Comparison of radiation damage in lead tungstate crystals under pion and gamma irradiation

Studies of the radiation hardness of lead tungstate crystals produced by the Bogoroditsk Techno-Chemical Plant in Russia and the Shanghai Institute of Ceramics in China have been carried out at IHEP, Protvino. The crystals were irradiated by a 40 GeV pion beam. After full recovery, the same crystals were irradiated using a ¹³⁷Cs γ-ray source. The dose rate profiles along the crystal length were observed to be quite similar. We compare the effects of the two types of radiation on the crystal's light output.     

Light collection uniformity of lead tungstate crystals for the CMS electromagnetic calorimeter

A technique has been developed to measure the light collection uniformity of lead tungstate crystals for the CMS electromagnetic calorimeter. The use of a hybrid photomultiplier tube allows a precision measurement despite the intrinsically low light yield. It is found that shading the chamfered edges of the crystals with a pencil can achieve a reduction in the front-non-uniformity of approximately 0.1%/X₀. Similar effects are observed by de-polishing the chamfers.     

A study on yttrium doping in lead tungstate crystals

In this paper we present results of a study on the yttrium doping in lead tungstate crystals. The crystal growth by modified Bridgman method is described. Results of trace analysis on raw materials and crystals are presented. The segregation coefficient of yttrium ions in lead tungstate crystals was determined. The scintillation emission and longitudinal transmittance spectra, light output, decay kinetics, light response uniformity and radiation damage were measured. It is found that yttrium doping suppresses slow scintillation component and improves radiation hardness of lead tungstate crystals.     

Organization of the production of 100 tons of lead tungstate crystals for the CMS experiment at CERN

The CMS collaboration at CERN has undertaken at the end of 1994 an ambitious R&D program on Lead Tugstate scintillating crystals for its electromagnetic calorimeter. All the parameters of this crystal have been extensively studied in order to optimize its performances in the context of the Large Hadron Collider. Full size crystals (23 cm in length, up to 2.5 × 2.5 cm² in section) with the desired trapezoidal geometry can now be grown and mechanically processed with a yield in excess of 80%. A thorough investigation of the raw material preparation and of the growing conditions has led to a significant improvement in the optical transparency and in the light yield of the crystals. A detailed understanding of the light emission mechanism was 1995. A systematic analysis of the parameters influencing the structural quality of the crystals was at the origin of a considerable improvement of the radiation hardness of full size crystals. All these progress will be illustrated by results of measurements on a statistically representative number of crystals. The conditions of these improvements will be discussed in the context of the mass production of more than 80,000 crystals in a cost effective way.     

Preparation of PbSe nanoparticles by electron beam irradiation method

A novel method has been developed by electron beam irradiation to prepare PbSe nanoparticles. 2 MeV 10mA GJ-2-II electronic accelerator was used as radiation source. Nanocrystalline PbSe was prepared rapidly at room temperature under atmospheric pressure without any kind of toxic reagents. The structure and morphology of prepared PbSe nanoparticles were analysed by X-ray diffraction, transmission electron microscope and atomic force microscope. The results indicated that the obtained materials were cubic nanocrystalline PbSe with an average grain size of 30 nm. The optical properties of prepared PbSe nanocrystalline were characterized by using photoluminescence spectroscopy. The possible mechanism of the PbSe grain growth by electron beam irradiation method is proposed.     

Theoretical study on influence of electron beam irradiation on the first-order hyperpolarizability of BBO crystals

A mechanism not based on the traditional thermodynamics effect but on the microscopic origin of the nonlinear effect was investigated for full consideration of the correlation between the e-beam irradiation electric field (IEF) and the properties of the nonlinear material BBO (β-BaB₂O₄). Firstly, the IEF magnitude is computed under different conditions of beam intensity, ray energy and radiation dose. Secondly, the relationship model of IEF and nonlinear coefficients is built according to quantum mechanics principle. The results show that low-energy irradiation of 0–400?MeV ray energy (corresponding to IEFs of 0–12?×?10^?4?a.u.) has no obvious effect on the nonlinear optical properties of BBO crystals. When the energy is higher than 420?MeV (corresponding to an IEF of 13?×?10^?4?a.u.), the hyperpolarizability changed significantly, indicating permanent damage of the BBO crystals. With an increase of the ray energy, βx and βy tend to decrease, but βz increases markedly especially when the ray energy is more than 450?MeV (corresponding to an IEF of 16?×?10^?4?a.u.).     

