Study of polypropylene/polybutene blends modified by gamma irradiation and (high melt strength polypropylene)/polybutene blends

It is well-known that polypropylene (PP) is difficult to process as a consequence of its linear structure. It is also known that grafting of long-chain branches on PP backbone using ionizing radiation is an effective approach to achieve high melt strength polypropylene (HMS PP). Chain-scission and, in minor extend, crosslinking and grafting are the predominant reaction in order to branch PP backbone. However, if multifunctional monomers are used to promote the grafting reaction, crosslinking can surpass chain scission and grafting, reducing drawability. Therefore, in an effort to enhance the processability and so the drawability, it has been found helpful to add a small amount of polybutene-1. Gamma irradiation technique was used to induce chemical changes in blends of PP and polybutene in acetylene atmosphere (crosslinker promoter) and in HMSPP/polybutene blends. The samples were irradiated with a ⁶⁰Co source with doses of 12.5 and 20 kGy in the presence of acetylene. In this work, two different methods of blends processing were compared regarding rheological and mechanical properties. Effects on the strength and elongation at the yield point and at rupture were observed by mechanical tests and showed decrease of tensile strength and increase of elongation at rupture for samples obtained by irradiation of blends. The results from rheology demonstrated an increase in melt strength and drawability of blends.     

Neutron radiation effects on metal oxide semiconductor (MOS) devices

The main purpose of this study is to provide the knowledge and data on Deuterium-Tritium (D-T) fusion neutron induced damage in MOS devices. Silicon metal oxide semiconductor (MOS) devices are currently the cornerstone of the modern microelectronics industry. However, when a MOS device is exposed to a flux of energetic radiation or particles, the resulting effects from this radiation can cause several degradation of the device performance and of its operating life. The part of MOS structure (metal oxide semiconductor) most sensitive to neutron radiation is the oxide insulating layer (SiO₂). When ionizing radiation passes through the oxide, the energy deposited creates electron-hole pairs. These electron-hole pairs have been seriously hazardous to the performance of these electronic components. The degradation of the current gain of the dual n-channel depletion mode MOS caused by neutron displacement defects, was measured using in situ method during neutron irradiation. The average degradation of the gain of the current is about 35 mA, and the change in channel current gain increased proportionally with neutron fluence. The total fusion neutron displacement damage was found to be 4.8 × 10⁻²¹ dpa per n/cm², while the average fraction of damage in the crystal of silicon was found to be 1.24 × 10⁻¹². All the MOS devices tested were found to be controllable after neutron irradiation and no permanent damage was caused by neutron fluence irradiation below 10¹⁰n/cm². The calculation results shows that (n,α) reaction induced soft-error cross-section about 8.7 × 10⁻¹⁴ cm², and for recoil atoms about 2.9 × 10⁻¹⁵ cm², respectively.     

Evaluation of alloy 690 process pot at the contact with borosilicate melt pool during vitrification of high-level nuclear waste

Understanding the material behaviour under service conditions is essential to enhance the life span of alloy 690 process pot used in vitrification of high-level nuclear waste. During vitrification process, interaction of alloy 690 with borosilicate melt takes place for substantial time period. Present experimental studies show that such interactions may result in Cr carbide precipitation along grain boundaries, Cr depletion in austenitic matrix and intergranular attack close to alloy 690/borosilicate melt pool interfaces. Widths of Cr depleted zone within alloy 690 is found to follow kinetics of the type x = 10.9 × 10⁻⁶ + 1 × 10⁻⁸t^1/2 m. Based on the experimental results it is recommended that compositional modification of alloy 690 process pot adjacent to borosilicate melt pool need to be considered seriously for any efforts towards reduction and/or prevention of process pot failures.     

A fast method for the determination of the efficiency coefficient of bare CR-39 detector

A fast and simple method for the determination of the efficiency coefficient (η) of bare CR-39 detector is presented and discussed. The efficiency coefficient of bare CR-39 detector is then calculated by different ways and the obtained values are found to be comparable to each other. The average value of η of bare CR-39 is found to be 0.20 ± 0.01 tracks cm⁻² day⁻¹ per Bq m⁻³.     

