Thermal Stability of γ-irradiated Tolbutamide

The thermal stability of tolbutamide before and after exposure to various γ-radiation doses was investigated. The data were followed by studying DTA, X-ray diffraction, IR, and UV absorption spectra before and after γ-irradiation. The results obtained were promising, and were explained, and discussed on the basis of γ-enhanced stabilization through recombination of free radicals. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of effects of γ-irradiation on Tuffak polycarbonate track detector by TG

Effects induced by r-irradiation in the dose range of 0–10 Mrad on Tuffak polycarbonate track detector films have been studied by thermogravimetry (TG). The samples were irradiated with ⁶⁰Co r-rays for doses of 3, 5 and 10 Mrad. The TG studies indicate that unirradiated and the r-irradiated samples degrade in two steps. The kinetics of the two steps of degradation was also evaluated from the TG curves. Irradiation enhances the degradation rate and the effect increases further with increasing radiation dose. The activation energy values calculated for all the steps decrease on irradiation. A linear relationship observed between the decrease in activation energy and the dose received by the sample suggests the possibility of the use of Tuffak polycarbonate detector as r dosimeter.The authors are thankful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his encouragement and support during this work.     

Sputtering and backscattering of keV light ions bombarding random targets

The fission fragment fluence required to render CaUO₄, Na₂U₂O₄, MgUO₄, Sr₂U₃O₁₁ and u₃O₈ x-ray amorphous was deduced as ～5 × 10¹⁵ events cm³. Significant annealing of the structural damage occurred in the 300–-500°C range.     

Investigation of dosimetric properties of barium and strontium dithionates

An investigation is made of the dosimetric properties of proposed spin-resonance γ-radiation dose meters based on Ba and Sr dithionates. Their operating range (0.1 Gy−50 kGy for Ba dithionate and 0.2 Gy−80 kGy for Sr dithionate) is established. Their advantages over the EPR/L-α dose meter are discussed: the narrow isotropic EPR signal, higher radiation sensitivity, large range of linear response. Conditions of storage and use of dithionate-based dose meters (temperature of 15–25°C, relative air humidity no more than 80%) are determined. Institute of Physical Organic Chemistry of the National Academy of Sciences of Belarus, 13, Surganov St., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 372–376, May–June, 1998.     

Immobilization of stationary liquids on silica particles by γ-radiation

Summary Continuing our work on new silanization reagents for producing chemically-modified small-particle, silica support material exhibiting improved chromatographic performance and especially good shielding of silanol groups in respect of solute-stationary phase interaction, we have developed new silica-based polymer phases with different polarities by crosslinking or polymerization reactions induced by -radiation.Polybutadienes or polysiloxanes were immobilized on non-, or specially presilanized, 5m silica particles by using different dose-rates of -radiation and by addition of different amounts of allylmethacrylate as a radical stabilizer.The materials obtained were tested by elemental analysis, scanning electron microscopy, ESCA and IR-reflexion measurements as well as by chemical Si–OH determinations. Chromatographic testing has been carried out with different, especially strongly basic solutes, under normal and reversed phase conditions.The dual retention mechanism model of Nahum and Horvath [1] was applied to the usual commercially available phases and those phases produced by ourselves. The influences of mobile phase additives such as acetonitrile or tetrahydrofuran were also investigated following the chromatographic test procedures for characterization of the support materials synthesized. The silicas obtained show excellent long term stability to all types of HPLC solvents. Their inertness with respect to irreversible adsorption of polar, especially basic, compounds can only be compared with that of reticular bulk polymer stationary phases without any silica skeleton. Unlike pure polymer particles these materials exhibit high pressure stability, only moderate shrinking and swelling effects, and most importantly, high plate numbers, comparable with normal brushtype stationary phases.Dedicated to Professor A. Zlatkis on the occasion of his 60th birthday.     

