X-ışını floresans analiz tekniğinde 99Tc ve 51Cr'in uyarıcı kaynak olarak kullanımı
Başlık çevirisi mevcut değil.
- Tez No: 66422
- Danışmanlar: PROF. DR. ŞARMAN GENÇAY
- Tez Türü: Doktora
- Konular: Nükleer Mühendislik, Nuclear Engineering
- Anahtar Kelimeler: Krom, Teknesyum, X ışını flüoresan analizi, Chromium, Technetium, X ray fluorence analysis
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Nükleer Mühendislik Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
ÖZET Bu çalışmanın amacı; XRF analizi için bilinen bazı uyarıcı kaynakların yerine, aynı işlevi gerçekleştirecek yeni kaynaklar sağlamak üzere gereken araştırmaların yapılmasıdır. Bu hedefin seçilmesinin ana nedeni bu yöntemin olanaklarının artırılması ve bilinen sınırlarının getirilmesidir. Ayrıca, üretim kolay yeni kaynaklar şu önemli yaran da sağlayabilir: Yurdumuzdaki XRF uygulamalarında uyarcı kaynakların dışarıdan ithal edilmesi ve yarı ömürlerinin pek uzun olmaması nedeniyle yarattıkları ekonomik güçlük, ithal gecikmesi ve bürokratik güçlüklerden kurtulunabilir. XRF uygulamalarında kullanılan üç önemli uyarıcı kaynak 55Fe, 57Co ve 109Cd izotoplarıdır. Bu elementler bu güne kadar yurt dışından ithal edilmiştir. Bu çalışmada, Çekmece Nükleer Araştırma ve Eğitim Merkezi'ndeki reaktörde kolayca üretilebilen 99mTc ve 51Cr'in aynı işlevi görebilecekleri yapılan deneyler ile ortaya konmaya çalışılmış ve olumlu sonuçlar alınmıştır. 55Fe yayınladığı; Mn Kx-ışını (5.89keV) ile atom numarası 15<Z<23 109Cd yayınladığı; AgKx-ışını (22.162keV) ile atom numarası 23<Z<42, 57Co yayınladığı; 122keV ve 136keV y-ışınlan ile atom numarası 53<Z<92 arasında olan elementlerin karakteristik x-ışınlan'nın uyarmakta kullanılmaktadır. Yapılan ve sonuçlan çalıma içerisinde verilen çok sayıda deney ile 99raTc izotopunun 140.5keV'lik y ışınlan ile 18.4 keV'lik Kx-ışınlarını uyancı olarak kullanılabileceği ve böylelikle I09Cd ile 57Co izotoplarının yerini alabileceği gösterilmiştir. Aynı şekilde düşük atom numaralı elementlerin analizinde 51Cr ile çalışmalar, bu elementin 4.95keV'lik VKx-ışınlarının uyancı olarak kullanılabileceğini göstermiştir. Dolayısıyla 51Cr'in uyancı kaynak olarak 55Fe'nin yerini alabileceği anlaşılmaktadır. Deneylerde Au, Pt, U, Sr, K, Ca elementlerinin nicel analizleri yapılmış ve elde edilen olumlu sonuçlar 99mTc ve 51Cr'in kullanılagelen l09Cd, S7Co ve 55Fe'nin yerini alabileceği gösterilmiştir. Çalışmada; uyancı element standart çözeltileri örnekler üzerine ilave edilmiş ve nicel analiz için standart ilave yöntemi kullanılmıştır. Radyonüklid ilavesi, kullanılan her örneğe ayn ayn yapılmıştır. Radyonüklidin, örneğin her tarafına homojen olarak yayılması sağlanmaya çalışılmıştır. Radyonüklid ilavesi ile yapılan analizlerde örnek miktarının çok az olabileceği saptanmıştır. Örnek miktarının artması algılayıcının ölü zamanını artırmaktadır ve ilave edilen radyonüklidin homojen bir şekilde dağılması mümkün olmamaktadır. xii
Özet (Çeviri)
SUMMARY The Use of“Tc and 51Cr as Fluorescing Sources in X-Ray Fluorescence Analysis Roentgen's discovery was a very significant theory and practice of science, technology and medicine. x-rays were widely applied in medical ( including dental) and industrial radiography within the year of their discovery. The wide application of x-ray lead to the development of commercial availability of x-ray tubes, generators, electronic detection and readout equipment. Moseley established the basis of quantitative and qualitative x-ray spectrochemical analysis in 1913. His first published photograph of x-ray spectra shows the relationship between wavelength of x-ray spectral lines and atomic number. The x-ray region is that part of the electromagnetic spectrum between about 0.1 and 200 A It is bounded by the gamma-ray region to short wavelength side, and by the ultraviolet region to long wavelength side. Only a relatively small part of the total x-ray region is covered by the conventional x-ray spectrometer, about 0.2 - 20 A, this being referred to as the analytical x- ray region. Wavelengths shorter than a few tenths of an Angstrom are difficult to excite and even more difficult to separate. Wavelengths in excess of 20 A