Radiation Damage Studies Research Articles

Energetic heavy ion irradiation effect in Fe layers studied by Mössbauer spectroscopy

Mössbauer spectroscopy was applied to study radiation damage in evaporated Fe layers irradiated with 209 MeV 84Kr ions at room temperature. Significant differences have been shown between the Mössbauer spectra of the unirradiated and the irradiated samples. The increase of a nonmagnetic component of the spectra as well as a magnetic component around 270 kOe was observed due to the irradiation. The changes were also analysed using the hyperfine field distribution obtained from the spectra. The results can be interpreted as the formation and the increase of proportion of highly disordered phases in Fe layer due to irradiation with energetic heavy ions.

First results on radiation damage studies using n +/p/p + diodes fabricated with multi-guard ring structures

First measurements of silicon PIN diodes and multi-guard structures, fabricated from 10 k Ω cm p-type material in an n +/p/p + configuration are presented. Studies of the effects of irradiation with 2.0×10 14 p/cm 2 at 63.3 MeV on the charge collection efficiency, leakage current, and breakdown are presented, along with studies of different guard ring configurations.

Radiation damage studies on the optical and mechanical properties of plastic scintillators

This paper describes the radiation damage studies on a large volume plastic scintillator based in polystyrene doped with PPO and POPOP. The consequences on their mechanical and scintillation properties were evaluated before and after irradiation with different dose rates of 60Co gamma radiation, in several doses. The optical results show a significant difference in the radiation susceptibility, when the plastic scintillator is irradiated at low rate (0.1 kGy/h) with that irradiated at high dose rate (85 kGy/h). The losses in the optical and mechanical properties increase as the irradiation dose is increased. The damage evaluated by the transmittance, emission intensity, pulse height and tensile strength was normalized as a damage fraction and fitted by a bi-exponential function. It was observed that the damage for irradiation is not permanent and it obeys a bi-exponential function.

Radiation damage studies on Ni implanted with high energy He and D ions

The behavior of hydrogen isotopes in metals is very important for the future nuclear fusion reactor. To study deuterium influence on helium pre-irradiated nickel, 0–28 MeV He ++ and 7 MeV D + beams were used. Thirty, 100 and 300 appm He pre-implanted samples were D + (10 18 ions per cm 2) irradiated and 1, 10, 100 and 1000 h high vacuum annealed (1273 K). After an electrochemical preparation (Struers jet), they were examined by transmission electron microscopy (TEM). Values for He bubbles’ radii and densities depending on He ions’ doses and annealing periods are reported. Two types of bubbles were observed: ‘small’ bubbles, predominantly in the matrix (from 5 nm radius for 30 appm, 1 h annealing to 35 nm for 300 appm, 100 h annealing) and ‘large’ bubbles, predominantly in the grain boundaries regions, but even in some dislocations (from 30 nm radius for 30 appm, 1 h annealing to 120 nm for 300 appm, 100 h annealing). A unique bubble coarsening mechanism, the Ostwald ripening, is considered. The influence of deuterium on the ‘small’ and ‘large’ bubbles’ radii values is discussed.

The Complementary Nature of Electron Microscopy and ION Channeling for the Assessment of Radiation Damage Evolution in Ceramics

In ion irradiation damage studies on ceramics, damage evolution is often assessed using Rutherford backscattering spectroscopy and ion channeling (RBS/C) techniques. In a typical experiment, a single crystal ceramic sample is irradiated with heavy ions and then the crystal is exposed to He ions along a low-index crystallographic orientation. Simultaneously, the backscattered He ion yield is measured as a function of ion energy loss. For He ions scattered from the heavy ion irradiated volume, the He ion yield increases in proportion to the heavy ion dose. The RBS/C yield rises because the He ion beam is dechanneled by, for instance, interstitial point defects and clusters and their associated strain fields. A quantitative measure of dechanneling is denoted by χmin, defined as the ratio of the He ion yield along a low-index crystal orientation, to the yield obtained in a random (non-channeling) orientation. The damage parameter xmin varies from 0 to 1, where 1 represents the maximum damage level that can be measured by RBS/C.

Computer simulation of a 10 keV Si displacement cascade in SiC

The threshold energy for atomic displacement and the evolution of high-energy displacement cascades in β-SiC have been examined using molecular dynamics simulations. A modified form of the Tersoff potential was used in combination with a repulsive potential obtained from density functional theory to describe the interactions between the atoms. The evolution of lattice damage in a 10 keV Si cascade was studied for about 10 ps. The system size varied from 8000 atoms for the displacement energy calculations to 192,000 atoms for the cascade simulations. The results indicate that the minimum displacement energy is about 36 eV for Si and 28 eV for C. The cascade lifetime was found to be of the order of 0.1 ps, and the surviving C vacancies and interstitials outnumbered the corresponding Si defects by a factor of about 3. These results are discussed in light of previous theoretical and experimental studies of radiation damage in SiC.

