Recovery Of Radiation Damage Research Articles

Radiation-damage recovery in undoped and oxidized Li doped MgO crystals implanted with lithium ions

Undoped MgO and oxidized Li-doped MgO single crystals were implanted with 1 × 10 17 Li +/cm 2 at 175 keV. The Rutherford backscattering spectrometry (RBS)/channeling data obtained after implantation shows that damage was produced throughout the entire range of the implanted ions. Optical absorption measurements indicate that after implantation the most intense band occurs at ≈5.0 eV, which has been associated with anion vacancies. After annealing at 450 K the intensity of the oxygen-vacancy band decreases monotonically with temperature and completely disappears at 950 K. A broad extinction band centered at ≈2.14 eV associated with lithium precipitates emerges gradually and anneals out at 1250 K. RBS/channeling shows that recovery of the implantation damage is completed after annealing the oxidized samples at 1250 K.

Characterization of Si(1 1 1) crystals implanted with Sb + ions and annealed by rapid thermal processing

Monocrystalline Si(1 1 1) targets are implanted (at room temperature) with antimony ions at 120 keV energy to 5×10 14 or 5×10 15 Sb + cm −2 dose. The samples are heat treated by means of rapid thermal processing (RTP) at 1000 °C during 60 s, under nitrogen atmosphere. In this work, we report the measured evolution of the silicon surface damage and the radiation damage recovery in relation to antimony dose and RTP processing. We also study the behavior of antimony dopant into Si(1 1 1) specimens. The investigation is carried out by He + Rutherford backscattering spectrometry (RBS; operating at 1.57 MeV energy in both random and channeling modes), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. It is shown that a good surface damage recovery is obtained for all the annealed samples. However, after RTP, a significant loss of antimony has occurred for the specimens which are implanted with 5×10 15 Sb + cm −2 dose. This suggests an antimony out-diffusion. Finally, a good morphological characterization of the specimens is provided by AFM.

Radiation damage of Si photodiodes by high-temperature irradiation

Results are presented of a detailed study of the effects of high-temperature 4-MeV neutron irradiation on the performance degradation of Si pin photodiodes. The macroscopic device performance is correlated with the radiation-induced defects observed by DLTS. It was found that the dark current increases after irradiation, while the photocurrent decreases. After irradiation, two majority electron capture levels (Ec 0.40 eV) were induced in the n-Si substrate. Additionally, degradation of device performance and the rate of introduction of lattice defects decrease with increasing irradiation temperature. For 250 °C irradiation, the reduction of the photocurrent is only 10% of the starting value. This result suggests that the creation and recovery of radiation damage proceed simultaneously at high temperatures.

Radiation damage of PbWO 4 crystals due to irradiation by 60Co gamma rays

Radiation resistivity of large tungstate crystals PbWO 4 from three suppliers has been studied for doses 10 4 Gy (10 6 rad) and 10 5 Gy (10 7 rad). Radiation resistivity was examined by the measurement of optical transmission through tungstate crystals before and after 60Co gamma-ray irradiations. The absolute degradation of transmission for 10 4 and 10 5 Gy doses at 480 nm wavelength of the peak emission of PbWO 4 doped with La 2+, was found to be lower than 12.3% and 14.2%, respectively. The results have been also compared with radiation hardness measurements for a large volume CeF 3 scintillation crystal. Complete recovery of radiation damage was observed between 10 and 15 days after irradiations.

Nanoindentation on neutron irradiated MgO crystals

Using a nanoindentation technique, hardness and Young's modulus were determined in as-grown MgO single crystals and after neutron irradiation with different doses up to 6.9×10 18 n/cm 2. The resulting defects were monitored by optical absorption spectroscopy. As-grown crystals have a hardness of (9.1±0.2) GPa. After neutron irradiation, hardness increases with dose, whereas Young's modulus remains practically constant, indicating that the elastic properties are not influenced by the irradiation. For the highest neutron dose of 6.9×10 18 n/cm 2, the resulting value for hardness was (12.3±0.2) GPa. The recovery of radiation damage following thermal treatments is also investigated. The hardening observed in n-irradiated crystals is attributed to interstitials.

