CONTENT
INTRODUCTION. 4
1. INTERACTION OF RADIATION WITH MATTER 21
1.1 The effect of gamraa-rays interaction with matter 21
1.2 Effect of neutron irradiation on matter 24
13 The effect of heavy ion irradiation 25
1.4 Sputtering 31
2. EXPERIMENTAL SET-UP 33
2.1 Irradiation of materials on various sources 33
2.2 Methods for studying the properties of materials " in situ *' and at post irradiation measurements 35
3. RESULTS
INFLUENCE OF NEUTRON AND GAMMA IRRADIATION ON THE PROPERTIES OF MATERIALS 42
3.1 Polyethylene samples 42
3.2 Alkali-silicate glass samples 50
33 Borosilicate samples 52
3.4 Polyvinyl alcohol samples 64
3.5 The effect of gamma irradiation on the microhardness of PVA 67
3.6 Mixed field effect on polyvinyl alcohol samples 68
3.7 Polytetrafluoroethylene samples. 72
3.8 Germanium doped sulphur samples (GeS). 74
4. INFLUENCE OF HEAVY ION IRRADIATION ON DIELECTRIC AND SEMICONDUCTOR. 83
4.1 The influence of heavy ion irradiation on the track formation in boron doped and natural diamond. 84
42 Damage formation in silicon irradiated with heavy ions 95
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4.3. The influence of heavy ion irradiation on the surface phenomena in stainless steel
109
4.3.1 Formation of needle structure 109
4.3.2 The model of behaviour of stainless steel under swift heavy ion irradiation 116
CONCLUSION 127
ACKNOWLEDGMENT 134
REFERENCES 135
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1. Introduction
Although and despite of the great achievements in the relearn of radiation physics some central problems are not yet satisfactory solved in this field, at least on the practical level. Among these problems the most challenging one is connected with the radiation effect on materials. As it is commonly known irradiation has different effects on matter and the result of irradiation depends sometimes quite significantly upon both the nature of the irradiated material, the sort of the ionizing radiation used, and the dose and intensity, too. Of great importance are also the conditions of irradiation, firstly the temperature and other outer macroscopic parameter. Besides, different materials react differently on the same radiation and up to now we have not any general theoretical approach to the process, except for some qualitative suggestions to predict, on the practical level, the results of such treating. Consequently we now need to investigate all materials being of interest. Such a task is difficult to carry out as being expensive, very time consuming and necessary effort should be made to investigate materials of strategic or of significant application. Such materials belonging to this class are widely used in nuclear industry, space technology, microelectronics, nano-technology etc. The appearance of the relevant research leads to the development of a new direction of investigation in the field of solid-state physics called solid-state radiation physics. This direction has fundamental scientific, cognitive value as well as wide practical, in particular technological applications. The creation of new materials and the modification of materials properties are carried out using different kinds of nuclear radiation: gamma rays, neutrons, light and heavy ions at low and high energies. Besides, a series of materials are broadly applied as radiation detectors. Therefore, it is of great practical meaning to understand what phenomena take place when irradiating the materials in order to predict the final effects and changes of their
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properties. As a result of irradiation, the materials experience changes in their physical properties. These changes are caused by the changes in their chemical properties, which, by turn occur due to the change of their chemical structure. Such changes can give the materials the privilege of having modifications as mentioned previously. The results of iterative experimental investigations in that concern helped to compose up new prospective materials, which could find applications in the fields of nuclear industry and radiation measurements. The materials, which are supposed to be used in the field of radiation measurements, must have the physical property change, which can be successively evaluated qualitatively and quantitatively in correspondence with the change of the irradiation dose. Such relation can be beneficially used in radiation dose assessment. The detectors, which are based on using these different materials and techniques to determine the irradiation dose, are called passive detectors in the difference with the well-known active detectors. However, the materials, which are suggested to be applied in this respect, must as well fulfill the following requirements:
a) Low fading of the irradiation dose as well as long-term stability of the stored trapped charges at normal temperatures.
b) The distribution of traps must be simple.
c) The material must be resistive to the radiation damage.
d) The environmental effects must be as low as possible.
e) There must be a linear relation between the measured change of the physical parameter and the change of the irradiation dose.
f) The material must possess high TL efficiency besides high TL- sensitivity (this property concerns the luminescent materials where TL is the luminescence intensity).
g) The results of the measurements must be reproducible.
h) There is a possibility of its reuse several times.
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i) The material should have a low cost and good quality.
Experiment showed that some luminescent materials, some polymeric materials, some kinds of glasses, some composite materials as well as some compounds are liable to be used in the field of radiation dose assessment The following may through some light on the efforts done in this direction.
The effect of irradiation on the luminescent materials was studied extensively in the last few decades. Many authors investigated the effect of gamma rays and neutron irradiation on the radiophotoluminescence (RPL) [1-11] and the radiothermolumunescence (RTL) [12-27] spectra of some materials. The results are showing that among those materials there were many compounds based on Li2F, Li2B407, Be|Al2 03, CaF2 and CaS04. Most of these materials were not applicable due to the high cost and their complicated behaviour under heat treatment [28,29] and radiation damage revealed to high level radiation exposure. So the search for low cost and available alternative luminescent materials, which possess the properties required for the use in irradiation dosimetry, declares about itself.