Ion beam channeling study on the damage accumulation in yttria-stabilized cubic zirconia

The lattice damage kinetics of defect accumulation in ion irradiated yttria-stabilized cubic zirconia (YSZ) was investigated by using in situ Rutherford backscattering spectrometry and channeling (RBS/C) techniques. The samples of single crystalline YSZ were irradiated with 400 keV Xe ++ ions over a range of doses and for sample temperatures of 170 and 300 K. Under all irradiation conditions studied, the samples remained crystalline. However, lattice damage, as measured by the minimum yield, χ min, was observed to have three distinct stages (stages I–III) in the rate of accumulation. Energy dependent channeling experiments revealed −1 and 1 2 power dependence for the dechanneling parameter in stage I and stage III, respectively. Corresponding transmission electron microscopy (TEM) studies detected defects which appear as tiny dot contrasts in stage I samples, ultimately leading to the overlaps of dislocations at stage III. The three stages of damage accumulations have been interpreted as an evolving defect structure which changes the dominant RBS/C ion scattering process from direct scattering to dechanneling. A comparison between RBS/C and TEM techniques has also been made for the effective use of in situ RBS/C techniques for the study of radiation damage.

Non-ionising energy deposition of pions in GaAs and Si for radiation damage studies

The dependence of the displacement damage induced by pions in GaAs has been evaluated, in the energy range 50 –1000 MeV, using the Lindhard theory and parametrised values of the pion-nucleus interaction. The curves corresponding to the NIEL produced by protons, neutrons, and pions in Si and in GaAs intersect, in the limit of calculation errors, in the region 50 – 80 MeV, at a NIEL of 2 – 5.5 MeV cm 2 /g. The energy dependence of the NIEL of pions in Si and GaAs is discussed in correlation with the simulated pion spectra at new hadron colliders.

Properties of dispersion strengthened copper made by high energy milling : B.F.Kieback et al. (Technical University of Dresden, Germany.)

The effects of neutron irradiation on the electrical resistivity of precipitation hardened (PH) and dispersion strengthened (DS) copper alloys are discussed. The analysis is based on the experimental study of radiation damage of PH and DS copper alloys, irradiated in the fast neutron reactor BOR-60 with doses of 8–16 × 1025 n/m2 and in the mixed spectrum neutron reactor SM-2 with doses of 3.7–5.5 × 1025 n/m2. The experimental data on the change Δϱ in electrical resistivity of DS-type copper alloys irradiated in the BOR-60 reactor show that irradiation to 7–10 dpa at T = 340–450°C causes a drop in electrical conductivity by not more than 20%. The obtained results show that in mixed-spectrum reactors the rate of Δϱ normalized to the dpa is about 20 times as high as in fast neutron reactors. The conclusion is made that the calculations performed for ITER must take into account the presence of appreciable fluxes of thermal neutrons in certain components of the reactor. The latter will play a decisive role in the drop in thermal conductivity of copper alloys in these components.

A review of in situ observation of defect production with energetic heavy ions

In situ transmission electron microscopy (TEM) observation of radiation damage with energetic heavy ions has been a powerful tool for the study of radiation effects since it provides means to observe evolution of cascade damage. The objective of the present paper is to summarize the status of this experimental technique, its major achievement and current problems and to suggest the future directions. Defect accumulation by irradiation with energetic heavy particles is quite different from that with electron irradiation. Spatial and temporal fluctuations occur in defect production and annihilation. These observations will be summarized together with the dependence of damage evolution on irradiation temperature, target materials, incident ions and specimen geometry. Self ion irradiation is particularly useful for the study of cascade damage. Successful results of self ion irradiation for ion-neutron correlation will be presented. The experimental issues in such in situ heavy ion radiation damage studies are that the samples have to be thin enough to be transparent to the TEM electrons and that the range of self ions to simulate a primary knock-on atom (PKA) is generally short. Moreover, damage distribution is strongly depth-dependent. We have been purposely utilizing ‘thin foils’, taking advantage of the strong sink effect of surfaces for mobile point defects. The issues will be discussed in terms of the potential use of this technique to derive cascade damage characteristics in the bulk. Additional techniques such as computer simulation of cascade should be incorporated in conjunction with the experiment in order to develop models of defect production, annihilation and evolution. Prospect of the experimental technique will be discussed.

