Increasing Gamma Irradiation Dose Research Articles

Analyzing point defect polarization in tungsten and tungsten carbide under high gamma irradiation for radiation shielding applications

In this study, polycrystalline tungsten and tungsten carbide samples were irradiated with gamma rays at energies of 1.17 MeV and 1.33 MeV, respectively. The irradiation was performed using an “MRX-γ-25 M” radiation camera with an activity of approximately 6.54 Gy/s. Doppler positron spectroscopy (DPS) and positron lifetime spectroscopy (PALS) were utilized to investigate the mechanisms of defect formation in the polycrystalline structure of tungsten samples at different doses of gamma irradiation. In the initial tungsten sample, a significant number of free monovacancy (1 V) clusters were present. An increase in the positron lifetime component τ1 was observed with increasing gamma irradiation, accompanied by a decrease in its intensity. The τ2 value (218 ± 2 ps) suggests the presence of divacancies with a considerable intensity (∼20%). As the gamma dose accumulated, a dynamic evolution of structural defects was evident. The tungsten carbide (WC) samples displayed greater plasticity in response to increasing gamma irradiation doses. Changes in the void volume ratio within the samples were recorded as the gamma dose increased, and movement of these voids towards the surface was observed. Additionally, the operational limits of gamma-irradiated tungsten were assessed, determining a functional threshold of up to 3.378 MGy. This study provides valuable insights into the defect dynamics and structural changes in tungsten and tungsten carbide under gamma irradiation, contributing to the understanding of their behavior in radiation environments.

Thermal, Mechanical and Tribological Properties of Gamma-Irradiated Plant-Derived Polyamide 1010.

In this study, we investigated the influence of the gamma-irradiation dose and the addition of the cross-linking agent (triallyl isocyanurate (TAIC)) on the thermal, mechanical and tribological properties of plant-derived polyamide 1010 (PA1010). PA1010 and PA1010/TAIC were extruded using a twin screw extruder and injection molded. These specimens were then irradiated with gamma-ray in air with doses of 20 and 50 kGy. After gamma-irradiation, the specimens were heat-treated to remove the free radicals generated in the polymer. The combination of gamma-irradiation and the addition of TAIC significantly changed the crystal structures of PA1010. Glass transition temperature increased with the addition of TAIC and, in particular, with increasing gamma-irradiation dose. Moreover, PA1010/TAIC showed a rubbery plateau originating from cross-links by gamma-irradiation, which was observed in the temperature regions above the melting point in DMA measurements. Mechanical properties such as strength, modulus and hardness, and tribological properties such as frictional coefficient, specific wear rate and limiting pv (pressure p × velocity v) value of PA1010 improved with change in the internal microstructure with the gamma-irradiation and addition of TAIC.

Application of gamma irradiation on morphological, biochemical, and molecular aspects of wheat (Triticum aestivum L.) under different seed moisture contents

Nuclear technology is currently used as a tool in mutation breeding to improve crops by increasing genetic variation. The ionization of gamma rays produces large amounts of free radicals, simulating stressors in the natural environment. To avoid gamma-ray-induced oxidative stress, plants use antioxidant defense systems. Exposure of plants to irradiation can affect the germination, growth, and production of metabolites. Plants' sensitivity to irradiation depends on genetic and environmental factors such as moisture content. For this purpose, the effects of different gamma irradiation doses [0, 100, 200, 300, and 400 Gray (Gy)] and different seed moisture contents (7, 13, and 19%) on traits such as seed germination, seedling growth, molecular and biochemical alterations in antioxidant enzymes were examined in the current study. Based on the results, the highest seed germination percentage was observed in the interaction effect of seed moisture at 13% with an irradiation dose of 400 Gy (98.89%). Seedling survival percent and seedling length decreased with increasing doses of gamma irradiation at different seed moisture contents. Increasing gamma irradiation doses were reduced root and stem fresh and dry weight, and root and stem length. The highest level of catalase enzyme activity and expression was observed at 200 and 300 Gy irradiation doses at different moisture contents. The peroxidase and polyphenol oxidase gene expression were reduced at all contents of gamma irradiation doses and seed moisture compared to the control. It can be concluded that the dose of 200–300 Gy of gamma irradiation reduced plant growth by 30% in terms of fresh and dry weight and length of plants, as well as enhanced the expression of antioxidant enzymes. The results of this study could help plant breeders select an appropriate dose rate in wheat for further research.

