Development of large area silicon detectors: Special properties and radiation stability

Large area totally depleted silicon detectors with a sensitive surface of up to 35 cm² have been developed for applications in high energy physics with emphasis on electromagnetic and hadronic shower calorimeters. Special fabrication processes and related diode properties, including long-term stability, will be discussed. Special attention is given to edge effects which are investigated with a scanning proton microbeam. The radiation sensitivity of such detectors was extensively studied through capacitance-voltage as well as capacitance-frequency measurements.     

Improvement of adhesion properties of polypropylene substrates by methyl methacrylate UV photografting surface treatment

Polypropylene is a widely used commodity plastic from an industrial point of view. Typical applications include both low and high technological content, as it has a good balance between overall properties, processability and cost. However, it is important to remark its intrinsic low surface energy which leads to high chemical inertness. This has an important restriction on some technical applications that require joining and/or finishing processes such as painting. Therefore, the use of polypropylene in these applications requires previous surface modification in order to increase surface activity. Surface modification can be carried out by physical processes such as plasmas or by chemical ways. Surface chemical modification is characterized by relatively low cost and easy implementation at industrial scale. In this work, we have used a chemical process to improve adhesion properties on polypropylene substrates. The selected method has been ultraviolet photografting of methyl methacrylate (MMA) monomer. This process allows increasing surface activity and this has a positive effect on polypropylene–polypropylene adhesion joints. Surface changes have been followed by contact angle measurements and subsequent surface free energy calculation. The evolution of mechanical properties of adhesion joints (T-peel and shear conditions) in terms of the previous exposure time to UV radiation has been evaluated. Optical microscopy (OM) and scanning electron microscopy (SEM) have been used to characterize adhesion fracture type.     

辐照对红外熔石英性质的影响(英文)

研究了高能电子、高能质子辐照对红外熔石英性质、光学面形的影响。研究了高能电子对红外熔石英面形的影响 ,结果表明 ,没有明显的面形变化。研究了高能质子对红外熔石英面形、可见和红外反射特性的影响。研究结果表明 ,没有观察到高能质子辐照对红外熔石英面形和反射特性的影响     

A database of frequency distributions of energy depositions in small-size targets by electrons and ions

Linear energy transfer (LET) is an average quantity, which cannot display the stochastics of the interactions of radiation tracks in the target volume. For this reason, microdosimetry distributions have been defined to overcome the LET shortcomings. In this paper, model calculations of frequency distributions for energy depositions in nanometre size targets, diameters 1-100 nm, and for a 1 μm diameter wall-less TEPC, for electrons, protons, alpha particles and carbon ions are reported. Frequency distributions for energy depositions in small-size targets with dimensions similar to those of biological molecules are useful for modelling and calculations of DNA damage. Monte Carlo track structure codes KURBUC and PITS99 were used to generate tracks of primary electrons 10 eV to 1 MeV, and ions 1 keV μm(-1) to 300 MeV μm(-1) energies. Distribution of absolute frequencies of energy depositions in volumes with diameters of 1-100 nm randomly positioned in unit density water irradiated with 1 Gy of the given radiation was obtained. Data are presented for frequency of energy depositions and microdosimetry quantities including mean lineal energy, dose mean lineal energy, frequency mean specific energy and dose mean specific energy. The modelling and calculations presented in this work are useful for characterisation of the quality of radiation beam in biophysical studies and in radiation therapy.     

Fabrication process for ion-implanted and Permalloy hybrid magneticbubble memory devices

A fabrication process for ion-implanted and Permalloy hybrid bubble memory devices has been developed. The mask patterns of polyimide (PIQ) for ion-implanted tracks are fabricated using a tri-level resist process where the top imaging resists are delineated by deep UV contact printing. The minimum feature of the PIQ pattern is 0.75 μm and can be controlled precisely. The sidewalls of PIQ patterns are smooth and vertical. At the junctions between ion-implanted and Permalloy tracks, tapered resist patterns are used as masks for implantation. Novolak-based resist is used and is reflowed thermally to obtain a tapered profile. Fabrication conditions, such as type of resist and baking temperature, were investigated to achieve good reproducibility. Tapered resist patterns are also used as masks for iron milling which reduces the thickness of garnet film in the area of the Permalloy tracks. This is necessary to adjust the operating bias field of Permalloy tracks to that of the ion-implanted tracks. A prototype of a 4-Mb memory device was fabricated, confirming the feasibility of the present process     

Modelling and calculations of the response of tissue equivalent proportional counter to charged particles

