High-energy Recoil Research Articles

MD Simulations of Collision Cascades in α-Ti. The Residual Number of Radiation Defects, Cascade Relaxation Time and Displacement Cascade Region Morphology

Molecular dynamics (MD) simulations were applied to study radiation damage formation in collision cascades created by the recoil of primary knock-on atoms (PKA) with PKA energies Epka = 5, 10, 15, 20 and 25 keV in α-Ti at temperatures T = 100, 300, 600 and 900 K. A series of 24 collision cascades with the same set of (Epka, T) parameters has been simulated to generate representative sampling. Sapling size was justified a posteriori. The number of Frenkel pairs Nfp and cascade relaxation time were obtained as functions of (Epka, T). It was shown that the average ⟨Nfp(Epka,T)⟩ fits within 0.3NRT, provided the threshold displacement energy is chosen in 28-40 eV range depending on the irradiation temperature. Under high PKA energy/low irradiation temperature conditions, displacement cascade region splits into subcascades expended along high-energy recoil trajectories. Cascade relaxation time does not depend on Epka in this case. Contrary, under low PKA energy/ high temperature simulation conditions, most of collision cascades possess equiaxial shape, and their relaxation time grows with PKA energy increase.

Simulation of defect build-up in tungsten during low energy irradiation

Tungsten is the material chosen to be used in some of the most demanding parts of fusion test reactors and planned fusion power plants. The irradiation present will degrade the material over time, which lead to the need for component replacement. In order to understand the material degradation and to be able to predict the need for replacement, there is a need to understand how defects are produced in the material. Even though there will be high energy recoils in the material, there will be a substantial amount of recoils in the low energy regime. We study the effect of irradiation on the hundred eV scale and compare it to the commonly used Frenkel-pair insertion method. By conducting this investigation we can investigate if this insertion method is a possible speed up to full cascade simulations. These low energy simulations are also comparable with the energy given to recoils during electron irradiation. We found that the low energy cascades will produce damage as expected and that Frenkel-pair insertion will qualitatively give a similar result. However, we found, quantitatively in the form of clustering, that the results differ between methods, especially for the higher energies investigated.

Energy resolution of the LZ detector for high-energy electronic recoils

The LUX-ZEPLIN (LZ) detector is a dual-phase liquid xenon time projection chamber (TPC) installed at the Sanford Underground Research Facility (Lead, South Dakota) at a depth of 1478 meters. Although the main objective of LZ is the direct detection of dark matter, its low background environment allows for the search of other rare processes, such as the neutrinoless double beta decay of xenon isotopes 134Xe and 136Xe with the respective Q-values of 826 keV and 2458 keV. The sensitivity of the detector to these decays is directly determined by the energy resolution, which, in turn, is degraded by non-uniformities in detector response. In this work, we present a novel method to correct, in the data, the non-uniformity of the light collected by an array of photosensors in a scintillation detector. This method is based on the knowledge of the light response functions of individual photosensors. With these techniques, we report, at a very early phase of the detector operations, a state-of-the-art energy resolution (σ/μ) of (0.67 ± 0.01)% at 2614 keV for the fiducial volume of 5.6 tonnes of liquid xenon.

Charged particles: Unique tools to study irradiation resistance of concentrated solid solution alloys

• Both energetic ions and high-energy primary recoils induce defect processes in complex alloys that are consequences of the spatial and temporal coupling of atomic displacement processes and energy dissipation from ionization. • Chemical disorder does not monotonically increase with more alloying elements but can be tuned by specific alloying elements and the corresponding concentrations. • Differences between ions and neutrons need to be taken when relying on ion beam testing for reactor applications. Many multicomponent concentrated solid solution alloys (CSAs), including high-entropy alloys (HEAs), exhibit improved radiation resistance and enhanced structural stability in harsh environments. To study and assess irradiation resistance of nuclear materials, energetic ion and electron beams are commonly used to create displacement damage. Moreover, charged particles of ions, electrons, and positrons are unique tools to create and characterize radiation effects. Ion beam analysis (e.g., Rutherford backscattering spectrometry, nuclear reaction analysis, and time-of-flight elastic recoil detection analysis), electron microscopy techniques (e.g., transmission or scanning electron microscopy, and electron diffraction), and positron annihilation spectroscopy have been applied to characterize irradiated CSAs or HEAs to understand defect formation and evolution together with chemical and microstructural information. Their distinctive analyzing power and some perspectives in these techniques are reviewed. In developing structural alloys desirable for applications in advanced reactors, neutron exposure is a critical test but the limitation in achievable high damage levels is, however, a bottleneck. Ion irradiation is often used as a surrogate for neutron irradiation, and the associated reduced transmutations and higher displacements per atom (dpa) rates are desirable for materials research. Nevertheless, cautions need to be taken when relying on ion irradiation results for reactor evaluations. Literature on differences between ions and neutrons is briefly reviewed. In addition, the links to bridge the current advances on fundamental understandings to reactor applications are discussed to lay the groundwork between neutrons and ions for radiation effects studies.

