Recovery Of Radiation Damage Research Articles

Effect of Neutron-Irradiation on Thermal Conductivity, Electric Resistivity and Thermal Expansion of Boron Carbide

Boron carbide possessing porosities of 91 and 77% theoretical density (T.D.) were irradiated at about 300 deg C to 6.0 x 10/sup 18/ ~ 3.3 x 10/sup 19/ n/cm/sup 2/ in helium atmosphere. The thermal conductivity, the electric resistivity and the linear thermal expansion were determined. Upon irradiation to 3.3 x 10/sup 19/ n/cm/sup 2/, cracking occurred in all of the 91% T.D. specimens and in two of the five 77% T.D. specimens. The thermal conductivity changed with irradiation more markedly in the case of the 77% T.D. specimen, which also increased its specific clectric resistivity by a factor of 10/sup 4/, while that of the 91% T.D. specimen increased by less than 10-fold. This significant difference in thermal and electric conductivity change by irradiation is attributed to the difference in microstructure. It was observed that the recovery of radiation damage began at about 300 deg C when the specimens were sub!ected to heating and the changes observed in respect of thermal conductivity, electric resistivity and linear thermal expansion. (auth)

Post irradiation recovery of irradiation damage

Abstract During irradiation, fast neutrons produce regions depleted of atoms. It is believed that these regions are responsible for most of the hardening observed after neutron irradiation. The present paper discusses the dissolution of the depleted zones during a post-irradiation anneal and the subsequent recovery of the yield strength. The zones dissolve by emitting vacancies and therefore have an activation energy made up of the sum of the vacancy binding energy to the zone and the vacancy migration energy. The resultant activation energy increases with recovery. For zirconium base alloys it was found that the activation energy varies from 49,700cal/mole at 10 per cent recovery to 61,600 cal/mole at 50 per cent recovery. Experimental data available indicate a similar increase in the activation energy with recovery.

A study of the effects of radiation on titanium and chromium carbides

1. A study of the effects of neutron bombardment on the structure and peoperties of Cr7C3 and TiC established that the cubic titanium carbide is more resistant to radiation than the hexagonal chromium carbide. 2. Neutron bombardment of chromium carbide produces an increase in its lattice parameters a and c. 3. The average grain size of neutron-bombarded carbides decreases and their electrical resistivity, microhardness and “microbrittleness” increase. All these properties recover after annealing at elevated temperatures. 4. At relatively low annealing temperatures (about 400° C), the recovery of radiation damage takes place as a result of the activated glide of dislocations. At higher temperatures, an important part is played by diffusion processes which facilitate coalescence of point defects and formation of precipitates; the latter may, in the early stages of their formation, lead to an increase in the strength of the material.

Theory of radiation embrittlement and recovery of radiation damage in ferritic steels

Abstract Utilizing theories developed to explain the behaviour of irradiated face-centred cubic metals, mechanisms are developed to explain neutron embrittlement and subsequent recovery of body-centred cubic metals (including ferritic steels). The proposed micro-mechanism is an adaptation of Seeger's damage theory combined with Makin's saturation effects concept and Cottrell's brittle fracture theory. It is suggested that annealing of the damage occurs by the thermally activated motion and coalescence of the damage zones as entities through surface diffusion of atoms on the zone interior surfaces. The overall zone motion is described by random-walk movement. The reasonableness of the model is demonstrated from various experimental data.

The Recovery of Vicia faba Meristem Cells from X-Radiation

With the roots of Vicia faba seedlings used as a test system, the effect of two doses of x rays separated by a variable time interval is described. The results are used to infer the rate of recovery of radiation damage in Vicia meristem celis, a rate shown to vary with the temperature at which the roots are stored between doses. (auth)

Recovery of aluminium after neutron-irradiation at 78 °K

Zone-refined Al and 99.995% purity Al samples were irradiated at liquid-nitrogen temperature at fast (> 1 MeV) neutron doses of 1.4·1018 n/cm2 and of about 2·1017n/cm2. The recovery of radiation damage, as revealed by electrical resistivity, takes place mainly in two stages, indicated as stageIn-2 andIn-3, centered respectively at-150 °C and at -60 °C. StageIn-2, controlled by an activation energy of about 0.3 eV, is sensitive to the impurity content and has been ascribed to the release of trapped interstitials. StageIn-3, controlled by an activation energy of 0.59 eV, follows a complex kinetics which can be considered a generalization of’ a second-order reaction. Although the interpretation of this stage is not conclusive, some evidence supports the idea that a multiple vacancy-type defect (quadri-vacancy) annihilates by recombination with an immobile interstitial aggregate.

