Recovery Of Radiation Damage Research Articles

Re-irradiation tolerance of rat spinal cord to fractionated X-ray doses

Experiments were performed to assess the re-irradiation fractionation sensitivity in the rat cervical spinal cord. Animals were given initially three daily fractions of 9 Gy representing 75% of tolerance at the ED 50 level. After an interval of 20 weeks, they were re-irradiated with graded doses of X-ray in single, 2, 5, 10 and 20 daily fractions, or a single retreatment top-up dose of 12.8 Gy (equivalent to 80% of retreatment tolerance) followed by doses in 1, 2, 4, 10 and 20 daily fractions. The end-point was paralysis of the forelimbs secondary to white matter necrosis. Latent periods to paralysis ranged from 188 to 245 days from initial irradiation, or from 48 to 105 days from re-irradiation. For a given fractionated retreatment schedule, shorter latent times were observed in animals re-irradiated to higher total doses. The re-irradiation ED 50 values for single, 2, 5, 10 and 20 fractions were 14.0 (95% CI 13.3, 14.2), 20.5 (19.9, 21.2), 29.1 (28.0, 30.1), 36.3 (35.1, 37.4) and 47.8 Gy (46.2, 48.3), respectively. For re-irradiations with a 12.8 Gy top-up dose followed by doses in single, 2, 4 and 20 fractions, the retreatment ED 50 values excluding the 12.8 Gy top-up dose were 4.5 (95% CI 3.0, 5.4), 6.5 (5.6, 7.3), 7.0 (5.0, 8.1) and 10.9 Gy (8.9, 12.5), respectively. Direct fit of the linear-quadratic (LQ) model to the data gave similar α β values of 3.07 Gy (95% CI 2.30, 3.95) and 3.34 Gy (95% CI 1.94, 4.74), respectively, p = 0.6, for the retreatment experiments without and with top-up doses. This fractionation sensitivity during retreatment compares well with that of previously un-irradiated animals, α β value of 2.41 Gy for fraction sizes down to 2 Gy/fraction. It is concluded that there is significant long-term recovery of radiation damage in rat spinal cord, and that previous radiation damage to a level of 75% of tolerance does not change the capacity for repair of sublethal damage when the spinal cord is re-irradiated with fractionated doses of X-ray at 20 weeks.

Dose-dependency of radiation on enzyme production in Trichoderma reesei.

Effect of irradiation dose on the production of cellulase and amylase related enzymes in Trichoderma reesei was studied, in which post-irradiation time response pattern was measured. The damage of the cells irradiated with certain irradiation doses (1.40 +/- 0.20 x 10(5), 2.20 +/- 0.10 x 10(5), 3.00 +/- 0.50 x 10(5) and 3.50 +/- 0.20 x 10(5) rad) was rapidly recovered. The increased enzyme production in the culture of the irradiated cells resulted from the recovery of radiation damage after irradiation. The function of cell growth was not affected by irradiation below dose of 5 x 10(5) rad, though the function of enzyme synthesis was drastically affected.

Radiation-induced defects in solid solutions and intermetallic compounds based on the Ni-Al system: II Recovery of radiation damage

For pt.I see ibid., vol.4, p.10199 (1992). The recovery of short-range ordered Ni(Al) and Ni(Al,Ti) solid solutions and long-range-ordered Ni3Al intermetallic compounds was investigated by residual electrical resistivity measurements as a function of composition and of fluence, after low-temperature (4-9 K) irradiation with 2.95 MeV electrons. In the solid solutions, long-range defect migration resulted in increases of local order, self-interstitials were found to be mobile above 110 K (at least in the binary alloys) and vacancies to be mobile above 330 K. The recovery spectrum of irradiated intermetallic compounds showed some similarity with that of pure nickel, with a smaller amount of fine structure. The mobility of self-interstitials (corresponding mainly to Ni-Ni dumbbells) occurs at a higher temperature (75 K) than in nickel (50 K) and does not induce significant ordering. By contrast, the Ni vacancies, which are the dominant vacancy species, are slightly less mobile than in nickel and promote some increase of long-range order.