DSC ofγ-irradiated ultra-high molecular weight polyethylene and high density polyethylene of normal molecular weight

The melting and the crystallization of-irradiated (doses: 0–6Mrad) ultra-high molecular weight nascent polyethylene (UHMWPE) and high density nascent polyethylene with normal molecular weight (NMWPE) were investigated by DSC. The heat of melting of the nascent UHMWPE (DSC degree of crystallinity, respectively) increases up to a dose of 3 Mrad, after which it slightly decreases. The heat of the second melting of UHMWPE and of the first and second melting of NMWPE increases slightly up to a dose of 3 Mrad, after which it does not change. The X-ray degree of crystallinity of the nascent non-irradiated and irradiated polymers was 0.62±0.02. The calorimetric crystallinity was compared to the X-ray one. The results show that radiation does not affect the polymer crystallinity, but influences the thermodynamic heat of melting. The increase ofH _m vs. dose in UHMWPE is explained in terms of processes of tie molecule scission within the amorphous regions and on the surface of the crystals, which predominate over crosslinking up to a dose of 3 Mrad. That leads to an increase in the conformational mobility of the molecules and to an increase in the enthalpy, according to Peterlin's formula. The scission of the chains at the points of entangling of the tie molecules leads to a decrease in the temperature and to an increase in the enthalpy of crystallization of UHMWPE vs. dose. In NMWPE these effects are considerably weaker.     

The atkermal stress component in neutron irradiated mild steel

Abstract

The temperature dependence of the tensile lower yield stress of an annealed aluminium grain size controlled mild steel has been investigated in the range 23–250 °C and at a strain rate of 1.67 × 10^?4 sec^?l before and after neutron irradiation to 2.3 × 10¹⁸ n/cm² (fission). The yield stress of the irradiated steel decreases with increasing temperature due to thermal activation of the radiation damage and is predicted to reach asymptotically that of the unirradiated steel at ～285 °C; the maximum test temperature was below that at which thermal annealing of the damage occurs. This implies that the athermal stress component due to irradiation is zero and hence there is negligible long range interaction between dislocations and radiation-induced defects.     

Synthesis and thermoluminescence characteristics of γ-irradiated K3Ca2(SO4)3F:Eu or Ce fluoride

New halophosphor K₃Ca₂(SO₄)₃F activated by Eu and Ce has been synthesized by a co-precipitation method and characterized according to its thermoluminescence. The formation of traps in rare earth doped K₃Ca₂(SO₄)₃F and the effects of γ-radiation dose on the glow curve are discussed. The glow curve of K₃Ca₂(SO₄)₃F:Ce shows a prominent single peak at 150°C, whereas K₃Ca₂(SO₄)₃F:Eu and K₃Ca₂(SO₄)₃F:Ce,Eu at 142°C and 192°C, respectively. A single glow peak indicates that there is only one set of trap being activated within the particular temperature range. The presented phosphors are also studied because of its fading, reusability and trapping parameters. There was just 2% fading during a period of 10 days, indicating no serious fading problem. Trapping parameters such as order of kinetics (b), activation energy (E) and frequency factor (S) were calculated by using Chen's half-width method. The observations presented in this paper are good for lamp phosphors as well as solid-state dosimeter.     

Properties of polymer track membranes modified by grafting with poly(2-methyl-5-vinylpyridine) and poly(N-isopropylacrylamide)

The properties of track membranes (TM) based on poly(ethylene terephthalate) (PETP) and polypropylene (PP) and modified by radiation-induced graft polymerization of 2-methyl-5-vinylpyridine (MVP) andN-isopropylacrylamide (NIPAA) were studied. The rate of grafting and the limiting degree of grafting increase linearly as the pore diameter of TM increases. The gasdynamic and hydrodynamic pore diameters of modified TM were determined. The dependence of water permeability of TM modified by grafting with poly(2-methyl-5-vinylpyridine) (PMVP) on the degree of grafting passes through a maximum, which, according to the data of wetting angle measurements, corresponds to the maximum hydrophilicity. The negative χ-potential of TM changes sign after modification by grafting with PMVP. Thermosensitive TM based on PETP and PP were prepared by radiation-induced graft polymerization of NIPAA. The structure of modified TM was studied by electron microscopy and atomic force microscopy. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 858–864, May, 2000.     

Syntheses of stationary phases for reversed-phase LC using silanization and polymer coating

Summary Various methods and reagents for silanization of silicas originating from different manufacturers were investigated in comparison to the method published by the authors which makes use of an enolate of acetylacetone. This reagent proved to be highly reactive. New types of reversed phase materials were also synthesized by polymer coating applying crosslinking and chemical bonding to the surfaces of silica and alumina. In this work dicumyl peroxide and azo-t-butane were used for radical generation. The reversed phase materials obtained with alumina can be used for separations at P_H-values up to 12. Silica materials begin to already be deteriorated at a P_H-value of 8. Dedicated to Professor G. Wilke on the occasion of his 60th birthday. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984