Fungal mycotoxins reduction by gamma irradiation in naturally contaminated sorghum

The objective of this study was the evaluation of the effects of different gamma irradiation doses on the survival of natural mycoflora as well as on the reduction of mycotoxin contamination (ochratoxin A [OTA] and aflatoxin B1 [AFB1]) in naturally contaminated sorghum samples. Mycotoxin levels were determined by ultra-high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UHPLC-QqQ-MS/MS). The results have demonstrated that the dose of 3 kGy was sufficient to eliminate 90% of the natural fungal load of sorghum. Increasing gamma irradiation dose showed significant effects (p < .05) on initial mycotoxin content. At radiation dose of 10 kGy, maximum reduction of 59% and 32% were achieved in naturally contaminated sorghum for AFB1 and OTA, respectively. The obtained results clearly showed that gamma irradiation can be a promising method to control fungal and mycotoxin contamination in sorghum. Practical applications Sorghum is an important staple cereal crop intended for human foods and animal feeds worldwide. This study investigated the potential application of gamma irradiation to reduce fungal load and the mycotoxins (OTA and AFB1) in naturally contaminated sorghum. The results showed significant decrease in the natural fungal load. The amounts of OTA and AFB1 in sorghum were also reduced by applying this method. The results showed that gamma irradiation was a promising method to control fungal and mycotoxin contamination in sorghum within the permissible dose range applicable to food preservation (≤10 kGy).

Effects of gamma irradiation under vacuum and air packaging atmospheres on the phytochemical contents, biological activities, and microbial loads of Kaempferia parviflora rhizomes

Kaempferia parviflora is a traditional herb for health promotion and therapy attributed to its methoxyflavone and phenolic constituents. This study was performed to determine the effects of gamma irradiation (0, 5, 7.5, and 10 kGy) under vacuum and air packaging atmospheres on the phytochemical contents, biological activities, and microbial loads of K. parviflora rhizomes. The optimal extraction condition for achieving high antioxidant activity was: ethanolic concentration, 40% v/v; solid/solvent ratio, 1 : 10 g/ml; extraction temperature, 30 °C; and extraction time, 1 h. This condition was used to prepare extracts of K. parviflora rhizomes for further determination. The high performance liquid chromatography-diode array detector method was employed for the determination of methoxyflavones in rhizome extracts. The contents of methoxyflavones and phenolic compounds were found to increase with increasing gamma irradiation dose. In contrast, the antioxidant activities decreased with increasing gamma radiation dose. However, all three doses applied did not affect total flavonoid contents and albumin denaturation inhibitory activities in all extracts. The highest contents of methoxyflavones and phenolic compounds were observed in 7.5 kGy irradiated rhizomes packaged under air atmosphere. Irradiation treatment at doses of 5–10 kGy was sufficient to control microbial contamination and Tribolium castaneum infestation in dried rhizomes. This study suggests that 7.5 kGy irradiation is the effective treatment to improve the quality of K. parviflora rhizomes.

Gamma irradiation effect towards photoluminescence and optical properties of Makrofol DE 6-2

