Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 2020"

Development and characterization of new tungsten and tantalum containing composites for radiation shielding in medicine

Abstract: Relevant shielding is a key issue implementing effective radiation protection of personnel working under radiation exposure conditions as it is a case of interventional radiology. Lead or lead containing materials are mostly used for this purpose, however lead is toxic, and its recycling is very expensive. In this paper we present newly developed flexible lead free polymeric composites for possible application in medical radiation shielding constructions thought for radiation protection of personnel working in radiology department. Characterisation of WO3 or Na2WO4 containing polydimethylsiloxane and Ta and Ta2O5 containing universal silicone composites is also provided and composites’ X-ray attenuation properties are discussed. It is shown that polymeric composites containing of 50% wt. Ta or Ta2O5 are most promising candidates to replace the toxic lead in medical radiation shielding constructions since they are characterized by lead equivalent of >0.25 mmPb, which is a standard requirement for radiation protection equipment in radiology department.

Estimation of fusion reaction cross-sections by artificial neural networks

Abstract: Accurate determination of total fusion and fusion-evaporation reaction cross-sections is an important task in experimental nuclear physics studies. In this study, we estimated the total fusion cross-sections and, as an example, one of the particular channels (2n) cross-sections for different reactions by using artificial neural network (ANN) methods. The root mean square errors for fusion reaction were obtained as 18.5 and 110.4 mb for the training and test data, which correspond to 1.8% and 10.5% deviations from the experimental cross-section values, respectively. These values for the 2n channel are 0.3% for training and 13.3% for test data of ANN. The deviations are mostly lower than the cross-section values from a commonly used theoretical calculation code. The results indicate that ANN methods might be a possible candidate tool for the estimation of cross-sections for fusion and fusion-evaporation reactions.

Thick solid targets for the production and online release of radioisotopes: The importance of the material characteristics - A review

Abstract: The target material microstructure development for ISOL targets has received special attention by the scientific community. In the past 10 years, the number of peer-reviewed articles in the field has been growing at steady rate. The development of more efficient materials which deliver high radioactive ion beam yields that are also constant over time, is now a priority for the ISOL facilities around the world. Most of the microstructure engineering work focused more on nanocomposite carbide-carbon targets (e.g. UC x ) but also in some oxide developments and others. An introduction is given to solid thick target microstructure engineering and respective limitations. This is followed by a complete review of the target material developments, in ISOL facilities around the world, focused on developments toward micro or nano scale dimensions.

A versatile time-of-flight medium-energy ion scattering setup using multiple delay-line detectors

Abstract: We present the most recent upgrades of the time-of-flight medium energy ion scattering (TOF-MEIS) system in Uppsala. The experimental chamber features a 6-axis goniometer with a sample annealing stage and two delay line detectors for composition analysis with high depth resolution and depth-resolved crystallography. The first detector has a large solid angle and can be moved circularly around the target position which allows to detect backscattered or transmitted ions. The second detector features increased flight distance from sample to detector resulting in enhanced energy resolution. A reduction from 1.4 keV to 0.4 keV is achieved for 100 keV He scattered from an Au surface for 1 ns time resolution, equivalent to a depth resolution of 6 A. This detector is equipped with an electrostatic electrode in order to deflect charged particles, which allows to study the charge state for scattered ions in the medium energy regime.

The MAGNEX magnetic spectrometer for double charge exchange reactions

Abstract: Physics cases of increasing interest in the recent years, such as the study of double charge exchange reactions for neutrino physics, require the study of very suppressed reaction channels in medium-heavy ion induced nuclear reactions. The main experimental challenges are the possibility to identify and detect the medium-heavy quasi-projectiles and the capability to measure very low cross-sections (few nb) with high sensitivity at very forward angles, including zero degree. The experimental techniques adopted in the setup of the MAGNEX magnetic spectrometer to face these issues are described in this paper.

