Radiation Damage Studies Research Articles

Study of radiation damage and possible upgrade of the CMS ECAL Laser Monitoring system

The Electromagnetic Calorimeter (ECAL), one of the main subsystems of the CMS detector, measures the energies of electrons and photons. The ECAL consists of 75848 lead tungstate (PbWO4) crystals. The transparency of crystals is affected by irradiation, and the laser monitoring system is designed to measure the transparency changes for each ECAL crystal over time. In the future, the High-Luminosity LHC upgrade will increase the integrated luminosuty of the LHC and lead to higher radiation damage in all components of the CMS detector. In this work we report the proposed upgrade for the laser monitoring system and the results of computing crystal transparencies based on Run 2 data.

Innovative method to study irradiation damage in silicon pixel detectors for HEP: TLM

Silicon detectors are playing a key role in High Energy Physics (HEP) experiments due to their superior tracking capabilities. This study of radiation damage in silicon detectors will give us some insight of changes in the active dopant concentration and how much electrically active carriers are lost after intense radiation exposure. Answering these questions will help us to understand if this loss of active carrier affect the performance of silicon detector used in experiments. This work presents the innovative Transmission Line Model (TLM) method used for the first time to measure the electrically active carrier concentration in silicon detectors. Hence, provide us with another way to study the radiation damage and its effects on the detector performance by studying the variation of the active dopant concentration before and after irradiation.

Positron Beam Studies of Radiation Damage Induced by Various Energy Heavy Ions of Xe26+ in Iron

Positron Beam Studies of Radiation Damage Induced by Various Energy Heavy Ions of Xe²⁶⁺ in Iron

BONNER CYLINDER SET FOR NEUTRON SPECTROSCOPY AT HIGH ENERGY ACCELERATORS.

At particle accelerators, the knowledge of neutron spectra is important for radiation protection to improve the accuracy of dose measurements, for activation and radiation damage studies. Classical Bonner sphere spectrometer is a common reliable tool for this kind of measurements. Here we present a new set of cylinders with TLD cards as a sensitive element to be used for neutron spectroscopy in a wide energy range for continuous and ultra-short pulse radiation. A simple layout, relatively small dimensions and weight, as well as implementation of common materials providing low construction costs make the set useful for spectroscopic purposes. The unfolding results for various simulated radiation scenarios are also presented.

Radiation damage studies in cardiac muscle cells and tissue using microfocused X-ray beams: experiment and simulation.

Soft materials are easily affected by radiation damage from intense, focused synchrotron beams, often limiting the use of scanning diffraction experiments to radiation-resistant samples. To minimize radiation damage in experiments on soft tissue and thus to improve data quality, radiation damage needs to be studied as a function of the experimental parameters. Here, the impact of radiation damage in scanning X-ray diffraction experiments on hydrated cardiac muscle cells and tissue is investigated. It is shown how the small-angle diffraction signal is affected by radiation damage upon variation of scan parameters and dose. The experimental study was complemented by simulations of dose distributions for microfocused X-ray beams in soft muscle tissue. As a simulation tool, the Monte Carlo software package EGSnrc was used that is widely used in radiation dosimetry research. Simulations also give additional guidance for a more careful planning of dose distribution in tissue.

Structural consequences of transforming growth factor beta-1 activation from near-therapeutic X-ray doses.

Dissociation of transforming growth factor beta-1 (TGFβ-1) from the inhibitory protein latency-associated peptide (LAP) can occur from low doses of X-ray irradiation of the LAP-TGFβ-1 complex, resulting in the activation of TGFβ-1, and can have health-related consequences. Using the tools and knowledge developed in the study of radiation damage in the crystallographic setting, small-angle X-ray scattering (SAXS) and complementary techniques suggest an activation process that is initiated but not driven by the initial X-ray exposure. LAP is revealed to be extended when not bound to TGFβ-1 and has a different structural conformation compared to the bound state. These studies pave the way for the structural understanding of systems impacted at therapeutic X-ray doses and show the potential impact of radiation damage studies beyond their original intent.