电子束照射下钼纳米微粒的形成

使用高分辨透射电子显微镜在室温台上通过电子束照射ＭｏＯ３，制备钼及钼的亚氧化物钠米微粒，实验发现微米级ＭｏＯ３颗粒强度为１０＾２１ｅ／ｃｍ＾２．ｓ的电子束照射下转变为纳米级亚氧化钼，经过电子束的进一步照射后，亚氧化钼转变为钼。这种现象可能是由于电子束的激发作用和通过撞击效应而使原子发生错排引起氧原子分离造成的。     

Precision measurement of energy and position resolutions of the BTeV electromagnetic calorimeter prototype

The energy dependence of the energy and position resolutions of the electromagnetic calorimeter prototype made of lead tungstate crystals produced in Bogoroditsk (Russia) and Shanghai (China) is presented. These measurements were carried out at the Protvino accelerator using a 1–45 GeV electron beam. The crystals were coupled to photomultiplier tubes. The dependence of energy and position resolutions on different factors as well as the measured electromagnetic shower lateral profile are presented.     

γ辐照和电子束辐照对猪肉火腿肠质量的影响研究

比较研究了经不同剂量的γ辐照(GR)(0,5,10,15,20 kGy)和电子束辐照(EB)(0,5,10,15,20kGy)处理的猪肉火腿肠在30℃下储藏10 d过程中的品质(TBARS值、硬度、色泽),感官特性和细菌总数的变化.结果显示,GR辐照与EB辐照对猪肉火腿肠在储藏过程中脂质氧化、硬度、色泽和感官特征变化的影响相似(P≥0.05);然而,经GR辐照处理的样品的细菌总数显著小于经EB辐照处理的样品细菌总数(P<0.05),并且当GR辐照剂量增至10 kGy,样品中细菌总数得到有效抑制,而对火腿肠的品质和主要感官特征(色泽,咀嚼性和味道)没有显著影响(P≥0.05).     

Application of accelerated electron beam and microwave irradiation to biological waste treatment

The comparative results obtained by applying separate electron beam (EB) irradiation, separate microwave (MW) heating and combined (successive and simultaneous) electron beam irradiation and microwave heating to reduction of viable cells of Escherichia coli, Salmonella typhi, Staphylococcus intermedius, Pseudomonas aeruginosa, and Trichinella spiralis are presented. The results of studies concerning the disinfection by separate and combined EB and MW irradiation of sewage sludge performed from a food industry wastewater treatment station (vegetable oil plant) are also presented. The research results demonstrated that the simultaneous EB and MW irradiation produces the biggest reduction of microorganisms.     

Morphology and phase modification of HVOF-sprayed MCrAlY-coatings remelted by electron beam irradiation

The electron beam remelting process is one of the most convenient processes to reduce the disadvantages of thermal-spray coatings. The effect of high-energy electron beam irradiation on surface remelting and microstructural modification in MCrAlY coatings are investigated in this study. This surface treatment is made to modify the morphology and the phases of the coated layer in order to improve the corrosion resistance. The specimens were remelted by using a high-energy electron beam accelerator. The microstructure, corrosion resistance and phase modification were examined. Scanning Electron Microscopy, light microscopy and X-Ray Diffraction were performed to characterize the phase modification and morphology before and after the treatment.     

The behaviour of ternary compounds InGaAs and GaAsN subjected to electron irradiation

This paper presents results of the effect of electron beam irradiation under UHV conditions on InGaAs/GaAs and GaAsN/GaAs systems using Auger electron spectroscopy (AES) and the electron energy loss spectroscopy (EELS) as surface analytical techniques. The ternary compounds In_0.53Ga_0.47As and In_0.2Ga_0.8As were irradiated by an electron beam under identical conditions (5 KeV; 10⁻³ A cm⁻²; for 60 min). The results showed that the compound In_0.53Ga_0.47As was stable under electron irradiation whereas changes in the Auger signal In-M₄₅N₄₅N₄₅ revealed that the electron beam had a significant effect on the compound In_0.2Ga_0.8As. GaAsN growth at 590 °C on GaAs is believed to produce a surface containing defects that is chemically unstable when bombarded by electrons. It was found that heating this compound at 730 °C stabilised the surface, protecting it from the effect of electron irradiation.     