The N = 126 factory: A new facility to produce very heavy neutron-rich isotopes

Abstract: A new facility, the N = 126 factory, is currently under construction at Argonne National Laboratory. It will use multi-nucleon transfer reactions to create neutron-rich isotopes of very heavy elements for studies of interest to the formation of the A ∼ 195 abundance peak in the r-process. This region of the nuclear chart is difficult to access by standard fragmentation or spallation reactions and as a result has remained mostly unexplored. The nuclei of interest, very neutron-rich isotopes around Z = 70–95, will be produced by multi-nucleon exchange of a high intensity 10 MeV/u heavy-ion beam on the most neutron-rich stable isotopes of heavy elements such as 198 Pt and 238 U . This reaction mechanism can transfer a large number of neutrons and create very neutron-rich isotopes with larger than mb cross-section. The reaction mechanism is a nuclear surface process and the reaction products come out close to the grazing angle, which makes them very difficult to collect. The N = 126 factory circumvents this difficulty by using a unique large high-intensity RF gas catcher, similar to the one currently in operation at CARIBU, to collect the target-like reaction products and transform them into a low-energy beam that will then be mass separated with a medium resolution electromagnetic separator ( Δ M/M ≃ 1/1500), followed by an RFQ buncher and an MR-TOF ( Δ M/M ≃ 1/100,000) system. The extracted radioactive beams will be essentially pure and available at low-energy for mass measurements with the CPT mass spectrometer or decay study with the X-array.

Beam thermalization in a large gas catcher

Abstract: Thermalization of fast ions in a buffer gas provides a method to transform the high-energy, exotic beams produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory (NSCL) into low-energy beams. The process includes slowing down the fast exotic beams in solid degraders combined with momentum compression and removal of the remaining kinetic energy by collisions with a buffer gas. The original beam thermalization area for mass measurements at the NSCL was reconfigured to accommodate a new momentum compression beam line, a large radio-frequency (RF) gas catcher constructed by Argonne National Lab and a low-energy beam transport system. A large variety of exotic isotopes produced by projectile fragmentation and selected by the A1900 fragment separator was thermalized in the 1.2 m long gas catcher filled with helium at approximately 100 mbar. The ions were guided to an extraction nozzle with a combination of electrostatic and RF potentials and ejected by the gas flow. A novel RF ion guide was used in a differential pumping system to remove the helium and transport the ions into ultrahigh vacuum. Finally, the ions were accelerated to 30 kV for transport to various experiments. The distribution of the thermalized ions among chemical adducts is one of the operational challenges. The important steps implemented to minimize the production of the chemical adducts in the gas catcher are discussed. The operational status of the facility and some example results from characterization of the gas catcher operation with 37 K and 47 K beams are presented.

Radiation-induced defects in sapphire single crystals irradiated by a pulsed ion beam

Abstract: The luminescence and thermal stability of defects formed in α-Al2O3 single crystals after powerful (300 keV) pulsed irradiation with C+/H+ ion beam were investigated. It was found by measuring of optical density, photoluminescence, and pulsed cathodoluminescence that ion irradiation induces both single F-, F+-centers and F2-type aggregate centers. An intense thermoluminescence band with a complex shape was observed in the broad temperature range of 350–700 K, its intensity decreases with increasing of the energy density of the ion beam. The thermal stability of the F-type defects produced in α-Al2O3 after irradiation with a pulsed ion beam is comparable to that in neutron-irradiated samples. The appropriate kinetics of annealing of radiation-induced defects has been analyzed in terms of the diffusion-controlled bimolecular reactions between F-type centers and complementary interstitial oxygen ions. Thus, two important kinetic parameters – the migration energy of mobile interstitials and pre-exponential – have been evaluated and discussed.

Current status of experimental facilities at RAON

Abstract: The Rare Isotope Science Project (RISP) was established in December 2011 for the construction of the accelerator complex RAON (Rare isotope Accelerator complex for ON-line experiments) which will be used for the rare isotope science in Korea. The rare isotope accelerator at RAON will provide both stable and rare isotope (RI) beams with an energy range from a few keV to a few hundreds of MeV per nucleon for research in the fields of basic and applied sciences. At the moment, there are 7 experimental facilities considered at RAON: KOrea Broad acceptance Recoil spectrometer and Apparatus (KOBRA) and Large Acceptance Multi-Purpose Spectrometer (LAMPS) for nuclear physics, High Precision Mass Measurement System (HPMMS) with Multi-Reflection Time-of-Flight (MR-ToF) and Collinear Laser Spectroscopy (CLS) for nuclear physics using atomic physics techniques, Nuclear Data Production System (NDPS) for nuclear reaction data, Muon Spin Rotation/Relaxation/Resonance ( μ SR) for material science, and Beam Irradiation System (BIS) for bio-medical science. In this paper, the current status including detail design and research goal of 7 experimental facilities at RAON will be discussed.