Ion implantation studies of UO 2 and UN

Ion implantation of fission products (rare gases Kr and Xe, volatiles Te, I, Rb, Cs) in UO 2 and UN has been used to perform separate effect studies to investigate formation and recovery of radiation damage as well as the behavior (lattice location, diffusion, release, precipitation, etc.) of the fission products. Both radioactive beams to provide tracers for release measurements and inactive beams were used, with widely varying doses between ~ 10 11 and 10 17 ions/cm 2 at energies between 40 and 500 keV. The implantation temperatures were varied between 5 and 770 K and furnace anneals were performed up to 2070 K. The analytical techniques applied were Rutherford backscattering (RBS) channeling supported by electron microscopy (TEM, SEM) and conventional counting methods for the tracers. A very large data base on damage formation and recovery for both UO 2 and UN and on fission product behavior has been obtained and is summarized. A large fraction of the damage formed is shown to recover instantaneously, helping to explain the structural stability of the fuels and the absence of amorphization. Half of the remaining metal defects (the interstitials) migrate to sinks below room temperature in both UO 2 and UN. Also, channeling results indicating coherent precipitation of volatiles even at room temperature are reported together with new data on low temperature release of these impurities.

Lattice location of fission products in UO2 single crystals

Heavy fission product ions (Te, Xe, Cs) were implanted in UO2 single crystals at 50 keV to high fluences between 5 × 1015 and 1 × 1017 ions/cm2. The implantations were performed at 77 K (Te, Xe) and 293 K (all three elements). The crystals were subsequently analyzed in situ using the Rutherford backscattering (RBS) channeling technique. All implants exhibited a large (apparent) substitutional fraction SF = 50–70% when implanted at 293 K. In contrast, SF = 0 for the implantations at 77 K. The annealing behaviour was also studied. For the crystals implanted at 293 K the release of impurity atoms (Te, Cs) sets in at temperatures above 750 K and is clearly correlated with radiation damage recovery. Xe-release starts above ~1300 K. The release of Te implanted at 77 K begins already at 400 K and is nearly completed at 600 K. In this temperature range, no changes in the damage distribution were noticed. These results give the first indication of coherent precipitation of solid rare gases and volatiles in UO2.

Comparison of recovery, inhibition and fixation of damage after heating and radiation

1. 1.|Aphidicolin and β ara A, which are known inhibitors of polymerases α and β, can be used to evaluate the role of polymerases in recovery of radiation damage. 2. 2.|In this study the effect of these compounds was tested on recovery of potentially lethal damage after irradiation (X-PLD) in normal and transformed cells. In addition, recovery of potentially lethal damage and its inhibition after hyperthermia (H-PLD) were also examined and compared to radiation. 3. 3.|X-PLD recovery was inhibited to different degrees by β Ara A in a host of transformed and normal C3H 10T1/2 cells. Aphidicolin had no effect on X-PLD recovery. These data indicated that polymerase β and not polymerase α was involved in X-PLD recovery after irradiation. 4. 4.|H-PLD recovery after hyperthermia was not affected by β Ara A or aphidicolin indicating that H-PLD after hyperthermia was different than XPLD after X-irradiation.

Photoluminescence study of Li- and Na-implanted ZnSe epitaxial layers grown by atmospheric pressure metalorganic vapor-phase epitaxy

We have investigated p-type doping of Li and Na impurities by ion implantation into ZnSe heteroepitaxial layers grown at very low temperatures (250 °C) by atmospheric pressure metalorganic vapor-phase epitaxy. The activation rates of shallow acceptor levels, the density of self-activated centers in the implanted-ZnSe epitaxial layers (epilayers), and the degradation of crystalline quality due to radiation damage are dependent on the ion implantation and annealing conditions. As the dose density changes, so do the optimum annealing conditions for the degrees of activation and the recovery of radiation damage. Also the depth profile of the implanted ions and damage is greatly influenced by the acceleration energy. It is difficult to decide on the optimum annealing conditions at the different acceleration energies and to assess the crystalline quality of the implanted epilayers with a nonuniform depth profile of the implanted ions, because the region analyzed is restricted near to the surface and does not always coincide with the implanted region in the epilayer. We have confirmed that the high-temperature annealing does not cause the damage to propagate deeply into the implanted epilayers, although it has been a cause of much concern in II-VI compounds.