arise mainly from outer orbital transitions and are less useful for element characterization. When a target is bombarded with photons or particles, the nuclei may be transformed into radioactive nuclei or there may be an interaction with the atomic- shell electrons. If the second event occurs, the electrons may be elevated to higher orbits and x-ray promptly emitted in the rearrangement of the electrons in the shell. The energies of these x rays are characteristic for each elements and in xuiparticular the K and sometimes also the L x rays can be effectively used for analytical purpose. X-rays are also produced when any electrically charged particle of sufficient kinetic energy is rapidly decelerated. This x-rays are called Bremsstrahlung and have continuous spectrum, also referred to as the general spectrum, white spectrum, continuum. Every atom emits characteristic x-rays with the discrete energy that identify the atom. For every atom, the x-rays are identified according to the final state of the electron transition. The energy state of atomic electrons are characterized by letters K, L, M, N, ect. The characteristic x-rays are created by electrons, photons, deuterons, a-particles and ion bombardment from particle accelerators or irradiation by primary x-rays from high-or low-power x-rays tubes or irradiation by a, |3, y, x-rays from radioisotope sources (Fe-55, Cd-109, Am-241 and Co-57). In general, energy dispersive x-ray spectroscopy consists of a high purity germanium or low energy photon detector which is usually Si(Li) (with a resolution as low as 150eV for the 5.9 keV MnKx-rays), preamplifier, bias supply, multichannel analyzer and an excitation source. Frequently used radioactive excitation sources are Fe-55 (MhKxrays), Cd-109 ( AgKx rays), Am-241 (y rays at 60 keV) and Co-57 (y rays at 122 keV and 136 keV). Fe-55, photon emitters can be used to excite elements from 15 <, Z <, 23 and characteristic x-rays can be detected with a Si(Li) detector. Cd-109 sources can excite elements from 23 < Z <, 42 and the characteristic x-rays of these elements can be detected with a Si(Li). Also, Co-57 is used to excite the elements from 53 <, Z <, 92 which can be detected with high purity germanium detector. The excitation sources usually have activities of several millicuries (mCi). The best choice for the energy of the excitation radiation is slightly above the K edge ( or L edge ) of the element to be detected, because the K-shell ionization cross section for a given element rapidly decreases with increasing energy above this edge. xivIn the excited x-ray fluorescence analysis (EDXRF), the sample-source-detector geometry ( arrangement) is one of the areas in which little scientific investigation has been performed. The ”annular“source is used with smaller detector windows. It is usual procedure in radioisotope excited XRF to keep the distance between the sample and detector short so that a high photon intensity of the characteristic x-rays from the sample can be detected. One of the disturbing features of the most common radioisotope source-sample- detector geometry is the large distance between source and compounds. To overcome the difficulties posed by the relatively large distance between the source-sample-detector, a technique was developed based on direct mixing the radionuclides with the sample. The most common and effective radionuclides are low energy photon emitters ( low y or x-rays). This type of excitation produce negligible amounts of bremsstrahlung background. Thus, the only background in the spectrum is scattered primary radiation from the source that reaches the detector. These radionuclides emit the radiation at discrete energies, contributing little to the background at other energies, unlike the bremsstrahlung from any x-ray tubes or radioactive sources. The disadvantages of using radioactive sources in our laboratory are their high price and their import from abroad. The objective of this study is to find some alternative sources which can replace the most common sources, ”Co, 109Cd and S5Fe and can be produced in our research reactor. In our analysis, radionuclide was mixed with a small