Pre-irradiation Heat Treatment Research Articles

Modification of recovery from radiation damage by hyperthermia in yeast

Recovery from radiation damage was studied in the diploid yeast Saccharomyces cerevisiae BZ 34 subjected to pre-irradiation, post-irradiation or simultaneous hyperthermic treatment. Pre-irradiation heat treatment at 51 degrees C for 20 m min sensitized the cells to lethal damage; however, these cells could efficiently recover from potentially lethal damage (PLD) on liquid holding. In contrast, post-irradiation hyperthermia (51 degrees C for 20 min or 52 degrees C for 15 min) partially inhibited recovery from PLD. For treatments at 40 and 45 degrees C the inhibition of recovery was restricted to the duration of heat treatment. As soon as the temperature of the cells was reduced to 30 degrees C for 48 h, they showed a significant recovery from PLD. The kinetics of the liquid holding recovery of cells exposed to 600 and 900 Gy of radiation followed by heat treatment at 51 degrees C, 20 min or 52 degrees C, 15 min was studied. Post-irradiation heat treatment inhibits PLD repair (PLDR) during the first 3 h. Subsequent liquid holding for longer durations results in recovery from PLD, reaching a maximum of nearly 50% of that obtained in cells exposed to radiation alone. When the cells were held for 0-48 h between radiation and heat treatment, they showed recovery from radiation damage such that sensitization by subsequent heat treatment was reduced significantly over the 48 h interval. The inhibition of PLDR by hyperthermia also decreases progressively with an increase in the time interval between the two treatments. When both heat and radiation treatments were carried out simultaneously by irradiating the cells at 48 degrees C, the inhibition of PLDR was partial. The recovery factor, calculated as the ratio of survival after recovery to that on immediate plating (without PLDR), was 2.6 +/- 0.9 for simultaneous heat and radiation treatment compared to 11.9 +/- 2.7 for radiation alone.

Irradiation growth in zirconium and its alloys

The UKAEA Northern Research Laboratories (Risley) have recently completed an underlying research study on irradiation growth in zirconium and its alloys. During this study, irradiation growth measurements have been made on a range of well-characterized single-crystal and polycrystalline iodide zirconium, commercial alloys Zircaloy-2 and Zr-2.5 wt% Nb, and high-purity zirconium-tin alloys in different metallurgical conditions following irradiation in the DIDO reactor at AERE Harwell. Irradiations were performed in three rigs operating at irradiation temperatures between 353 and 673 K. An important feature of the experimental programme was the capability to perform repeat length measurements on individual growth specimens at intervals during their irradiation programme. This facility has allowed accurate monitoring of the growth phenomenon and changes in growth behaviour induced by the combined effects of irradiation temperature and accumulated fast neutron dose over large dose ranges. This paper reviews the main experimental results from this programme and discusses them in terms of current understanding of the growth process. Thus, it has been observed that, in annealed Zircaloy-2 at temperatures between 553 and 673 K, a transition from saturating growth to accelerating growth rates occurs with increasing dose. The dose above which this “growth breakaway” takes place is seen to be inversely dependent on irradiation temperature in mis temperature range. The well-documented difference in growth behaviour between annealed and cold-worked Zircaloy-2 observed at relatively low irradiation temperatures, in which cold-worked material grows at a high linear rate over large dose ranges, is not observed at 673 K. Comparison is made with reported results on similar material irradiated in other irradiation facilities. The growth data are interpreted in terms of recent theories regarding the development during fast neutron irradiation of a cold-worked microstructure consisting of 〈 a〉- and 〈 c〉-type dislocations. Irradiation growth behaviour of annealed polycrystalline iodide zirconium between 353 and 673 K contrasts strongly with that in annealed Zircaloy-2 with low irradiation growth rates being observed over a large dose and temperature range. The influence of key irradiation parameters on the growth process have been examined in a series of studies initiated as part of a collaborative programme with AECL Chalk River Nuclear Labs. Final results from the studies on annealed and deformed single-crystal zirconium are reported here. They show that growth saturates rapidly at low dose in annealed single-crystal material irradiated at 353 and 553 K but that a gradual increase in growth strain is observed on irradiation to high dose at 553 K. Single-crystal specimens heavily swaged prior to irradiation at 353 K and given different pre-irradiation heat-treatments exhibit high near-linear or accelerating growth rates. These growth data are interpreted in terms of the importance of grain boundaries and twin boundaries as sinks for point defects which allow point defect separation and hence growth to continue to high dose. Finally, the results of growth experiments performed on Zr-0.1% Sn and Zr-1.5% Sn alloys at 353 and 553 K are reviewed. These experiments confirm the important role played by alloying additions and impurities on the growth process in zirconium and Zircaloy-2.