RBS-channeling measurements of sapphire (0 0 1) substrate implanted with high-energy O and Cu ions

Sapphire (0 0 1) substrates were implanted with 1.0 MeV O ions and 2.1 MeV Cu ions and subsequently annealed at different temperatures in vacuum, and recovery of radiation damage and redistribution of Cu in the sapphire substrate were examined by Rutherford backscattering spectrometry measurements with channeling technique. In addition, the formation of copper oxide nanoparticles has also been examined by X-ray diffraction (XRD) measurements. It is found that radiation damage in the sample is almost retained up to 800 °C. Further increase of annealing temperature causes significant recovery of radiation damage. Concurrently, annealing temperatures higher than 800 °C cause the enhancement of Cu diffusion. The results of XRD measurements show that nanoparticles are grown above 800 °C. These results suggest that the recovery of radiation damage gives rise to the redistribution of Cu and the formation of copper oxide nanoparticles.

Radiation resistivity of PbF 2 crystals

Radiation hardness of a 4×4×24 cm 3 PbF 2 crystal has been studied for doses up to 10 5 Gy. Radiation resistivity was examined by the measurement of optical transmission through the lead fluoride crystal before and after gamma-ray irradiations. The results have been compared with radiation hardness measurements for a 4×4×40 cm 3 Pb-glasses SF 5 and SF 6 and a 3×3×6 cm 3 CeF 3 scintillation crystal, as well. Complete recovery of radiation damage was observed a few day after the irradiations.

Cation disordering in magnesium aluminate spinel crystals induced by electron or ion irradiation

Structural changes in magnesium aluminate spinel (MgO · nAl 2O 3) single crystals, which were irradiated with 900 keV electrons or 1 MeV Ne + ions at 873 K, were examined by electron channeling enhanced X-ray microanalysis. Unirradiated MgO · Al 2O 3 has a tendency to form the normal spinel configuration, where Mg 2+ ions and Al 3+ ions occupy mainly the tetrahedral and the octahedral sites, respectively. Electron irradiation induces simple cation disordering between the tetrahedral sites and the octahedral sites in MgO · Al 2O 3. In addition to cation disordering, slight evacuation of cations from the tetrahedral sites to the octahedral sites occurs in a peak-damaged area in MgO · Al 2O 3 irradiated with Ne + ions. In contrast, cation disordering is suppressed in MgO · 2.4Al 2O 3 irradiated with electrons. The structural vacancies, present in the non-stoichiometric compound, appear to be effective in promoting irradiation damage recovery through interstitial–vacancy recombination.

Radiation resistivity of large tungstate crystals

Radiation resistivity of large tungstate crystals PbWO 4 and CdWO 4 has been studied for doses up to 10 5 Gy. Radiation resistivity was examined by the measurement of optical transmission through tungstate crystals before and after gamma-ray irradiations. The absolute degradation of transmission for 10 5 Gy dose at the wavelength of the peak emission of both tungstate crystals PbWO 4 and CdWO 4 were found to be lower than 12.5 and 8.0%, respectively. The complete recovery of radiation damage was observed 15 days after irradiations.

Room-temperature minority-carrier injection-enhanced recovery of radiation-induced defects in p-InGaP and solar cells

We present here the direct observation of minority-carrier injection-enhanced annealing of radiation-induced defects in metalorganic chemical vapor deposition grown p-InGaP at room temperature, and the consequent recovery of radiation damage in InGaP n+-p junction solar cells. Deep level transient spectroscopy analysis shows that the main defect H2 (Ev+0.55 eV) in p-InGaP exhibits minority-carrier injection-enhanced annealing characterized by an activation energy (ΔE=0.51 eV) close to the activation energy for the recovery (ΔE=0.54 eV) of the defect responsible for diffusion length degradation in n+-p solar cells. The marked recovery of radiation damage in InGaP solar cells induced by minority-carrier injection is found to be correlated with the annihilation of the H2 defect.

Microstructure and Post-Irradiation Annealing Behavior of 20% Cold-Worked 316 Stainless Steel

ABSTRACTMicrostructural examination and in situ post-irradiation annealing studies were carried out on 20% cold-worked 316 stainless steel (SS) hexagonal duct material following irradiation in the reflector region of the EBR-II reactor. Stainless steel hexagonal ducts were used to house reactor subassemblies and provide a valuable source of information on irradiation behavior of reactor structural materials at lower dose-rates (on the order of 10-8 dpa/sec) than previously examined. The microstructural development of samples irradiated to doses of 1, 20 and 30 dpa is examined, while the post-irradiation annealing behavior of a sample irradiated to 20 dpa is described. Annealing studies were performed at 370 and 500°C to examine the kinetics of radiation damage recovery as a function of annealing temperature. The initial (pre-annealed) microstructures consists of a substantial density of irradiation induced chromium-rich M23C6 and M6C carbides which form both on the grain boundaries and within the grain interiors. Recovery of the cold- work is evident in the 1 dpa sample while samples irradiated to 20 and 30 dpa possess dense populations of voids and dislocation structures consisting of networks of line dislocations and faulted dislocation loops. Results indicate that post-irradiation annealing of the samples at 370°C for 1 hour has little effect on the microstructure, while further annealing at 500°C for 1 hour results in void shrinkage, the formation of small cavities, and a reduction in the dislocation loop and network density.

