Mikroradyografi ve mikro odaklı radyografi

Abstract

ÖZET Bu çalışmada mikroradyografi ve mikro odaklı radyografi teknik]ör i 4 mm odak boyutlu Balteau GR 30O, klasik X-ışınları cihazı i. I e gerçekleştirilmeye çalışılmıştır. Normal radyografik çekimler ile bir kaç parametre dışında farklılık göstermeyen mikroradyografi çekim tek¬ niği ve radyografik filmlerin istenilen oranlarda, çok duyarlı olarak büyütülmesi uygulaması, Nükleer Ugulamalar Anabilim Dalında bulunan cihazlar ile gerçekleştir¬ ilmiş tir.Radyografik çekimler bu teknikte,büyütme tekniği uygulanmadan yapılmıştır.Elde edilen duyarlı filmler, projeksiyon cihazlarında ortalama 60 kat büyütme oranının problemsiz bir şekilde gerçekleştirildiği,bunun yanında cihazların zorlanması ile bu oranın yaklaşık 200 kat büyütme oranına çıkarılabileceği görülmüştür. ' / Mikro odaklı radyografi tekniği için, cihazin/4 mm olan odak boyutu,mikron mertebesine indirilmeye çalışıl¬ mıştır. Bu nedenle cihaza yerleştirilebilecek şekilde kollimatörler tasarlanmış.bunlara mikron mertebesinde odaklar açı imiş tır. Teknik zorluklardan dolaya 100 /ı'luk odak boyutunun altına inilememiştir.Gerçekleştirilen uy¬ gulama l ar, yar ı gölge değerlerinin standardları aşmasından dolayı, yaklaşık 14 defa büyütme oranı ile sınırlandır¬ ılmıştır. 5 kat büyütme oranına kadar yarı gölge değer¬ leri 0.3mm altında kalmış,14 defa büyütme oranında bu değer,l.25mm boyutlarına yükselerek, filmdeki görüntüyü bulanık hale getirmiştir.Bundan dolayı çoğunlukla 4-5 kat gibi küçük oranlı,.büyütmeler gerçekleştirilebilmiştir. IV

SUMMARY in this study, microradiography and microfocus radiography technigues, have been evaluated by using a conventional X-ray tube which has a foca l spot of 4mm. in the second part of this work, the special feature of X-rays and effects on materials have been summarised. Three effecfcs of X-rays on materials which are photoelectric event, Compton scattering and pair production and absorbsion process of X-râys in materials have also been expla.ined in detail. Microradiography technique have been explained in detail. The method of microradiography is to analyse and exaraine the small and miniature discontinuties nondestructively in thin specimens. The image can be visualized by enlargement of the radiograph[4].This is a simple and obvious technigue can provide more detail images on a radiograph. in this method, especially soft X-rays, between 5 and 50 kV is used but voltages up to 50 kV is applied to metallic materials whose mass absorbtion coefficents are high.The exposure position of microradiography technigue is almost same as conventional X-rays radiography. in other wordr, specimen and film are in contact with each ofcher during the. exposure period.lt is most important Vthat in microradiographic technique the contact between and specimen must be extremelly good, so that, geo,metric unsharpness could be so small. The geometric unsharpness is between 0.02 to O.lmm, because of this, geometric unsharpness is seen much more than the standards on the photographic card after magnification. Exremelly good contact between specimen and film is neccesary. If the maximum enlargement of which the film is capable, is to be achived,good contact can be obtained with a simple mechanical jig which presses the specimen against fhe film ör plate, but best results are probably obtained with a vacuum exposure holder[4]. The photographic emulsion is usually single coated and finer grained than the emulsion of ordinary x-rays films.ASTM class I films l ike Dupond NDT 35,45 are apropriate to use in microradiography.According to AŞTM class II films used in industrial applications.The exposure time is longer comparing with ASTM class I films,för the same specimen and constant dîstance. / If a microradiograph is going to be enlarged more than 50 diameters, conventional photo microradiographic techniques and eguipments must be used[8], The experimental study, some Integrated circuits and a steel plate with small failure and cracks used as specimens. First of ali, microradiographic technigue applied för ali specimens.The thickness of Integrated circuits were between 4-5mm.Steel plate has 6mm thickness. Ali exposure parameters have been chosen VIcarefully so that radiographic density, image guality and geometic unsharpnees were almost same before as calculated.The technical parameters are: exposure time 3 min at 100 kV.Kodak industriex MX low speed(fine grain films with 0.125mm lead screens,was used.Film focus distance chosen as 700 mm. it is much more four times,than DÎN 54111 category B sensitiv£ technique.This values are Therefore the geometric unsharpness obtained nearly, 0.028mm för integrated circuits,O.035mm för steel piate on radiographic films. Before projection, ali radiographic films were developed by using,Agfa G-350 developer ( 6 min., 18°C ) and AGFA G-150 fixer ( 12 min.,18°C ) At the primary projection steps, negative films of so small area of radigraphic films,like chips ör wires inside integrated cicuits ör cracks inside steel plate, have been taken by projection device.Magnification factor was about 10 times.End of this stage,negative films of radiographic image were obtained. / At the secondary stage of magnification, image on negative films have been printed on photographic cards by using an agrandizor. Magnification factor in this stage was between 10-20 times. At the end of microradiographic application, it was seen that doing magnification between 20-80 times is possible.For more than these magnification is also possible, but it is neccesary to use the magnification devices at limits. VIIacollimator was calculated as approximately 8° according to vertical line between focus and specimen or film, during the exposure. In order to protect the back side of the film a quantity of lead bricks have been placed. As a result, maximum magnification factor (M) have been obtained until 14 times in that application.But geometic unsharpness has been obtained as 1.25 mm even in that magnification. This value was so high because of focal spot diameter. Magnification factors according to geometrical unsharpness, are given in tables. Magnifications bigger than 4 times the value of unsharpnesses were extremely high and therefore the maximum magnification was obtained for this type of work was only 4 timesa) The sample need not to be in contact with the film during exposure. This makes fine structural detail easier to observe (1]. b) The seperation of sample from film means that scatter and secondary radiation from within the sample are attenuated compared with the direct image forming radiation. Therefore proportion of scattered radiation, reaching the film is much smal ler [1, 17]. c) No expensive. and time consuming secondary magnif ication[17]. d) A fine focal spot provides better `dept of focus` and so gives more uniform definition for structural features spread through the section thickness any detail inside a part will be imaged with same sharpness [ 17]. e) One disadvantage of the magnification technique is that the area of specimen examined is in inverse proportion to the magnification so that if a large magnification is used. Only a very small area of specimen is examined at each exposure also large films are neccesary [17]. For microfocus radiography, a conventional X-ray tube has also been used. But it's focal spot diameter is not appropriate for this purpose.During the experimental work a new collimator made in order to focus the X-ray. A lead collimator with nearly 100 y,m focal spot, has been made for this work. Angle of X-rays beam that exit from IXcollimator was calculated as approximately 8° according to vertical line between focus and specimen or film, during the exposure. In order to protect the back side of the film a quantity of lead bricks have been placed. As a result, maximum magnification factor (M) have been obtained until 14 times in that application.But geometic unsharpness has been obtained as 1.25 mm even in that magnification. This value was so high because of focal spot diameter. Magnification factors according to geometrical unsharpness, are given in tables. Magnifications bigger than 4 times the value of unsharpnesses were extremely high and therefore the maximum magnification was obtained for this type of work was only 4 times