Space activities in earth orbit or in deep space pose challenges to the estimation of risk factors for both astronauts and instrumentation. In space, risk from exposure to ionising radiation is one of the main factors limiting manned space exploration. Therefore, characterising the radiation environment in terms of the types of radiations and the quantity of radiation that the astronauts are exposed to is of critical importance in planning space missions. In this paper, calculations of the response of TEPC to protons and carbon ions were reported. The calculations have been carried out using Monte Carlo track structure simulation codes for the walled and the wall-less TEPC counters. The model simulates nonhomogenous tracks in the sensitive volume of the counter and accounts for direct and indirect events. Calculated frequency- and dose-averaged lineal energies 0.3 MeV-1 GeV protons are presented and compared with the experimental data. The calculation of quality factors (QF) were made using individual track histories. Additionally, calculations of absolute frequencies of energy depositions in cylindrical targets, 100 nm height by 100 nm diameter, when randomly positioned and oriented in water irradiated with 1 Gy of protons of energy 0.3-100 MeV, is presented. The distributions show the clustering properties of protons of different energies in a 100 nm by 100 nm cylinder.     

Measurements of trapped protons and cosmic rays from recent Shuttle flights

Two new charged particle detectors have been flown in five recent Shuttle flights. The tissue-equivalent proportional counter measures the lineal energy spectrum of space radiation in the 0.26-300 keV micrometer-1 range. The charged particle spectrometer is a double dE/dx x E and dE/dx x Chrenekov detector system which provides a measurement of the differential energy spectrum of protons from 13 to 350 MeV and dose rate in silicon. In this paper the dose rate, equivalent dose rate, and radiation, quality factor for trapped protons and cosmic radiation are reported on separately. A comparison of the integral LET spectra with recent transport code calculations shows significant disagreement. Using the calculated dose rate from the omnidirectional AP8MAX model with IGRF reference magnetic field epoch 1970, and observed dose rate as a function of geographic latitude and longitude, the westward drift of the south Atlantic anomaly has been determined. The east-west effect has also been studied and a 'second' radiation belt observed. A comparison of the galactic cosmic radiation (GCR) lineal energy transfer spectra with model calculations shows disagreement comparable with those of the trapped protons.     

On the biophysical interpretation of lethal DNA lesions induced by ionising radiation

Although DNA damage is widely viewed as a critical target for the induction of cell killing by ionising radiation, the exact nature of DNA damage responsible for these effects is unknown. To address this issue, the probability of forming lethal damage by single proton tracks, derived from published survival data for Chinese hamster V79 cells irradiated by protons with energies from 0.57 to 5.01 MeV, has been compared to estimated yields of clustered DNA lesions and repair outcomes calculated with Monte Carlo models. The reported studies provide new information about the potential relationship between the induction and repair of clustered DNA damage and trends in the expected number of lethal events for protons with increasing linear energy transfer (LET). A good correlation was found between the number of lethal events in V79 cells and the induction of double-strand breaks (DSBs) consisting of three or more elementary DNA lesions. For the yields of other types of DNA damage, as well as point mutations formed through the misrepair of base damage and single-strand breaks, observed trends with increasing LET are not consistent with trends in the yields of lethal events. This observation suggests that the relative biological effectiveness (RBE) of protons of varying quality may be more closely related to the induction of complex DSBs rather than other forms of damage.     

Effect of Surface Free Energy of Film Laminated Steel Sheets on Content Release Properties

Polyethylene terephthalate (PET) sheets that are now widely used in beverage cans have excellent properties of formability, corrosion resistance and adhesion to steel sheets. To expand their application, we have sought to develop a new PET film laminated steel sheet for use in food cans. Content release properties are necessary for easy removal of the can contents in food can applications. However, PET film laminated steel sheets have poor content release properties. Investigations of these properties have revealed dependence on the strength of adhesion between the films and can contents. The surface free energy of PET films has been inferred to be the main factor in poor content release properties. Therefore, using films with widely diverse surface free energy values, we studied the effects of surface free energy on the content release properties of materials in contact with cans. The results showed that these properties are closely related to the surface free energy of the film material, and that materials with surface free energy of less than 23 mN/m or greater than 44 mN/m show excellent properties for processed meat products with high protein content. The material with PET film coated with mixture of polyester resin and fatty acid is the most promising material for use in food cans in this study. The work has also shown that content release properties can be expressed as a function of adhesion in water between a material and protein. Reducing adhesion can significantly improve content release properties.     

A two-step deposition process for electrode fabrication of CdZnTe detectors

The method of the electrode deposition process plays a vital role in determining the contact characteristics, which is often one of the dominant factors influencing the CdZnTe detector performance. In this work, a modified deposition process named two-step process for the electrode fabrication of CdZnTe detectors, was developed. This deposition process can dramatically increase the adhesion strength and reduce the inhomogeneity of the metal/semiconductor interface, and improve the detection ability of high energy radiation such as X-rays and gamma-rays. Scanning acoustic microscopy, shear tests, current-voltage test and energy spectra characteristics measurements were carried out in this work.     