DNA Lesions in Hyperthermic Cell Killing: Effects of Thermotolerance, Procaine, and Erythritol

When HeLa S3 cells were subjected to 45 degrees C hyperthermia, DNA lesions were detected by the use of the alkaline unwinding/hydroxylapatite method. The number of lesions formed was not affected when the cells were made thermotolerant by either an acute (15 min 44 degrees C + 5 h 37 degrees C) or a chronic (5 h 42 degrees C) pretreatment before 45 degrees C hyperthermia. The presence of 10 mM procaine (heat sensitizer) or 0.5 M erythritol (heat protector) during hyperthermia also had no effect on the rate of formation of heat-induced alkali labile DNA lesions. These observations do not support a concept where DNA lesions are considered to be the ultimate cause of hyperthermic cell killing. Both drugs, however, influenced the rate of repair of radiation-induced strand breaks when present during preirradiation heat treatment. We conclude that the initial number of heat-induced alkali labile DNA lesions is not directly related to cell survival. It cannot be excluded, however, that differences in posthyperthermic repair of these lesions may lead to a positive correlation between residual DNA damage and survival after the different experimental conditions.

Low-dose neutron-irradiation damage in α-iron

Irradiation damage structures induced in α-iron by low-dose fisson-neutron irradiation at reactor ambient temperature have been investigated by transmission electron microscopy. Materials of three purities were irradiated to doses between 10 22 and 10 24 neutrons (with E > 1 MeV) m −2 in the PLUTO experimental reactor at Harwell. In a high-purity iron no visible damage was observed below a dose of 8 × 10 22 neutrons m −2. Above this dose the damage was restricted to the decoration of in-grown dislocations and low-angle boundaries by dislocation loops. No visible damage was found in the less pure materials after irradiation to doses < 3 × 10 23 neutrons m −2, although in the as-received iron the α″-nitride precipitates which were formed by the pre-irradiation heat treatment, redissolved during the irradiation; the dissolution being complete after an irradiation of 3 × 10 23 neutrons m −2. The results of post-irradiation annealing are also reported.

Factors Influencing Radiation Resistance of Vegetative Bacteria and Spores Associated with Radappertization of Meat

ABSTRACTThe influence of some factors involved in radappertization of meats on the radiation resistance of two isolates of Moraxella‐Acinetobacter (M‐A), Microcodes radiodurans, Escherichia coli, and Bacillus cereus spores was determined. Combinaton of subfreezing temperature and lyophilization increased the resistance of vegetative cells and showed M‐A isolates to be most resistant. Cells lyophilized in ground beef were less resistant than cells lyophilized in a commercial culture medium. A preirradiation heat treatment prior to lyophilization sensitized the cells to radiation. No appreciable difference in resistance was found with the presence of up to 8% sodium chloride during irradiation of M‐A and M. radiodurans. The radiation resistance of B. cereus spores was not affected by changes in temperature, drying, or suspending medium to the same extent as were the vegetative cells. B. cereus spores were more resistant at ambient temperature than at ‐30 ± 10°C. All these factors must be considered in assessing the magnitude of radiation resistance of various organisms, be cause there is no predictable pattern of radiation resistance.

