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Co-60 ile çelik parçaların radyografisi için oluşturulan tek ve çift ekranların ağırlıklı ortalama yöntemiyle değerlendirilmesi

Başlık çevirisi mevcut değil.

  1. Tez No: 45445
  2. Yazar: ÜLKÜ BULUBAY
  3. Danışmanlar: PROF.DR. BERİL TUĞRUL
  4. Tez Türü: Doktora
  5. Konular: Nükleer Mühendislik, Nuclear Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1995
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 257

Özet

ÖZET Bu tez çalışmasında, Co-60 radyoizotopu kullanılarak gerçeklenen gama radyografisinde görtintU kalitesini arttırmak için yeni bir ön ekran ve/veya ekran cifti oluşturulması konusunda özgtfn bir çalışma yapılması hedeflenmiştir. Bu amaçla, zayıflatma katsayılarının incelenmesinden hareketle,“uygun”olabilecekleri tahmin edilerek seçilen 8 farklı malzeme Cçelik, bakır, kadmiyum, indiyum, gadolinyum, disprosiyum, altın ve kurşunî ile çalışılmıştır. Bu çalışma çerçevesinde çalışılan söz konusu sekiz malzemeyle ve bu sekiz radyografi k ekranla kombinasyonel olarak gerçeklenen çift ekran çalışmaları, tümtlyle orijinaldir. Bu şekilde 28 farklı çift ekran İçin deneyler yapılmıştır. Böylelikle, Co-60 radyoizotopunun radyografi çekimleri için kullanılabileceği en az bes farklı çelik kalınlığı için radyografik çekim deneyleri Cekransız hal için yapılan deneyler ile birlikte) 200* Un Üzerinde olmuş ve yapılan deneyler sonucunda elde edilen sonuçlar İçin ölctimlemeler ve hesaplamalarla, bes veri tabanında 1000* in Üzerinde datadan oluşan bir deney sonuçları seti biraraya toplanmıştır. Mukayeseli değerlendirmeler için, kuvvetlendirme oranı ile rezollisyon ana kriterler olarak seçilmiş. bunlara ilave olarak bir de fiyat kriteri göz önüne alınmıştır. öncelikle, her bir kriter için, farklı radyografik ekranlarla yapılan deneyler sonucunda elde edilen veriler, her kriter faktörüne ilişkin olarak kendi içinde sıralanmıştır. Böylesi çok sayıdaki deney sonuçlarının rasyonel olarak mukayeseli değerlendirilmesi için çok kriter li çoktan seçim yöntemlerinden biri olan“ağırlıklı ortalama veya ağırlıklı sıralama”yönteminden yararlanılması benimsenmiş ve yazılan EKRAN Bilgisayar programı ile yoruma gidilmiştir. Böylelikle, bes farklı açıdan yenilik içeren ve bunların yanısıra, biri radyografik değerlendirme, diğeri ise deneyler sonucunda elde edilen dataların değerlendirilmesine İlişkin olarak kullanılan iki matematik model çerçevesinde, bu doktora tez çalışması gerçeklenmiş olup, nadir toprak elementi veya nadir toprak elementi içeren ön ekran elemanlarının gelişen teknolojiyle önem kazanacağı kanı t lanmış olmaktadı r. VIII

Özet (Çeviri)