The optical, Raman and Photoluminescence properties of Makrofol DE 6-2 polycarbonates were explored in detail. A set of polymeric Makrofol samples were subjected to γ-ray source at various doses ranging between 1 and 200 kGy. UV–Vis spectra depicted that Makrofol DE 6-2 has a high absorption maximum band at about 230 nm and decreases sharply at about 285 nm. The optical energy band gap was calculated using different methods, Ineffective Thickness Method (ITM), Derivation of Ineffective Thickness Method (DITM), Absorption Spectrum Fitting (ASF) and Derivation of Absorption Spectrum Fitting (DASF) methods. All used methods revealed an observable decrease in the optical energy band gap values with increasing gamma irradiation doses for both the indirect and direct transitions, whereas the refractive index showed the reverse trend. Also, the photoluminescence intensity decreases with increasing gamma dose up to 200 kGy due to formation of defects. Peaks at 884, 1364, 1394 and 1854 cm−1 are registered corroborative its structure in the Raman spectrum. Its intensity showed a decrease with increasing the gamma dose which may be attributed to the formation of non-irradiative levels as a result of degradation. Color change of the polymer from transparent to faint yellowish after γ-irradiation of doses higher than 1 kGy was observed which may be due to formation of color centers appeared in the range 305–315 nm. The present results should be taken into account before utilization of Makrofol DE 6–2 in photoelectric devices and medical applications related to gamma radiation.

Structural, electrical and optical properties of gamma irradiated methyl para-hydroxy benzoate single crystals

ABSTRACTNonlinear optical materials (NLO) have been garnering attention due to their role in optical data storage, optical communication and laser technology. Organic crystals have emerged as an extremely important class of NLO materials, since their NLO properties compare very well with traditional inorganic NLO materials like KCl, LiNbO3, KDP (potassium dihydrogen phosphate), etc. They offer the additional advantage that they can be grown relatively inexpensively from solution close to room temperature, unlike the inorganic NLO materials which are grown from high temperature melts. In the present work, organic transparent single crystals of methyl para-hydroxy benzoate (MHB) were grown by slow evaporation solution growth technique (SEST) from aqueous solution at room temperature. The changes in structural, electrical and optical properties of gamma irradiated MHB single crystals were studied using X-ray diffraction (XRD), UV–Visible absorption spectroscopy, Photo-luminescence (PL), Fourier transform infrared (FTIR) spectroscopy and AC conductivity measurements at room temperature. The polished MHB single crystals were irradiated with gamma rays of doses 10 and 15 kilogray (kGy). From the XRD analysis, it was observed that gamma irradiation for these doses drastically decreases the crystallinity. The optical absorption constants were examined by UV-Visible absorption spectroscopy, measured over the wavelength range of 200–800 nm, at normal incidence. The optical band gap as estimated from the Tauc plot ((αhν)2 vs hν) was found to be reduced with increasing gamma irradiation doses. PL spectra showed emission at wavelengths of 361 nm (3.43 eV) and 452 nm (2.74 eV), with enhanced intensities for the irradiated crystals. FTIR spectroscopy was utilised to identify the functional groups of MHB and indicated the rupture of specific types of bonds with gamma irradiation. Apart from that, the enhancement of AC conductivity with gamma irradiation was also observed for the gamma irradiated crystals.

Mechanical and electrical properties of radiation-vulcanized natural rubber latex with waste eggshell powder as bio-fillers

ABSTRACTThis work investigated the mechanical, physical, morphological, and electrical (volume) resistivity properties of radiation-vulcanized natural rubber latex (RVNRL) with additions of waste eggshell (WES) powder, which contained primarily CaCO3 (calcite). The results showed that increasing gamma irradiation doses from 0 to 30 kGy in 10-kGy increments led to decreases in the swelling ratio and elongation at break but increases in the crosslink density, tensile modulus at 500% elongation, and tensile strength of the composites. The results also suggested that increasing the WES contents from 0 to 2, 4, or 6 parts per hundred parts of rubber by weight (phr) in the composites improved the tensile modulus at 500% elongation, tensile strength, hardness (Shore A), and electrical (volume) resistivity. In addition, after undergoing thermal aging at 70°C for 96 h, the tensile modulus and hardness (Shore A) increased, while the tensile strength and elongation at break decreased. This work also compared the properties of WES/RVNRL with commercial CaCO3/RVNRL samples at the same 4-phr content. The results indicated that both composites had similar tensile properties, implying possible replacement of commercial CaCO3 with WES powder as an effective reinforcing filler in RVNRL.