Hyperthermic Enhancement of Radiation Cell Killing in HeLa S3 Cells and Its Effect on the Production and Repair of DNA Strand Breaks

Cell killing and the induction and repair of DNA strand breaks have been examined after hyperthermia and electron irradiation treatments of HeLa S3 cells. Heat alone did not produce any detectable DNA strand breaks. Preirradiation heat treatment did not alter the initial levels of radiation-induced DNA strand breaks. However, the subsequent rate and extent of DNA strand break repair were significantly reduced by preirradiation heat treatments of 44/sup 0/C for 30 or 60 min. When a time gap of up to 1 h was introduced between heating and irradiation there was no significant reduction of the thermal enhancement effect for cell killing or recovery from the reduced ability to repair DNA strand breaks.

Solute segregation to point-defect sinks in neutron-irradiated nimonic PE16

Nimonic PE16, a gamma-prime Ni 3(Al,Ti) precipitate-strengthened alloy under consideration for fast reactor structural applications, has been neutron irradiated in three heat treatment conditions: solution treated, aged, and overaged. After irradiation at 600° C to 5.4 × 10 22 n/ cm 2 ( E > 0.1 MeV), or 27 dpa, specimens were characterized for gamma-prime precipitate stability by transmission electron microscopy. The precipitate microstructures after irradiation reflected the influence of the preirradiation heat treatment; and indeed the precipitate particles present prior to irradiation remained stable. However, additional precipitation occurred during irradiation in each of the specimens examined. The in-reactor gamma-prime precipitation process decorated such microstructural features as voids, dislocations and carbide precipitates. Examples were found in the solution-treated condition where gamma prime in the form of Archimedes' screws had precipitated on climbing screw dislocations. The precipitation behavior observed is compared with predictions from existing models. It is concluded that models for solute diffusion to point-defect sinks and for Ostwald coarsening can account for the observations, but that the models for precipitate stability controlled by cascade dissolution during neutron irradiation do not.

The effects of cold working and pre-irradiation heat treatment on void formation in neutron-irradiated type 316 stainless steel

Abstract The effect of fast-neutron irradiation on void formation in Type 316 stainless steel having undergone specific thermalmechanical treatments was investigated by transmission electron microscopy. The study showed that, for irradiation at the three lower temperatures (420, 475 and 580°C): (1) the void volume decreased with increasing cold work; (2) the reduction in swelling was due to a decrease in both void-number density and void size; (3) the decrease in void size with increasing cold-work level was enhanced at higher irradiation temperatures; (4) cold working from 0 to 10% decreased the voidnumber density, and void volume, more than in the range from 10 to 20%; (5) void formation in the 20% cw steel which had been heat treated 100 h at 650°C before irradiation was similar to that of the solution-treated steel. The temperature dependence of swelling of the cold-worked material was different from that of the solution-treated steel. Irradiation at 650°C resulted in a larger void volume in the cold-worked material than for irradiation at 475 or 580°C. The effects of cold work and irradiation temperature on void growth are consistent with the predictions of a diffusion-controlled model.

Electron microprobe analysis of HgTe thin films : A. Szummer and S. A. Ignatowicz. Electron. Technol.4, No. 1/2 (1971), p. 227