portion of samples and placed directly on the detector window. This is a good geometric arrangements for the determination of low Z elements when the analysis is performed under an air path. In this work, two radionuclides were studied which are Tc-99m and Cr-51. These radioisotopes commonly used in the nuclear medicine. Tc-99m emits y - rays at 140.0 keV and these y - rays can be used to excite the elements of 56 < Z <> 92. At the same time, Tc-99m emits characteristic K-x rays at 18.4 keV and can excite the elements between the atomic number 26 to 40. xvTherefore Tc-99m may be employed instead of Cd-109 and Co-57 commercial radioactive sources. A set of experiments performed to show the validity of this replacement. Cr-51 emits x-ray at 4.95keV which can be used to excite the elements of 15<Z<23. A set of experiments also performed to show the validity of this argument. Thus, it was shown that 51Cr can be used instead of S5Fe. In this work, a high-pure planar germanium detector was used for the efficient detection of high energy x-rays, and a Si(Li) detector was used to detect the characteristic K-x rays from the elements of 26 ^ Z < 40. To study higher Z elements ( uranium, gold and platinum) by corresponding K-x-rays, the synthetic mixtures (20mg) were prepared. The source-sample were stored in small Plexiglas cells until they are placed on the face of the detector window for analysis. The first set of samples contained the solution of 5580 ug/g gold (Au) which were mixed with cellulose and then the samples were dried. The sample-sources were prepared by using different activities of Tc-99m namely 375 [i Ci, 210u, Ci, 26u, Ci, and 15ji Ci. The most suitable result was found that 26 jj. Ci ofTc-99m for 5580 ug/g Au and the counting time was chosen 1000 seconds. The second experiment was the samples included 4980 ug/g Au. Different activities of Tc-99m ( 440 uCi, 28 uCi, 2 uCi and 0.2 uCi) solutions were added to the samples. The best result was found with 28 uCi Tc-99m. - The other experiments have been performed with different concentration of gold ( 1660ug/g, 830ug/g, 500ug/g and 300ug/g). It was shown that Tc-99m activity can be chosen between 20u?i and 3 OuCi. Another high Z element, Pt was analyzed by using 29u?i Tc-99m. The concentration was found 254ug/g with an error of 8%. Strontium analysis was done by using 18.4 keV photons and Si(Li) detector. The concentration of strontium was calculated with the addition of 2400 uCi, 375uCi, 210uCi and 26 uCi Tc-99m. It was shown that the most XVIsuitable result was obtained by using 210jj,Ci activity of Tc-99m. The uranium in the sample IAEA S-12 ( International Standard reference material from IAEA) was also analyzed and satisfactory result was obtain. Cr-51 was used as excitation source for the determination of low Z elements like Ca and K in standard samples provided from IAEA ( standard V-10) and NBS (NBS 1646). 20 mg of samples were mixed with lOOuCi Cr-51. Satisfactory result were obtained. The data acquisition system is the same as typical XRF system for energy dispersive x-ray analysis. We have employed Canberra Accuspec B acquisition board. The difference in this x-ray instrumentation is basically the source-sample mixing which act as the excitation system instead of a x-ray tube or an excitation radioactive sources. In general to achieve lower detection limits one needs either, to increase the excitation or detection efficiency. The various elements of importance can be determined with suitable detection limits in very small biological and other samples using mixed sample-source technique. It has been shown that the mixed sample-source technique as previously suggested can provide comparable results in respect to precision, accuracy, limits of detection, sensitivities as compared to conventional energy dispersive x-ray fluorescence methods. In conclusion, the possibility of replacement of conventional excitation sources with Tc-99m and Cr-51 has been verified. The results of the analysis have shown that Tc-99m can be used instead of Cd-109 and Co-57, and Cr-51 can also be used in place of Fe-55. xvu
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