EVALUATION OF Co-60 RADIOGRAPHY FOR STEEL PARTS WITH USING SINGLE AND DOUBLE FRONT SCREENS BY WEIGHTED MEANVALUE METHOD SUMMARY The industrial use of non-destructive testing (NOT) greatly expanded during World War II, although some of the techniques were known and used on a limited scale long before that date. NDT has no clearly defined boundaries, but it used to be considered that were five major methods (radiographic inspections, ultrasonic tests, magnetic particle tests, eddy current test and liquid penetrant tests 5 for worldwide industrial applications. All these techniques can be subdivided, and to them must be added a range of important new techniques such as acoustic emmission methods, thermography and holography. Further, a large number of even more specialised methods have been investigated and found to have applications in particular limited fields; these are methods such as proton anhllation, neutron scattering, proton radiography, microwaves and nuclear magnetic resonance. A great deal of non-destructive testing is carried out for flaw detection in materials such as the detection of defects of the materials, lack of bound in adhesive Joints, and fatigue cracks developing during service. For the quality control criteria, the requirements are based on a more general engineering experience and the inspection is directed towards detecting the most common defects, with an implication of less-severe NDT reqiurements. These concepts emphasise the need of having a knowledge of the defect sensitivities required, in detail, before applying NDT methods. The use of minimum detectable defect size in any specific application is not an efficient assessment of either a technique or an operator. Probabilities and confidence levels are also needed and laboratory trials can not necessarily be extrapolated to field results. Most NDT techniques have a wide range of specific type of defect, an particular material. IXEver since discovery of X-rays in 1893, it ha3 been realised that they can be used for the non-destructive testing of materials. Gamma rays are also widely used in industrial radiography. X-rays and gamma rays are a form of electromagnetic radiation, of the same physical nature as visible light, radiowaves, etc., but which have a wavelength which allows them to penetrate all materials with partial absorption during transmission. X-rays and gamma rays travel in straight lines outwards from a source. By conventional, definitions,“a radiograph”is a photographic image produced by a beam of penetrating ionising radiation after passing through a specimen, and“radiography”is the production of radiographs. The effects of build-up factor and absorption coefficient values in radiography can be combined with the radiographic parameters, such as, source factor, geometry factor, film factor, intensifying screen factor and exposure time factor. Even with double-coated radiographic films, only a small fraction of the transmitted the X-ray or gamma ray energy reaching the film is absorbed in the film emulsions, but this can be increased by employing intensifying screens. In industrial radiography, intensifying screens are usually thin metal foil, especially lead. A screen is pressed as closely as possible on each emulsion, so that there is a front and a back screen. The X-rays or gamma rays absorbed in the metal screen release electrons which pass into the film emulsion to add to the action of the directly absorbed radiation. The screens are very thin and dense material, so that the electrons can not spread sideways and the image unsharpness with a pair of screens is only very slightly poorer than with no screens. The intensifying action of the screens allows the exposure time to be produced by a factor depending on the energy level of electromagnetic radiation. The use of metal screens has a secondary effect in preferentially absorbing the lower-energy Compton scatter and so reducing the build-up factor. The prime purpose of metal intensifying screens is to reduce the required exposure, although the front screen also has a useful secondary effect in reducing the intensity of the scattered radiation generated in the specimen which reaches the film.It is desirable to have some means of measuring the ability of the radiographic image to show detail. The ability to detect a flaw by radiography depends on the nature of the individual flaw» its shape and orientation to the beam of radiation, as well as on the various radiographic parameters. A distinction must be made between radiographic quality and radiographic sensitivity. In many applications of radiography, such as flaw detection, the two are virtually synonymous; the ability to show a smaller flaw, i.e. an improvement in sensitivity, is regarded as an improvement in radiographic quality. However a large proportion of radiography is concerned with flaw detection and as there must obviously be limits to the dimensions of flaws which can be revealed by radiography. It is important to know these limits, the factors which control them, and the methods of measuring f law-sensi t i vl ty. For the calculation of sensitivity some success has been achieved in representing a flaw by some equivalent artificial cavity. Radiographic sensitivity is more usually measured in terms of some artificial element which does not necessarily bear much resemblance to a flaw in metal. There are some widely used methods. Ever since the earliest days of radiography devices called“penetremeters”have been used. The originally consisted a small flaw simulation element of the same material as the specimen. The penetremeter placed on the surface of the specimen, and then taking radiographs. One of them is to specify sensitivity in terms of the ability to detect a wire for drill or hole) of the same material as the specimen being examined, when the wire is laid on the surface of the specimen remote from the film. The diameter of the thinnest detectable wire Cor drill or hole) is used a criterion of sensitivity. An important point is resolution of the image on the radiographs. It can be determined by using“modulation transfer function CMTF)”like as appllying other imaging techniques. Evaluation of MTF, it can be used sinisoidal or square wave devices. XIIn this thesis, it İ3 aimed to be done an original study on new front screens and/or double front screens for increasing of the Imaging quality for Co-60 gama radiography. For this purpose, eight different materials (steel, copper, cadmium, indium, gadolinium, disprosium, gold and lead} are selected as front screen by evaluation of absorbtion coefficient of the materials. In this circumtances, experiments have been done by using eight single front screens materials and their combinational double screens that are totally 28 different combinational materials. In the experiments, all the other exposure parameters are the same except the front screen materials. The experiments have been done on five different thickness for steel parts. Therefore, more than 200 radiographic exposures have been done including experiments without screens, and results of them consist of more than 1000 data on five different data bases. For the comparative evaluation of the results, intensifying effect and resolution are selected as two main criteria. In addition to them cost value of the materials are placed an another comperative criteria. At first, result data which are collected from different experiments with different front screens, are set up according to each criteria. In order to rational comperative evaluation for the various data sets,“weighted meanvalue method”is used as multicholse and multicriteria method and a computer program as namely EKRAN is written in Fortran 77, and then the results of experiments are evaluated. Two different mathematical models are used in this thesis. One of them is applied with using test aparat on having square-wave shape for determination of modulation transfer function, and the other is evaluation of the result data. XIIIn the literature, there İ3 no study on these eight front screens and combinational double screens together, and no more study on modulation transfer function and sensitivity for evaluation radiographic image quality. Moreover, any study with the three comparative criteria < intensifyingef feet, resolution and cost), and also any study with using weighted meanvalue method for evaluation of radiographic experiments data are not existed. Therefore, the thesis have five originality in it. Finally, it can be said that rare-earth front screens for Co-60 radiography will gain importance with developing of the technology. Moreover, some new rare-earth alloys, which are sign in this thesis, can be developed. XIII

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