Neutron Induced Radiation Damage Research Articles

Calculation of neutron-induced radiation damage to gold and lutetium-aluminium microstructures using MCNP6.2

Interaction of particles and photons with materials in extreme radiation environments like the nuclear reactor may lead to basic alterations in the microstructural properties of crystalline solids. These changes accumulate over time into defects on the macrostructure translating to changes in the material's physical and mechanical properties. Studying the level of damage in the materials requires a good prediction of damage using statistical approaches like Monte Carlo simulations. This study aims to calculate the level of damage to Gold (Au) and Lutetium-Aluminium (Lu-Al) due to neutron irradiation, owing to the applications of the materials in reactor technology and other extreme radiation environments. Neutron fluxes, displacement per atom (dpa) rates, and heat deposition expected during irradiation were calculated with Monte Carlo N-particle transport code, MCNP6.2, using the SAFARI-1 research reactor model. The total neutron flux incident on gold and Lutetium-Aluminium was 2.26×1011 ncm−2s−1 and 6.94×1012 ncm−2s−1 respectively, while the dpa rate in Au and Lu-Al was estimated to be 1.96×10−7 s−1 and 6.56×10−5 s−1. The calculated neutron dpa rates and fluence for the materials suggest an elevated level of damage to the microstructure of the materials.

Hadron-Induced Radiation Damage in Fast Heavy Inorganic Scintillators

Fast and heavy inorganic scintillators with suitable radiation tolerance are required to face the challenges presented at future hadron colliders of high energy and intensity. Up to 5 GGy and 5 × 1018 neq/cm2 of one-MeV-equivalent neutron fluence is expected by the forward calorimeter at the Future Hadron Circular Collider. This paper reports the results of an investigation of proton- and neutron-induced radiation damage in various fast and heavy inorganic scintillators, such as LYSO:Ce crystals, LuAG:Ce ceramics, and BaF2 crystals. The experiments were carried out at the Blue Room with 800 MeV proton fluence up to 3.0 × 1015 p/cm2 and at the East Port with one MeV equivalent neutron fluence up to 9.2 × 1015 neq/cm2, respectively, at the Los Alamos Neutron Science Center. Experiments were also carried out at the CERN PS-IRRAD proton facility with 24 GeV proton fluence up to 8.2 × 1015 p/cm2. Research and development will continue to develop LuAG:Ce ceramics and BaF2:Y crystals with improved optical quality, F/T ratio, and radiation hardness.

Preliminary Study on the Remaining Life Estimation Method for Research Reactor Tank Liner

The reactor tank liner is one of the most crucial safety barriers in a research reactor as it retains the radioactive material released from the fuel during the accident condition. It also contains the primary coolant for fission heat removal. The integrity of the tank liner determines the service life of the research reactor. So far, the remaining life estimation of pressure vessels in nuclear power plants is more widely applied and established than that of the research reactor tank liner. Therefore, a study on the remaining life estimation method of the research reactor tank liner is needed to ensure the research reactor operation safety. This paper aims to preliminarily study several methods applied to estimate the remaining life of a research reactor tank liner. The preliminary study consists of a qualitative assessment and a quantitative assessment. The qualitative assessment aims to propose several techniques or methods applied in estimating the remaining life of the reactor tank liner. The quantitative assessment applies one of the remaining life estimation methods discussed in the previous assessment. Generally, the remaining life of the research reactor tank liner can be estimated using the theoretical method and the experimental method. The theoretical methods are applied by calculating the neutron fluence received by the tank liner or by analyzing the fracture mechanics using numerical modeling if the cracks or other defects exist. The calculation of atom displacement number (dpa), as a standard measure of the neutron-induced radiation damage of the materials, can support the neutron fluence calculation. The experimental method is conducted by measuring several parameters of the tank liner material, such as the corrosion rate or the mechanical properties. In the quantitative assessment, the remaining life estimation of the Kartini Reactor tank liner was performed by neutron fluence calculation method using MCNP6 computer code. The result shows that the maximum neutron fluence received by the tank wall is 2.950E+17 n/cm2 for 40 years operating period. By comparing the cumulative neutron fluence received for 40 years to the thermal neutron fluence limit value of 1.18E+23 n/cm2, the Kartini Reactor tank liner can still be used for the next 1.6E+07 operation years. The result of the quantitative assessment implicitly shows that the remaining life estimation of the tank liner needs to: 1) consider all defects experienced by the tank liner and all factors (e.g., thermal, radiation, chemical, cyclic loading) which affect the tank liner material condition, and 2) perform the combination of theoretical and experimental methods. For an open-pool type reactor, corrosion monitoring and corrosion rate measurement are essential to perform the remaining life assessment of the tank liner.

