Some 14 MeV neutron sputtering characteristics of a polycrystalline Nb sample

A sample of cold-rolled, polycrystallinc niobium was exposed to a fluence of 1.5 X 10 14 MeV neutrons/cm. Material sputtered from this sample was collected on a single crystal silicon disk placed in close juxtaposition to the Nb target. The collector was examined by three techniques, IMMA, SEM and Rutherford back-scatter of He ions. The sputtered material was found to be in two forms. The entire collector was covered with a background of “atomically” sputtered material. Superimposed on this were a number of irregular areas of high Nb concentration, patches or clusters of sputtered Nb atoms. When the total sputter yield is calculated from both of these forms a value of the order of 2–5 × 10^?5 is obtained.     

The disordering of Zr3Al by 1 MeV electron irradiation

The effect of 1 MeV electron radiation on the L1₂ ordered intermetallic compound, Zr₃Al, has been studied over the temperature range 130–775 K, using a high voltage electron microscope. At temperatures in the range 130–375 K, complete disorder was produced by irradiation to a dose of approximately one displacement per atom (dpa), independent of damage rate over the range 5 × 10^?4 to 5 × 10^?3 dpa/s. After irradiation to a few dpa at higher temperatures, 575–775 K, a steady-state was established which was characterized in part by an intermediate degree of long-range order which increased with irradiation temperature. By comparison with published results from ion irradiation experiments, it appears that the number of atomic displacements to cause complete disordering at low temperatures is independent of the nature of the damage events. At the higher temperatures, neither dislocation loops, dislocation networks nor voids were observed. Generally, the crystalline perfection was markedly reduced at all temperatures by irradiation to doses exceeding a few dpa.     

The irradiation creep of nickel and AISI 321 stainless steel during 4 MeV proton bombardment

An apparatus has been developed to study the creep of thin metal specimens under tensile stress during bombardment by 4 MeV protons from the Harwell Van de Graaff Accelerator. The specimen is held in a helium atmosphere and the proton beam reaches it through a thin metal window at the end of the accelerator beam line. The proton beam passes through the thin (25 μm) specimen, losing ~1.5 MeV in the process (most of which contributes to heating the specimen) and creating almost uniform radiation damage at the rate of $\text{(1–10) × 10}{}^{\mathrm{?7}}$ displacements per atom per second (dpa s^?1). The specimen temperature is monitored by infra-red pyrometry and controlled to ± 0.2°C by additional DC heating via the infra-red pyrometer output to compensate for ion beam fluctuations. The irradiation creep strain of the specimen is continuously measured with a sensitivity of $\text{5 × 10}{}^{\mathrm{?6}}$ by a linear variable differential transformer. Irradiation times up to about 100h with reasonable beam stability are possible. Results are presented of the irradiation creep behaviour of pure Ni and both solution treated and cold-worked AISI 321 stainless steel bombarded in the temperature range 400–600°C under tensile stresses in the range 20–250 MPa.     

Effects of neutron irradiation on polymer matrix composites at 5 K and at room temperature: II. Degradation of mechanical properties

Neutron irradiation with a low flux of accompanying γ-rays in the Intense Pulsed Neutron Source was carried out at 5 K and at room temperature on four kinds of polymer matrix composites (filler: E-glass or carbon fiber cloth; matrix: epoxy or polyimide resin). The specimen irradiated at 5 K was warmed up to room temperature before the mechanical test was performed at 77 K. The Young's modulus of these composites scarcely decreases even when a total neutron fluence is 3.0 × 10¹⁸n/cm² (2.1 × 10¹⁸n/cm² for E > 0.1 MeV) for the 5 K irradiation and 1.6 × 10¹⁹n/cm² (8.0 f 10¹⁸ n/cm² for E > 0.1 MeV) for the room-temperature irradiation. The ultimate strength, however, decreases significantly at this neutron fluence for all the composites except the carbon/epoxy composite whose initial strength is comparatively low. Comparison of this result with that obtained for ⁶⁰Co γ-ray irradiation demonstrates that the radiation sensitivity of the glass/epoxy and glass/polyimide composites is 1.8–2.6 times higher towards neutrons than γ-rays. As to the irradiation temperature of 5 K and room temperature, no significant influence on the degradation efficiency of the composite strength is observed under the present conditions of mechanical test.     