Tailoring the bioactivity of commercially pure titanium by grain refinement using groove pressing

Commercial pure titanium (cpTi) sheets have been processed by groove pressing (GP) at room temperature to refine the grains so as to improve its properties for bone implant applications. Atomic force microscopy revealed submicron/nano roughness features on the processed cpTi. The contact angle measurements show good wettability and higher surface energy when compared to unprocessed cpTi. The bioactivity of the GP samples in simulated body fluid was also found to be enhanced with the formation of a homogenous and dense globular hydroxyapatite layer. The Ca/P ratio of the apatite layer was around 1.66 as similar to the bone mineral phase. The bioactivity enhancement of GP samples has been related to the submicron grain features which results in an increase in the surface roughness and wettability.     

Feasibility study of extremity dosemeter based on polyallyldiglycolcarbonate (CR-39) for neutron exposure

In nuclear facilities, some activities such as reprocessing, recycling and production of bare fuel rods expose the workers to mixed neutron-photon fields. For several workplaces, particularly in glove boxes, some workers expose their hands to mixed fields. The mastery of the photon extremity dosimetry is relatively good, whereas the neutron dosimetry still raises difficulties. In this context, the Institute for Radiological Protection and Nuclear Safety (IRSN) has proposed a study on a passive neutron extremity dosemeter based on chemically etched CR-39 (PADC: polyallyldiglycolcarbonate), named PN-3, already used in routine practice for whole body dosimetry. This dosemeter is a chip of plastic sensitive to recoil protons. The chemical etching process amplifies the size of the impact. The reading system for tracks counting is composed of a microscope, a video camera and an image analyser. This system is combined with the dose evaluation algorithm. The performance of the dosemeter PN-3 has been largely studied and proved by several laboratories in terms of passive individual neutron dosemeter which is used in routine production by different companies. This study focuses on the sensitivity of the extremity dosemeter, as well as its performance in the function of the level of the neutron energy. The dosemeter was exposed to monoenergetic neutron fields in laboratory conditions and to mixed fields in glove boxes at workplaces.     

A neural network for positron identification by transition radiation detector

A neural network algorithm has been applied in order to distinguish positrons from protons by a transition radiation detector (TRD). New variables are introduced, that simultaneously take into account spatial and energy TRD information. This method is found to be better than the one based on classical analysis: the results improve the detector performance in particle identification for efficiency higher than 90%. The high accuracy achieved with this method is used to identify positrons versus protons with 3 × 10⁻³ contamination, as required by TRAMP-SI cosmic ray space experiment on the NASA Balloon-Borne Magnet Facility.     

EXPERIMENTAL TECHNIQUES TO CUT AND WELD COPPER BY LASER - A REVIEW

This paper reports on the cutting and welding of copper sheets using a CO₂ laser. For the cutting process, the experimental data from tests on 0.2 to 4.0 mm thick copper sheets with a 2 kW CO₂ laser are described. The behavior of the critical cutting speed V, cutting widths a, the product V × b and the melted volume versus the thickness (b) for a 2 kW CO₂ laser using different focusing lenses has been investigated, The cutting speeds have been found to be significant and micrographic examinations have shown that the laser cutting quality is good. The laser welding of copper sheets is possible by overlapping layers of cupric oxide, CuO, with a small quantity of cuprous oxide, Cu₂O grown under laser beam irradiation. This experimental approach, similar to the one used for the cutting process, allows one to increase the copper surface absorption of the laser radiation. The weld tests done in this way have shown a bad quality of the butt joint; in fact, a number of inclusions in the melted zone and growth of the copper grains surrounding the weld have always been observed. Another experimental technique has also been tested using a better coating to increase surface absorptive power without producing weld defects. The first results are interesting, though the research is still in progress. Finally, by using e pulsed Nd-YAG laser and the same coated samples - cited above - some good welds have been obtained.     

Microdosimetry distributions for 40-200 MeV protons

Theoretical calculations have been performed to obtain microdosimetrical characteristics for protons in energy range from 40 to 200 MeV. This energy range is a representative of proton energies in tissue during radiation therapy and it also represents a large portion of the proton fluency in the South Atlantic Anomaly. Distributions of deposited energy calculated using Monte Carlo track structure code TRIOL and own-made programs were compared with experimental data obtained using spherical tissue-equivalent proportional counter. A good agreement between calculated and experimentally obtained microdosimetry spectra has been found.     

Ionisation density dependence of the optically and thermally stimulated luminescence from Al2O3:C

This paper presents an overview of recent results on ionisation density dependence of the thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL) signals from Al2O3:C, with emphasis on the sensitivity, efficiency, shape of the TL/OSL curves and the emission spectrum. High-ionisation densities are created uniformly by accumulated high doses of low-linear energy transfer radiation (gamma, beta, X rays) or non-uniformly in heavy charged particle tracks, even at low fluences, as in the case of space radiation fields. Significant deep trap filling, which occurs at these high-ionisation densities, ultimately results in changes in the concentration of recombination centres (F+-centres) and, consequently, in sensitivity changes and other effects. An OSL emission band at 335 nm has been observed in addition to the main F-centre luminescence band, and the relative intensities of these bands have been observed to be dependent on the ionisation density. The implications of these results and open issues are discussed.     