Investigations of radiation damaged arranged scintillating particle composites

Composites consisting of periodically arranged scintillating particles within an acrylic (poly methyl methacrylate) matrix are excellent templates for the gamma-insensitive detection of fast neutrons. In order to study the impact of radiation damage on acrylic-based scintillating particle composites, we exposed acrylic samples to different doses of fast neutrons up to 119.7 kGy and investigated the change in optical characteristics using optical absorption spectroscopy in the 200–800 nm wavelength range. The experimental results are compared to coupled MCNP6 and optical ray-tracing (FRED) simulations, and qualitative agreement is found. Neutron-induced radiation damage in the acrylic matrix manifests as a red-shift in the ultra-violet absorption edge of the acrylic and a corresponding decrease in the light propagation efficiency, which leads to detector performance degradation. We show for the first time that the effects of radiation damage can be mitigated by the use of wavelength-shifting coatings. We predict that composites with wavelength-shifting coatings can enable neutron detectors with high tolerance against neutron-induced radiation damage, a property that is particularly desired for neutron detection in high radiation environments.

Monte Carlo simulation of proton- and neutron-induced radiation damage in a tantalum target irradiated by 70 MeV protons

Beams of free neutrons are an important probe to analyze the structure and dynamics of condensed matter and are produced at neutron research reactors, neutron spallation sources or compact accelerator-based neutron sources (CANS). An efficient construction of CANS with a maximized neutron yield and brilliance requires reliable knowledge of the consequences of radiation-induced material damage, the predominating bottleneck of a target’s lifetime. In the framework of the Jülich High-Brilliance neutron Source project, the impact of proton- and neutron-induced material damage of a tantalum target was investigated. The Monte Carlo codes FLUKA and SRIM were utilized to extract the number of displacements per atom resulting from atomic rearrangements. The simulations performed distinctly identify the rear of the neutron target as the most vulnerable area, with the protons as main damage contributors. The minor contribution of neutrons is a material-specific phenomenon due to their high mean free path length in tantalum. Numerical results of the simulations served to calculate average and peak damage rates {R}_{mathrm{d}} (dpa/s), both in turn scaled to annual displacement doses for continuous operation in a full power year (dpa/fpy). Supplemented by the literature, a minimum target lifetime tau _{min } of 2.6 years (33 Ah) is concluded.

Neutron-Induced Radiation Damage in LYSO, BaF2, and PWO Crystals

One crucial issue for the application of scintillation crystals in future high-energy physics experiments is radiation damage in a severe radiation environment, such as the high luminosity large hadron collider. While radiation damage induced by ionization dose in inorganic scintillators is well understood, investigations are ongoing to understand radiation damage induced by hadrons, including both charged hadrons and neutrons. Aiming at understanding neutron-induced radiation damage in fast inorganic scintillators, lutetium yttrium oxyorthosilicate (LYSO)/lutetium fine silicate (LFS), BaF2, and PWO crystals were irradiated at Los Alamos Neutron Science Center by a combination of particles, including neutrons, protons, and $\gamma $ -rays. The results indicate that LYSO/LFS and BaF2 crystal plates are radiation hard up to a 1-MeV equivalent neutrons fluence of $9 \times 10^{15}$ equivalent neutron (neq)/cm2, but not PWO, and the neutron-induced radiation damage in LYSO crystals is a factor of ten less than protons.

Modeling of neutron radiation-induced defects in silicon particle detectors

Radiation damage of the silicon detectors in future hadron colliders poses a major challenge for its reliable operation. It is crucial to investigate the neutron-induced radiation damage owing to its large flux in the calorimeters and the trackers. Measurement results on irradiated detectors are complemented by modeling for getting a deep insight into the device behavior. This work presents the development of neutron-induced radiation damage model in silicon detectors using TCAD simulation. A wide spectrum of measurement results available on neutron-irradiated silicon detectors, viz. full depletion voltage, leakage current, charge collection, and effective trapping times, helps in constraining the model parameters, resulting in a robust model for neutron damage. Modeling has been performed within the phase-space of the measurements, i.e. for different initial bulk resistivities, active thicknesses and for both polarities up to the fluence values of 9 × 1014 1 MeV neq cm−2 (where, 1 MeV neq refers to the equivalent fluence for monoenergetic neutrons of energy 1 MeV) and for two measurement temperatures, 253 and 263 K. The results obtained from the devised neutron damage model show a good agreement with the measurement results.