Optimising the Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at CERN-ISOLDE

Abstract: The CRIS experiment at CERN-ISOLDE is a dedicated laser spectroscopy setup for high-resolution hyperfine structure measurements of nuclear observables of exotic isotopes. Between 2015 and 2018 developments have been made to improve the background suppression, laser-atom overlap and automation of the beamline. Furthermore, a new ion source setup has been developed for offline studies. Here we present the latest technical developments and future perspectives for the experiment.

Very high specific activity erbium 169Er production for potential receptor-targeted radiotherapy

Abstract: Erbium 169Er is one of the most interesting radiolanthanides for new potential receptor-targeted β− therapy applications due to its low energy β− emissions, very low intensity ɣ rays and the possibility to use 68Ga or 44Sc as companion for diagnostic in a theranostics approach. Currently it can be produced in reactors through the neutron activation of highly enriched 168Er. The low specific activity of the produced carrier-added 169Er is limiting its use for receptor-targeted therapy. Nonetheless it is used for radiosynoviorthesis of small joints. The aim of this work is to develop a new large-scale production method for the supply of very high specific activity 169Er. Highly enriched 168Er target has been irradiated at ILL nuclear reactor and shipped to CERN-MEDICIS. There, the irradiated sample has been mass separated in order to isolate 169Er from the high amount of remaining stable 168Er. The proof of principle for a preclinical dose production has been demonstrated with a collection of ≈17 MBq. The specific activity obtained was ≈240 GBq/mg (≈200 times higher than the product obtained at End of Bombardment – EOB) and the overall separation efficiency was ≈0.2%. Several improvements for the future have been identified and are promising. One of them is the installation of the new laser laboratory at CERN-MEDICIS that will allow to improve the selective ionization of erbium atoms leading to an increase of the efficiency of the method. This method can provide the supply of high specific activity 168Er, first for preclinical studies, and opens also the potential for future large-scale supply.

Accumulation of radiation defects and modification of micromechanical properties under MgO crystal irradiation with swift 132Xe ions

Abstract: Accumulation of F-type defects under irradiation of MgO crystals by 0.23-GeV 132Xe ions with fluence varying by three orders of magnitude has been investigated via the spectra of optical absorption and low-temperature cathodoluminescence. The number of single centers continuously increases with fluence without any marks of saturation. At the highest fluence, a mean volume concentration of 3.1 × 1019 and 3.35 × 1019 cm−3 is reached for F and F+ centers, respectively. The F+ emission strongly dominates in the cathodoluminescence of irradiated MgO and its enhancement with fluence is detected. However, the creation efficiency of the F2 aggregate centers is very low and fluence dependence has a complicated shape. Radiation-induced changes of micro-mechanical properties of the same samples have been analysed; the depth profiles of hardening correlate with the ion energy loss. A joint contribution of ionization and impact mechanisms in the formation of structural defects under MgO irradiation with Xe ions is considered.

Changes in voids induced by ion irradiations in UO2: In situ TEM studies

Abstract: Transmission electron microscopy experiments coupled with 4 MeV Au and 390 keV Xe implantations were conducted on polycrystalline UO2 thin foils in order to study the void change with damage, temperature (ranging from −180 to 1100 °C) and exogenous xenon atoms incorporation. Void size is weakly dependent on the ion dose in the range of [0.01–10] × 1014 i/cm2, whereas void density increases strongly at the early beginning of irradiation and then saturates after 3–4 × 1013 i/cm2. Change in void size and density are shown as weak functions of temperature and xenon atoms incorporation in these experimental conditions. These results indicate a heterogeneous void nucleation and a change monitored by ballistic effects. Studying voids is very tricky. This work also highlights the strong dependence of the measured void size on the TEM settings and capabilities. Thus, it is important to discuss only data obtained in the same conditions to derive influence parameters.

Correlating chemical composition and optical properties of photochromic rare-earth oxyhydrides using ion beam analysis

Abstract: We relate the photochromic response of rare-earth oxyhydride thin films (YHO, NdHO, GdHO and DyHO) synthesized by reactive magnetron sputtering to chemical composition. Depth profiles of the sample composition are extracted by a multi-method ion beam analysis approach. The total areal density of the thin films is deduced from Rutherford Backscattering Spectrometry while coincidence Time-of-Flight/Energy Elastic Recoil Detection Analysis provides depth-profiles of the film constituents. High-resolution depth profiles of the concentration of light species, i.e. hydrogen and oxygen, are additionally extracted from Nuclear Reaction Analysis and Elastic Backscattering Spectrometry, respectively. The photochromic response of the films is measured by optical transmission spectroscopy before and after illumination. We report photochromic properties for YHO, NdHO, GdHO and DyHO for chemical compositions described by the formula REH2−δOδ in the range of 0.45