Irradiation creep properties and strength of a fine-grained isotropic graphite

An irradiation creep test was conducted on a fine-grained isotropic graphite, IG-110, for the high temperature gas-cooled reactor under development in Japan Atomic Energy Research Institute (JAERI). The dimensions, Young's modulus, tensile and bending strengths of specimens were measured before and after the irradiation creep test. Irradiation creep coefficients were obtained on the basis of the difference of dimensions of the unstressed and creeped specimens before and after the irradiation creep test. As a result, the irradiation creep coefficient was determined to be 3.4 × 10−29 −4.8 × 10−29 (MPa· nm2)−1 at 756–984°C up to 1.8 × 1025nm2 (E > 29 fJ). The average value was (4.22 ± 0.65) ×10−29 (MPa· nm2)−1, provided that the difference in irradiation temperature is neglected. Young's modulus increased 38–48% after irradiation. The increase in tensile strength of irradiation creeped specimen was 23–45% smaller than the bending strength. This suggests that the applied stress to the creep specimens under neutron irradiation gives rise to recovery of irradiation damage, compared with the case of unstressed specimens. The relation between the Young'a modulus ratio (E/E0) and the bending strength ratio (σb/σ0) can be expressed by the equation: σb/σo = (EE0)z, where z is a constant.

Investigation of defects in boron implanted silicon by means of p-n junction

A simple electrical method for the evaluation of radiation damage in implanted silicon is described. It is based on the measurement of reverse current of a p-n junction. Radiation defects were formed by implantation of boron at the doses of N d = 10 11 and 10 12 cm −2, respectively. The maxima of the distribution of defects were within the depletion region of the junctions. Samples were annealed at temperatures up to 500°C. These conditions were sufficient for the recombination of practically all defects. The activation energy of the radiation damage recovery had values between 0.14 and 0.26 eV. The maximum of the concentration of defects is proportional to N d 0.57. The recovery of defects during ion implantation was observed.

Radiation Induced Si–SiO2 Interface States and Positive Charge Buildup of MOS Capacitors Annealed in Nitrogen and in Hydrogen After Metalization

The density of Si–SiO2 interface states (ΔDit) and the density of trapped oxide charges (ΔNot) generated by Co-60 gamma ray irradiation are examined for MOS capacitors with post metalization annealing (PMA) in hydrogen and in nitrogen. A good correlation between |ΔVmg-ΔVFB| and \\int Dit dE is found, and it verifies that the charging at the interface states affects the estimation of ΔNot from the VFB shift. The radiation hardness of the MOS structure is sensitive to annealing conditions. PMA is effective in decreasing ΔDit and ΔNot. The PMA effect is discussed in terms of weak bond and interstitial hydrogen atoms. Moreover annealing after irradiation is found to be effective in recovery of radiation damage on MOS devices.

Point defect diffusion in α-Zr

The present review of defects in α-Zr is concerned with atomic and vacancy diffusion and with solute effects on radiation damage. The primary aim, in addressing atomic diffusion, is to try to expose the characteristics and systematics of intrinsic diffusion. This is done, both in a general context and in terms of problems and features more specifically associated with α-Zr. Among the latter are the anisotropic crystal structure, the limited temperature interval of α-phase stability, imposed by the α-β (hcp-bcc) transformation, and the tendency for Zr to have high residual impurity levels. It is emphasized that reliable, intrinsic, diffusion data can only be obtained through the use of high-purity single-crystal material. Vacancy diffusion is considered in terms of experimental data on irradiation damage. Solute effects on irradiation damage are discussed on the basis of the interactions of solutes with vacancies and self-interstitial atoms (SIA). A consideration of atomic diffusion data indicates that self-diffusion in α-Zr is intrinsically normal and that self-diffusion data associated with abnormal behaviour are probably expressive of diffusion dominated by extrinsic mechanisms: both structural and impurity-related defects appear to be important here. Intrinsic diffusion characteristics (diffusion coefficients ( D) and associated activation energies and pre-exponential factors) tend to scale in a remarkably simple manner with atomic size, with diffusion taking place by both interstitial and substitutional mechanisms. Small atoms diffuse mainly by interstitial paths, with associated D values which may be many orders of magnitude higher than those associated with substitutional solutes. Measurements of diffusion anisotropy show that diffusion is generally faster parallel to the c- axis than perpendicular to it: this is well established for fast-diffusing, interstitial-like solutes but not well known for substitutional solutes. The vacancy migration characteristics of α-Zr present an ongoing enigma. Experimental data from electron microscopic and positron annihilation spectroscopic (PAS) measurements of irradiation damage recovery are readily interpreted in terms of abnormally facile vacancy migration, however there does not appear to be any evident theoretical support for such a phenomenon as an intrinsic process. This raises the possibility of an extrinsic mechanism. In addition, there seems to be sufficient ambiguity associated with the data to allow their interpretation in terms of a model wherein vacancy migration is inherently normal. Solute effects on irradiation damage and recovery are discussed in a general context with a consideration of the attraction of SIAs for small solute atoms and of solute-vacancy interactions in terms of electrostatic and bond-strength approaches. Specific attention is given to the role of Sn, since it is shown, from PAS measurements, that radiation damage and recovery in Zr can be profoundly altered by alloying additions of this element. Some understanding of these results can be found in terms of defect interactions with clustered configurations of solute atoms. The results suggest the basis of a general approach towards the development of irradiation-damage resistant alloys.