Effect of Nano-Filler Content and Fiber Treatment on the Characteristics of Gamma-irradiated Rice Husk-Epoxy Particleboard Composites.‎

In this study, both untreated and treated rice husk fibers with a silane coupling agent are incorporated with epoxy resin to prepare particleboard composites. The effect of different ratios of nanoclay 5%, 10%, 15%, and 20% (by the weight of the polymer) on the physicomechanical properties of the prepared particleboard composites is investigated. The results show that the flexural, and impact strengths as a function of mechanical properties getting better with increasing nanoclay content up to 10%. While the addition of nanoclay to the samples decreases the water absorption percentage. This decrease is almost constant with nanoclay (%). In addition, the effect of different doses of gamma-irradiation on the properties of both untreated and treated rice husk-epoxy particleboard composites that containing 10% of nanoclay is also discussed. The results show that the irradiated specimens at a dose of 10kGy achieved a good enhancement in mechanical properties whereas the water absorption percentage as a physical property decreases at a dose of 10kGy and starts to increase with increasing gamma irradiation doses. TGA, and SEM are carried out to confirm the data obtained.

Sterilization effects on the handling and degradation properties of calcium phosphate cements containing poly (D,L -lactic-co-glycolic acid) porogens and carboxymethyl cellulose.

Injectable, self-setting calcium phosphate cements (CPCs) are synthetic bone substitutes considered favorable for the repair and regeneration of bone due to their osteocompatibility and unique handling properties. However, their clinical applicability can be compromised due to insufficient cohesion upon injection into the body coupled with poor degradation rates that restricts new bone formation. Consequently, carboxymethyl cellulose (CMC) was incorporated into CPC formulations to improve their cohesion and injectability while poly (D,L -lactic-co-glycolic acid) (PLGA) porogens were added to introduce macroporosity and improve their biodegradation rate. Like most biomaterials, CPCs are gamma irradiated before clinical use to ensure sufficient sterilization. However, it is well known that gamma irradiation also reduces the molecular weight of CMC and PLGA via chain scission, which affects their material properties. Therefore, the aim of this study is to measure the effect that gamma irradiation has on the molecular weight of CMC at varying doses of 15, 40, or 80 kGy and investigate how this affects the handling (i.e., injectability, cohesion, washout, and setting times) and in vitro degradation behavior of CPC formulations. Results reveal that the molecular weight of CMC decreases with increasing gamma irradiation dose, thereby reducing the viscosifying capabilities of CMC, which causes CPCs to deteriorate more readily. Further, the addition of CMC seems to inhibit the degree of phase transformation during cement setting while the subsequent reduction in molecular weight of PLGA after gamma irradiation improves the in vitro degradation rate of CPCs due to the faster degradation rate of low molecular weight PLGA. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2216-2228, 2019.

Effect of gamma irradiation dose on the structure and pH sensitivity of ITO thin films in extended gate field effect transistor

Abstract Even though several studies have demonstrated the use of Indium Tin Oxides (ITO) as an extended gate field effect transistor (EGFET), the effect of different doses of gamma radiation on the intrinsic properties of the ITO films has not been considered. This study investigates the effect of gamma irradiation on the structural, optical, morphological and electrical properties as well as pH sensitivity (as an extended gate field effect transistor) of ITO thin films. ITO thin films with thickness of 400 nm were prepared using a radio frequency sputtering technique. The samples were then subjected to various doses of gamma radiation from a Co-60 radio-isotope (0.5 kGy, 1 kGy, 1.5 kGy, and 2 kGy). The structural and morphological changes as well as transmission and absorption of the thin films were analyzed using X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Field-Emission Scanning Electron Microscope (FESEM) and UV–Vis spectrophotometry, before and after irradiation. The irradiated ITO thin films were then used as an extended gate field effect transistor to determine its ability to improve sensitivity as pH sensors. The grain size and transmittance in the range 300–900 nm of the ITO films were found to decrease with increasing gamma irradiation dose. In contrast, the uniformity and surface roughness of ITO thin films increased with increasing gamma radiation dose due to the formation of lattice defects. Moreover, the electrical resistance of the thin films increased with increasing dose because of the low current density and high number of surface defects associated with irradiation. The pH sensitivity of the ITO thin films improved after irradiation, possibly due to the concomitant increase in surface roughness with increasing radiation dose. The improvements in the pH sensitivity of ITO thin films after irradiation justify their potential use as pH sensors.