The effect of neutron irradiation on the mechanical properties of precipitation hardened copper alloys

The effects of neutron irradiation on strength and ductility properties of precipitation hardened (PH) copper alloys are discussed. The analysis is based on the experimental study of radiation damage of PH alloys irradiated in the mixed spectrum reactor SM-2 to fluences of 3.7–5.5 × 10 25 n/m 2 ( E > 0.1 MeV), corresponding to NRT displacement dose levels of 2.6–3.8 dpa. At irradiation temperatures of 100–285°C the processes of radiation hardening and reduction in the uniform elongation are the major effects. Irradiation at temperatures higher than 300°C causes a dramatic softening and improvement in uniform elongation of the CuCrZr and CuCrZrMg alloys. The threshold softening temperature for the PH alloys is shown to be about 300°C at a dose of 4.5 × 10 25 n/m 2 ( E > 0.1 MeV). The effect of the irradiation dose and temperature on the shift of the threshold temperature of PH copper-alloys softening is also considered.

The effect of neutron irradiation on the electrical resistivity of high-strength copper alloys

The effects of neutron irradiation on the electrical resistivity of precipitation hardened (PH) and dispersion strengthened (DS) copper alloys are discussed. The analysis is based on the experimental study of radiation damage of PH and DS copper alloys, irradiated in the fast neutron reactor BOR-60 with doses of 8–16 × 10 25 n/m 2 and in the mixed spectrum neutron reactor SM-2 with doses of 3.7–5.5 × 10 25 n/m 2. The experimental data on the change Δϱ in electrical resistivity of DS-type copper alloys irradiated in the BOR-60 reactor show that irradiation to 7–10 dpa at T = 340–450°C causes a drop in electrical conductivity by not more than 20%. The obtained results show that in mixed-spectrum reactors the rate of Δϱ normalized to the dpa is about 20 times as high as in fast neutron reactors. The conclusion is made that the calculations performed for ITER must take into account the presence of appreciable fluxes of thermal neutrons in certain components of the reactor. The latter will play a decisive role in the drop in thermal conductivity of copper alloys in these components.

HVEM-Tandem and Eels Study of Radiation Damage in Zirconolite

Zirconolite (CaZrTi2O7) is the major host phase for actinides in Synroc, a promising waste form for the immobilisation of high-level radioactive waste. The effect of radiation damage on the structure and durability of zirconolite are important to predictive modelling of zirconolite's behaviour in the repository environment and risk assessment.In this study, radiation damage effects in zirconolite were investigated by irradiating samples with 1.5 MeV Kr+ ions using the HVEM-Tandem at Argonne National Laboratory (ANL) and energy loss electron spectroscopy (EELS). The HVEM-Tandem consists of a modified AEI high votage transmission electron microscope interfaced to to a 2 MV tandem ion accelerator. EELS spectra were collected using a Philips 420 TEM, operated at 120 kV, fitted with a Gatan Model 607 Serial EELS. EELS data were recorded at resolutions of ˜1.0 eV and at a dispersion of about ˜0.25 eV.Selected area diffraction patterns (SADs) of individual grains of various zirconolites were monitored as a function of dose to establish the critical dose for aniorphisation (Dc).

Gamma and neutron radiation damage studies of optical fibres

An optical data link is under development at CERN for readout of the tracking detectors in the future compact muon solenoid experiment (CMS) at the CERN large hadron collider (LHC). Radiation doses inside the experiment will be ∼ 20 Mrad and ∼ 10 14 n/cm 2 over a 10 year period of operation. The effects of neutron and gamma irradiation on the attenuation at 1550 nm wavelength have been studied in both germanium-doped and pure-silica core single-mode optical fibres. The induced attenuation was greater in the Ge-doped fibre than in the pure-silica core fibres for both neutron and gamma damage. Pure-silica core fibres will be therefore be used in the CMS tracker. The gamma induced attenuation in the pure-silica core fibres was dependent on total dose, allowing a prediction to be made for the transmission losses during LHC operation.

Study of localised radiation damage to PIPS detectors by a scanning ion microprobe: Measured effects and the consequences for STIM analysis

Radiation damage effects in a PIPS particle detector have been studied by direct irradiation with a 4 MeV He + focused ion beam, using the Eindhoven scanning ion microprobe set-up. This set-up enables extreme sensitivity and accuracy in pulse-height measurement. Pulse-height dependence on ion dose and the lateral variations of pulse-height response after damaging were studied, for different bias voltages. Pulse height was found to decrease linearly with ion dose and this could be observed after only a few ions per scan position, corresponding to a dose of 10 8/cm 2. Pulse-height loss was found to be restricted to damaged detector areas. Consequences of this pulse-height dependence on ion dose and scan position for the accuracy of STIM analyses are discussed.