Another kind of available materials, which possesses high degree of sensitivity towards the ionizing irradiation, was found to be some polymeric materials. Polyethylene and polyvinyl alcohol belong to that class of materials.
The effect of irradiation on polyethylene had been reported by many authors [30-35]. In case of polyethylene it is found that the structural modifications which are caused by ionizing radiation strongly affect the electrical properties such as the electric resisitivity of the polymer [36-39]. The possibility of applying the electric resistivity measurement technique to measure the change in the electric resistivity of polyethylene, which is caused by irradiation, may help to find a relation between these two parameters. Such a relation may be used in the process of determining the radiation dose.
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Polyvinyl alcohol (PVA) is an example of high polymers. It is required as a net work matrix of polyethylene within which a hydroxyl group is replacing the hydrogen atom on each carbon [40]. The addition of certain threshold concentrations of dopant metallic salts to the PVA matrix improves and
enhances the physical properties as well as the elasticity [41]. Many
investigators [42,43] have reported such viscoelastic behaviour relaxation process, temperature transitions and density as well as the effect of gamma ray irradiation in doses 10' up to 10' Gy on the molecular weight, infrared spectra and electrical properties. Meantime, none of these studies arc of easy use and direct performance in the field of processing level. The UV-visible optical absorption spectrophotometry is an easy procedure, available in different research laboratories due to its multiuse purposes. This technique can be used for radiation dose assessment.
The experiments on PVA assured that on doping the polymer with certain threshold metallic salts concentration the elasticity of the polymer improves [44]. The irradiation of this polymer causes decrease of the elasticity of the polymer with increasing the irradiation dose. Consequently its microhardness
increases with increasing the irradiation dose. So, the microhardness may have
some coefficient relation with the irradiation dose. This coefficient relation may }e used beneficially in measuring the irradiation doses.
Ionizing radiation can produce free holes and electrons in glass, which may then become trapped thus forming defect centers. These defect centers :ause an increase in the optical absorption of the visible portion of spectrum .eading to darkening of the glass. The use of glasses as a gamma irradiation iosimeter as well as neutron detectors [1,45-47] has several advantages that nake them especially attractive for the use in this field. These include rigidity, nsolubility, small size and permanence. The induced radiation damage to the >ptical glass, which is revealed as a change in the transmitted visible light, may
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be beneficially used in radiation measurements. This needs a glass composition, which produces optical absorption peak whose value is increasing with the increase of the irradiation dose at a definite wavelength. In other words there must be a coefficient relation between these two quantities.
Another important direction is the investigation of the influence of irradiation on the properties of the materials used in building nuclear reactors, nuclear power stations, being developed thermonuclear reactors and accelerators. These units produce powerful neutron beams, gamma irradiation and fission fragments, which by turn, interact with the materials of the nuclear device itself (the first wall of the fusion nuclear reactor and the zirconium rods which contain the nuclear fuel in the fission reactors). Investigation was carried out in that direction to explore the effect of the interaction of such species with the structural materials of the reactors. A great deal of work was carried out immediately in this field after noticing great changes in the materials. These changes were of negative effects on the device maintenance period and the adequacy of their working functions. A series of such harmful effects epresented by swelling, anisotropy growth, radiation brittleness, phase ransformation, radiation stimulated diffusion and other effects appeared among hese harmful effects [48-73].
A very long period of time was needed to test the resistivity to radiation )f materials in a nuclear reactor. Such procedure was done in order to reach ugh fluence of neutrons Fxt, where t-is the time needed to attain the required lamage dose and F- is the beam intensity. The damage dose is D=ad xFxt where Td is the damage production cross-section. In turn this time-consuming »rocedure lead to the activation of the materials, which are investigated. After he process of such activation it became difficult to achieve post-irradiation neasurements. There appeared the need of using hot cells or keeping the amples aside for long times in order to decrease their induced activity.
The programme of studying the possibility of building new type of energetic i.e. thermonuclear reactors introduced special criteria concerning the structural materials of these piles [73,75]. These materials have to operate in the field of irradiation of 14 MeV neutrons and under the influence of plasma [76-78]. The development of the accelerator technique and the creation of the powerful sources of charged particles (electrons, protons, light and heavy ions) provided the possibility of modulating the influence of neutrons by using these charged particles. The use of charged particles got widespread application in modulating the influence of the neutrons not only on the materials, which are already functioning in nuclear energetic complexes but also on those new worked out materials suggested for use in nuclear power and research plants [79-85].
This is firstly connected with the high velocity of defect creation in the materials, which are irradiated with light and heavy ions. In comparison with the case of neutron irradiation the time of irradiating with heavy ions, which is needed to reach the required damage dose is saved in 103-106 times. Besides the activation of the samples is greatly lower than the activation caused by reactors. Vloreover, the use of charged particle accelerators makes it easy to change and :o control the irradiation conditions with a great degree of accuracy. One of the nost important privileges of such modulation procedure is the possibility of jsing different methods of studying the processes of accumulated radiation iamage in materials directly during their irradiation (on beam measurements). These methods include electrical resistivity measurements, determination of the :hange in mechanical properties, optical methods and a series of other methods 81-87].