Atomic displacement damage energy model up to high recoil energy

Current analytical displacement damage models are derived for recoil energy below 24.9AZ4/3 keV. The present work studies the damage energy beyond this theoretical limit using SRIM Full Cascade (FC) and DART calculations. Notably, the three damage energies computed with different methods from the same SRIM simulation are not equal, whereas they are believed to be the same in principle. The method of directly subtracting the ionization energy from total recoil energy is recommended for both FC and Quick Calculation (QC) options. It is also observed that the damage energy seems to unphysically depend on the density of monatomic material in SRIM FC. While the classical analytical models imply the saturated damage energy for high recoil energy, this saturation is not observed in SRIM FC nor in the numerical solution of the Lindhard equation using reasonable electronic stopping powers.

Calibrating the scintillation and ionization responses of xenon recoils for high-energy dark matter searches

Liquid xenon-based direct detection dark matter experiments have recently expanded their searches to include high-energy nuclear recoil events as motivated by effective field theory dark matter and inelastic dark matter interaction models, but few xenon recoil calibrations above 100 keV are currently available. In this work, we measured the scintillation and ionization yields of xenon recoils up to 426 keV. The experiment uses 14.1 MeV neutrons to scatter off xenon in a compact liquid xenon time projection chamber and produce quasi-monoenergetic xenon recoils between 39 keV and 426 keV. We report the xenon recoil responses and their electric field-dependence for recoil energies up to 306 keV; due to the low event statistics and the relatively mild field dependence, the yield values at higher energies are reported as the average of xenon responses for electric fields between 0.2-2.0 kV/cm. This result will enable xenon-based dark matter experiments to significantly increase their high energy dark matter sensitivities by including energy regions that were previously inaccessible due to lack of calibrations.

Suction Feeding by Small Organisms: Performance Limits in Larval Vertebrates and Carnivorous Plants.

Suction feeding has evolved independently in two highly disparate animal and plant systems, aquatic vertebrates and carnivorous bladderworts. We review the suction performance of animal and plant suction feeders to explore biomechanical performance limits for aquatic feeders based on morphology and kinematics, in the context of current knowledge of suction feeding. While vertebrates have the greatest diversity and size range of suction feeders, bladderworts are the smallest and fastest known suction feeders. Body size has profound effects on aquatic organismal function, including suction feeding, particularly in the intermediate flow regime that tiny organisms can experience. A minority of tiny organisms suction feed, consistent with model predictions that generating effective suction flow is less energetically efficient and also requires more flow-rate specific power at small size. Although the speed of suction flows generally increases with body and gape size, some specialized tiny plant and animal predators generate suction flows greater than those of suction feeders 100 times larger. Bladderworts generate rapid flow via high-energy and high-power elastic recoil and suction feed for nutrients (relying on photosynthesis for energy). Small animals may be limited by available muscle energy and power, although mouth protrusion can offset the performance cost of not generating high suction pressure. We hypothesize that both the high energetic costs and high power requirements of generating rapid suction flow shape the biomechanics of small suction feeders, and that plants and animals have arrived at different solutions due in part to their different energy budgets.

An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO4

Rare-earth phosphates adopting the xenotime (REPO4; RE = Tb − Lu & Y, Sc) structure are proposed as a potential matrix for the confinement of minor actinides. Minor actinides (e.g., Np, Am, Cm) undergo a radioactive decay process in which high-energy recoil atom (70–100 keV) and energetic alpha particles (4.5–5.8 MeV) are produced. In this study, the impact of these energetic decay products on the structure of xenotime-type ErPO4 has been investigated via high energy dual ion-beam irradiation of ErPO4 ceramics. Au2+ (1.5 MeV) and He+ (160 keV) ions were used to simulate the effects of recoil atom and α-particles, respectively. Multiple experiments were carried out in which the Au2+ and He+ ions with varying ion-fluences (ions/cm2) and ion-flux (ions/cm2/s) were implanted sequentially (Au2+ followed by He+ irradiation) and simultaneously (Au2+ + He+ irradiation) into ErPO4 ceramics. Sequential ion-irradiation experiments have shown that the xenotime structure was amorphized by Au2+ ions at a relatively lower ion-fluence (5 × 1013 ions/cm2) in comparison to the monazite structure. Upon irradiation of the amorphous ErPO4 with He+ ions, recrystallization of the amorphous xenotime due to α-particles was not observed. However, simultaneous ion-irradiation experiments on ErPO4 showed that the amorphization of the xenotime structure was prevented upon deposition of higher amounts of electronic energy (Eelectronic) in the lamella. Likewise monazite samples, the α-healing mechanism was also experimentally demonstrated in synthetic xenotime samples.

Decay microscope for trapped neon isotopes

We review the design, simulation, and tests, of a detection system for measuring the energy distribution of daughter nuclei recoiling from the beta-decay of laser trapped neon isotopes. This distribution is sensitive to several new physics effects in the weak sector. Our `decay microscope' relies on imaging the velocity distribution of high energy recoil ions in coincidence with electrons shaken-off in the decay. We demonstrate by way of Monte-Carlo simulation, that the nuclear microscope increases the statistical sensitivity of kinematic measurements to the underlying energy distribution, and limits the main systematic bias caused by discrepancy in the trap position along the detection axis.