The UKAEA Northern Research Laboratories (Risley) have recently completed an underlying research study on irradiation growth in zirconium and its alloys. During this study, irradiation growth measurements have been made on a range of well-characterized single-crystal and polycrystalline iodide zirconium, commercial alloys Zircaloy-2 and Zr-2.5 wt% Nb, and high-purity zirconium-tin alloys in different metallurgical conditions following irradiation in the DIDO reactor at AERE Harwell. Irradiations were performed in three rigs operating at irradiation temperatures between 353 and 673 K. An important feature of the experimental programme was the capability to perform repeat length measurements on individual growth specimens at intervals during their irradiation programme. This facility has allowed accurate monitoring of the growth phenomenon and changes in growth behaviour induced by the combined effects of irradiation temperature and accumulated fast neutron dose over large dose ranges.This paper reviews the main experimental results from this programme and discusses them in terms of current understanding of the growth process.Thus, it has been observed that, in annealed Zircaloy-2 at temperatures between 553 and 673 K, a transition from saturating growth to accelerating growth rates occurs with increasing dose. The dose above which this “growth breakaway” takes place is seen to be inversely dependent on irradiation temperature in mis temperature range. The well-documented difference in growth behaviour between annealed and cold-worked Zircaloy-2 observed at relatively low irradiation temperatures, in which cold-worked material grows at a high linear rate over large dose ranges, is not observed at 673 K. Comparison is made with reported results on similar material irradiated in other irradiation facilities. The growth data are interpreted in terms of recent theories regarding the development during fast neutron irradiation of a cold-worked microstructure consisting of 〈a〉- and 〈c〉-type dislocations.Irradiation growth behaviour of annealed polycrystalline iodide zirconium between 353 and 673 K contrasts strongly with that in annealed Zircaloy-2 with low irradiation growth rates being observed over a large dose and temperature range.The influence of key irradiation parameters on the growth process have been examined in a series of studies initiated as part of a collaborative programme with AECL Chalk River Nuclear Labs. Final results from the studies on annealed and deformed single-crystal zirconium are reported here. They show that growth saturates rapidly at low dose in annealed single-crystal material irradiated at 353 and 553 K but that a gradual increase in growth strain is observed on irradiation to high dose at 553 K. Single-crystal specimens heavily swaged prior to irradiation at 353 K and given different pre-irradiation heat-treatments exhibit high near-linear or accelerating growth rates. These growth data are interpreted in terms of the importance of grain boundaries and twin boundaries as sinks for point defects which allow point defect separation and hence growth to continue to high dose.Finally, the results of growth experiments performed on Zr-0.1% Sn and Zr-1.5% Sn alloys at 353 and 553 K are reviewed. These experiments confirm the important role played by alloying additions and impurities on the growth process in zirconium and Zircaloy-2.

Behavior of Helium Gas Bubbles in Neutron-Irradiated Beryllium

Transmission electron microscopic observations were made on hot-rolled Be sheet prepared from cast ingots irradiated to about 5 × 1019 nvt(fast) in JRR-2. The aim of the study was to elucidate the effect of irradiation on changes in microstructure and the effect of pre-irradiation heat treatment on the formation of He gas bubbles during post-irradiation annealing. The formation and growth of He bubbles during post-irradiation annealing was distinctly less inhibited in the Be irradiated as hot-rolled than in the metal irradiated after recrystallization treatment. In the former case, He bubbles could be observed upon post-irradiation treatment of only 3hr at 750°C, while in the latter case, a similar formation of bubbles could, only be seen after a final treatment at 900°C for 50 hr. The difference thus observed in the tendency of bubble formation depends upon the grain boundary mobility during post-irradiation heat treatment. The nucleation and growth of bubbles occurred preferentially at the grain boundar...

Influence of Preirradiation Heat Treatment on the Postirradiation Ductility of Stainless Steel

The ductility of irradiated structural alloys is of concern in reactor design. The purpose of this study is to determine some of the parameters affecting such ductility. Type-304 stainless steel ha...

The effect of pre-irradiation heat treatment and a brief postirradiation beta anneal on swelling of alpha uranium

The effect of pre-irradiation heat treatment and of a brief postirradiation anneal at a temperature in the beta range on the swelling of irradiated uranium during annealing at 620° C is described. The experimental data show that irradiated specimens deformed and recrystallized before irradiation decrease in density on annealing at 620° C substantially more than irradiated specimens quenched from a beta temperature before irradiation for burnups greater than 0.04 %. The data also show that extensive swelling of irradiated uranium on annealing at 620° C can be minimized by a prior brief anneal of the irradiated uranium in the beta phase. The interpretation of these results is supported with photomicrographs of the swelled specimens.