Influence of neutron radiation on majority and minority carrier traps in n-type 4H-SiC

Abstract: We report on influence of neutron radiation on majority and minority carrier traps in n-type 4H-SiC. Together with the increase of the well-known carbon vacancy (VC) majority carrier related trap, neutron irradiation has introduced two deep traps, labeled as EH1 and EH3 with the activation energies for electron emission estimated as 0.4 and 0.7 eV bellow the conduction band, respectively. Based on Laplace deep level transient spectroscopy (DLTS) results, we have assigned EH1 trap to silicon vacancy (VSi). Two minority carrier traps labelled as B and D-center were detected by minority transient spectroscopy (MCTS) and assigned to substitutional boron BSi and BC, respectively. Activation energies for hole emission for B and D-center are estimated as 0.27 and 0.60 eV above the valence band, respectively. We have identified two emission lines for D-center by Laplace-MCTS measurements and assigned them to BC sitting at hexagonal (−h) and cubic (−k) lattice sites.

Time-resolved luminescence of YAG:Ce and YAGG:Ce ceramics prepared by electron beam assisted synthesis

Abstract: The luminescence characteristics of YAG:Ce and YAGG:Ce ceramic phosphors produced by electron beam assisted synthesis have been investigated. The obtained emission and decay kinetics characteristics have been compared with those for commercial phosphors synthesized by conventional methods and showed good qualitative and quantitative correspondence. In our opinion, the used electron-beam-assisted synthesis method could be considered as a perspective production method of high refractory multicomponent oxide ceramics.

Upgrades to the collinear laser spectroscopy experiment at the IGISOL

Abstract: We give an overview of recent changes to the collinear laser spectroscopy beamline in the IGISOL laboratory. We present a new data acquisition system, commissioning of a newly installed charge exchange cell, and cooler-voltage calibration measurements. Currently ongoing modifications to the RFQ cooler-buncher are also discussed.

Luminescence spectroscopy under synchrotron radiation: From SUPERLUMI to FINESTLUMI

Abstract: Luminescence spectroscopy under synchrotron radiation excitation is the unique tool for materials characterization. In the current work we are reporting recent activity in this research field implemented in the Finnish-Estonian beamline (FinEstBeAMS) which is installed at the 1.5 GeV storage ring of the MAX IV Laboratory at Lund, Sweden. It has been designed to cover an unusually wide energy range from ultraviolet (4.3 eV) to soft X-rays (1500 eV), which is perfectly suited for luminescence spectroscopy experiments. The past development and the present technical parameters of the luminescence experimental stations FINESTLUMI of FinEstBeAMS beamline are described. The comparison of the experimental parameters of the FINESTLUMI and SUPERLUMI (this endstation was operated long period of time at DORIS III storage ring of DESY synchrotron at Hamburg, Germany) setups will be demonstrated. The experimental possibilities and limitations of the FINESTLUMI as well as the recent luminescence experiments at FinEstBeAMS are briefly discussed.

Improving the measurement sensitivity of the Canadian Penning Trap mass spectrometer through PI-ICR

Abstract: For the past two decades the Canadian Penning Trap mass spectrometer (CPT) has been utilized to study various disciplines of nuclear physics through precision mass measurements. Since moving to the Californium Rare Isotope Breeder Upgrade (CARIBU) facility, the CPT experimental program has focused on neutron-rich nuclei whose masses may play an important role in the astrophysical r process. Through a recent upgrade of the detector system, the phase-imaging ion-cyclotron-resonance (PI-ICR) technique has been successfully implemented. This method offers several benefits which drastically improve the experimental sensitivity of the CPT to the most neutron-rich nuclei produced at CARIBU. Here we describe the PI-ICR procedure at the CPT, give an overview of the systematic sources of uncertainty in the system, and provide new mass results for 142I, 146La, and 163Gd which were made possible through this upgrade.

On the accuracy of Total-IBA

Abstract: “Total-IBA” implies the synergistic use of multiple IBA techniques. It has been claimed that Total–IBA inherits the accuracy of the most accurate IBA technique used. A specific example is now given of this where (in vacuo) EBS/PIXE of a glass sample uniform in depth is validated against absolutely calibrated EPMA of the same sample. The EPMA results had a mass closure gap of 2.0 ± 0.6 wt%; the full PIXE analysis determined the composition of this missing 2 wt%. The PIXE calibration was against a single certified glass sample, with uncertainties per line ~10%. Benchmarking also demonstrates ~10% underestimation of the Si scattering cross-section at proton energies ~3 MeV. But the Total-IBA determination of the silica content had a low standard uncertainty of about 2%. This is due to the strong constraints of both the chemical prior and also the mass closure properties of the EBS. Irradiation-induced sodium migration in this soda-lime glass is explored.

