Normal beton ve özel amaçlı betonların gama radyasyonunu zırhlama özelliklerinin incelenmesi
Investigation of gamma radiation shielding properties of normal and special purpose concretes
Yazar: DİLEK KAYA ÇELİK
Danışman: PROF. DR. NESRİN ALTINSOY
İstanbul Teknik Üniversitesi / Enerji Enstitüsü / Nükleer Araştırmalar Ana Bilim Dalı / Radyasyon Bilim ve Teknoloji Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Fizik ve Fizik Mühendisliği = Physics and Physics Engineering ; Nükleer Mühendislik = Nuclear Engineering
Dizin: Ağır beton = Heavyweight concrete ; Hafif beton = Lightweight concrete ; Hazır beton = Ready-mixed concrete ; Lif takviyeli beton = Fiber reinforce concrete

Özet:
Gelişen teknolojiyle beraber toplum üyelerinin maruz kaldığı radyasyon miktarının artttığı bilinmektedir. Bireylerin aldığı radyasyon dozu, yaşanılan bölge, bölgenin toprak yapısı, binalarda kullanılan malzemeler, mevsimler, kutuplara olan uzaklık ve hava koşulları gibi birçok faktöre bağlıdır. Günümüzde sudan sonra en çok kullanılan malzemelerden birinin de beton olduğu göz önünde bulundurulduğunda, betonun radyasyon karşısındaki davranışının incelenmesinin gerekliliği ortaya çıkmaktadır. Bu yüksek lisans tez çalışmasında son zamanlarda Türkiye'de de kullanımı yaygınlaşan özel amaçlı betonların gama radyasyonunu zırhlama özelliğinin deneysel yöntemlerle incelenmesi ve normal beton için bulunan değerlerle kıyaslanması amaçlanmıştır.
Çalışmada normal beton ve özel amaçlı üretilen hafif, ağır ve çelik lifli betonların radyasyonu zayıflatma özellikleri Co-60 ve Cs-137 gama radyoizotop kaynakları kullanılarak incelenmiştir. Bunun için sayımlar her bir beton numune için üçer kez tekrarlanmıştır. Ortalama sayım değerleri  kullanılarak beton numunelerin gama radyasyonunu zayıflatma özellikleri belirlenmiştir. 
Deney düzeneğinde beton numune yokken alınan boş sayım değerleri ile numunenin yedi farklı kalınlığından alınan sayımlar dikkate alınarak gama radyasyonunu zayıflatma oranları bulunmuştur. Elde edilen zayıflatma oranlarının kalınlığa göre değişimi grafiklerle gösterilmiştir. Tüm beton tipleri için bu zayıflatma oranlarının kalınlıkla değişimi çizdirilerek kıyaslama yapılmıştır. Grafiklerin çiziminde kullanılan Origin8 bilgisayar programı ile lineer zayıflatma katsayıları ve standart sapmalar elde edilmiştir. Lineer zayıflatma katsayısı ve numune yoğunluklarından kütle zayıflatma katsayılarına ulaşılmıştır. Son olarak da zırhlama ve radyasyondan korunmanın en önemli parametrelerinden biri olan yarı değer kalınlıklar tüm beton çeşitleri için hesaplanmış ve elde edilen değerler kıyaslanmıştır. Bunların yanı sıra numunelerin basınç dayanım testleri yapılarak mukavemet değerleri tespit edilmiştir. Çalışılan beton numunelerin radyasyonu zayıflatma oranları ve yarı değer kalınlıklarının, malzemelerin yoğunluk ve karakteristik özellikleri ile uyumlu olduğu gözlenmiştir

Abstract:
With the developing technology, it is known that the amount of radiation exposure to community depends on many factors such as the place of residence, the soil structure of the region, the materials used in buildings, the seasons, the distance to the poles and the weather conditions. Considering that one of the most commonly used materials, after water, is concrete, it is necessary to examine the behavior of concrete against radiation. This graduate thesis, investigation of the gamma radiation shielding properties of widely used special purpose concretes in Turkey and comparison of these results to the results of normal concrete is aimed. 
By considering specific needs of usage, light concrete which is produced by using light materials as aggregate and heavy concrete which is produced by using generally barite as aggregate was chosen. Light concrete production is carried out by choosing appropriate aggregate. Recently, it has become one of the most common type of concrete because of its characteristics such as being efficient in terms of isolating sound and heat. It is known by studies that to produce light concrete, pumice is used, generally. The reason of using pumice is its acoustic and heat insulation advantages. Also, it is preferrable to be light in weight and not to overload the structures.