The characteristics of 15 MeV and fission neutron damage in niobium

Displacement damage by 15 MeV (d-Be source) and fission neutrons at 30°C in high purity niobium single crystals has been studied by transmission electron microscopy. The fluence of the 15 MeV neutrons was 1.8 × 10¹⁷n/cm² and the fluence of the fission neutrons (5 × 10¹⁷ n/cm²) was chosen so that samples from both types of irradiations had approximately the same damage energy. In both 15 MeV and fission neutron irradiated specimens, the loops were observed to be about $\text{2}\text{3}$ interstitial and $\text{1}\text{3}$ vacancy type. The analysis of Burgers vectors of the dislocation loops showed that more than $\text{2}\text{3}$ of the loops were perfect $\text{a}\text{2}\text{〈111〉}$ and that the rest were $\text{a}\text{2}\text{〈110〉}$ faulted. It is concluded that at equal damage energies, the detailed nature of the damage is the same for 15 MeV and fission neutron irradiated niobium.     

Microstructural evolution in medium copper low alloy steels irradiated in a pressurized water reactor and a material test reactor

A533B steels containing 0.12% and 0.16% Cu were irradiated to 3×10²³ and 6×10²³ n/m² (E>1 MeV) at 290 °C in a pressurized water reactor (PWR) and a material test reactor (MTR). Microstructural changes were examined using atom probe, small angle neutron scattering, field emission gun scanning transmission electron microscopy and post-irradiation annealing (PIA) coupled with positron annihilation (PA) and hardness testing (Hv). Cu rich precipitates had a Cu enriched core with surrounding Ni, Mn and Si rich region and the atomic composition was Fe–(7–16)Cu–(2–8)Mn–(0–4)Ni–(0–4)Si. The size and number density of Cu rich precipitates and the residual Cu concentration in matrix were almost saturated at above 3×10²³ n/m². Low flux irradiation in PWR produced slightly larger precipitates of a lower density with a higher Cu concentration in the precipitates. PIA (PA and Hv) examination showed that vacancy type matrix defects after PWR irradiation were more stable and more effective for hardening than those after MTR irradiation.     

Low temperature fatigue crack propagation in neutron-irradiated type 316 steel and weld metal

The fast cycling fatigue crack propagation characteristics of type 316 steel and weld metal have been investigated at 380°C after irradiation to 1.72–1.92 × 10²⁰n/cm² (E>1 MeV) and 2.03×10²¹n/cm² (E>1 MeV) at the same temperature. With mill-annealed type 316 steel, modest decreases in the rates of crack propagation were observed for both dose levels considered, whereas for cold-worked type 316 steel irradiation to 2.03 ×10²¹ n/cm² (E>1 MeV) caused increases in the rate of crack propagation. For type 316 weld metal, increases in the rate of crack propagation were observed for both dose levels considered.The diverse influences of irradiation upon fatigue crack propagation in these materials are explained by considering a simple continuum mechanics model of crack propagation, together with the results of control tensile experiments made on similarly irradiated materials.     

Void formation in solution-treated aisi 316 and 321 stainless steels under 46.5 mev ni6+ irradiation

The swelling and radiation damage structure developed in solution-treated 316 and 321 stainless steels bombarded by 46.5 MeV Ni⁶⁺ ions in the Variable Energy Cyclotron (VEC) have been determined. Foils were pre-injected with 10^?5 a/a He at room temperature and subsequently bombarded by Ni⁶⁺ ions in the temperature range 450–750°C at a damage rate of 1–3 × 10^?3 dpa per second to doses up to 300 dpa and specimens from the foils were examined by transmission electron microscopy. The data obtained were compared with data from other experiments aimed at simulating the fast-neutron irradiation of 316 and 321 steels, in particular previous work with 20 MeV C²⁺ ions and with data on fast-reactor bombarded material. The swelling rates in Ni-ion bombarded specimens were about a factor two less than those in C-ion bombarded specimens and in good agreement with swelling rates in 5 MeV Ni⁺- and neutron-bombarded material. The peak swelling temperature after a dose of 40 dpa was 650°C in 316 steel and 625°C in 321 steel where the swelling was about 5.8% and 4.6% respectively.     