Tensile properties of irradiated thorium

The effects of neutron exposure to 5 × 10 21 nvt (1.9 at % burnup) on the tensile properties and hardness of two lots of thorium differing in carbon content are described. The thorium lot, which was initially stronger by virtue of a higher carbon content, continued to be stronger throughout the range of exposures employed. Significant increases in strength and hardness result from an exposure of 2 × 10 20 nvt. This exposure also induces a pronounced yield and greatly decreases strain hardenability. The yield point is reduced and eventually removed with increased exposure, which is believed to be due to dislocation glide impedance caused by fission products. Brittle fracture at less than 4 % elongation occurs with burnups greater than 1.0 at %. Effective recovery of irradiation damage can be obtained by annealing at 750° C; however, some nonrecoverable damage occurs with burnups greater than 0.005 at %. The effects of neutron irradiation on the mechanical properties of thorium and uranium are compared and discussed.

The recovery of radiation damage in molybdenum

AbstractMolybdenum wires were neutron irradiated at liquid nitrogen temperature and subsequently annealed up to 800 °K. The residual resistivity showed two main recovery peaks, one at 130 °K and one at 440 °K, with associated activation energies of 0.40 ± 0.04 eV and 1.23 ± 0.06 eV respectively. The activation energy increases linearly with temperature between 80 °K and 350 °K where in a rather discontinuous way a 0.25 eV higher value is reached, which remains practically constant up to 480 °K.It is suggested that the 1.23 eV stage is basically governed by the same processes as the third annealing stage in the f.c.c. metals.

食品微生物に対するガンマ線の作用-I ガンマ線照射を受けた細菌の増殖(その1)

In the dose range for commercial sterilization or radiopasteurization, gamma radiation generally produces certain limited changes in living cells of microorganisms. By these treat-ments, most of the microorganisms are inactivated and usually fail to grow any more. Some of the cells of microorganisms treated with ionizing radiations at such low or medium dose levels, however, are known to recover to a certain extent if exposed to some suitable condi-tions after irradiation, e. g. STAPLETON et all-3) demonstrated that incubation of Escherichia coli B/r at suboptimal temperatures after irradiation produced a greater survival than incuba-tion at the optimum temperature. Since the first commercial applications of irradiation of foodstuff seem to be in the low or medium dosage field, the practical importance of these postirradiation effects will need no emphasis. Most of the investigations in the literature dealing with the recovery of radiation damage of microorganisms by postirradiation treatments, however, have been made with Es-cherichia coli, which seems to be atypical from the viewpoint of food microbiology, and little is still known about these problems with common food microorganisms. The present work is concerned mainly with the effects of some postirradiation treatments on the growth of several food microorganisms and Escherichia coli irradiated with 60Co gam-ma rays. The results obtained were as shown in figures 1-9, and may be summarized as follows: 1) With respect to the effect of postirradiation incubation temperature on the observed survival, there was relatively wide difference between Escherichia coli and Proteus morganii or spores of Bacillus mesentericus. The strain of Escherichia coli employed in this experi-ment showed marked increase in the observed survival at suboptimal postirradiation incubation temperatures. Proteus morganii also showed a slight increase in the survival at suboptimal postirradiation temperatures, but its increasing tendency was not so marked as was the case with Escherichia coli. With the strain of Bacillus mesentericus, on the other hand, such an increase in the survival was never found at any suboptimal temperature; this organism rather showed the highest survival at its optimum temperature. 2) In all cases the surviving fractions differed to some extent with pH values of the post-irradiation culture media. In the cases of Escherichia coli and Proteus morganii the survi-ving fraction more or less decreased with increasing pH value of the media within certain limited range. The pH optima for the survival of irradiated cells of these bacteria, therefore, were somewhat lower than the optimum pH for the growth of unirradiated cells of these or-ganisms. On the contrary, Bacillus mesentericus showed the highest survival at pH 7 which is the optimum pH for its growth. It may be concluded that the effects of postirradiation treatments on the survival of bac-teria entirely differ with species. It appears that these effects generally decrease with the increase of the variety of the nutritional substance required for bacteria.