Heavy concrete is widely used as a shielding material. Due to its shielding properties, it is generally used as building materials in hospitals, laboratories or in places where there are radioactive sources. Heavy concretes are produced by using heavy materials as aggregate. As heavy aggregate barite is used generally since its unit volume weight is high.
The last special purpose concrete chosen in this study is steel fiber concrete, which is called dramix in concrete industry. It is preferred because of its ductility and high tensile strength. In terms of density, it is not much different from normal concrete.  Lastly, normal concrete is produced in order to be able to compare the most common building material`s properties with the special purposed ones. Six samples were produced from each type of concretes. Each of them were labeled during production process in order to prevent any problem. 
When concrete mixtures produced, their mass and  unit volume weights were measured. Consistency tests were also applied which tells the producer that the fresh concrete mix has high quality enough to use it as building material since the quality of concrete is defined according to its workability when it is fresh, and its strength when it is hardened. 
After the mixtures poured in cylindrical templates and labeled, they were left to dry and harden. During hardening process, the samples were waited in a pool which is rich in mineral and this process lasts 28 days to accomplish. This mineral rich pool provides concrete samples to reach their properties more quickly and depending on mineral type it also helps to increase the pressure strength value of the concrete.
To be able to identify all the radiation attenuation properties and half value thicknesses, the concretes were chosen and then produced. This production process took 28 days in mineral rich pool to gain enough compressive strength to form an appropriate building material. In order to make compressive strength assessments and make concrete samples suitable for experiments, all the surfaces of the samples were smoothed. Then, three of each type of samples were used in compressive strength tests. The average of these three results were calculated and recorded as mean strength. 
The rest of the samples were used to obtain 2,3,4,8 cm of blocks which provides to find radiation attenuation values of  2,3,4,5,6,7 and 8 cm thicknesses of these blocks. For instance, while assessing radiation attenuation of 5 cm of material thickness, 2 cm and 3 cm samples are used together to form a 5 cm sample. In this way, it was possible to make measurements of 7 blocks of different thickness by using 4 different thickness of these blocks. 
When the blocks of different thickness were produced and smoothed, they were all ready to assess radiation attenuation and shielding properties of all concrete types in  gamma calibration laboratories. The radiation attenuation properties of normal and special purpose light, heavy and steel fiber concretes are obtained by using Co-60 and Cs-137 radioactive sources.
First, Co-60 radioactive source is used to take counts. In the experimental setup, the system is installed as the distance between the source and the sample is 50 cm, and the distance between the sample and the ion chamber is 43 cm. Before taking counts, a blank count was taken when the radioactive source is off and the material was absent. Radioactive source can be controlled from outside of the laboratory by computer systems. This blank count is automatically recorded to the systems and the system calculates the rest of the taken counts by considering this background radioactivity level. For each thickness this control system is used and counts were taken. Then all values were recorded and radiation amount that passed through the material was calculated.
Secondly, Cs-137 source is used. Same process with Co-60 is applied, blank count was taken to determine the background radiation level when the source is off. System automatically recorded this background radiation and excluded from other counts. This experimental set-up is installed as the sample is located 19 cm away from the source and the distance between the sample and the ion chamber is 21 cm. 
Every count has taken for each thickness and for each type of concrete for 3 times in order to make accurate calculations.The averages and standard deviations of the counts were calculated and the attenuated radiation intensity data were obtained from here. Tables for all concrete types and thicknesses were prepared to make interpretation easier. 
The change of these attenuation ratios according to thickness are shown in graphs. First, graphs were drawn to compare the value of two different radioactive sources in one concrete type. For instance, a graph is drawn for normal concrete which shows the half value thickness for both Co-60 and Cs-137 source. Then, some other graphs were drawn which allows to compare all the values for one radioactive source. 
For all types of concrete, attenuation ratios were compared to the thickness. Linear attenuation coefficients were found and compared. Linear attenuation coefficients and standard deviations were obtained by using the Origin 8 program. The mass attenuation coefficients were reached by the ratio of these values to the densities. Finally, half-value thicknesses, which are one of the most important factors of shielding and radiation protection, are calculated for all types of concrete and the values are compared. Radiation attenuation ratios and half-value thicknesses were consistent with the density and characteristics of the materials.