Probing swift heavy ion irradiation damage in Nd-doped zirconolite

Synroc minerals have been studied since decades for immobilization of high-level radioactive wastes released from nuclear weapons and nuclear reactors. Among them, the zirconolite, due to its high radiation and aqueous resistance and high waste loading, is considered as a potential candidate for containment purposes. Though irradiation damage effects of swift heavy ions in the material remain a major concern of study, a single phase Nd-doped zirconolite samples prepared through conventional solid-state reaction were irradiated with 120 MeV Au+ ions to study radiation damage effects. Irradiation-induced effects were investigated using ex-situ XRD and micro-Raman spectroscopic techniques. Zirconolite has been observed to undergo amorphization which is confirmed through disappearance of characteristic x-ray diffraction peaks and appearance of broad diffuse scattering bands. Amorphization trend with fluence appeared linear at lower fluences followed by saturation at higher fluences inferring therewith the formation of ion tracks. The ion fluence dependent Raman examination was also found to be in line with the XRD observations. However, the presence of Raman modes, characteristic of zirconolite in the 100–1000 cm−1 region, showed intact behavior of the local structure. To sum up, the 120 MeV heavy Au+ ions developed columnar defects, vacancies and induced micro-strains that lead to the bonds distortion and eventually amorphization of the zirconolite though retaining local ordering.

Molecular dynamics study of primary radiation damage in PuO2 and (U0.5Pu0.5)O2

In this study, primary radiation damage in PuO2 and (U0.5Pu0.5)O2 is investigated as a function of temperature (300–1500 K) using MD simulations with 5 keV cascade. UO2 data from our previous work are used as reference. The interatomic potential develop by Cooper et al. has been used in this study. Time evolution of cascade generated defects is similar for different directions of primary knock on atom (PKA). Our results shows that the number of defects remaining after the cascade events in PuO2 is higher than that in UO2 at all temperatures. Defect concentration in (U,Pu)O2 is observed to be in between that of the pure oxides. The number of residual defects decreases as the temperature increases and finally tends to approach a plateau at elevated temperatures. The concentration of residual anion defects is considerably higher than that of cations in all oxides, while a decrease in the ratio of anion to cation defects with increasing temperature is observed. At lower temperature, the annihilation efficiency (ξ) of defect follows the trend ξPuO2 < ξUPuO2 < ξUO2. It is reported that both pure and mixed oxide fuels form defect clusters in the residual damage. The fraction of interstitial clusters is higher than the vacancy clusters; however, the size of these clusters is smaller than that of voids.

MD simulations of primary damage formation in L12 Ni3Al intermetallics

Computer modelling by molecular dynamics (MD) was employed to study radiation damage created in collision cascades in L12 Ni3Al intermetallic compound. Either Al or Ni primary knock-on atoms (PKA) with PKA energy 5 keV ≤EPKA≤ 20 keV were initiated in the intermetallic crystals at ambient temperatures 100 K ≤T≤ 1200 K. At least 24 different cascades for each (EPKA, T, PKA type) set were simulated in order to mimic an isotropic spatial and random temporal distribution of PKAs. The total yield of nearly 1000 simulated cascades provides the largest yet reported sampling to get statistically reliable quantitative results. The obtained MD simulation data were analysed to get the number of Frenkel pairs, the fraction of point defects in point defect clusters, the fraction of Al and Ni vacancies, self-interstitial atoms (SIA) and anti-sites created in collision cascades as a function of (EPKA, T, PKA type). It was found that under identical simulation conditions, collision cascades in L12 Ni3Al initiated by Al PKAs generate more radiation damage, whereas collision cascades initiated by Ni PKAs produce more chemical disorder. Preferred formation of Ni SIAs in collision cascades in Ni3Al was observed under all ambient temperatures and PKA energies.