The implication of heavy and light ions possessing high specific onization energy loss for studying radiation phenomena in condensed matter illowed the possibility of observing a series of peculiarities in the process of
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defect production [88-95]. These peculiarities cannot be explained from the point of view of the traditional approach of using only the mechanism of elastic collision [54,56,57].
The manufacturing of heavy ion accelerators having high intensity ion beams (F) and energy (E/A), higher than 1 MeV/amu helped the developing of the physics of radiation damage, from the point of view of material modification in order to achieve radiation work of stimulated changes of their properties and create new semiconductor technology [96,97]. First of all this is connected with great enlargement of the projective range Rp of the projectile ion in the irradiated material up to 10pm and more. This in turn permits the exclusion of he effect of surface accumulation of point defects. In this way such layers are 'egarded as macroscopic. Moreover, the formation of deep implanted layers vith previously given certain configuration in the ion-irradiated uonocrystalline becomes actual (possible). The increase of the ion energy leads o great increase of the specific ionization energy loss (dE/dx)inei compared to he elastic loss (dE/dx)C| (for the ions with energy up to 1 MeV the conditions dE/dx)c)> (dE/dx)inC| are fulfilled). This in turn changes the character of the lefcct accumulation and their evolution on irradiation especially for dielectric nd semiconductors due to the local heating regions which appear around the rajcctories of heavy ions (tracks). The lifetime of these structures (tracks) may e comparatively enough long to permit crystallization and diffusion processes d take place [98-102].
The above mentioned formulated statements determine the actuality of te present work and reveal as proof that this direction of investigation is a new nd important in the field of the physics of radiation interaction with condensed latter.
The aim of the present work is the creation of materials for working out >simeter detectors having quite accurate and reproducible metrical
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characteristics for use in dosimetric measurements of different kinds of radiation (neutrons and gamma rays). The other part of the work is achieved in order to receive experimental data about the interaction of the high-energy heavy ions with condensed matter, the study of radiation defect creation, and the change in microscopic properties and microstructure of metals and alloys as well as the investigation of defect evolution process in case of post-irradiation annealing and to reach the formation of thermal and mechanical stable electrically conducting layers at the far depth of the semiconductor single crystal. Moreover, it is intended to develop a model for describing the micro structural changes, which take place in the materials as a result of bombardment with high-energy heavy ions
It was necessary to carry out the following experimental investigation in Drdcr to reach a solution of the given problem:
- investigating the optical transmission spectra of alkali silicate glasses, :ontaining different K20 and Na20 impurity concentrations and polyvinyl Ucohol containing different concentrations of a series of metallic salts (C0CI2, vIiSo4, CuSo4 and Cu(CH3COO)2) before and after irradiation with neutrons and ;amma rays.
- investigating the induced changes, which is caused by neutron and ;amma rays irradiation on the radiothermolumunescence and the radiophoto-uminescence of borosilicate glasses containing U3O8 different impurity oncentrations, Pb203/ polytetraftouroethylene composite as well as ,ermanium-sulphur alloys.
- the investigation of micro-hardness of polyvinyl alcohol containing ifferent impurity concentrations before and after irradiation with gamma rays.
- the study of the effect of neutron and gamma rays irradiation on the Iectrical properties of polyethylene at post irradiation different temperatures.
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- the investigation of the micro-structural changes of the surface of diamond semiconductor, metallic alloys including stainless steel and to study the defect production and their evolution in silicon after irradiation with high-energy heavy ions having energy of about 1 MeV/amu.
A laboratory was based and equipped with high temperature furnace and platinum crossbills for preparing glass samples, the chemicals, which are required for preparing other composites, and the installations, which are required for measuring the parameters characterizing the materials (microhardness, electric resistivity, optical absorption spectra, and luminescence spectra). This part of the experimental investigations was achieved at the nuclear research center, Cairo, while the other part (which is connected with high energy heavy ion irradiation) was achieved at the laboratory of nuclear reactions of the JINR, Dubna.
The scientific novelty is:
For the first time detailed investigations were achieved in order to study the influence of hard electromagnetic radiation and neutrons on the basic properties of a series of materials (glasses, polyvinyl alcohol, polyethylene, Pb203 and GeS alloys), which are of great practical interest. The conditions of applying the investigated materials as radiation detectors under the influence of different outer circumstances are defined.
The irradiation effect on polycrystalline and monocrystalline (silicon) naterials, dielectric (natural and synthetic diamond), and structural metallic alloys (chromium-nickel steel) with high fluences of high-energy heavy ions (B, \r, Kr, Xe and Ne) with energy E~1 MeV/amu is investigated.
For the first time the Kr, Xe ion tracks were observed in diamond ;emiconductor by (direct observation) and the diameter of the track was neasured by using the scanning transmission microscope.
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