Radiation damage and surface deformation effects on stainless steel produced by helium-ion bombardment

Radiation damage and surface deformation by neutrons to first-wall CTR materials were simulated by means of 3 MeV helium ions. The irradiation was performed at a CIP cyclotron, with beam intensities of 1–2 μA at room temperature. We have irradiated commercial Romanian, Soviet and Japanese stainless steels (W 4016, 12KH18N10T, W 4541) at doses between 2 × 10¹⁷ and 6 × 10¹⁸ ions per cm². The exfoliations were investigated by means of a TEMSCAN 200-CX electron microscope and a metallographic ORTHOPLAN POL LEITZ microscope. The main post-irradiation characteristics for each type of stainless steel (critical doses for exfoliation, dominant surface morphologies) are discussed. An irradiation facility for obtaining a homogeneous distribution of damage for 27 MeV helium ions (rotating energy degrader) is also presented.     

Measurement of the thermoluminescent response (supralinearity and efficiency) of LiF : Mg,Ti exposed to 0.7 MeV protons

The irradiation of LiF : Mg,Ti (TLD-100) chips by a defocused 0.7 MeV proton beam from an electrostatic accelerator has been achieved using radiochromic dye film to evaluate the beam transversal intensity distribution. The dose-response has been measured at fluences between 2.4 × 10⁸ and 5.7 × 10¹¹ p/cm² and peaks 3–9 show linear-supralinear-sublinear response. The efficiency, relative to ⁶⁰Co γ-rays, measured for the total thermoluminescent (TL) signal and peaks 5 and 7, equals 0.33, 0.22 and 1.4, respectively. The comparison of these and other low-energy data for peak 5 with Track Structure Theory (TST) efficiency calculations indicate that the latter must take into account the stopping of the incident ions in the dosimeter to achieve a reasonable agreement with the observations. In general, neither TST, nor Modified Track Structure Theory (MTST) are able to simultaneously predict the response to 5.3 MeV α-particles and 0.7 MeV protons for all the studied glow curve peaks. Track Interaction Model (TIM) and Unified Track/Defect Interaction Model. (UNIM) calculations of the supralinearity function f(D) of peaks 5 to 8 for 5.3 MeV α-particles and peaks 5 to 9 for 0.7 MeV protons, qualitatively describe the general trends measured in this work; only the UNIM agrees quantitatively with the data in both systems.     

Doping of 6H–SiC pn structures by proton irradiation

The influence of proton irradiation on current–voltage characteristics, N_d − N_a values and parameters of deep centres in 6H–SiC pn structures grown by sublimation epitaxy has been studied. The irradiation was carried out with 8 MeV protons in the range of doses from 10¹⁴ to 10¹⁶ cm⁻². Irradiation with a dose of 3.6 × 10¹⁴ cm⁻² leaves the voltage drop at high forward currents (10 A/cm²) practically unchanged. For higher irradiation dose of 1.8 × 10¹⁵ cm⁻², the forward voltage drop and the degree of compensation in the samples increased ; partial annealing of the radiation defects and partial recovery of the electrical parameters occurred after annealing at T∼400–800 K. Irradiation with a dose of 5.4 × 10¹⁵ cm⁻² resulted in very high resistance in forward biased pn structures which remained high even after heating to 500°C. It is suggested that proton irradiation causes decreasing of the lifetime and formation of an i- or an additional p-layer.     