Alterations in phosphate metabolism during cellular recovery of radiation damage in yeast.

We have examined alterations in phosphate pools during cellular recovery from radiation damage in intact, wild-type diploid yeast cells using 31P nuclear magnetic resonance (NMR) spectroscopy. Concurrent cell survival analysis was determined following exposure to 60Co gamma-radiation. Cells held in citrate-buffered saline (CBS) showed increased survival with increasing time after irradiation (liquid holding recovery, LHR) with no further recovery beyond 48 h. Addition of 100 mmol dm-3 glucose to the recovery medium resulted in greater recovery. In the presence of 5 mmol dm-3 2-deoxyglucose (2-DG), LHR was completely inhibited. NMR analyses were done on cells perfused in agarose threads and maintained under conditions similar to those in the survival studies. ATP was observable by NMR only when glucose was present in the recovery medium. In control cells, ATP concentrations increased and plateaued with increasing recovery time. With increasing radiation dose the increase in ATP was of lesser magnitude, and after 2000 Gy no increase was observed. These observations suggest that either the production of ATP in irradiated cells is suppressed or there is enhanced ATP utilization for repair of radiation damage. In CBS with 100 mmol dm-3 glucose, a dose-dependent decrease in polyphosphate (polyP) was detectable with no concurrent increase in inorganic phosphate (Pi). In the absence of an external energy source, such as glucose, there was a slight increase in Pi. This suggests that polyP may be used as an alternative energy supply. When 2-DG was present in the recovery medium, polyP decreased, but there was a simultaneous increase in Pi with increasing radiation dose and recovery time. This suggests that the polyP are hydrolyzed as a source of phosphates for repair of radiation damage.

Recovery of Radiation Damage in Niobium with Various Dopants

Recovery of Radiation Damage in Niobium with Various Dopants

Interaction of Interstitial Impurities with Radiation-Induced Defects Leading to Improved Elevated Temperature Mechanical Properties of Mild Steel

Improvements in both the yield strength and ductility were noted in mild steel at elevated temperatures (greater than or equal to315 K) following neutron irradiation to 2 X 10/sup 22/ n/m/sup 2/, in contrast to hitherto observed radiation hardening and embrittlement. This beneficial effect was shown to be due to the interaction of interstitial impurities with radiation-produced defects resulting in reduced concentration of interstitial carbon and nitrogen in solution, and thus blue brittleness is suppressed following radiation exposure. Consequently, the energy absorbed by the irradiated material (a measure of toughness) improved at these temperatures. In the temperature range examined, namely from 300 to 550 K, Luders strain increased following neutron irradiation. While the Luders strain of unirradiated material exhibited a peatk at about 460 K due to dynamic strain aging, it decreased continuously with test temperature following neutron irradiation. Radiation exposure resulted in decreased rates of work hardening at all of the test temperatures. Peaks in the temperature dependence of the work-hardening parameter are noted for the unirradiated material in the serrated flow regime. Thermal recovery of radiation damage resulted in increased rates of work hardening at elevated temperatures.