A contribution of L10 ordered crystal structure to the high radiation tolerance of γ-TiAl intermetallics

Molecular dynamics simulations were employed to study radiation damage created in collision cascades in L10 TiAl intermetallic compound and fcc Ti-50at.%Al disordered solid solution. Either Al or Ti primary knock-on atoms (PKA) with PKA energy 5 keV⩽EPKA⩽20 keV were initiated in the two materials at temperature T ranging from 100 K to 1200 K. From 36 to 48 different cascades for each (EPKA,T) set were simulated in order to emulate an isotropic spatial and random temporal distribution of PKAs, generate representative sampling and obtain statistically reliable quantitative results. The number of Frenkel pairs, 〈NFPγ-TiAl〉 and 〈NFPTi-50Al〉, formed in L10 TiAl intermetallics and Ti-50at.%Al disordered solid solution, respectively, and averaged over collision cascades with the same (EPKA,T) was used as a quantitative measure of radiation resistance against primary damage formation. It is shown that the relationship 〈NFPγ-TiAl〉⩽〈NFPTi-50Al〉 is fulfilled under all simulation conditions, i.e. L10 ordered crystal structure of TiAl intermetallics is essential for its high radiation tolerance. However, a relatively high resistance to the formation of primary radiation defects is retained even after complete disordering of L10 TiAl that points out to the existence of additional mechanisms contributing to its radiation tolerance.

Monte Carlo simulation of hybrid pixel detectors

Semiconductor sensors are extensively used for X-ray detection, both for spectroscopy and 2D imaging. In this work, the Monte Carlo code PENELOPE v. 2014 with the PenEasy v. 2015 extension was applied for simulating a Medipix3RX detector, including the sensor and the ASIC layers. The code was modified to include the charge dispersion effect modelling at the Pixelated Imaging Detector tally, and validated by investigating the influence of the electric field, incident energy, beam position, pixel size and also by determining the Modulation Transfer Function. The results were compared to experimental data and presented a very good agreement. The Monte Carlo simulation can be used to investigate the detector response and its influence on measured data, such as spatial resolution and X-ray spectra distortion. Besides, the simulation can be applied to determine the energy deposition in each layer of the detector, useful for detection efficiency characterization or radiation damage studies.

Calculation of threshold displacement energies in UO2

Despite the extensive utilization of uranium dioxide (UO2) as a fuel in commercial nuclear reactors, there is only minimal information regarding the fundamental nature of radiation damage at high temperatures, such as those experienced by the fuel under operation. In this work, molecular dynamics simulations have been performed to determine the threshold displacement energy (Ed) for oxygen and uranium in UO2 at 1500 K. Three definitions of displacement energy were employed to fully study the nature of low energy radiation damage: 1) the probability of having the primary knock-on atom (PKA) leave its original lattice site, 2) the probability that the PKA will permanently displace atoms from their original lattice site, and 3) the probability of forming a stable Frenkel pair. Additionally, four unique interatomic potentials were utilized to investigate uncertainties associated with potential choice in high temperature radiation damage studies in UO2. This work provides critical insight into the high temperature behavior of radiation damage in UO2, as well as the variation in behavior between oxygen and uranium PKAs.

Heavy ion ranges from first-principles electron dynamics

The effects of incident energetic particles, and the modification of materials under irradiation, are governed by the mechanisms of energy losses of ions in matter. The complex processes affecting projectiles spanning many orders of magnitude in energy depend on both ion and electron interactions. Developing multi-scale modeling methods that correctly capture the relevant processes is crucial for predicting radiation effects in diverse conditions. In this work, we obtain channeling ion ranges for tungsten, a prototypical heavy ion, by explicitly simulating ion trajectories with a method that takes into account both the nuclear and the electronic stopping power. The electronic stopping power of self-ion irradiated tungsten is obtained from first-principles time-dependent density functional theory (TDDFT). Although the TDDFT calculations predict a lower stopping power than SRIM by a factor of three, our result shows very good agreement in a direct comparison with ion range experiments. These results demonstrate the validity of the TDDFT method for determining electronic energy losses of heavy projectiles, and in turn its viability for the study of radiation damage.