A gas-jet apparatus for high-resolution laser spectroscopy on the heaviest elements at SHIP

Abstract: Laser spectroscopy enables the determination of fundamental atomic and nuclear properties with high precision. In view of the low production rates of the heaviest elements, a high total efficiency is a crucial requirement for any experimental setup to be used in on-line experiments. The setup requires the use of gas stopping techniques to slow down the radionuclides of interest. In previous studies laser spectroscopy was performed inside a gas-filled stopping cell with a limited spectral resolution of a few GHz. Collisional broadening inside stopping cells ultimately limits the precision of laser spectroscopic studies and hampers in particular hyperfine spectroscopy. The spectral linewidth is reduced by an order of magnitude when the laser spectroscopy is performed in a well-collimated gas jet formed by the exit nozzle of a gas stopping cell. In addition, the exposure of the jet to high-repetition rate laser light which saturates the optical transitions allows maintaining a high total efficiency. Here, we present a new setup dedicated to laser spectroscopy of the heaviest elements with an improved resolution, which is presently under construction. This setup combines the efficient filament neutralization demonstrated for nobelium with the improved resolution of in-gas-jet spectroscopy.

Luminescence of divalent lanthanide doped BaBrI single crystal under synchrotron radiation excitations

Abstract: Luminescence excitation spectra of BaBrI single crystals doped by divalent lanthanide ions are studied using synchrotron radiation excitations from the MAX IV 1.5 GeV storage ring. The energy of the edge and the formation of core cation exciton as well as the energy threshold of the multiplications of electronic excitations is found. It was clearly established the energy transfer from intrinsic luminescence centers to Sm2+ and Eu2+ ions.

Impact of nuclear reactor radiation on the performance of AlN/sapphire surface acoustic wave devices

Abstract: The performance of an AlN/sapphire surface acoustic wave (SAW) delay line device was characterized in real time under irradiation inside a nuclear reactor. Both its resonant frequency and transmission efficiency were observed to respond to a change in reactor power. The response follows an exponentially saturating behavior after a step power increase, followed by an exponentially decaying recovery after reactor shutdown. A sensitivity analysis based on the governing electro-mechanical equations shows that the frequency shift can be attributed to the softening of sapphire’s elastic constants under neutron radiation. A kinetic rate equation is adopted to interpret device response and describe its microstructural evolution. These results suggest that the AlN/sapphire SAW device remains functional under irradiation, is sensitive to neutron and gamma ray fluxes, and offers an opportunity for remote sensing and in-situ measurement of material properties when exposed to nuclear reactor environment.

Machine learning for the prediction of stopping powers

Abstract: The stopping power of a material upon interaction with an energetic ion is the key measure of how far that ion will travel. The implications of accurate particle range calculations are tremendous, affecting every single application in which particle radiation is involved, from nuclear power to medicine. An approach is presented which attempts to overcome current shortcomings in the theoretical understanding of stopping power, as well as the methods used to interpret and exploit measured data. This is a considerable challenge, however the use of a novel machine learning methodology is shown to hold great promise in this endeavour: the ultimate aim being the ability to correctly predict the stopping value for any energy, ion and target combination, having no pre-existing experimental data. A random forest regression algorithm is trained using over 34,000 experimental measurements, representing stopping power values for 522 ion-target combinations across the energy range 10 - 3 to 10 2 MeV/amu, and ion and target atomic masses 1 to >240. Evaluation is carried out using several fundamental error metrics, over the whole dataset as well as for individual combinations, to provide the most comprehensive understanding of performance when tested under strict cross-validation criteria. The resulting model is shown to yield predicted stopping power curves corresponding closely to those of the true experimental values, with an ability to generalise across target elements, compounds, mixtures, alloys and polymers, irrespective of phase, and for a wide range of ion masses.