Rutherford backscattering spectrometry channeling study of ion-irradiated 6H-SiC

Single-crystal 6H-SiC (α-SiC) wafers were irradiated with He + , C + and Si + ions to fluences ranging from 7.5 x 10 17 to 1 x 10 20 ions m -2 at various temperatures (160-870 K). Damage accumulation and subsequent defect annealing (up to 1170 K) have been studied using in situ 2.0 MeV He + Rutherford backscattering spectrometry combined with ion channeling (RBS/C) methods. The defect concentration at the damage peak is observed to increase sigmoidally with increasing ion fluence during irradiation at low temperatures The isochronal recovery of irradiation damage induced at low temperatures is observed to follow an exponential dependence on temperature. The relative disorder accumulated under 550 keV C + ion irradiation as a function of irradiation temperature exhibits a significant decrease between 300 K and 670 K. Irradiation with 550 keV Si + at 180 K to a fluence of 6.0 x 10 19 Si + m -2 produces an amorphous layer extending from the surface to a depth of 0.6 μm. The thickness of this amorphous layer decreases linearly with annealing temperature up to 870 K. At low ion fluences, the defects produced by He + irradiation at 160 K are more difficult to anneal at 300 K than those produced by Si + irradiation, which suggests that trapping of helium may inhibit recombination.

Accumulation and recovery of irradiation damage in He + implanted α-SiC

In situ RBS/Channeling (RBS/C) has been used to investigate damage accumulation and subsequent annealing behavior in single-crystal wafers of 6H-silicon carbide (α-SiC) irradiated at temperatures from 160 to 300 K with 390 keV He + ions to fluences ranging from 7.5 × 10 18 to 1.0 × 10 20 He +/m 2. Damage recovery in the irradiated crystals was studied by isochronal annealing at temperatures up to 1170 K. The RBS/C results show that complete amorphization in α-SiC does not occur at 190 K for irradiation fluences up to 1.0 × 10 20 He +/m 2 (0.38 dpa at the damage peak). For a fluence of 4.5 × 10 19 He +/m 2, the relative amount of damage accumulated during irradiation at 190 K is a factor of 5 larger than that accumulated under irradiation at 300 K, which suggests a higher rate of simultaneous point defect recombination at 300 K. In post-irradiation isochronal annealing studies, the integrated damage profile for all irradiated samples decreased exponentially with increasing annealing temperature. At low relative ion fluences and comparable irradiation-induced defect concentrations, the defects produced by He + irradiation at 160 K are more difficult to anneal at 300 K than those produced by Si + irradiation at 160 K, which suggests that trapping of He atoms at defects may be inhibiting recombination.

Observation of dynamic annealing effects in oxide single crystals after high-dose18O+implantation at 500 °C

Dynamic annealing effects and the behavior of oxygen trapping and migration in the perovskite oxide single crystals following high dose ${}^{18}{\mathrm{O}}^{+}$ implantation at 500 \ifmmode^\circ\else\textdegree\fi{}C and at room temperature have been studied. We report that the cascade collision induced by room-temperature irradiation with ${}^{18}\mathrm{O}$ ions (200 keV $5\ifmmode\times\else\texttimes\fi{}{10}^{16}/{\mathrm{cm}}^{2}$) into ${\mathrm{SrTiO}}_{3}$ single crystal induces an essentially amorphous $({\ensuremath{\chi}}_{\mathrm{min}}\ensuremath{\approx}96%)$ surface layer to a depth of 400 nm. However, irradiation at 500 \ifmmode^\circ\else\textdegree\fi{}C results in dynamic annealing effects since ion channeling shows ${\ensuremath{\chi}}_{\mathrm{min}}$ of 3% in the near surface region. ${}^{18}\mathrm{O}$ depth profiles measured by the ${}^{18}\mathrm{O}(p,\ensuremath{\alpha}{)}^{15}\mathrm{N}$ nuclear reaction show that high-temperature implantation results in a flat-topped ${}^{18}\mathrm{O}$ distribution with only 48% (compared with room-temperature implantation) of implanted ${}^{18}\mathrm{O}$ retained, and more importantly, channeled nuclear reaction analysis shows that at least 77% of the retained ${}^{18}\mathrm{O}$ occupies substitutional sites. Room-temperature implantation plus post-irradiation annealing at 500 \ifmmode^\circ\else\textdegree\fi{}C in flowing oxygen ambient resulted in much less recovery of irradiation damage (${\ensuremath{\chi}}_{\mathrm{min}}\ensuremath{\approx}33$ to 72%). Similar effects were observed in ${}^{18}\mathrm{O}$ implanted single crystal ${\mathrm{LaAlO}}_{3}.$

