Neutron irradiation effect in two-dimensional electron gas of AlGaN/GaN heterostructures

AlGaN/GaN heterostructures have been irradiated by neutrons with different influences and characterized by means of temperature-dependent Hall measurements and Micro-Raman scattering techniques. It is found that the carrier mobility of two-dimensional electron gas (2DEG) is very sensitive to neutrons. At a low influence of 6.13 x 10(15) cm(-2), the carrier mobility drops sharply, while the sheet carrier density remains the same as that of an unirradiated sample. Moreover, even for a fluence of up to 3.66 x 10(16) cm(-2), the sheet carrier density shows only a slight drop. We attribute the degradation of the figure-of-merit (product of n(s) x mu) of 2DEG to the defects induced by neutron irradiation. Raman measurements show that neutron irradiation does not yield obvious change to the strain state of AlGaN/GaN heterostructures, which proves that degradation of sheet carrier density has no relation to strain relaxation in the present study. The increase of the product of n(s) x mu of 2DEG during rapid thermal annealing processes at relatively high temperature has been attributed to the activation of Ge-Ga transmuted from Ga and the recovery of displaced defects.

Raman Spectroscopy of Irradiation Effect in Three Carbon Allotropes Induced by Low Energy B Ions

Irradiation efect in three carbon allotropes C60, diamond and highly oriented pyrolytic graphite (HOPG) induced by 170 keV B ions, mainly including the process of the damage creation, is investigated by means of Raman spectroscopy technique. The diferences on irradiation sensitivity and structural stability for C60, HOPG and diamond are compared. The analysis results indicate that C60 is the most sensitive for B ions irradiation,diamond is the second one and the structure of HOPG is the most stable under B ion irradiation. The damage cross sections ? of C60, diamond and HOPG deduced from the Raman spectra are 7.78×10−15 , 6.38×10−15 and1.31 × 10−15cm2, respectively.

Molecular vibration spectroscopy study of irradiation effect in C-60 films induced by low energy ion

Irradiation effect in C-60 films induced by 170 keV B ion was investigated by means of Fourier transform infrared (FTIR) and Raman spectroscopies. The damage cross section sigma and the effective damage radius R are deduced from the experimental data of all four IR active modes and evident four Raman active modes of C-60 molecule. The differences on irradiation sensitivity and structural stability of the different active modes of C-60 molecule are compared. The results indicate that T-1u (4) of infrared active mode and A(g) (1) of Raman active mode are most sensitive for B ion irradiation. On the other hand T-1u (2) of infrared active mode and H-g (3) of Raman active mode are comparatively stable under B ion irradiation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3512968]

Disinfection of Bovine Enamel by Microwave Irradiation: Effect on the Surface Microhardness and Demineralization/Remineralization Processes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nd:YAG Laser Irradiation effect on apical intracanal dentin-a microleakage and SEM evaluation

The purpose of this in vitro study was to evaluate the effect of neodymium:yttrium-aluminum-garnet (Nd:YAG) laser irradiation on intracanal dentin surface by SEM analysis and its interference in the apical seal of filled canals. After endodontic treatment procedures, 34 maxillary human incisors were randomly assigned to 2 groups. In the negative control group (n=17), no additional treatment was performed and teeth were filled with vertically condensed gutta-percha; in the laser-treated group (n=17), the root canals were irradiated with Nd:YAG laser (1.5 W, 100 mJ, 15 Hz) before filling as described for the control group. Two specimens of each group were prepared for SEM analysis to evaluate the presence and extent of morphological changes and removal of debris; the other specimens were immersed in 0.5% methylene blue dye (pH 7.2) for 24 h for evaluation of the linear dye leakage at the apical third. SEM analysis of the laser-treated group showed dentin fusion and resolidification without smear layer or debris. The Student's t-test showed that the laser-treated group had significantly less leakage in apical third than the control group. Within the limitations of this study, it may be concluded that the morphological changes on the apical intraradicular dentin surface caused by Nd:YAG laser resulted in less linear dye apical leakage.