An upgrade of the materials irradiation facility with in-situ electrical resistivity measurement at the Demokritos TANDEM accelerator

As an important part of fusion materials research, evaluation of radiation damage in fusion materials has been emphasized more than a half century. In order to improve our understanding of radiation damage in fusion materials, an upgrade has been performed of the materials irradiation facility IR2, which is located at the NCSR “Demokritos” 5.5 MV TANDEM accelerator. The upgraded facility allows irradiation at higher ion beam currents while ensuring that the target temperature remains below 10 K. It provides in-situ electrical resistivity measurements on several samples for real-time monitoring of radiation damage as well as in-situ post-irradiation annealing up to 300 K. The upgraded IR2 facility has been successfully employed in radiation damage and recovery studies of metallic materials with applications in fusion research.

An insight into radiation resistance of D019 Ti3Al intermetallics

A molecular dynamics study of radiation damage created in collision cascades in D019 Ti3Al intermetallic compound and a Ti-Al binary disordered solid solution with the same chemical composition is carried out. Collision cascades are initiated by either Al or Ti primary knock-on atoms (PKA) with PKA energy 5 keV ≤EPKA≤ 20 keV in the two materials at temperature T ranging from 100 K to 900 K. A series of at least 32 different cascades for each (EPKA, T) set was simulated in order to imitate an isotropic spatial and random temporal distribution of PKAs, generate representative sampling and obtain statistically reliable quantitative results. The numbers of Frenkel pairs, 〈NFPα2〉 and 〈NFPα〉, formed in D019 Ti3Al intermetallics and Ti-25at.%Al disordered solid solution, respectively, were averaged over collision cascades with the same (EPKA, T) and used to quantify the radiation resistance against primary damage formation. It is shown that the relationship 〈NFPα2〉≤〈NFPα〉 is satisfied under all simulation conditions, i.e. D019 ordered crystal structure of Ti3Al intermetallics is an important feature affecting its radiation tolerance. Nevertheless, a relatively high resistance against the formation of primary radiation defects has been retained even after complete disordering of D019 Ti3Al, which points out to the existence of additional mechanisms governing its radiation tolerance.

An estimation of neutron-induced production of gases with propagation of uncertainties in nuclear data for structural materials of fission and fusion reactors

An accurate estimation of production of gases due to interactions of neutron in structural materials of nuclear systems is an important aspect within the purview of studies of primary radiation damage. Towards this objective, the indigenous code CRaD, which computes neutron primary radiation damage due to displacements of atoms, has been added with the capability to compute gas production for applications in Indian fast reactors. It includes the computation of gas production cross sections by using standard ENDF-6 procedure, estimation of gases in structural materials due to different types of neutron spectra and propagation of nuclear data uncertainties by Total Monte Carlo (TMC) methodology. A comparison of gas production cross sections from CRaD and NJOY (NJOY-2016.31 and NJOY21) is made and a few discrepancies noted with the processing of charged particle production cross sections using the above versions of NJOY are briefly outlined. A simple linear transmutation methodology is adapted in CRaD to estimate the concentrations of gases and validated with the published theoretical data which were obtained using a similar methodology. The study shows that the representation of charged particle data in different ENDF-6 files is not unique and spectrum-averaged gas production cross sections show large variations. The effect of spread in the activation cross sections from different libraries on the two-step processes of gas production in Nickel under different spectra is also discussed. Detailed TMC-based statistical analyses of gas production in Fe are performed and the mean, standard deviation, skewness and channel-wise and isotope-wise correlation coefficients are quantified. The uncertainties in the production of gases in Fe are estimated to be in the range of 16–56%, with the larger uncertainties being observed in the productions of tritium and helium-3 gases. The gas production parameters have shown non-Gaussian distributions.

The REX irradiation facility and its applications

Abstract The REX system is based on a linear electron accelerator and a removable head containing an electron to X-ray converter with its collimator. The machine and the irradiation chamber were manufactured and commissioned at ENEA Frascati Research Center. The activity of the Laboratory for Development of Particle Accelerators and Medical Applications is dedicated to the development of particle accelerators (electrons and protons) for medical, industrial and research applications, realized as sections of complex equipment or as stand-alone machine and offers related services to the scientific community. The REX facility is a versatile irradiation machine thought to be used for experimental campaigns in different research fields thanks to its customizable beam. Some of the cases we performed are related to irradiation of biological systems, development of in-beam monitoring devices, test of beam monitors, material radiation damage studies and cultural heritage. Experiments are carried out for specimen treatment with the two-radiation quality: electrons and X-rays. An overview of the laboratory and of the activities performed with the REX facility in its present status are given in this work and specific attention is devoted to the application on the cultural heritage for the preservation and conservation of artefacts.