Long-term recovery kinetics of radiation damage in rat spinal cord

Purpose : This study aimed to asses the influence of the level of initial injury on the long-term recovery kinetics of radiation damage in the central nervous system using a rat spinal cord model. Methods and Materials : The adult rat spinal cord (C2-T2) was initially given two or three daily fractions of 9 Gy, or three daily fractions of 10.25 Gy. At day 4 or weeks, 6, 8, 12, 20, 28, 40, or 52, animals were reirradiated with grated single doses of X rays. The end point was forelimb paralysis caused by white-matter necrosis. Results : Latent times to paralysis as measured from the date of the initial treatment increased with increaing time interval between initial treatment and reirradiation but decreased with increasing size of initi8al injury. Retreatment ED 50s were 14.1, 14.8, 15.4, 16.3, and 16.2 Gy for animals reirradiated at day 4 and weeks 8, 12, 20, and 28, respectively, after an initial dose of 9 Gy × 2. After 9 Gy × 3, the retreatment ED 50s at day 4 and weeks 6, 8, 12, 20, 28, 40, and 52 were 10.0, 9.9, 9.8, 12.0, 13.9, 14.6, 14.7, and 15.5 Gy, respectively. For an initial dose of 10.25 Gy × 3, the retreatment ED 50s at day 4 and weeks 8, 12, 20, 28, and 40 were 5.8, 6.1, 8.4, 10.6, 12.2, and 13.3 Gy, respectively. Using the linear-quadratic (LQ) model, α gb of 3.0 Gy, to quantitate the biological effect of the different retreatment schedules, the initital doses of 9 Gy × 2 or 3, or 10.25 Gy × 3 were found to represent 47, 71, and 89% of the extrapolated response dose (ERD), respectively, and no significant increase in tolerance was observed for retreatment given within 8 weeks of initial treatment. Significant long-term recovery was observed thereafter and increased with increasing time interval to retreatment. The retreatment tolerance and radiation damage recovered at different intervals were influenced by the initial dose. Using direct analysis, the recovery kinetics could be best described by introducing a time function consisting of a linear and quadratic time component dependent on initial dose to the LQ model. Conclusion : These results are consistent with the presence of significant long-term recovery of radiation damage in rat spinal cord, and suggest that the size of the initial damage influences the recovery kinetics, and hence the retreatment tolerance.

Temperature dependent microstructural modification in ion-irradiated Tl-type high temperature superconductors

Ion irradiation damage creation and recovery were examined in Tl-based high temperature superconductors, HTSC, using TEM, resistivity, and magnetic measurements for irradiation temperatures of 20 to 650 K. During 1.5 MeV Kr + and Xe + ion irradiations of single-crystal Tl-1212 and Tl-1212 TlBaCaCuO HTSC, microstructural modification was observed in situ by electron diffraction and shows a remarkable temperature dependence. At selected sample temperatures, irradiations continued until a critical fluence, D c, was reached where the original structure disappeared. The temperature dependence of D c shows a minimum near the superconducting transition temperature, T c, and is correlated with the temperature dependence of the thermal conductivity, which has a maximum near T c. At an irradiation temperature near this maximum in thermal conductivity, a minimum amount of damage recovery occurs because heat can be dissipated away from the displacement cascade. Ion irradiation suppresses the T c. The rate of decrease in the T c as a function of damage (measured in displacements per atom, dpa) was found to be the same for various incident ions (He +, O 2+, Au 5+ which shows that the damage accumulation is a result of atomic collisions. Further, the rate of decrease in T c was found to be the same for both transport and magnetization measurements, indicating that the displacements effect the bulk of the samples through point defect creation. An activation energy of 0.4 eV for ion irradiation damage recovery over the temperature range from 100 to 650 K was determined from normal state resistance versus time immediately after irradiation.