Measurement of density distribution of a cracking catalyst in experimental riser with a sampling procedure for gamma ray tomography

By scanning a riser the number of the gamma ray trajectories and the beam width involve temporal, spatial and density resolutions as they are closely correlated parameters. Therefore, evaluation of parameters and their interaction quantification, certainly, are required in the imaging process. Measuring the density distribution of the catalyst from the FCC - fluid cracking catalytic process in an experimental riser in single beam tomographic system, density resolution is evaluated and correlated with spatial resolution. The beam width Δs inside riser is measured and a criterion for determining spatial resolution is proposed. Experiments are carried out to demonstrate resolution effects of three Δs values: 3.30 × 10⁻³, 6.20 × 10⁻³ and 12.00 × 10⁻³ m. The gamma beam profile is modeled and a sampling rate according to Nyquist criterion is analyzed. The 4.3%, 8.1% and 15.6% ratios of Δs/R to internal riser radius are correlated to counting time in the sampling procedure. Results are discussed by comparison with values from literature.     

Radiation-induced grafting of N-isopropylacrylamide and acrylic acid onto polypropylene films by two step method

Binary graft copolymerization of pH sensitive acrylic acid (AAc) and thermosensitive N-isopropylacrylamide (NIPAAm) monomers onto pre-irradiated polypropylene films (PP) was carried out by two individual steps using a Co⁶⁰ gamma radiation source. The influence of preparation conditions, such as pre-irradiation dose and reaction time on grafting yield was studied. The swelling behavior and FTIR-ATR study for PP films grafted films were investigated.     

Synchrotron X-ray induced damage in polymer (PS) thin films

Thin polystyrene (PS) films (M_w = 234,000) are spin coated on silicon substrates with a Chromium (Cr) layer as a sandwiched metallic layer that produces photoelectrons (by synchrotron X-rays). Earlier studies on synchrotron radiation damage in PS films, without metallic layer, have shown a decrease in interfacial roughness and a slight increase in thickness, at temperatures below T_g [A.G. Richter, R. Guico, K. Shull, J. Wang, Macromolecules 39 (2006) 1545]. Similar trend is observed in the presence of a thin layer of Cr film (∼2.5 nm). For the sample with a thick Cr layer the opposite effect was observed for X-ray radiation damage. For the 50 nm thick Cr film system thickness of the polystyrene film decreased by ≈4.4% which amount to a loss of about 0.021 nm³ per incident photon in the fluence range studied (6.8 × 10⁹ photons mm⁻² to 1 × 10¹⁴ photons mm⁻²). Interfacial roughness also increased from about 1.0 nm to 2.1 nm in the process. These effects are explained by invoking the presence of more number of X-ray induced photoelectrons and secondary electrons for 50 nm thick Cr film case compared to 2.5 nm thin film case.     

Measurement of natural radioactivity and radon exhalation rate from rock samples of Jaduguda uranium mines and its radiological implications

The Singhbhum shear zone is a 200 km long arcuate belt in Jharkhand state situated in eastern India. The central part between Jaduguda-Bhatin-Nimdih, Narwapahr-Garadih-Turamdih is rich in uranium. Presence of uranium in the host rocks and the prevalence of a confined atmosphere within mines could result in enhanced concentration of radon (²²²Rn) gas and its progeny. Inhalation of radon daughter products is a major contributor to the radiation dose to exposed subjects. By using high resolution γ-ray spectroscopic system various radionuclides in the rock samples, collected from different places of Jaduguda uranium mines have been identified quantitatively based on the characteristic spectral peaks. The activity concentrations of the natural radionuclides, uranium (²³⁸U), thorium (²³²Th) and potassium (⁴⁰K) were measured in the rock samples and radiological parameters were calculated. Uranium concentration was found to vary from 123 ± 7 Bq kg⁻¹ to 40,858 ± 174 Bq kg⁻¹. Activity of thorium was not significant in the samples, whereas, few samples have shown potassium activity from 162 ± 11 Bq kg⁻¹ to 9024 ± 189 Bq kg⁻¹. Radon exhalation rates from these samples were also measured using “Sealed Can technique” and found to vary from 4.2 ± 0.05 to 13.7 ± 0.08 Bq m⁻² h⁻¹. A positive correlation was found between the radon exhalation rate and the uranium activity. The absorbed dose rates vary from 63.6 to 18876.4 nGy h⁻¹, with an average value of 7054.2 nGy h⁻¹. The annual external effective dose rates vary from 0.7 to 23.2 mSv y⁻¹. Radium equivalent activities (Ra_eq) varied from 134.3 to 40858.0 Bq kg⁻¹. Value of external hazard index (H_ex) varied from 0.4 to 110.4 with an average value of 41.2.     