Crystal growth and scintillation properties of (NaxCa1−2xLux−yNdy)F2 single crystals

Na_xCa_1−2xLu_x−yNd_yF₂ single crystals were grown from the melt using the precise atmosphere control type Micro-Pulling-Down (μ-PD) method to investigate their potential as a vacuum-ultraviolet (VUV) scintillators. The grown crystals were single-phase materials with fluorite-type structure (Fm-3m, Z = 4) as confirmed by XRD. The crystals demonstrated 80-90% transmittance above 200 nm wavelength and Nd³⁺ 5d-4f luminescence (when exited by X-ray) observed around 185 nm. The radioluminescence measurements under 5.5 MeV α-ray excitation (²⁴¹Am) demonstrated the light yield of 48 [Ph/5.5 MeV-α] and the decay time of 6.4-7.7 ns.     

Controlled nucleation and growth kinetics of lead nitrate phosphate in silica hydrogel and characterization of grown crystals

Lead nitrate phosphate (LNP) single crystals were grown in silica hydrogel at an ambient temperature employing various nucleation control methods. The effect of concentration of feed solution, gel density, gel pH, ageing of gels and temperature on reduction of nucleation centres is reported. Kinetic studies of the nucleation and growth of LNP crystals and dentrites were studied. The crystals are characterized by X-ray diffraction, density measurements, magnetic susceptibility, mechanical strength measurements and dissolution behaviour.     

Fluorescence properties and energy transfer mechanism of Sm ion in lead telluroborate glasses

We report the fluorescence properties of Sm³⁺-doped lead telluroborate glasses of composition PbF₂.TeO₂.H₃BO₃.Sm₂O₃ as a function of Sm³⁺ concentration. A Judd-Ofelt scheme was used to determine the intensity parameters and radiative properties of Sm³⁺ ion. The emission and decay measurements were carried out at 402 nm excitation. Beyond 1.0 mol% Sm³⁺ concentration, the luminescence quenching is observed. The decay curves of ⁴G_5/2 level are well fitted to a single exponential function. The evaluated radiative properties suggest that the ⁴G_5/2 → ⁶H_7/2 transition is responsible for reddish-orange luminescence which might be used in the development of visible lasers.     

Effects of electron beam irradiation on antioxidants in commercial polyolefins: Determination and quantification of products formed

The influence of electron beam irradiation on antioxidants present in food packaging materials (OPP and LDPE) was studied. After irradiating the materials at dose levels of 2, 5,10 and 25 kGy, we have shown a partial disappearance of the antioxidant (Irganox 1010, Irganox 1076 and Irgafos 168) and a release of three compounds resulting from the antioxidants degradation related to the irradiation dose. Two of these degradation compounds have been analysed quantitatively: the 2,4-di-tert.-butyl-phenol and the 2,6-di-tert -butyl-p-benzoquinone. The third compound is a phosphate resulting from a phosphite stabilizer (Irgafos 168).     

A temperature and rate-dependent micromechanical model of molybdenum under neutron irradiation