A comparison of hyperthermia inhibition of sublethal radiation damage recovery in four human cell lines with different radiosensitivity

Four human cell lines, one normal fibroblast and three tumour lines of differing radiosensitivities were evaluated for recovery from radiation damage, and for inhibition of this recovery by hyperthermia. The normal fibroblast, the glioma and the resistant ovarian carcinoma had about the same radiation resistance and sublethal damage recovery (SLDR) capacity. The sensitive ovarian carcinoma cell line had a much lower SLDR capacity. The potentially lethal damage repair (PLDR) capacity was greatest in the fibroblast and least in the resistant ovarian carcinoma. Hyperthermia for 30 min at 43 degrees C resulted in inhibition of SLDR and PLDR in all cell lines. Heating immediately after irradiation was most effective. In general, SLDR inhibition was greatest in the cell lines with the highest SLDR capacity while there was no such correlation with PLDR. Hyperthermia was most effective in the four cell lines tested when given immediately after the first dose of radiation of the split dose regimen. Thus, for clinical fractionated treatment, it may be most efficacious to give hyperthermia immediately after irradiation.

Radiation myelopathy following single courses of radiotherapy and retreatment

Purpose : To assess the latent time, survival and dose-fractionation factors associated with permanent radiation myelopathy following single and multiple courses of radiotherapy to the spinal cord. Methods and Materials : A retrospective analysis was undertaken of all patients who were registered at the Princess Margaret Hospital between 1955 and 1985, and who developed permanent radiation myelopathy. There were 22 males and 13 females with ages ranging from 30 to 72 years. Twenty-four patients developed permanent myelopathy after one course of radiation therapy and 11 patients following retreatment. Seven patients had histological confirmation of radiation myelopathy at autopsy. Results : The actuarial survival was 14% at 5 years (median: 8.3 months) from the date of diagnosis of radiation myelopathy. Latent times for myelopathy following a single course of treatment (mean: 18.5 months, 7–57 months), were significantly longer than those after reirradiation (mean: 11.4 months, 4–25 months), p = 0.03. There was not a single incident of myelopathy in patients who received fractionated radiotherapy given once daily to an extrapolated response dose (ERD) of ≤ 100 Gy 2 (equivalent to 50 Gy in 25 daily fractions). Four patients who developed myelopathy after an ERD of < 100 Gy 2 were all treated on accelerated fractionation protocols with multiple fractions given per day. Patients who were reirradiated received significantly higher doses (mean ERD of 148 Gy 2) than those who had a single course of treatment (mean ERD of 121 GY 2 p = 0.001. Conclusion : We conclude that the risk of radiation myelopathy following conventionally fractionated radiotherapy to the spinal cord is extremely small; giving multiple fractions per day reduces the spinal cord tolerance; latent time to myelopathy decreases following retreatment; and there is possible long-term recovery of radiation damage in the human spinal cord.

ESCA investigation of SnOx films used as gas sensors

AbstractThe electronic properties of amorphous and ion‐implanted polycrystalline SnO2 films have been studied using x‐ray photoemission spectromicroscopy. First, we analysed the degree of oxidation and the homogeneity of as‐deposited films. The SnO and SnO2 phases were identified from their valence band spectra rather than from the Sn 3d core level spectra. Then we studied the damage effects due to the implantation of Pd+ and Ga+ ions in polycrystalline films. The ion bombardment of SnO2 films results in drastic changes of valence‐band spectra which is correlated to compositional changes. Annealing in air at 600 °C for 4 h leads to complete recovery of radiation damage. However, after such thermal annealings, the film surface still contains a relatively high amount of SnO (5–10%).

Boron and Phosphorus Ion Implantation In a-SixC1−x:H Thin Films

ABSTRACTIn this paper we report results on the optoelectronic and structural properties of device-quality a-SixC1−x:H intrinsic films with energy gap of 1.94 eV and Urbach energy of 70 MeV, grown by PECVD of SiH4+CH4 Mixture, which have been doped by means of boron or phosphorus ion implantation. Doping levels varied in the range 1018 to 5×1020 atoms/cm3. The behaviour of electrical characteristics, as well as energy gap and defect density, Measured on samples annealed in the range 150–400°C, showed that the optimum annealing temperature for the recovery of radiation damage is in the range 250–270°C independent of the implanted dose. Our results also show that after ion implantation and annealing, an increase of the SiH bonds concentration is detected, which is associated to a decrease of the contribution of SiH2, SiCH3, and SiCH vibrations in IR spectra.