Thermal annealing of radiation damage produced by swift 132Xe ions in MgO single crystals

Abstract: The annealing kinetics of the electron-type F+ and F color centers in highly pure MgO single crystals irradiated by 0.23-GeV 132Xe ions with fluences covering three orders of magnitude (Φ = 5 × 1011 –3.3 × 1014 ions/cm2) are studied experimentally via dependence of the optical absorption on preheating temperature. The annealing data are analyzed in terms of the diffusion-controlled bimolecular reactions between F-type centers and complementary interstitial oxygen ions. The behavior of the main kinetic parameters – the migration energies and pre-exponential factors – for different irradiation fluences is discussed and compared with that for other wide-gap binary materials from previous studies.

SIGMA: A Set-up for In-situ Growth, Material modification and Analysis by ion beams

Abstract: We present a set-up for in-situ non-destructive high-resolution composition depth profiling by ion beams developed at the 5 MV 15 SDH-2 Tandem accelerator at the Angstrom laboratory at Uppsala Univ ...

The performance of the cryogenic buffer-gas stopping cell of SHIPTRAP

Abstract: Direct high-precision mass spectrometry of the heaviest elements with SHIPTRAP, at GSI in Darmstadt, Germany, requires high efficiency to deal with the low production rates of such exotic nuclides. A second-generation gas stopping cell, operating at cryogenic temperatures, was developed and recently integrated into the relocated system to boost the overall efficiency. Offline measurements using 223Ra and 225Ac recoil-ion sources placed inside the gas volume were performed to characterize the gas stopping cell with respect to purity and extraction efficiency. In addition, a first online test using the fusion-evaporation residue 254No was performed, resulting in a combined stopping and extraction efficiency of 33(5)%. An extraction time of 55(44) ms was achieved. The overall efficiency of SHIPTRAP for fusion-evaporation reaction products was increased by an order of magnitude to 6(1)%. This will pave the way for direct mass spectrometry of heavier and more exotic nuclei, eventually in the region of superheavy elements with proton numbers Z ⩾ 104 .

Insights into different stages of formation of swift heavy ion tracks

Abstract: This review summarizes our results on effects of different stages of the formation kinetics of swift heavy ion (SHI) tracks on final structural changes. The developed multiscale approach describes in detail the formation of individual tracks and inter-track interaction in various amorphizable (Y3Al5O12, Mg2SiO4) and non-amorphizable (Al2O3, MgO) dielectrics. A comparison between the modeling and high-resolution transmission electron microscopy analysis of SHI irradiated samples allows to validate the developed model and to investigate links between the basic properties of the materials and features of the kinetics of structural transformations of the targets. We outline an influence and importance of each successive stage of excitation and relaxation on final observable structure modifications within tracks, starting from the SHI induced electronic excitation, electrons and holes transport, energy exchange with the target lattice, transient excitation and relaxation of the atomic system, and ultimate damage formation.

Dynamic Surface evolution and scaling studies on TiO2 thin films by Ti ion implantation

Abstract: The surface dynamics of TiO2 thin films, evolving under the implantation of 50 keV Ti ions, have been investigated. The morphological evolution, as investigated with atomic force microscopy, delineates a surface smoothening by ion implantation.The nanoscale structures at surfaces also undergo a size reduction. Scaling formalism has been applied to understand this temporal and spatial dynamics by estimating the scaling exponents ( α , β and γ ) via Height-height correlation function (HHCF) and power spectral density (PSD) investigations. The roughness exponent α (0.5 α β ) also delineates surface smoothening. Exponent, γ , is observed to increase from ~ 2 at lower ion fluences to 2.5 at the highest fluence. This behavior suggests that diffusion is predominantly controlling the dynamical evolution of the ion irradiated TiO2 surfaces at the highest fluence, similar to that in the bulk case.

γ-Irradiation effects in borosilicate glass studied by EPR and UV–Vis spectroscopies

Abstract: Assessing the behavior of borosilicate glass used for nuclear waste immobilization under irradiation is essential for determining the long-term behavior of the high-level waste. In this work, the γ irradiation induced structural properties of the borosilicate glass have been studied via ultraviolet–visible (UV–Vis) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. The optical band gap (Eg) and the Urbach energy (Eu) deduced from the UV–Vis spectra of borosilicate glasses. The Eg decreased and the Eu increased with the increase of absorbed dose, which indicated the increase of non-bridging oxygen and disorder in the glass network. The EPR results revealed that there formed the following paramagnetic defects: hole center associated with boron (BOHC), hole centers near alkaline ions (HC1 center), E′ centers ( Si ), peroxy radical (Oxy defect), non-bridging oxygen hole centers (NBOHC), BO3− center, Si − BOHC ( B O Si ) and B–O–B–iso center ( HO HO B OH - O · - B OH OH ) .