Neutron spectrum and transmutation effects on the radiation damage of copper alloys

Experimental results on the neutron spectrum effect on strength and ductility properties, transmutation rate and change in electric conductivity of copper-based alloys are presented in the paper. The analysis is based on the experimental study of radiation damage of pure copper, precipitation-hardened (PH) and dispersion-strengthened (DS) alloys, irradiated in the mixed spectrum reactor SM-2 and in the fast neutron spectrum reactor BOR-60 with the doses of (1–16) × 10 21 neutrons cm −2. It is shown that accumulation rate of the transmutants (Ni, Zn and He) in the SM-2 reactor is higher than in the BOR-60 reactor, which can be attributed to a high power flux of thermal neutrons in the SM-2 reactor. This causes a significant reduction in electric resistivity and mechanical properties of copper-based alloys. The effect of irradiation dose and temperature upon DS and PH copper alloy characteristics is analyzed. A threshold softening temperature for PH alloys is shown to be 300°C at a dose of 5 × 10 21 neutrons cm −2. The mechanism of the spectrum effect on the shift of the threshold softening temperature of PH copper alloys is also considered.

Radiation damage studies on stainless steel, Ni, Cu, Mo for nuclear fusion reactors

Studies on dose and energy dependence of blistering and flaking on stainless steels, Ni, Cu, Mo produced by 3.0, 4.7 and 6.8 MeV He + ions irradiation are presented. Using SEM and TEM techniques, irradiation phenomena such as sponge- and wave-like structures, submicronic cracks, microcraters, helium bubbles on matrix, grain boundaries, loops and TiC precipitates are illustrated. The appearance of an amorphous phase in the Ti-modified austenitic steel 12KH18N10T is discussed. QTMD preliminary results on H reemission in He preimplanted Ni samples are reported.

Status and future plans of the canadian ATLAS Collaboration

The Canadian ATLAS collaboration has assumed responsibility for the construction of key elements of the ATLAS liquid argon calorimeter system. The group will construct parts of the hadronic endcap calorimeter, the forward calorimeter, and the calorimeter readout electronics. Canadians are also leading in the areas of radiation damage studies and optimization of the endcap region. Physics simulation studies in Canada have concentrated on searches for heavy Higgs particles using reconstructed jets in the endcap calorimeters.

Application of analytical electron microscopy to the study of radiation damage in the complex oxide mineral zirconolite

An AEM ratio technique for the analysis of 25 elements in finely zoned natural zirconolite was used in conjunction with electron diffraction and imaging techniques to examine the effects of alpha-decay damage on zirconolites from Bergell, Switzerland-Italy and Adamello, northern Italy. Comparison of AEM and EPMA results confirms that the AFM technique can be used to obtain accurate information on the chemical formula of zirconolite. The TEM images and diffraction patterns in this study are analogous to those of previous authors. They support the proposition that radiation damage ingrowth can be adequately described by the accumulation and overlap of isolated alpha-recoil collision cascades, producing progressively larger amorphous domains. Careful determination of Th and U contents by AEM gives an accurate indication of the dose range of the crystalline-amorphous transformation. For the samples from Bergell and Adamello, the transformation occurs over a dose range of 0.05 × 1016 to just over 1 × 1016a/mg, consistent with studies of synthetic zirconolite doped with 238Pu or 244Cm. The Bergell zirconolites all exhibited diffraction patterns characteristic of the zirconolite-2M. Those grains containing REE and Th+U contents up to ≈0.1 and ≈0.03 atoms per formula unit, respectively, exhibit a high level of crystallographic perfection. While those grains containing ≈0.2 REE and 0.06 Th+U atoms per formula unit, exhibit twinning and stacking disorder.

Study of the Radiation Damage Induced by High Energy Gamma-Ray in CdTe Detectors

AbstractIn recent years the performance of room-temperature semiconductor detectors such as CdTe are improved and they are now suitable candidates for several applications. However, some key parameters that can severely affect such perfomances have not been measured yet. Thus we have studied the damaging of a set of CdTe detectors irradiated in a 60Co gamma-cell in a wide range of doses and dose-rates. A full characterization of the performance of irradiated detectors has been obtained by means of spectroscopic, electrostatic, photo-induced current transient spectroscopy and photo-deep level transient spectroscopy measurements to quote the energy resolution, the leakage current, the activation energy and capture cross-section of deep level defects, respectively.