Studies On Vulcanization, Rheology And Reinforcement Of Natural Rubber Latex With Special Reference To Accelerator Combinations, Surface Active Agents And Gamma Irradiation

In the present work, studies on vulcanization, rheology and reinforcement of natural rubber latex with special reference to accelerator combinations, surface active agents and gamma irradiation have been undertaken. In vulcanization, the choice of vulcanization system, the extent and mc-zie of vulcanization and network structure of the vulcanizate are important factors contributing to the overall quality of the product. The vulcanization system may be conventional type using elemental sulfur or a system involving sulfur donors. The latter type is used mainly in the manufacture of heat resistant products. For improving the technical properties of the products such as modulus and tensile strength, different accelerator combinations are used. It is known that accelerators have a strong effect on the physical properties of rubber vulcanizates. A perusal of the literature indicates that fundamental studies on the above aspects of latex technology are very limited. Thereforea systematic study on vulcanization, rheology and reinforcement of natural rubber latex with reference to the effect of accelerator combinations, surface active agents and gamma irradiation has been undertaken. The preparation and evaluation of some products like latex thread was also undertaken as a part of the study. The thesis consists of six chapter

Unusual surface and edge morphologies, sp2 to sp3 hybridized transformation and electronic damage after Ar+ ion irradiation of few-layer graphene surfaces

Roughness and defects induced on few-layer graphene (FLG) irradiated by Ar+ ions at different energies were investigated using X-ray photoemission spectroscopy (XPS) and atomic force microscopy techniques. The results provide direct experimental evidence of ripple formation, sp2 to sp3 hybridized carbon transformation, electronic damage, Ar+ implantation, unusual defects and edge reconstructions in FLG, which depend on the irradiation energy. In addition, shadowing effects similar to those found in oblique-angle growth of thin films were seen. Reliable quantification of the transition from the sp2-bonding to sp3-hybridized state as a result of Ar+ ion irradiation is achieved from the deconvolution of the XPS C (1s) peak. Although the ion irradiation effect is demonstrated through the shape of the derivative of the Auger transition C KVV spectra, we show that the D parameter values obtained from these spectra which are normally used in the literature fail to account for the sp2 to sp3 hybridization transition. In contrast to what is known, it is revealed that using ion irradiation at large FLG sample tilt angles can lead to edge reconstructions. Furthermore, FLG irradiation by low energy of 0.25 keV can be a plausible way of peeling graphene layers without the need of Joule heating reported previously

Effect of disinfection on adhesion of reline polymers

Cylinders (3.5 x 5.0 mm) of the reline resins Kooliner (K), New Truliner (N), Tokuso Rebase Fast (T), and Ufi Gel Hard (U) were bonded to cylinders (20 x 20 mm) of the denture base resin Lucitone 550 (L), and samples were divided into two controls and four test groups (n = 8). Shear tests (0.5 mm/min) were performed after polymerization or immersion in water (37 degrees C) for 7 days (controls); two or seven cycles of disinfection by immersion in sodium perborate (50 degrees C/10 min) or microwave irradiation (650 W/6 min). Statistical analyses (alpha = 0.05) revealed that two cycles of microwave and chemical disinfection increased the mean bond strengths of materials T (9.08 to 12.93 MPa) and L (18.89 to 23.02 MPa). For resin L, seven cycles of chemical (15.72 MPa) and microwave (17.82 MPa) disinfection decreased the shear bond strength compared with the respective control (21.74 MPa). Resins U (13.12 MPa), K (8.44 MPa), and N (7.98 MPa) remained unaffected.

Effect of proteolytic enzyme and fiber of papaya fruit on human digestive health

The World Health Organization (WHO, 2005) recommends consumption of fruits and vegetables as part of a healthy diet with daily recommendation of 5 servings or at least 400 g per day. Fruits and vegetables are good sources of vitamins, minerals, antioxidants, and fiber. Papaya fruit is known for his high nutrient and fiber content, and with few exceptions, it is generally consumed ripe due to its characteristic flavor and aroma. Digestion improvement has been attributed to consumption of papaya; this we speculate is attributed to the fiber content and proteolytic enzymes associated with this highly nutritious fruit. However, research is lacking that evaluates the impact of papaya fruit on human digestion. Papain is a proteolytic enzyme generally extracted from the latex of unripe papaya. Previous research has focused on evaluating papain activity from the latex of different parts of the plant; however there are no reports about papain activity in papaya pulp through fruit maturation. The activity of papain through different stages of ripeness of papaya and its capacity of dislodging meat bolus in an in vitro model was addressed. The objective of this study was to investigate whether papain activity and fiber content are responsible for the digestive properties attributed to papaya and to find a processing method that preserves papaya health properties with minimal impact on flavor. Our results indicated that papain was active at all maturation stages of the fruit. Ripe papaya pulp displayed the highest enzyme activity and also presented the largest meat bolus displacement. The in vitro digestion study indicated that ripe papaya displayed the highest protein digestibility; this is associated with proteolytic enzymes still active at the acidity of the stomach. Results from the in vitro fermentation study indicated that ripe papaya produced the highest amount of Short Chain Fatty Acids SCFA of the three papaya substrates (unripe, ripe, and processed). SCFA are the most important product of fermentation and are used as indicators of the amount of substrate fermented by microorganisms in the colon. The combination of proteolytic enzymes and fiber content found in papaya make of this fruit not only a potential digestive aid, but also a good source of SCFA and their associated potential health benefits. Irradiation processing had minimal impact on flavor compounds of papaya nectar. However, processed papaya experienced the lowest protein digestibility and SCFA production among the papaya substrates. Future research needs to explore new processing methods for papaya that minimize the detrimental impact on enzyme activity and SCFA production.