Annealing effects on electrical properties of thermal neutron transmutation doped Ge

A neutron transmutation doping technique was applied to the high purity n-type germanium with 50 Ω cm (n=5.9×1013/cm3). For a neutron flux density of 5×1011/cm2 s and an irradiation time of 60 min, the doped Ge was converted into p type with 7 Ω cm ( p=3.5×1014/cm3). By neutron irradiation it has been possible to introduce the shallow acceptors resulting from the damage in addition to gallium atoms as acceptors. The recovery of radiation damage was evaluated by the improvements of some electrical properties for various annealing stages. By annealing at 600 °C, a room temperature hole mobility of 2200 cm2/Vs has been achieved at p=6.2×1013/cm3 and ρ=45 Ω cm. And, also, we found that higher mobility holes in p-type Ge play an important role for the weak magnetic field as the lattice atoms recover from the radiation damage. Finally, the direct observation of the recovery of damage was performed by the measurement of channeling effects using a helium ion beam.

Recovery of radiation damage in platinum, studied by Mössbauer spectroscopy

Mössbauer effect measurements are reported with sources of radioactive 133Xe implanted in platinum at 100 and 300 K. Information about the nearby environment of an implanted probe atom is obtained through the hyperfine interaction of the daughter nucleus 133Cs with its surroundings. The sources are subjected to an isochronal annealing sequence in order to study the recovery of the radiation damage in platinum. Five different components are visible in the Mössbauer spectra. Those are associated with substitutional Xe atoms and Xe atoms which have trapped one, two, three and four or more vacancies. Vacancy trapping at the Xe impurities occurs around 300 and 400 K. We ascribe this to the free migration of divancies and monovacancies, indicating that this recovery stage in platinum is due to vacancy migration. Around 550 K dissolution of interstitial clusters is observed and around 700 K vacancy loops start dissolving.

Recovery of radiation damage in neutron transmutation doped silicon by isochronal and isothermal annealing

The recovery of the radiation damage of silicon FZ ingots, irradiated with neutrons in the Dido reactor at Harwell with a dose of 6.5 · 10 1 7 (n cm −2), has been studied by structural and electrical techniques. The study has been made on slices using the isochronal annealing method in the range 100–800°C by steps of 40°C for 30 mins duration. Five stages of recovery in the range 100–800°C have been identified. The isotherms, made at typical temperatures, have established that in the range 580–710°C, the kinetics of recovery of lattice defects are of the first order and with an activation energy of 3.47 eV.

Development of a liquid-holding technique for the study of DNA-repair in human diploid fibroblasts

Liquid-holding conditions can be obtained for human diploid skin fibroblasts by keeping confluent cultures stationary over periods of 7 days or longer by means of conditioned medium. Under this condition recovery of radiation damage induced by ultraviolet light of X-rays is observed as an increase in cloning efficiency. The amount of recovery when expressed in a dose-modifying-factor appears higher than in bacteria and yeast. The repair-deficient human cells strains XP25Ro and XP7Be (xeroderma pigmentosum from complementation groups A and D respectively) exhibit less but still discernible recovery after UV-irradiation and the same was observed for AT6Bi (ataxia telangiectasia) after X-irradiation. Experiments on mutation induction indicated that the repair which takes place during liquid holding of UV-irradiated XP7Be cells reduces the mutant frequency considerably while after liquid holding of UV-irradiated wild-type cells the same or lower mutant frequencies were found for the lower exposures and the same or higher mutant frequencies for the higher exposures.

Stage III migration of point defects in molybdenum

Abstract In a continuing discussion concerning the migrating species in Stage III annealing of metals with a fairly compact crystal structure, it is demonstrated that positron annihilation can be used to give information on this problem. The general principle is to measure the recovery of radiation damage in a crystal containing an unbiased sink relative to another crystal where this sink is not present. The consequences of the two models are discussed. It is found that, in molybdenum, vacancies are the migrating species.

Resonance mode hopping and the stage I annealing of metals

Abstract The diffusion of heavy particles and their associated resonance modes through solids is discussed and attention is focussed on the specific example of the self-interstitial in f.c.c. metals. We show why classical diffusion ideas retain a considerable validity despite the fact that typical temperatures for recovery of radiation damage may be about 0.1 to 0.2 of the Debye temperature of the host lattice.