The Effects of Preirradiation and Postirradiation Temperature Treatments on the X-Ray Sensitivity of Seeds of Hordeum

Dry (approximately 4% water content) seeds of Himalaya barley, when heated prior to irradiation, underwent little or no storage injury; also, the increase in injury due to aerobic hydration was as great 48 hours after irradiation as it was immediately thereafter. The effectiveness of preirradiation heat-treatments in reducing seedling injury depended on both the length of the heat-treatment and the temperature; it had no effect if hydration intervened between heating and irradiation. Postirradiation storage of seeds at elevated temperatures (75 deg C) caused an increase in injury over short storage periods but brought about a thermorecovery over longer storage periods. Preliminary experiments with acute postirradiation heat-treatments indicated that they, like preirradiation heat-treatments, decreased the amount of injury throughout the storage period. lrradiated seeds stored at dry ice temperature (- 78 deg C) showed virtually no increase in injury over long storage periods, and, as with preirradiation heat-treated seeds, they retained their sensitivity to aerobic hydration. The effects of preirradiation heat-treatment and postirradiation storage over a wide range of temperatures on the response of irradiated seeds to storage and to aerobic hydration, when combined with earlier work on these two parameters, suggest that they are alternative ways of magnifying a primarymore » radiation event. (auth)« less

INACTIVATION OF THE RADIATION-RESISTANT SPOILAGE BACTERIUM MICROCOCCUS RADIODURANS. II. RADIATION INACTIVATION RATES AS INFLUENCED BY MENSTRUUM TEMPERATURE, PREIRRADIATION HEAT TREATMENT, AND CERTAIN REDUCING AGENTS.

The R(1) strain of Micrococcus radiodurans, previously determined to be more resistant than three other strains exposed to gamma radiation, was studied further to determine the influence of certain environmental factors on resistance to radiation inactivation. The frozen state offered insignificant protection to the organisms irradiated in raw puréed beef. Resistance was reduced by higher menstruum temperatures (40 and 50 C) during irradiation. Preirradiation heat treatment was found to lower resistance to subsequent irradiation. When the cells were irradiated in buffer at pH 5, 7, or 9, no differences in resistance were noted. Cell suspensions in buffer were protected to some extent by cysteine but not by thioglycolate. Ascorbate enhanced radiation inactivation.

Influence of temperature and phase state on x-ray sensitivity of yeast

1. 1. The radiosensitivity of haploid yeast increases slowly for increased irradiation temperatures in the range from 0 to 40 ° with a temperature coefficient of 0.0034/deg. 2. 2. At temperatures where heat inactivation of yeast becomes important (50 ° and above), there is a greatly increased radiosensitivity. 3. 3. Additivity studies using heat and x-rays show that heat applied during irradiation is most effective in killing yeast; preirradiation heat treatment is more effective than postirradiation heat treatment. However, delays between consecutive treatments with heat and x-rays allow the cell to recovery possibly because of some metabolic processes. 4. 4. Supercooled (−0.5 to −10 °, liquid phase) yeast suspensions have the radiosensitivity characteristic of the temperature region from 0 to 40 °. 5. 5. Yeast suspensions irradiated at −10 °, solid phase, are approximately twice as resistant to x-rays as yeast suspensions irradiated at −10 °, liquid phase. This difference is believed to be due to a decrease in the diffusion of irradiation “poisons” in the solid phase. 6. 6. In the region from −10 to −0.5 °, solid phase, the sensitivity of yeast to x-rays increases approximately linearly with temperature. This may be due to an increasing amount of free water within the cell. 7. 7. There is no significant change in the radiosensitivity from −10 to −30 °, solid phase; this suggests that inactivation of yeast for temperatures below −10 ° is due to the “direct action” of the radiations. 8. 8. The fact that there is no significant difference in the radiosensitivity at 0 ° and at −2.5 °, solid phase, indicates that diffusing poisons are largely produced within the cell. 9. 9. From the low-temperature studies it is believed that approximately half of the x-ray inactivation of haploid yeast in the temperature region from 0 to 40 ° is due to diffusing poisons. 10. 10. Supplementary studies on T2 bacteriophage give results that are consistent with the above interpretations.