Raman study of ion beam irradiation damage on nanostructured TiO2 thin film

90 MeV Xe and 25.78 MeV Cu ion irradiation effect on nanostructured anatase TiO2 thin film, prepared by sol-gel method, was investigated by Raman spectroscopy. The nonirradiated films show five Raman modes corresponding to the anatase phase. Raman spectra of irradiated films reveal crystalline-amorphous phase transition, fact evidenced by a progressive vanishing of Raman peaks correlated by emergence of a novel broad band at higher fluence, attributed to the amorphous structure. The broadening and blue shift of Raman peaks after irradiation indicate the generation of non-stoichiometric oxygen deficiency caused eventually by a preferential sputtering upon irradiation. A compressive stress was thus developed in the lattice which leads to the shortening of Ti–O bonds and the reduction of the crystallinity. The strain calculations reveal a correlation between the amorphization process and lattice strain enhancement. At higher fluence, the relaxation of the compressive stress may occur and results in volume expansion and hillocks formation. The strain and disorder calculations indicate that Xe irradiated films are completely amorphous, whereas, the anatase phase may still be present in Cu irradiated films. This behavior is explained by the difference in the electronic stopping power, which is manifested also in the disorder damage cross section. This latter is similar to that obtained by strain calculations and previously by XRD analysis.

Microscopic characterisation of photodetectors used in the hadron calorimeter of the Compact Muon Solenoid experiment.

The Hybrid Photodetector (HPD) is a hybrid unit with a single accelerating gap between a common photocathode and an array of PIN diodes. Customised HPDs with 19 channels were used to detect scintillation light from hadron calorimeter in the Compact Muon Solenoid (CMS) experiment. In this paper, we present results on radiation damage studies carried out on the used HPDs in the outer hadron (HO) and the end-cap hadron (HE) calorimeter of the CMS experiment operating at CERN. The calorimeter is made of alternating layers of scintillating tiles and metals, such as brass or iron. The scintillating light was transmitted to the HPDs by means of optical fibres. Due to excessive exposure to scintillation light and ionising radiation during data taking at the Large Hadron Collider, the performance of the HPDs was expected to degrade significantly in the HE detector. Independent studies on radiation damage of these used photosensors were important to assess the degradation in the performance of the calorimeter. Microscopic scans of relative photon detection efficiencies for two HPDs (one each from HO and HE detector) were made using micron resolution optical scanner. The scanner was specially designed and built for microscopic characterisation of photosensors. Imprints of each fibre (∼1 mm in diameter) on the photocathode with varying damage within the same pixel of the HPD were observed. The localised damage of the photocathode was determined to vary with the amount of scintillation (or calibration) light transmitted by optical fibres to the HPD.

A New Analytical Tool for the Study of Radiation Effects in 3-D Integrated Circuits: Near-Zero Field Magnetoresistance Spectroscopy

We demonstrate that a new technique, near-zero field magnetoresistance (NZFMR) spectroscopy, can explore radiation damage in a wide variety of devices in a proof-of-concept study. The technique has great potential for the study of atomic-scale mechanisms of radiation damage in 3-D integrated circuits. In our study, we explore radiation damage in structures relevant to 3-D integrated circuits, but not on 3-D test structures themselves. Five structures of great technological importance to 3-D integrated circuits are investigated. We utilize both NZFMR and electrically detected magnetic resonance to investigate radiation effects in these structures. The structures involved in this paper are planar silicon metal–oxide–semiconductor field-effect transistors, silicon–germanium alloy-based transistors, fin-based transistors, silicon dioxide-based flowable oxides, and low-k dielectrics. Our study indicates that NZFMR has great potential in radiation damage studies, with exceptional promise in systems in which more conventional resonance is not possible.