Thermal and physicomechanical properties of gamma‐irradiated EPDM/waste newsprint microfibers composites treated using acrylic styrene emulsion as a coupling agent

This investigation deals mainly with thermal stability and crosslinking density of EPDM/newsprint microfibers composites. The recycled newsprint microfibers were treated using a different ratio of acrylic styrene emulsion (5, 10, and 15 wt% fiber) as a bonding agent to reinforce EPDM rubber matrix. The effect of microfibers content, namely, 5 up to 50 phr (part per hundred part of rubber) and the effect of ionizing radiation on EPDM/newsprint microfibers composites properties were investigated. The microfibers structure and EPDM/microfibers composite were investigated using X‐ray diffraction and FTIR analysis; the results indicate that bonding has occurred between the treated newsprint microfibers and EPDM polymer matrix. EPDM/untreated newsprint microfibers composites have achieved higher crosslinking density than EPDM matrix up to 50 phr microfibers content and up to 100 kGy then decreased with increasing gamma irradiation dose. Meanwhile treatment of the microfibers using 10 wt% acrylic styrene leads to improve crosslinking density at any microfibers content. Thermogravimetric analysis (TGA) was carried out for the microfibers and their composites. TGA indicated that the thermal stability of microfiber was enhanced using acrylic styrene. Whereas there is a slight improvement in thermal stability and activation energy of the composites due to adding treated microfibers using 10 phr microfiber content treated using10 wt% acrylic styrene emulsion and irradiated with 60 kGy gamma radiation dose. J. VINYL ADDIT. TECHNOL., 25:E91–E106, 2019. © 2018 Society of Plastics Engineers

Influence of gamma irradiation on physical and chemical properties of Makrofol (NTD) material

Physical and chemical alterations induced in Makrofol LT 6-4 Nuclear Track Detector (MK-NTD) films after gamma irradiation with different doses (150–950 kGy) were studied. The induced modifications in irradiated samples were analyzed by various procedures namely: X-ray diffraction (XRD), Fourier-Transform-Infrared (FT-IR) spectroscopy, Photoluminescence (PL) spectroscopy, UV–Visible spectroscopy and electrical measurements, as well. XRD results show a broadening of the XRD peak after gamma irradiation, indicating a change in crystallite size of the irradiated polymeric samples. The spectra of FT-IR show overall changes in the band intensities after gamma irradiation, which indicates degradation and cross-linking of polymer chains at specified doses. The PL emission spectra reveal that the intensities of PL peaks descend with increasing gamma irradiation dose and concern the increase in the number of defects, acceptors and donors. Our UV–Vis results show a shift in the spectra of MK-NTD samples towards longer wavelengths with the increase in the gamma-dose. This shift indicates a reduction in the band gap energy, which, in turn, could be attributed to the formation of defects in the gamma irradiated samples. Additionally, the electrical results show some changes in dielectric constant according to the values of frequencies. Upon irradiation, a considerable increase in the dielectric constant and loss was observed, which could be attributed to the creation of dipoles like C˭O and C–O inside the irradiated polymer.

Enhancement of the conductivity and dielectric properties of PVA/Ag nanocomposite films using γ irradiation

Polymer based composites with tunable dielectric properties have many applications in organic electronics. This manuscript reports the influence of gamma irradiation on the electrical and dielectric properties of silver/polymer composite (Ag/PVA) films with thickness 0.18 mm. The films were prepared by the in-situ chemical reduction and later irradiated with gamma (γ) radiation doses (25, 50, 75, 100, 125 KGy). The content of Ag (0.4 wt %) in the PVA films were determined by the atomic absorption spectroscopy (AA). The films were characterized by the dielectric spectroscopy and Current-Voltage (IV) measurements. The dielectric constant (ε′) value decreased with the increasing gamma irradiation doses. The conductivity films and dielectric loss increased with the increasing gamma irradiation doses. The optimum conductivity: σ = 4.9 × 10−8 S m−1 was found at gamma radiation dose of 125 KGy. The Poole-Frenkel emission is the prevailing transport mechanism for all the samples.