Irradiation-creep in a materials testing reactor

Helical springs made from titanium, zirconium, Nimonic PE 16 alloy and two austenitic stainless steels namely Firth-Vickers FV 548 and a steel with a composition within the AISI 316 specification have been irradiated in the Dounreay Materials Testing Reactor, at temperatures between 85 °C and 100 °C and to neutron fluences up to about 4 × 10²⁴ m^?2 (> 1 MeV), whilst loaded in tension. Irradiation-creep was observed in all the materials studied and initial strain rates/unit stressneutron ranged from 1 to 1.9 × 10^?35 m⁴/N for Nimonic PE 16 and zirconium respectively. Data obtained from an earlier experiment are re-presented and compared with the present results.Springs which received no heat-treatment after coiling unwound during irradiation at rates which were independent of the supported loads. The phenomenon is attributed to the relaxation of internal stresses (produced during the manufacture of the springs) with an irradiation-creep constant which is an increasing function of prior cold-work.A mechanism of irradiation-creep is proposed which involves the re-arrangement of the dislocation network in a crystal as the dislocations climb by absorbing interstitials produced by irradiation.     

Theory of irradiation induced growth of fatigue cracks

A new type of irradiation damage is considered. It is proposed that the localized stresses that fluctuate both with time and with position in solids subjected to bombardment by energetic neutrons (or ions) can cause pre-existing cracks to grow in the same manner that fatigue cracks grow. Using a suitably modified Paris equation for fatigue crack growth it is calculated that cracks in niobium subjected to bombardment by 14 MeV neutrons grow at a rate of about 5 × 10^?10 m per stress pulse exerted at the crack tip. This growth rate is at the threshold level measured in conventional fatigue crack growth experiments. Thus it is not certain whether indeed cracks in irradiated solids will grow. If cracks do grow by the proposed fatigue mechanism they may seriously limit the life of the first wall material of fusion reactors. The crack growth mechanism cannot explain the chunk formation observed in the experiments of Kaminsky et al. but they might explain chunk formation under fluences many orders of magnitude greater than used by them.     

Design a 10 kJ IS Mather Type Plasma Focus for Solid Target Activation to Produce Short-Lived Radioisotopes 12C(d,n)13N

A 10 kJ (15 kV, 88 μF) IS (Iranian Sun) Mather type plasma focus device has been studied to determine the activity of a compound exogenous carbon solid target through ¹²C(d,n)¹³N nuclear reaction. The produced ¹³N is a short-lived radioisotope with a half-life of 9.97 min and threshold energy of 0.28 MeV. The results indicate that energetic deuterons impinging on the solid target can produce yield of $ \langle y\rangle $  = 6.7 × 10^?5 with an activity of A = 6.8 × 10⁴ Bq for one plasma focus shut and A _ν  = 4 × 10⁵ Bq for 6 shut per mint when the projectile maximum deuterons energy is E _max = 3 MeV.     

Effect of microstructure on irradiation creep and growth of zircaloy pressure tubes in power reactors

Cold-worked zircaloy pressure tubes fabricated by eight different routes and irradiated in four power reactors have diametral strain rates varying from ?1 to 11 × 10^?29 m²/n (>1 MeV) and elongation rates varying from 5 to 16 × 10^?29 m²/n (>1 MeV). X-ray diffraction and optical metallography show large differences in crystallographic texture, dislocation density and grain shape amongst the eight types of tubes. A quantitative correlation of the elongation and diametral rates of seven types of tubes with their texture, grain shape and dislocation density is developed assuming additive creep and growth components. The derived magnitudes of the creep and growth components in the pressure tube agree with published uniaxial creep and growth data for cold-worked zircaloy. The growth rate is approximately proportional to dislocation density and increases in a given direction as the grains become more elongated in that direction and as the proportion of basal plane normals in that direction decreases. The creep rate is insensitive to dislocation density. For internally pressurized tubes the diametral creep rate increases and the axial creep rate decreases as the proportion of basal plane normals in the radial direction increases. The model developed to describe the total long term dimensional changes of the pressure tubes successfully predicts the diametral and longitudinal rates for tubes which experienced end loads during operation.     