Evaluation of neutron radiation damage in zircaloy fuel clad of nuclear power plants: a study based on PKA and dpa calculations

During the lifetime of nuclear power plants, irradiation and mechanical interactions can cause permanent damage to their structural materials. In nuclear reactors, one of the most important of these materials is fuel clad that, in addition to its main role in transferring heat from fuel to coolant, restrains most of the radioactive fission products within its volume. In this article, neutron-induced radiation damage based on Primary Knock-on Atom (PKA) and displacement per atom (dpa) calculations are evaluated on fuel clad in Hot Fuel Assembly (HFA) in a WWER-1000 reactor core as a case study. New couplings of existing nuclear and radiation damage codes and methods are developed for dpa calculations and results are compared together and against experimental results. In the first step, the full reactor core is simulated with MCNPX code (v2.7) to determine the HFA and its relevant neutron-energy spectrum. SPECTER, SPECTRA-PKA and PTRAC card of MCNPX are then employed to evaluate the PKA spectrum under neutron bombardment. Finally, dpa calculated with the Binary Collision Approximation approach is achieved through the use of SRIM-2013 code. A MATLAB interchange program is developed to prepare and transfer the data between the mentioned codes and SRIM. Comprehensive comparisons are performed between results in terms of dpa obtained by (i) NRT calculation (NRT-dpa) (SPECTER and SPECTRA-PKA results), (ii) arc-dpa calculation (MCNPX+arc-dpa), (iii) BCA calculation (PTRAC+SRIM) and (iv) coupled calculation (SPECTRA-PKA+SRIM) (all generations of knock-on atoms and clusters are tracked in the last two methods). These comparisons reveal the portions of damage in Zircaloy due to PKAs, secondary knock-on atoms and cascade atoms, the effect of position-depended PKA and the fraction of displaced atoms that come back to their lattice positions as a result of thermal effects and annealing. Effects of elemental PKA are obtained by means of SPECTRA-PKA code and a visualization map of radiation damage in the clad is presented as an outcome of the SRIM code simulation. Results confirm that value of dpa calculated by MCNPX+arc-dpa is closer to experimental ones as the recombination effect in radiation damage is considered in this method.

Neutron-Induced Radiation Damage in BaF2, LYSO/LFS and PWO Crystals

One crucial issue for applications of inorganic scintillators in future HEP experiments is radiation damage in a severe radiation environment, such as the HL-LHC. While radiation damage induced by ionization dose is well understood, investigations are on-going to understand radiation damage induced by hadrons, including both charged hadrons and neutrons. Aiming at understanding neutron induced radiation damage in fast inorganic scintillators, BaF2, LYSO/LFS and PWO crystals were irradiated at LANSCE by a combination of particles, including neutrons, protons and γ-rays. The results indicate that LYSO/LFS and BaF2 crystal plates are radiation hard up to 4 × 1015 fast neutrons/cm2.

The Soreq Applied Research Accelerator Facility (SARAF): Overview, research programs and future plans

The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. When completed at the beginning of the next decade, SARAF will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. Phase I of SARAF (SARAF-I, 4 MeV, 2 mA CW protons, 5 MeV 1 mA CW deuterons) is already in operation, generating scientific results in several fields of interest. The main ongoing program at SARAF-I is the production of 30 keV neutrons and measurement of Maxwellian Averaged Cross Sections (MACS), important for the astrophysical s-process. The world leading Maxwellian epithermal neutron yield at SARAF-I ($5\times 10^{10}$ epithermal neutrons/sec), generated by a novel Liquid-Lithium Target (LiLiT), enables improved precision of known MACSs, and new measurements of low-abundance and radioactive isotopes. Research plans for SARAF-II span several disciplines: Precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes, such as $^6$He, $^8$Li and $^{18,19,23}$Ne, in unprecedented amounts (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the rapid (r-) process; nuclear structure of exotic isotopes; high energy neutron cross sections for basic nuclear physics and material science research, including neutron induced radiation damage; neutron based imaging and therapy; and novel radiopharmaceuticals development and production. In this paper we present a technical overview of SARAF-I and II, including a description of the accelerator and its irradiation targets; a survey of existing research programs at SARAF-I; and the research potential at the completed facility (SARAF-II).

Neutron induced radiation damage of plastic scintillators for the upgrade of the Tile Calorimeter of the ATLAS detector.

