Bazı çevresel örneklerin nükleer spektroskopisi

Abstract

Çağımızda Fizik bilimindeki en önemli gelişmelerden biri nükleer enerjinin keşfe- dilmesidir. Çünkü nükleer enerjinin keşfi ile insanoğlu enerji açığını azaltma yönünde yeni bir kaynak bulmuştur. Nükleer enerji reaktör denen tesislerde önce ısı enerjisine, daha sonrada elektrik veya mekanik enerjiye dönüştürülmektedir. Bu dönüşümler sonunda nükleer enerji, insanoğlunun istediği gibi kullanımına girmektedir. Nükleer enerjinin dezavantajlarıda vardır. Her şeyden önce nükleer tesisin, yani reaktörün kurulması, diğer enerji tesislerine oranla çok pahalıdır. Ayrıca çalışan personel ve çevre sağlığı açısından büyük tehlike oluşabilir. Çernobil kazasının radyasyonları, Çernobil'e binlerce km. uzakta olan kimseleride etkilemiştir. Reaktörün yakınında oturanlarda kanser riskinin artacağı beklenir. Bu ka zanın sonucu olarak radyasyonlu çay, et, süt ve diğer gıda maddelerindeki radyasyon konusu kamuoyunu uzun bir süredir, meşgul etmektedir. Sovyetler Birliği'nde 26 Nisan 1986 tarihinde Amerikan Nuclear Society yayın organı tahminlerine göre saat 01.23'de bir nükleer kaza meydana gelmiştir. Reaktörün çekirdeğindeki radyoaktif maddelerin bir kısmı atmosfere karışmıştır. Önce havada radyoaktif kirlenme meydana gelmiş daha sonra yağışlarla yeryüzünde önemli miktarlara varan radyoaktif kirlenmeler ortaya çıkarak solunum ve besin zinciriyle insanlara kadar ulaşmıştır. Bu çalışmada 1986 yılı ürünü bir kaç Türk çayı örneği ile kaplıca suyunda ölçümler yapıldı. Deneylerde öncelikle alfa spektrumları alınmak üzere, üzeri elektrolizle ince filmlerle kaplanarak paslanmaz çelik diskler hazırlandı. Bunun yanında bir Nal (Tl) dedektörü ve çok kanallı analizör ile gamma spektrumları da alındı. Sayısal değerlendirmeler için tek kanallı analizör sistemi ile sayımlar elde edildi. Kullanılan çay örnekleri 1986 yılı mahsûlleri olmasına karşılık ölçümler Aralık 1990'da yapılmıştır. İncelenen kaplıca suyu ise Gönen Kaplıcalarına aittir. Bu ölçümlerin değerlendirilmesinden incelenen örnek çayda sözü edilen tarihte bulunan Cs-134 aklivitesi 4507 Bq/kg, Cs-137 aktivitesi ise 13979 Bq/kg dır. Bunlara oranla oldukça az olan K-40 aktivitesi ihmal edilirse bu örneğin 1990 Aralık'da toplam gamma aktivitesi için 18486 Bq/kg bulunur.

The most important contemporary development in the fi eld of physics has been the discovery of nuclear energy. On acco unt of this discovery, mankind has found a new source of e- nergy. By atomic energy we in fact mean nuclear energy. Nuclear energy is converted at the reactor stations, first of all into heat energy and then into electrical or mechanical e- nergy. As a result of these conversions, nuclear energy is crea ted, ready to serve mankind according to its needs. However, nuclear energy has its disadvantages. The foun ding of a nuclear station, that is a reactor, is more expersive than other sources of energy. It also poses a great danger to per sonnel and to the environment These dangers have been remo ved to a great extent by the precoutions formulated by reactor engineering. In the cae of Chernobyl, technical committees estab lished that some of the essential precoutions had not been taken. Radiation from Chernobyl affected people thousands of ki lometers from the area. It is said that the cancer risk will increa se for people living near Chernobyl. The radiation caused by this accident and its effect on tea, meat, milk and other foods, IV precocapied public opinion for a considerable time. Atoms, which form the living organism, are in a particu lar order with relation to the dispersal of electric charge, mass and energy. The fusion of atoms creates molecules and the mole cules join to form cells. If a person becomes radiated it means that his body has absorbed radiation energy. In the case of an accident at a nuclear reactor, although rare, it is possible in certain conditions for radioactive materials to leak out. In such an event, people may contract certain disea ses or such a position may lead to a change in the genetic struc ture which would cause hereditary defects. One of the gravest reactor accidents to date, fook place at Chernobyl Nuclear Power station near Kiev in the Soviet Union on 26 April, 1986. According to the American Nuclear Society, this nuclear accident took place at 1.23 A.m of lokal time on 26 April, 1986. AH the radiactive materials in the reactor core fused into the atmosphere. The accident at the power station occurred during a test before the programmed shutting of of the reactor. The test was carried out to observe whether, in the case of an electricity cut, o- ne of the turbo-generators could provide the electric power nee ded by the reactor. Due to the accident in the fourth section of the reactor, fis sion products and radioactive materials leaked out into the at mosphere for a long period of time. According to meteorological conditions, gas and particles were dispersed and these affected Turkey. First of all, the air was radioactively polluted ard to this was added radioactive pollution carried by the rain. As a con sequence of this people were affected through their respiratory system and food intake. Radioactive materials were scattered into the atmosphere in the form of clouds and these were carried along by prevailing winds over the Baltic Sea to Scandinavia. A few days later, when the wind changed direction, these some clouds reacted the Soviet Union and Turkey. The thracian region on the Turco-Greak bor der and the eastern Black Sea region were severely contamina ted as a result of heavy rain fall. In the case of Turkey and many other countries, fission products of concentrated gamma radiaters, became Iodine -131, Caesium -137, Caesium - 134. These radionuclids accumulated on the ground first and then transferred to food products. The radioactive caesium on the ground gamma radiated for a long time. In various countries the average concentration for Iodine - 131 changed from betwe en 0,01 and 120 kBq /km2 and for caesium - 137 between 0,04 and 23 kBq / km2. As is well-known, alpha, beta and gamma type radiation spreads from radioactive materials. Alpha and beta rays are tho se which become charged particles and gamma rays are those of an electromagnetic nature. The short range of alpha and beta rays pose a danger of internal radiation whereas gamma rays present the danger of external radiation. Subsequent to the accident at Chernobyl, a group of equip ped personnel at Ç.N.A.E.M. (Çekmece Nuclear Research and E- ducation (entre) took measurements of radiation in Trakya, the eastern Black Sea and other regions in Turkey. A lot of the samples Mere sent for analysis to the Ç.N.A.E.M. laboratories. Within a few days of the Chernobyl accident, measure ments of the extent of radiation caused by the fissiom products scattered on the earth by way of clouds, were taken meter above the earth's surface. The concentration of radioactivity on the ground was es tablished by evaluating the radioactive rainfall which was collec- tedeach day. In this work, we wanted to make our measurements on se veral samples of tea and spa water, preserved in Turkey since 1986, with an alpha and gamma spectrometer. We established procedures and an experiment setup. We have made both counting with a single channel analyser and taken spectra using a multichannel analyser sys tem with a Nal (Tl) dedektor. In this e-periment, dated November 1990, we took measu rements of the samples from 1986. We brought samples of Spa water from Gönen and we studied its spectrum only. As a result of these experiments, it can be observed that the activity is coming mainly from Cs 131 and Cs 134. We can see that if we were to compare our results with taht of many sci* entists in other countries, it is the same in many aspects.