Tailoring of the thermal, mechanical and dielectric properties of the polypropylene foams using gamma-irradiation

This study investigate the influence of gamma-irradiation (GI) doses from 0 up to 50 kGy on the polypropylene (PP) foams, mainly the impact on their structural and physical properties. It was found that structural properties were not significantly changed and the cellular structure of the PP foams sustain the same, while the thermal properties were significantly enhanced with increasing GI doses, due to the present cross-linking created within the irradiation. The cross-linking was confirmed also by the swelling measurements. The dielectric properties shows the three time increase of capacitance with increasing GI doses, due to the additional charges created in the foam voids by GI. Investigated mechanical properties in case of tensile tests as well as dynamical mechanical analysis proved, that enhanced behaviour was observed only in case of samples with irradiated by low doses, 1 kGy and 5 kGy, respectively, while the higher doses significantly decrease these ones, due to the present scission confirmed by FTIR and other investigations. Finally, it was found the competition between the cross-linking of the PP foam and present scission due to the applied GI and therefore the physical properties can be easily tailored.

Effect of Gamma Ray Irradiation on Epitaxial Pb(Zr,Ti)O3 /SrRuO3 Tunable Varactor Devices

Epitaxial morphotropic PbZr0.52Ti0.48O3 (PZT) thin films were employed to enhance the dielectric tunability of microwave filter devices without compromising the device impedance matching and low bias voltage (<10 V) requirements. Epitaxial heterostructure of ferroelectric PZT(001)/SrRuO3 (SRO) were grown on single crystal SrTiO3 (001) substrates by pulsed laser deposition, and a platinum (Pt) electrode was deposited on top of the PZT film. The tunability of the Pt/PZT/SRO varactor devices are strongly dependent on bias voltage and exhibited good dielectric tunability of 55% at 100 kHz and 10 V. The capacitance (CP) of the heteroepitaxial varactor devices was 105 pF at 10 V applied bias with a corresponding small leakage current of 1 nA. The influence of gamma (γ-ray) irradiation on the intrinsic electrical properties of the epitaxial PZT varactor devices was investigated as a function of the irradiation dose from 0 kGy to 400 kGy, in terms of the capacitance–voltage (C–V) characteristics and loss tangent response. With enhancing γ-ray irradiation doses the ferroelectric capacitance was found to decrease accompanying degradation in the loss tangent values. The results indicate that tunability of the epitaxial PZT ferroelectric thin-film capacitors decreased with increasing gamma irradiation dose and degraded ∼25% at 400 kGy dose than unexposed devices. Possible reasons for the degradation behavior of dielectric properties and tunability due to radiation-induced defects has been discussed.

Structural, optical and electrical properties of gamma-rays exposed selenium nanowires

The increasing use of semiconducting nanowires in applications that require prolonged exposure to high energy photons (X-rays and gamma rays) necessitates a better understanding of the effects of irradiation on them. In this context, we synthesized selenium nanowires of 80 nm diameter using template assisted electro-deposition technique and exposed them to gamma rays using Co-60 source at Inter University Accelerator Centre, New Delhi, India. The effect of gamma irradiation on their structural, optical and electrical properties was investigated. The analysis of XRD of pre- and post- irradiated Se nanowires showed no shifting in the peak positions. However, Texture analysis demonstrates the variation in the relative intensity with changing preferred orientation at the higher doses. The optical study was done using UV–Vis spectrophotometer and was found that the optical band gap decreased with increasing gamma irradiation dose. Current–Voltage characteristics of pristine and irradiated Se nanowires also exhibit an enhancement in the current with the exposed dose. The decrease in band gap and an increase in current conduction may be attributed to the decrease in scattering of charge carriers from the grain boundaries and creation of more number of electron-hole pairs.