Production of microfibrillated cellulose (MFC)-reinforced polylactic acid (PLA) nanocomposites from sheets obtained by a papermaking-like process

The fabrication of cellulose nanofiber-reinforced composites has been so far problematic due to difficulties in obtaining good dispersion of hydrophilic cellulose fibers in a hydrophobic polymer matrix. A new manufacturing process similar to papermaking, which enables the production of thin sheets made of uniformly dispersed microfibrillated cellulose (MFC) with polylactic acid (PLA) fibers was devised, and the composites were obtained by compression molding of the stacked sheets. The process is suitable for adoption at an industrial scale owing to the high yields and fast dewatering times. The measurement of tensile properties revealed that the modulus, strength, and strain at fracture increased linearly with the MFC content. The improvement in toughness was considered one of the key benefits brought by MFC reinforcement.     

Tailoring nanostructured, graded, and particle-reinforced Al laminates by accumulative roll bonding

Accumulative roll bonding (ARB) is a very attractive process for processing large sheets to achieve ultrafine-grained microstructure and high strength. Commercial purity Al and many Al alloys from the 5xxx and the precipitation strengthened 6xxx alloy series have been successfully processed by the ARB process into an ultrafine-grained state and superior ductility have been achieved for some materials like technical purity Al. It has also been shown that the ARB process can be successfully used to produce multi-component materials with tailored properties by reinforcement or grading, respectively. This allows optimizing the properties based on two or more materials/alloys. For example, to achieve high corrosion resistance and good visual surface properties it is interesting to produce a composite of two different Al alloys, where for example a high strength alloy of the 5xxx series is used as the core material and a 6xxx series alloy as the clad material. It has been shown that such a composite achieves more or less the same strength as the core material although 50% of the composite consists of the significant softer clad alloy. Furthermore, it has been found, that the serrated yielding which typically appears in 5xxx series alloys and limits applications as outer skin materials completely disappears. Moreover, the ARB process allows many other attractive ways to design new composites and graded material structures with unique properties by the introduction of particles, fibres and sheets. Strengthening with nanoparticles for example is a very attractive way to improve the properties and accelerate the grain refining used in the severe plastic deformation process. With an addition of only 0.1 vol.-% Al2O3 nanoparticles a significantly accelerated grain refinement has been found which reduces the number of ARB passes necessary to achieve the maximum in strength. The paper provides a short review on recent developments in the field of ARB processing for producing multicomponent ultrafine-grained sheet materials with tailored properties.     

Progress in cold roll bonding of metals

Layered composite materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB), as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing large layered composite sheets and foils. In this paper, we provide a brief overview of a technology using layered composite materials produced by CRB and discuss the suitability of this technology in the fabrication of layered composite materials. The effects of process parameters on bonding, mainly including process and surface preparation conditions, have been analyzed. Bonding between two sheets can be realized when deformation reduction reaches a threshold value. However, it is essential to remove surface contamination layers to produce a satisfactory bond in CRB. It has been suggested that the degreasing and then scratch brushing of surfaces create a strong bonding between the layers. Bonding mechanisms, in which the film theory is expressed as the major mechanism in CRB, as well as bonding theoretical models, have also been reviewed. It has also been showed that it is easy for bcc structure metals to bond compared with fcc and hcp structure metals. In addition, hardness on bonding same metals plays an important part in CRB. Applications of composites produced by CRB in industrial fields are briefly reviewed and possible developments of CRB in the future are also described.     

Progress in cold roll bonding of metals

Abstract

Layered composite materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB), as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing large layered composite sheets and foils. In this paper, we provide a brief overview of a technology using layered composite materials produced by CRB and discuss the suitability of this technology in the fabrication of layered composite materials. The effects of process parameters on bonding, mainly including process and surface preparation conditions, have been analyzed. Bonding between two sheets can be realized when deformation reduction reaches a threshold value. However, it is essential to remove surface contamination layers to produce a satisfactory bond in CRB. It has been suggested that the degreasing and then scratch brushing of surfaces create a strong bonding between the layers. Bonding mechanisms, in which the film theory is expressed as the major mechanism in CRB, as well as bonding theoretical models, have also been reviewed. It has also been showed that it is easy for bcc structure metals to bond compared with fcc and hcp structure metals. In addition, hardness on bonding same metals plays an important part in CRB. Applications of composites produced by CRB in industrial fields are briefly reviewed and possible developments of CRB in the future are also described.