Radiation-damage

A close study of the chronology of this episode teaches another lesson. The early observation on irradiation-induced growth of uranium was purely phenomeno- 

In Britain, a population of thermal reactors fuelled by metallic uranium have remained in use, side by side with more modern ones (to that extent. Lander et al. were not quite correct about the universal abandonment of metallic uranium). In 1956, Cottrell (who was then w orking for the Atomic Energy Authority) identified from first principles a mechanism which would cause metallic (ot) uranium to creep rapidly under small applied stress this was linked with the differential expansion of 

By 1969, when a major survey (Thompson 1969) was published, the behaviour of point defeets and also of dislocations in crystals subject to collisions with neutrons and to the eonsequential collision cascades had become a major field of researeh. Another decade later, the subjeet had developed a good deal further and a highly quantitative body of theory, as well as of phenomenological knowledge, had been assembled. Gittus (1978) published an all-embracing text that eovered a number of new topics chapter headings include Bubbles , Voids and Irradi-ation(-enhanced) Creep . 

(1992) Maieriah Selection in Mechanical Design (Pergamon Press, Oxford). 

and Abel, C.A. (1995) in High-Temperature Structural Materials, eds. Cahn, R.W., Eivans, A.G. and McLean, M. (Chapman Hall, London) p. 33. 

From the resulting linear decay curve in logarithmic representation, Xg is obtained. 

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Egerton R F 1976 Measurement of inelastic/elastic scattering ratio for fast electrons and its use in the study of radiation damage Phys. Status Solid a 37 663-8... 

Gibson J B, Goland A N, Milgram M and Vineyard G H 1960 Dynamics of radiation damage Rhys. Rev. Series 2 120 1229-53... 

Radiation Damage. It has been known for many years that bombardment of a crystal with energetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a soHd with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 due to both electronic and nuclear coUisions. As an ion slows down and comes to rest in a crystal, it makes a number of coUisions with the lattice atoms. In these coUisions, sufficient energy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are caUed primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic coUisions and is coUectively referred to as the coUision, or displacement, cascade. The disorder can be directiy observed by techniques sensitive to lattice stmcture, such as electron-transmission microscopy, MeV-particle channeling, and electron diffraction. 

The simplest calculation of radiation damage involves only monatomic materials and has been described by many authors (17—20). For polyatomic materials, a calculation procedure for estimating damage energy from ion implantation has been outlined (8). The extension of this formalism (8) to direct calculations of damage energies in polyatomic materials has been addressed by several authors (11,21—24). 

M. W. Thompson, Defects and Radiation Damage in Metals, Cambridge University Press, New York 1969. 

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

SiHcon carbide s relatively low neutron cross section and good resistance to radiation damage make it useful in some of its new forms in nuclear reactors (qv). SiHcon carbide temperature-sensing devices and stmctural shapes fabricated from the new dense types are expected to have increased stabiHty. SiHcon carbide coatings (qv) may be appHed to nuclear fuel elements, especially those of pebble-bed reactors, or siHcon carbide may be incorporated as a matrix in these elements (153,154). 

Susceptibility to radiation damage must be considered seriously if reference samples are to be calibrated for use in place of absolute systems. For the measurement of absolute C He, H) cross sections, films of polystyrene (CH) (which is relatively radiation hard) have been used successfiiUy, the RBS determination of carbon providing implied quantitation for the hydrogen present in the film. For a durable laboratory reference sample, however, there is much to recommend a known ion-implanted dose of H deep within Si or SiC, where the loss of hydrogen under room temperature irradiation will be neghgible. 

The total energy, E, is obtained from the total charge accumulated in both sections of the anode. The second part of the ionization chamber, which measures the energy E - AE, can be replaced by an SBD [3.167], and the first part, which measures the energy loss AE, by a transmission SBD [3.168, 3.169]. When SBDs are used to measure heavy ions, radiation damage of the detector by the ions must be taken into account. 

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