Characterization of gamma-stabilized PP with blends of hindered amine/phenolic stabilizers

In this work, the effect of γ radiation at doses of 25 and 50 kGy on polypropylene (PP) stabilized with a binary system of antioxidants of the phenol-hindered amine type (BHT-Chimassorb 994) at different compositions (0.1/0.2, 0.1/0.5, 0.1/0.8) was studied. The results showed that the carbonyl index (I_c) of the stabilized samples drastically decreases when compared to that of the pure PP sample. Nonetheless, the I_c values of the different stabilized samples were very similar after irradiation. On the other hand, the average molecular weights (M_w and M_n) and melt flow index (MFI) values decrease in all the samples after irradiation. This effect is less pronounced in PP with 0.1/0.8 of the binary blend of antioxidants. The melting and crystallization peak temperatures and the crystallinity degree remained almost unchanged and the tensile properties such as Young’s modulus and tensile strength did not vary either, except for the elongation at break, which decreases in less proportion in those blends of PP with the antioxidants, independently of the absorbed dose.     

Effect of gamma irradiation on a polymer electrolyte: Variation in crystallinity, viscosity and ion-conductivity with dose

PEO(1 − x)NH₄ClO₄(x) samples with x = 0.18 are irradiated with gamma doses varying up to 50 kGy. DSC and XRD studies indicate, in general, a decrease in crystallinity with dose. Measurement of viscosity of aqueous solutions of the irradiated samples at the same concentration, shows that there is overall chain scission on irradiation, though there is evidence of some cross-linking also at higher doses. This is corroborated by FTIR measurements. The ion-conductivity shows a strong increase for irradiation dose 35 kGy. This suggests that there is a possibility of improving polymer electrolyte properties on gamma irradiation.     

In situ determination of radon concentration and total gamma radiation in Kastel Gomilica, Croatia

To determine current radiation background of the environment at the “Giricic” location in Kastel Gomilica, Croatia, in situ measurement of radon concentration (²²²Rn and ²²⁰Rn) in an open atmosphere on a ground level and at the height of 1.5 m has been made as well as total gamma radiation at the height of 1 m in an energy range of 15 keV to 2 MeV. The researched location was divided in three specific parts: (i) regulated area with the bottom ash and flying ash in the basis (“old” depot), (ii) unregulated area with waste materials, including bottom ash and flying ash, in the basis (“new” depot), (iii) uncontaminated area with no waste materials deposited on. Average radon concentration on a ground level was 213 Bq/m³ for the “old” depot, 214 Bq/m³ for the “new” depot and 59 Bq/m³ for the uncontaminated area and at the height of 1.5 m 20 Bq/m³ for the “old” depot, 34 Bq/m³ for the “new” depot and 26 Bq/m³ for the uncontaminated area. Average total gamma radiation values in selected energy range were 109.92 cps (counts per second) for the “old” depot, 357.76 cps for the “new” depot and 65.97 cps for the uncontaminated area. For selected radionuclides (²¹⁴Pb, ¹³⁷Cs, ²²⁸Ac, ^234mPa, ⁴⁰K and ²¹⁴Bi) average gamma radiation values at characteristic energies have been determined as well.     