Low temperature fatigue crack propagation in neutron-irradiated type 316 steel and weld metal

The fast cycling fatigue crack propagation characteristics of type 316 steel and weld metal have been investigated at 380°C after irradiation to 1.72?1.92 × 10²⁰ n/cm²($\text{E > 1}$ MeV) and 2.03 × 10²¹ n/cm² ($\text{E > 1}$ MeV)at the same temperature. With mill-annealed type 316 steel, modest decreases in the rates of crack propagation were observed for both dose levels considered, whereas for cold-worked type 316 steel irradiation to 2.03 × 10²¹ n/cm² ($\text{E > 1}$ MeV) caused increases in the rate of crack propagation. For type 316 weld metal, increases in the rate of crack propagation were observed for both dose levels considered.The diverse influences of irradiation upon fatigue crack propagation in these materials are explained by considering a simple continuum mechanics model of crack propagation, together with the results of control tensile experiments made on similarly irradiated materials.     

Magnetic properties of a highly neutron-irradiated nuclear reactor pressure vessel steel

We report results of minor B–H loop measurements on a highly neutron-irradiated A533B-type reactor pressure vessel steel. A minor-loop coefficient, which is a sensitive indicator of internal stress, changes with neutron fluence, but depends on relative orientation to the rolling direction in the low fluence regime. At a higher fluence of ～10 × 10²³ m^?2, on the other hand, an anomalous increase of the coefficient was detected irrespective of the orientation. The results were interpreted as due to competing irradiation mechanisms of the formation of Cu-rich precipitates, recovery process, and the formation of late-blooming Mn–Ni–Si-rich clusters.     

Argon ion impact desorption cross sections of chlorine and carbon from molybdenum

Total desorption cross sections have been measured for Cl (σ_Cl) and C(σ_C) on molybdenum by argon ion bombardment for an incidence angle of 60° from the surface normal. For the bombardment an ion gun with low current density (i₀ ~ 1 × 10 ^?7 A cm^?2) at low system pressure (~10^?9 Torr) was used. The detection was performed by AES and the data were sensitivity factor corrected. The AES analysis of the surface after adsorption showed that Mo, C and Cl contributed to more than 94% of the atomic composition. With known i₀, it is possible to obtain σ from the adsorbate signal vs ion bombardment time curve. For ion energies between 0.2 keV to 1.0 keV the measured value for σ_Cl and σ_C are 0.5?3 × 10^?15 cm² and 0.2?4 × 10^?15 cm², respectively. The possible effects of the surface roughness due to prebombardment are discussed.     

Micro-Raman studies of swift heavy ion irradiation induced structural and conformational changes in polyaniline nanofibers

Polyaniline (PAni) nanofibers doped with camphor sulfonic acid have been irradiated with 90 MeV O⁷⁺ ions at different fluences (3 × 10¹⁰?1 × 10¹² ions/cm²) using a 15UD Pelletron accelerator under ultra-high vacuum. XRD studies reveal a decrease in the domain length and an increase in the strain upon SHI irradiation. The increase in d-spacing corresponding to the (1 0 0) reflection of PAni nanofibers with increasing irradiation fluence has been attributed to the increase in the tilt angle of the chains with respect to the (a, b) basal plane of PAni. Decrease in the integral intensity upon SHI irradiation indicates amorphization of the material. Micro-Raman (μR) studies confirm amorphization of the PAni nanofibers and also show that the PAni nanofibers get de-doped upon SHI irradiation. μR spectroscopy also reveals a benzenoid to quinoid transition in the PAni chain upon SHI irradiation. TEM results show that the size of PAni nanofibers decreases with the increase in irradiation fluence, which has been attributed to the fragmentation of PAni nanofibers in the core of amorphized tracks caused by SHI irradiation.