With the prediction that the plastic scintillators in the gap region of the Tile Calorimeter will sustain a significantly large amount of radiation damage during the HL-LHC run time, the current plastic scintillators will need to be replaced during the phase 2 upgrade in 2018. The scintillators in the gap region were exposed to a radiation environment of up to 10 kGy/year during the first run of data taking and with the luminosity being increased by a factor of 10, the radiation environment will be extremely harsh. We report on the radiation damage to the optical properties of plastic scintillators following irradiation using a neutron beam of the IBR-2 pulsed reactor in Joint Institute for Nuclear Research (JINR), Dubna. A comparison is drawn between polyvinyl toluene based commercial scintillators EJ200, EJ208 and EJ260 as well as polystyrene based scintillator from Kharkov. The samples were subjected to irradiation with high energy neutrons and a flux density range of 1 × 106–7.7 × 106. Light transmission, Raman spectroscopy, fluorescence spectroscopy and light yield testing was performed to characterize the damage induced in the samples. Preliminary results from the tests done indicate a minute change in the optical properties of the scintillators with further studies underway to gain a better understanding of the interaction between neutrons with plastic scintillators.

Effect of defect imbalance on void swelling distributions produced in pure iron irradiated with 3.5 MeV self-ions

Ion irradiation has been widely used to simulate neutron-induced radiation damage. There are a number of features of ion-induced damage that differ from neutron-induced damage, however, and these differences require investigation before ion data can be confidently used to predict behavior arising from neutron bombardment. In this study 3.5MeV self-ion irradiation of pure iron was used to study the influence on void swelling of the depth-dependent defect imbalance between vacancies and interstitials that arises from various surface effects, forward scattering of displaced atoms, and especially the injected interstitial effect. It was observed that the depth dependence of void swelling does not follow the behavior anticipated from the depth dependence of the damage rate. Void nucleation and growth develop first in the lower-dose, near-surface region, and then moves to progressively deeper and higher-damage depths during continued irradiation. This indicates a strong initial suppression of void nucleation in the peak damage region that is eventually overcome with continued irradiation. Using the Boltzmann transport equation method, this phenomenon is shown to be due to depth-dependent defect imbalances created under ion irradiation. These findings demonstrate that void swelling does not depend solely on the local dose level and that this sensitivity of swelling to depth must be considered in extraction and interpretation of ion-induced swelling data.

Influence of radiation damage on plasma facing material erosion

New experimental approach is developed to explore plasma facing materials accounting for neutron induced radiation damage on erosion of these materials in plasma. The radiation damage has been produced in carbon materials by 5 MeV 12C + ions accelerated on cyclotron of Kurchatov Institute. A high level of radiation damage (1–10 dpa) has been obtained on these materials. The erosion of irradiated materials including CFC under plasma impact was studied on the LENTA linear plasma simulator. Surface modification was analyzed and the erosion rate was evaluated. Enhancement of the erosion process was detected for the radiation-damaged materials.

Neutron induced damage in reactor pressure vessel steel: An X-ray absorption fine structure study

The radiation damage produced in reactor pressure vessel (RPV) steels during neutron irradiation is a long-standing problem of considerable practical interest. In this study, an extended X-ray absorption fine structure (EXAFS) spectroscopy has been applied at Cu, Ni and Mn K-edges to systematically investigate neutron induced radiation damage to the metal-site bcc structure of RPV steels, irradiated with neutrons in the fluence range from 0.85 to 5.0×1019cm−2. An overall similarity of Cu, Ni and Mn atomic environment in the iron matrix is observed. The radial distribution functions (RDFs), derived from EXAFS data have been found to evolve continuously as a function of neutron fluence describing the atomic-scale structural modifications in RPVs by neutron irradiations. From the pristine data, long range order beyond the first- and second-shell is apparent in the RDF spectra. In the irradiated specimens, all near-neighbour peaks are greatly reduced in magnitude, typical of damaged material. Prolonged annealing leads annihilation of point defects to give rise to an increase in the coordination numbers of near-neighbour atomic shells approaching values close to that of non-irradiated material, but does not suppress the formation of nano-sized Cu and/or Ni-rich-precipitates. Total amount of radiation damage under a given irradiation condition has been determined. The average structural parameters estimated from the EXAFS data are presented and discussed.