Effect of external gamma irradiation on dissolution of the spent UO2 fuel matrix

Leaching experiments were performed on UO₂ pellets doped with alpha-emitters (^238/239Pu) and on spent fuel, in the presence of an external gamma irradiation source (A⁶⁰Co = 260 Ci,  Gy h⁻¹). The effects of α, β, γ radiation, the fuel chemistry and the nature of the cover gas (aerated or Ar + 4%H₂) on water radiolysis and on oxidizing dissolution of the UO₂ matrix are quantified and discussed. For the doped UO₂ pellets, the nature of the cover gas clearly has a major role in the effect of gamma radiolysis. The uranium dissolution rate in an aerated medium is 83 mg m⁻² d⁻¹ compared with only 6 mg m⁻² d⁻¹ in Ar + 4%H₂. The rate drop is accompanied by a reduction of about four orders of magnitude in the hydrogen peroxide concentrations in the homogeneous solution. The uranium dissolution rates also underestimate the matrix alteration rate because of major precipitation phenomena at the UO₂ pellet surface. The presence of studtite in particular was demonstrated in aerated media; this is consistent with the measured H₂O₂ concentrations (1.2 × 10⁻⁴ mol L⁻¹). For spent fuel, the presence of fission products (Cs and Sr), matrix alteration tracers, allowed us to determine the alteration rates under external gamma irradiation. The fission product release rates were higher by a factor of 5-10 than those of the actinides (80-90% of the actinides precipitated on the surface of the fragments) and also depended to a large extent on the nature of the cover gas. No significant effect of the fuel chemistry compared with UO₂ was observed on uranium dissolution and H₂O₂ production in the presence of the ⁶⁰Co source in aerated conditions. Conversely, in Ar + 4%H₂ the fuel self-irradiation field cannot be disregarded since the H₂O₂ concentrations drop by only three orders of magnitude compared with UO₂.     

Radiation-induced phenomena related to electrical properties of hydrogen-doped strontium-cerium-ytterbium oxides under reactor irradiation

The effects of radiation on the electrical properties of hydrogen-doped (H-doped) strontium-cerium-ytterbium oxide (SrCe_0.95Yb_0.05O_3−δ), a perovskite-type ceramic, were investigated by irradiating specimens with thermal and fast neutrons and gamma rays in a fission reactor. The electrical conductivities of the H-doped SrCe_0.95Yb_0.05O_3−δ, which were measured at thermal and fast neutron fluxes of 4.1 × 10¹⁷ and 2.7 × 10¹⁶ n/m²s and an ionizing dose rate of 0.5 kGy/s, were approximately two orders of magnitude higher than the base conductivity in the absence of radiation and slightly higher compared to those of the non-doped SrCe_0.95Yb_0.05O_3−δ. The radiation-induced phenomena on the electrical properties can allow radiation-enhanced diffusion of H as well as electronic excitation, which is caused by ionization effects. It was observed that the radiation-enhanced diffusion of H significantly depended on the irradiation temperatures in the range 384-519 K, whereas it was not affected by radiation-induced defects produced with a fast neutron fluence of approximately 1.3 × 10²³ n/m² under the present experimental conditions.     

Thermal conductivities of hypostoichiometric (U, Pu, Am)O2−x oxide

The thermal conductivities of (U_0.68Pu_0.30Am_0.02)O_2.00−x solid solutions (x = 0.00-0.08) were studied at temperatures from 900 to 1773 K. The thermal conductivities were obtained from the thermal diffusivities measured by the laser flash method. The thermal conductivities obtained experimentally up to about 1400 K could be expressed by a classical phonon transport model, λ = (A + BT)⁻¹, A(x) = 3.31 × x + 9.92 × 10⁻³ (mK/W) and B(x) = (−6.68 × x + 2.46) × 10⁻⁴ (m/W). The experimental A values showed a good agreement with theoretical predictions, but the experimental B values showed not so good agreement with the theoretical ones in the low O/M ratio region. From the comparison of A and B values obtained in this study with the ones of (U,Pu)O_2−x obtained by Duriez et al. [C. Duriez, J.P. Alessandri, T. Gervais, Y. Philipponneau, J. Nucl. Mater. 277 (2000) 143], the addition of Am into (U, Pu)O_2−x gave no significant effect on the O/M dependency of A and B values.     

