simulation giving excitation and ionization yields, the Fano factor and the subexcitation spectra for initial energies up to 1 MeV.

The bimolecular rate constants for the reaction of e^-_aq with chlorotoluenes, chloronitrobenzenes and chloronitrotoluenes have been determined from the decay of e^-_aq. With chlorotoluenes, e^-_aq reacts by dissociative electron capture without any transient absorption band in 270–500 nm region. In case of chloronitrobenzenes and chloronitrotoluenes, e^-_aq forms a transient band with λ_max in 290–310 nm region without any Cl^- formation. Hydroxyl alkyl radicals, derived from alcohols, do not seem to react with chlorotoluenes whereas a transient species with λ_max=305–315 nm region are formed on addition of hydroxy alkyl radical to —NO₂ group of chloronitrobenzenes.

Additive effects of hydroaromatics towards radiation degradation and post-oxidation of high density polyethylene and isotactic polypropylene were investigated. At the same time, the radical scavenging effects of hydroaromatics were examined using DPPH(N,N-diphenyl-N'-picrylhydrazyl). It was found that:

• 1.

  (1) the addition of HHAP (multi-component type hydroaromatics, produced by the hydrogenation of highly aromatic heavy fraction from petroleum) was obviously effective in inhibiting both radiation (electron beam in air) degradation and post-oxidation of polyolefins,

• 2.

  (2) hydroaromatics (tetralin, octahydrophenanthrene and HHAP) have evident radical scavenging abilities from the tests using DPPH and

• 3.

  (3) the inhibiting effects of HHAP can be attributed to its radical scavenging ability.

Wood-plastic composite (WPC) has been prepared with simul using acrylamide (AM), a water soluble monomer, in place of styrene (ST) and butylmethacrylate (BA). The highest polymer loading (PL) is achieved with AM along with the highest tensile strengths (TS) among the three bulk monomers studied. Effect of urea, NVP and TMPTA has been investigated in these systems. Co-additive (urea) has played a significant role in presence of NVP and TMPTA with AM compared to ST and BA systems. Methanol, water and water/methanol mixtures have been used as swelling agents in order to study their effect on PL and T_f values. TS loss due to the weathering effect is minimum with the WPC, particularly if prepared with swelling agent methanol.

Wood-plastic composite (WPC) formation has been studied with simul+styrene system at various compositions of styrene with methanol as the swelling solvent. Effect of additives, e.g. multifunctional monomers (MFM) and oligomers used in very low quantity (1% v/v) on the polymer loading (PL) and tensile strength (TS) of the WPC has been elaborately investigated. Enhanced PL and TS values are observed. Inorganic co-additives like Lithium (Li⁺), Copper (Cu²⁺) and acid (H⁺) and urea (U) used in combinations with additives (MFM or oligomers) have influenced the results of PL and TS in these systems. Li⁺ ion has been a good replacement for H⁺ ion; U has substantially enhanced the PL values with retention of the TS values of WPC. Co-additive Cu²⁺ used in these system can act as a preservative and protective agent for WPC.

Evidence is presented for the radiation-induced transmethylation and transsulfuration in a DNA-methionine model system. The extent of such alkylation of DNA is found to be comparable with that of alkylating agents. Therefore, both processes could be initial steps in radiation carcinogenesis.

The protective effect of methionine on DNA strand breaks, due to scavenging of OH radicals, causes the formation of methyl and thiyl radicals.

The pulse radiolysis of low density polyethylene (LPDE), using optical absorption detection and emission spectroscopy, has been investigated in the temperature range 6–150 K, the experiments being complemented by a study of the photoluminescence.

It was found that excitons can be autolocalized at temperatures below 20 K, and this process is strongly dependent on the thermal history of the sample.