Radiation Induced Response of &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;${\rm Ba}_{0.5}{\rm Sr}_{0.5}{\rm TiO}_3$&lt;/tex&gt;&lt;/formula&gt; Based Tunable Capacitors Under Gamma Irradiation

${\rm Ba}_{0.5}{\rm Sr}_{0.5}{\rm TiO}_3$ (BST) thin films were deposited on sapphire substrate by RF magnetron sputtering techniques and interdigital capacitor (IDC) structures were fabricated using photolithography. Gamma irradiation induced changes of the BST based tunable capacitor have been investigated under various doses from 0 kGy to 600 kGy. Structural and surface morphological studies have been carried out for un-irradiated and irradiated film and revealed that the grain sizes and crystallinity are strongly depended on gamma irradiation doses. The leakage current is increased with increasing gamma irradiation doses due to creation of charge carriers and large numbers of defect in close proximity, provided path for charge carriers. The capacitance of the IDC devices decreased with increasing gamma dose up to 50 kGy and thereafter capacitance gradually increased with radiation doses and reached higher than the un-irradiated device at 600 kGy for 1 MHz frequency. The observed tunability ( $\sim 25\% $ ) of the un-irradiated device was found nearly constant with gamma irradiation doses. This study shows that gamma ray induced defects play important role to the electrical properties of the devices and the BST based devices are highly resistant to gamma radiation, which reflects possible use in space and nuclear applications.

Chemical composition and lipoxygenase activity in soybeans (Glycine max L. Merr.) submitted to gamma irradiation

Soybeans are an important food due to their functional and nutritional characteristics. However, consumption by western populations is limited by the astringent taste of soybeans and their derivatives which results from the action of lipoxygenase, an enzyme activated during product processing. The aim of this study was to evaluate the effect of gamma irradiation on the chemical composition and specific activity of lipoxygenase in different soybean cultivars. Soybeans were stored in plastic bags and irradiated with doses of 2.5, 5 and 10kGy. The chemical composition (moisture, protein, lipids, ashes, crude fiber, and carbohydrates) and lipoxygenase specific activity were determined for each sample. Gamma irradiation induced a small increase of protein and lipid content in some soybean cultivars, which did not exceed the highest content of 5% and 26%, respectively, when compared to control. Lipoxygenase specific activity decreased in the three cultivars with increasing gamma irradiation dose. In conclusion, the gamma irradiation doses used are suitable to inactivate part of lipoxygenase while not causing expressive changes in the chemical composition of the cultivars studied.

Effects of various sterilization methods on the setting and mechanical properties of apatite cement.

Sterilization capability is a necessary requirement for any material that is to be used in a medical application. Therefore, it is necessary for apatite cement (AC) to be sterilized. Because there is little information on the sterilization methods of AC, the aims of this investigation were to evaluate the effects of various sterilization methods, including steam, dry heat, ethylene oxide (EtO) gas, and gamma irradiation sterilizations, on the setting and mechanical properties of AC. In the case of steam sterilization, because AC powder aggregated before setting-time measurements, the setting time could not be measured. When the powder was sterilized by dry heat or EtO gas, the setting time was prolonged significantly and the wet diametral tensile strength (DTS) value decreased significantly. Therefore, sterilizations with steam, dry heat, or EtO gas were suggested to be inappropriate methods for AC. Accordingly, the following experiments focused on gamma sterilization. The setting time of AC was retarded with an increase in gamma irradiation dose. The wet DTS value decreased with the increase in gamma irradiation dose. There was no compositional change due to the gamma irradiation. The following tests were carried out in order to examine the effect of the gamma irradiation on the setting reaction of AC in detail. Tetracalcium phosphate [TTCP: Ca(4)(PO(4))(2)O] and dicalcium phosphate anhydrous (DCPA: CaHPO(4)) were separately irradiated, and the cements were produced with the use of irradiated powder and nonirradiated powder. Although the wet DTS value of AC produced from irradiated TTCP and nonirradiated DCPA decreased with increasing gamma irradiation dose, there was no significant difference. In contrast, the wet DTS value of AC produced from irradiated DCPA and nonirradiated TTCP significantly decreased with the increase in gamma irradiation dose. In conclusion, although the detailed mechanism of the delayed setting time and decreased DTS value was not clarified by the present study, it was found that gamma irradiation affected DCPA more than TTCP.