Formation of silicon hydride using hyperthermal negative hydrogen ions (H) extracted from an argon-seeded hydrogen sheet plasma source

An E × B probe (a modified Wien filter) is constructed to function both as a mass spectrometer and ion implanter. The device, given the acronym EXBII selects negative hydrogen ions (H⁻) from a premixed 10% argon-seeded hydrogen sheet plasma. With a vacuum background of 1.0 × 10⁻⁶ Torr, H⁻ extraction ensues at a total gas feed of 1.8 mTorr, 0.5 A plasma discharge. The EXBII is positioned 3 cm distance from the sheet core as this is the region densely populated by cold electrons (T_e ∼ 2 eV, N_e ∼ 3.4 × 10¹¹ cm⁻³) best suited for H⁻ formation. The extracted H⁻ ions of flux density ∼0.26 A/m² are segregated, accelerated to hyperthermal range (<100 eV) and subsequently deposited into a palladium-coated 1.1 × 1.1 cm², n-type Si (1 0 0) substrate held at the rear end of the EXBII, placed in lieu of its Faraday cup. The palladium membrane plays the role of a catalyst initiating the reaction between Si atoms and H⁻ ions simultaneously capping the sample from oxidation and other undesirable adsorbents. AFM and FTIR characterization tests confirm the formation of SiH₂. Absorbance peaks between 900-970 cm⁻¹ (bending modes) and 2050-2260 cm⁻¹ (stretching modes) are observed in the FTIR spectra of the processed samples. It is found that varying hydrogen exposure time results in the shifting of wavenumbers which may be interpreted as changes in the frequencies of vibration for SiH₂. These are manifestations of chemical changes accompanying alterations in the force constant of the molecule. The sample with longer exposure time exhibits an additional peak at 2036 cm⁻¹ which are hydrides of nano-crystalline silicon.     

Electrical properties of silicon diodes with pn junctions irradiated with Au swift heavy ions

Electrical properties of silicon diodes with p⁺n junctions irradiated with ¹⁹⁷Au⁺²⁶ swift heavy ions (energy E = 350 MeV, fluences of 10⁷ cm⁻² and 10⁸ cm⁻²) and silicon diodes irradiated with electrons (energy E = 3.5 MeV, fluences of 10¹⁵ cm⁻², 5 × 10¹⁵ cm⁻² and 10¹⁶ cm⁻²) have been investigated. Frequency dependences of the impedance, current-voltage characteristics and switching characteristics of these devices have been studied. Irradiation of the diodes with ¹⁹⁷Au⁺²⁶ ions at a fluence of 10⁸ cm⁻² leads to the formation of a quasi-continuous layer of irradiation-induced defects that enable a combination of characteristics such as a reverse resistance recovery time and direct voltage drop that are better than those for electron-irradiated diodes. Still, the irradiation of high-energy ions results in an increase in recombination currents that are larger than those obtained with electron irradiation, and causes more complicated frequency dispersion of the diode parameters.     

Quantitative elemental localisation in leaves and stems of nickel hyperaccumulating shrub Hybanthusfloribundus subsp. floribundus using micro-PIXE spectroscopy

Hybanthusfloribundus (Lindl.) F.Muell. subsp. floribundus is a native Australian nickel (Ni) hyperaccumulating shrub and a promising species for rehabilitation and phytoremediation of Ni tailings. Spatial localisation and quantification of Ni in leaf and stem tissues of H.floribundus subsp. floribundus was studied using micro-proton-induced X-ray emission (micro-PIXE) spectroscopy. Young plants, grown in a potting mix under controlled glasshouse conditions were exposed to Ni concentrations of 0 and 26 mM kg⁻¹ for 20 weeks. Leaf and stem samples were hand-sectioned and freeze-dried prior to micro-PIXE analysis. Elemental distribution maps of leaves revealed Ni concentration of 7800 mg kg⁻¹ dry weight (DW) in whole leaf sections, which was identical to the bulk tissue analysis. Elemental maps showed that Ni was preferentially localised in the adaxial epidermis (10,000 mg kg⁻¹ DW) and reached a maximum of up to 10,000 mg kg⁻¹ DW in the leaf margin. Freeze-dried stem sections from the same plants contained lower Ni than leaf tissues (1800 mg kg⁻¹ versus 7800 mg kg⁻¹ DW, respectively), however did not resolve a clear pattern of compartmentalisation across different anatomical regions. Our results suggest localisation in epidermal cells is an important physiological mechanism involved in Ni accumulation and tolerance in leaves of H.floribundus subsp. floribundus.     