蓝宝石中子辐照色心的研究

研究了中子辐照对蓝宝石(α-Al2O3)单晶体缺陷形成及光学性能的影响，对采用提拉法与温度梯度法生长的蓝宝石晶体进行中子辐照，通过对比辐照前后的吸收及荧光光谱变化，发现辐照使得蓝宝石晶体内形成F、F^+和F2^+色心缺陷，但不同方法生长的晶体样品中色心浓度差异明显。其中提拉法样品的F心浓度要高于温度梯度法样品，而温度梯度法样品中F^+色心浓度要高于提拉法样品。分析表明，这与两种方法生长的晶体中杂质含量差异有关。通过研究辐照后晶体的热致发光谱发现提拉法与温度梯度法生长的蓝宝石晶体分别在145℃与150℃有明

重离子在C60薄膜中引起的辐照效应研究

本项工作选择了不同种类、不同电荷态的从低能到高能的多种荷能重离子，对C60薄膜进行了辐照。并且通过多种分析测试手段（Raman、FTIR、XPS、AFM）分析了荷能重离子在C60薄膜中的辐照效应，并对机理进行了研究。同时也研究了低能B离子在碳的三种同素异构体：石墨、金刚石和C60中引起效应的差异。对于以弹性碰撞为主导的低能区，用170keV B离子辐照了碳的三种同素异构体，并从这些辐照样品的Raman谱数据演绎出了C60、金刚石和石墨的损伤截面σ。首次在完全相同的辐照条件下，研究了碳的三种同素异构体对辐照的敏感性和结构稳定性的差异，研究结果表明：C60对B离子辐照的敏感性最强，金刚石次之，相比之下石墨在B离子辐照下结构最为稳定，而且在辐照过程中，随辐照量的增加三种靶材料遭破坏的程度截然不同，表明它们的辐照敏感性差异随辐照量而变化。由XPS谱得知，在最高辐照量下石墨的sp2 C转变不多；而金刚石的sp3 C基本转变成了sp2 C。再次证明在B离子辐照下石墨的结构最为稳定。随着170keV B离子辐照量的增加，C60薄膜的FTIR和Raman谱中各激活模的强度都有不同程度的衰减，最终消失，即C60分子完全被破坏。在B离子的辐照下，C60分子的不同红外激活模和Raman激活模的辐照敏感性和结构稳定性也有差异：在C60分子的4个红外激活模中，T1u(4)对辐照最为敏感，而T1u(2)最为稳定。并率先确定了明显可见的5个Raman激活模对辐照的敏感性和结构稳定性的差异，其中Hg(4)对辐照最敏感，而Hg(3)最稳定。在以非弹性碰撞为主导的高能区，用2.15GeV的Kr离子辐照了多层堆叠的C60样品，辐照样品的分析结果表明：在相同能量或相同电子能损下，C60分子的辐照损伤随辐照量的增加趋于严重；而在相同辐照量下，C60的损伤程度随电子能损的增加而增强；但C60分子的损伤在某居中的电子能损值和辐照量下有一定的恢复。在电子能损相同或相近时，速度较低的Kr离子对C60分子的损伤更为严重，揭示了团簇材料的快重离子损伤建立过程中的离子速度效应。为了研究低速高电荷态离子在C60薄膜中引起的辐照效应，用不同电荷态的Xe离子辐照了C60薄膜。由AFM形貌图可知，不同电荷态Xe离子辐照C60薄膜，使其表面形貌发生了不同程度的改变。其粗糙度随着辐照Xe离子电荷态的不断增加而不断减小

Highly radiation sensitive type IA FBGs for future dosimetry applications

We have studied Co60 gamma-irradiation effect on the characteristics of Type IA fiber Bragg gratings. A record Bragg peak shift of 190 pm was observed for a grating written in Fibercore PS-1250/1500 photosensitive fiber at a radiation dose of 116 kGy. Type IA and Type I gratings show different kinetics under radiation and during post-radiation annealing, which can be used for the design of a grating based dosimetry system.