Neutron induced radiation damage of a n-type Ge detector influence of the operating temperature

The energy resolution of a n-type HPGe detector has been measured as function of the operating temperature before and after inducing radiation damage by neutrons from a fusion evaporation reaction. The aim of the investigation was to determine an appropriate operating temperature for Ge multidetector arrays. In the undamaged condition the leakage current due to thermal production of charge carriers limits the operating temperature to below 125 K. With neutron induced trapping levels the operating temperature has to be decreased to below 100 K because of thermal activation of trapping levels and defect migrations.

Neutron-induced radiation damage in silicon detectors

Ion-implanted silicon pad detectors fabricated on different n-type and p-type silicon wafers with initial resistivities between 2.6 and 12.9 k Omega -cm have been irradiated with neutrons of approximately 1 MeV energy, up to a fluence of 5*10/sup 13/ n cm/sup -2/. The evolution of diode leakage current and capacitance characteristics is presented as a function of the neutron fluence. The reverse diode current increases proportionally to the neutron fluence. There is evidence that the doping of the initial n-type material evolves towards an intrinsic and inverts to an apparent p-type at fluences between 1*10/sup 13/ and 3*10/sup 13/ n cm/sup -2/, depending on the initial silicon resistivity. There is also evidence that p-type material remains of the same conduction type with a slight increase of the acceptor doping with fluence. The signal shape and the charge collection efficiency for incident beta particles have also been measured. >

In situ TEM studies of irradiation effects for materials improvement

Irradiation effects studies employing TEMs as analytical tools have been conducted for almost as many years as materials people have done TEM, motivated largely by materials needs for nuclear reactor development. Such studies have focussed on the behavior both of nuclear fuels and of materials for other reactor components which are subjected to radiation-induced degradation. Especially in the 1950s and 60s, post-irradiation TEM analysis may have been coupled to in situ (in reactor or in pile) experiments (e.g., irradiation-induced creep experiments of austenitic stainless steels). Although necessary from a technological point of view, such experiments are difficult to instrument (measure strain dynamically, e.g.) and control (temperature, e.g.) and require months or even years to perform in a nuclear reactor or in a spallation neutron source. Consequently, methods were sought for simulation of neutroninduced radiation damage of materials, the simulations employing other forms of radiation; in the case of metals and alloys, high energy electrons and high energy ions.

The effects of a static magnetic field on DNA synthesis and survival of mammalian cells irradiated with fast neutrons.

The effects of a static magnetic field (0.75 T) on DNA synthesis and survival were examined with Chinese hamster V79 cells in cultures with and without fast-neutron irradiation. We found that the magnetic field applied alone for up to several hours did not cause a significant effect in either the rate of DNA synthesis or cell viability; the latter was assayed by colony formation. When cells were exposed simultaneously to the magnetic field and fast neutrons, the effects resembled those observed with neutrons alone. This was the case for both inhibition of DNA synthesis and cell killing. Cells irradiated first with neutrons followed immediately by 1 h of magnetic field exposure showed a dose-survival response curve indistinguishable from that of neutrons alone. These data suggest that the biological effect due to the magnetic field is negligible and that the presence of the magnetic field either during or subsequent to fast-neutron irradiation does not affect the neutron-induced radiation damage or its repair.

Impact of the injected interstitial on the correlation of charged particle and neutron-induced radiation damage

The successful conclusion of an intercorrelation program developed in the US Breeder program has provided significant insight on the factors governing the swelling that develops in ion-bombardment studies and its relationship to the swelling that occurs during neutron irradiation. It appears that the injected interstitial or a related phenomenon exerts a pronounced influence on ion-induced swelling. This conclusion has ramifications with respect to the conduct and interpretation of ion irradiation experiments employed to study the effect of helium or composition on swelling.

Calculation of radiation damage effects of 800 MeV protons in a “thin” copper target

Radiation damage effects of 800 MeV protons incident on a 1 cm thick copper target have been calculated by using the nucleon-meson transport code to determine the nuclear reactions produced by the protons, and the theory of Lindhard et al. to evaluate the resultant damage energy deposited in the target. Damage effects were found to be nearly uniform across the 1 cm target thickness, and the results obtained can be expressed in cross section form applicable to target thicknesses from about 0.01 cm to 2 cm. The calculation yielded a damage energy cross section (depending slightly on target geometry) of about 350 barn-keV, a nuclear transmutation cross section of 1.0 barn, and indicated copious proton, neutron, and helium production. Comparison of the cross sections obtained with those of several neutron spectra of reactor interest suggests that medium energy proton bombardment may be a useful method for simulating neutron-induced radiation damage effects.