Thermal and structural properties of low-fluence irradiated graphite

The release of Wigner energy from graphite irradiated by fast neutrons at a TRIGA Mark II research reactor has been studied by differential scanning calorimetry and simultaneous differential scanning calorimetry / synchrotron powder X-ray diffraction between 25 and 725 °C at a heating rate of 10 °C min⁻¹. The graphite, having been subject to a fast-neutron fluence from 5.67 × 10²⁰ to 1.13 × 10²² n m⁻² at a fast-neutron flux (E > 0.1 MeV) of 7.88 × 10¹⁶ n m⁻² s⁻¹ and at temperatures not exceeding 100 °C, exhibits Wigner energies ranging from 1.2 to 21.8 J g⁻¹ and a Wigner energy accumulation rate of 1.9 × 10⁻²¹ J g⁻¹ n⁻¹ m². The differential-scanning-calorimeter curves exhibit, in addition to the well known peak at ∼200 °C, a pronounced fine structure consisting of additional peaks at ∼150, ∼230, and ∼280 °C. These peaks correspond to activation energies of 1.31, 1.47, 1.57, and 1.72 eV, respectively. Crystal structure of the samples is intact. The dependence of the c lattice parameter on temperature between 25 and 725 °C as determined by Rietveld refinement leads to the expected microscopic thermal expansion coefficient along the c axis of ∼26 × 10⁻⁶ °C⁻¹. At 200 °C, coinciding with the maximum in the differential-scanning-calorimeter curves, no measurable changes in the rate of thermal expansion have been detected - unlike its decrease previously seen in more highly irradiated graphite.     

FTIR and DSC studies on gamma irradiated P(VdF-HFP) fluoropolymers applied to dosimetry

Radiation effects on semicrystalline poly(fluorovinylidene-co-hexafluoropropylene) copolymer [P(VdF-HFP)] induced by high-energy irradiation were investigated. Films with 150 μm thickness were irradiated with gamma doses ranging from 1.0 kGy to 3.0 MGy. Fourier transform infrared (FTIR) spectroscopy was used to follow the radio-induction of new molecular bonds. Differential scanning calorimetry (DSC) was employed to study the crystalline degradation of the irradiated samples. P(VdF-HFP) copolymers have fluorinated monomers [-CF₂-CF-CF₃-] randomly added to the [-CH₂-CF₂-] main chain of PVdF homopolymer. In this case, the [-CF₃-] molecular bonds are branched to the main chain. There is an increasing interest about the effect of high gamma radiation dose on the P(VdF-HFP) radiolysis, once it could enhance some of their already known interesting properties such as biomedical applications and electrostrictive transducers/actuators. FTIR spectroscopic data revealed two optical absorption bands at 1730 and 1754 cm⁻¹ whose intensities are unambiguously related to gamma delivered dose ranging from 0.0 to 1000 kGy. Fading analysis has demonstrated no loss of signal until 11 months after irradiation. DSC and XRD data revealed a continuous decrease in both the melting latent heat and crystalline dimensions for doses ranging from 250 to 3000 kGy. Because of the low fading and the linear behavior with respect to delivered gamma doses of the absorption band at 1754 cm⁻¹, P(VdF-HFP) copolymers are good candidates for being explored for high gamma dose dosimetry application.     

Irradiation effect on dielectric properties and electrical conductivity of Au/SiO2/n-Si (MOS) structures

The Au/SiO₂/n-Si (MOS) structures were exposed to beta-ray irradiation to a total dose of 30 kGy at room temperature. Irradiation effect on dielectric properties of MOS structures were investigated using capacitance−voltage (C−V) and conductance−voltage (G/ω−V) characteristics. The C−V and G/ω−V measurements carried out in the frequency range from 1 kHz to 10 MHz and at various radiation doses, while the dc voltage was swept from positive bias to negative bias for MOS structures. The dielectric constant (ε′), dielectric loss (ε″), loss factor (tan δ) and ac electrical conductivity (σ_ac) were calculated from the C−V and G/ω−V measurements and plotted as a function of frequency at various radiation doses. A decrease in the ε′ and ε″ were observed when the irradiation dose increased. The decrease in the ε′ and ε″ of irradiated MOS structures in magnitude is explained on the basis of Maxwell−Wagner interfacial polarization. Also, the σ_ac is found to decrease with increasing radiation dose. In addition, the values of the tan δ decrease with increasing radiation dose and give a peak. From the experimental results, it is confirmed that the peak of loss tangent is due to the interaction between majority carriers and interface states which induced by radiation.