In this paper we present a micromechanics-based model for neutron-irradiated single and polycrystalline BCC molybdenum which is capable of representing not only the effects of radiation hardening, yield drop and non-zero stress offset from the unirradiated stress-strain curves, but also the unique “radiation softening” effect observed in Mo at low to intermediate homologous temperatures (0.05 ? T/T_m ? 0.2) (Li et al., 2008) and low radiation doses. Specifically, a single smooth viscoplastic potential has been developed in which the critical resolved shear stress is decomposed into thermal and athermal components that overcome short range and long range barriers, respectively. The evolution of the athermal part is dependent on dislocation and defect densities, whereas the thermal part is modeled to be a function of temperature only. Impediment of dislocation motion due to defects results in hardening while defect annihilation due to dislocation motion accounts for yield drop and stress offset. Radiation softening is explained by invoking a critical temperature (T_c), with increase in radiation dose below which the thermal part of the flow stress undergoes a reduction due to increase in mobile point defects in the dislocation core area, whereas the athermal part increases. Beyond the critical temperature, however, thermal activation is sufficient for dislocation motion and the thermal component disappears. We argue that for low radiation doses, this critical temperature decreases with increase in radiation dose, resulting in a temperature range over which the flow stress actually drops below its value corresponding to the unirradiated condition. Polycrystalline response has been simulated based on a Taylor type homogenization scheme. The model is validated with experimental data for a range of temperatures and strain rates with increasing radiation dose.     

Effects of APTEOS content and electron beam irradiation on physical and separation properties of hybrid nylon-66 membranes

Nylon-66 contains functional groups which form hydrogen bonds with inorganic silica networks and allow the creation of hybrid membranes. As a typical semicrystalline polymer, nylon-66 can be crosslinked through electron beam (EB) irradiation to form nanofiltration membranes. The effects of γ-aminopropyltriethoxylsilane (APTEOS) and EB irradiation on the physical and separation properties of nylon-66 membranes were studied in this work. Hybrid nylon-66 membranes were prepared by adding an APTEOS solution (5 wt%, 10 wt% and 20 wt%) into nylon-66 which was dissolved in formic acid. Before air drying, membranes were irradiated at 60 kGy, 70 kGy and 80 kGy. More cellular pores were formed in nylon-66 membranes with the addition of APTEOS. However, increased irradiation dose caused the formation of a dense layer in nylon-66 membranes. Crosslinked silica in nylon-66 membranes was confirmed by FT-IR and DMA, while XRD results showed that there was a high degree of crystallinity in some membranes after irradiation. With improvements in membrane pore size and the ratio of membrane thickness to porosity, nylon-66 membrane with 10 wt% of APTEOS irradiated at 70 kGy exhibited satisfactory permeability, excellent removal of neutral solutes and improved rejection of divalent ions.     

Effects of electron beam irradiation on mechanical properties and nanostructural–morphology of montmorillonite added polyvinyl alcohol composite

This paper is aiming to analyze the effects of electron beam irradiation on the mechanical properties and structural–morphology of nano-sized montmorillonite (MMT) added polyvinyl alcohol (PVOH) composite. MMT particles were added to the PVOH matrix at various loading level that ranges from 0.5 to 4.5 phr MMT and electron beam irradiated with dosages ranging from 6 to 36 kGy. The results showed that tensile strength of MMT added PVOH composites at 1.5 and 2.5 phr MMT were observed marginally higher compare to neat PVOH when irradiation dosages increased to 26 kGy. However, when the concentration of MMT exceeded 2.5 phr, the application of irradiation seems to cause adverse effect to the PVOH–MMT composite. Besides, according to the X-ray diffraction analysis, the application of low irradiation dosage (⩽16 kGy) has significantly enhanced the intercalation effect of MMT particles at high loading (4.5 phr) in PVOH matrix. This also found to be consistent with the scanning electron microscopy observation where the dispersion of MMT particles in PVOH matrix was noted to be more homogeneous than non-irradiated samples. Further increment in irradiation dosage up to 36 kGy has significantly reduced the crystallinity which indicates the higher radiation energy could rupture the crystallite structures in PVOH matrix.     

Structure and properties of coatings on Ni base deposited using a plasma jet before and after electron a beam irradiation

Experimental results for structure, morphology, phase composition and measurements of nano- and microhardness, wear resistance, and adhesion of coatings on a Ni base, which were deposited using a plasma jet, before and after pulsed plasma jet and high-current electron beam melting are presented. Newly formed phases like Cr₃Ni₂ and CrB and intermetallic compounds with molybdenum like Fe₇Mo₆, Fe₃Mo and possibly Fe Mo were found. We also found an effect of phase composition, changed grain dimension and smoothed relief resulting in a factor of three increase in micro- and nanohardness, almost a factor of 20 increase in friction wear resistance and several times increase in coating to substrate adhesion.