Studies on liquid argon S1 and S2 properties for low mass WIMP search experiments

Liquid argon is known as an excellent target material for WIMP dark matter direct search experiment. Relatively small atomic mass (A=40) gives high nuclear recoil energy for WIMP-Ar nuclear scattering, thus it potentially has high sensitivity for low mass WIMP (<10 GeV/c2) . There are two crucial R&D topics for the liquid argon detector to explore such low mass WIMP signal, namely, deep understanding the liquid argon scintillation and ionization process for low energy deposition (<10 keV), and increasing the signal light yield by improving the argon scintillation light collection efficiency. In this paper, we report recent results from Waseda university liquid argon test facility.

Time of flight assisted [formula omitted] method for enhanced isotope separation capabilities in heavy ion elastic recoil detection analysis

The time of flight energy (TOF-E) setup installed at the scattering chamber of the Q3D magnetic spectrograph to perform heavy ion elastic recoil detection (ERD) analysis at the 14MV Munich Tandem Accelerator has recently been upgraded. Now, the energy detector of the TOF-E setup is additionally capable of performing ΔE-E measurements for high energy recoil ions obtained from e.g. a 170MeV 127I projectile beam. Time of flight information is simultaneously acquired with the ΔE-E data for each detected ion. The combination of the TOF-E and the ΔE-E data gives the opportunity to set effective filter conditions to select for both, the elemental and the mass of the detected ion. As an example a boron doped carbon layer is analyzed and 10B and 11B is separated with the help of the combination of both methods.

Recoil energy during ion motion in a crystal

Computer calculations of the recoil energy during the motion of accelerated ions in a crystal with the bcc (body-centered cubic) lattice are carried out using the molecular dynamics method. The spatial distributions of the recoil energy in the target volume are obtained. Anisotropy of the energy distribution caused by the crystal structure of the target is observed. It is established that a high recoil energy is characteristic of close-packed atomic layers of the crystal that are perpendicular to its surface. The recoil energy maximum is related to the second atomic layer.

Dynamical response of dark matter to galaxy evolution affects direct-detection experiments

Over a handful of rotation periods, dynamical processes in barred galaxies induce non-axisymmetric structure in dark matter halos. Using n-body simulations of a Milky Way-like barred galaxy, we identify both a trapped dark-matter component, a shadow bar, and a strong response wake in the dark-matter distribution that affects the predicted dark-matter detection rates for current experiments. The presence of a baryonic disk together with well-known dynamical processes (e.g. spiral structure and bar instabilities) increase the dark matter density in the disk plane. We find that the magnitude of the combined stellar and shadow bar evolution, when isolated from the effect of the axisymmetric gravitational potential of the disk, accounts for >30% of this overall increase in disk-plane density. This is significantly larger that of previously claimed deviations from the standard halo model. The dark-matter density and kinematic wakes driven by the Milky Way bar increase the detectability of dark matter overall, especially for the experiments with higher $v_{min}$. These astrophysical features increase the detection rate by more than a factor of two when compared to the standard halo model and by a factor of ten for experiments with high minimum recoil energy thresholds. These same features increase (decrease) the annual modulation for low (high) minimum recoil energy experiments. We present physical arguments for why these dynamics are generic for barred galaxies such as the Milky Way rather than contingent on a specific galaxy model.

Inelastic frontier: Discovering dark matter at high recoil energy

There exist well motivated models of particle dark matter which predominantly scatter inelastically off nuclei in direct detection experiments. This inelastic transition causes the DM to up-scatter in terrestrial experiments into an excited state up to 550 keV heavier than the DM itself. An inelastic transition of this size is highly suppressed by both kinematics and nuclear form factors. We extend previous studies of inelastic DM to determine the present bounds on the scattering cross section, and the prospects for improvements in sensitivity. Three scenarios provide illustrative examples: nearly pure Higgsino DM; magnetic inelastic DM; and inelastic models with dark photon exchange. We determine the elastic scattering rate as well as verify that exothermic transitions are negligible. Presently, the strongest bounds on the cross section are from xenon at LUX-PandaX (\delta < 160 keV), iodine at PICO (160 < \delta < 300 keV), and tungsten at CRESST (when \delta > 300 keV). Amusingly, once \delta > 200 keV, weak scale (and larger) DM - nucleon scattering cross sections are allowed. The relative competitiveness of these experiments is governed by the upper bound on the recoil energies employed by each experiment, as well as strong sensitivity to the mass of the heaviest element in the detector. Several implications, including sizable recoil energy-dependent annual modulation, and improvements for future experiments are discussed. We show that the xenon experiments can improve on the PICO results, if they were to analyze their existing data over a larger range of recoil energies, i.e., 20-500 keV. We also speculate about several reported events at CRESST between 45-100 keV, that could be interpreted as inelastic DM scattering. Future data from PICO, CRESST and xenon experiments can test this with anaylses of high energy recoil data.

The effect of alloying nickel with iron on the supersonic ballistic stage of high energy displacement cascades

Previous experimental and theoretical studies suggest that the production of extended defect structures by collision cascades is inhibited in equiatomic NiFe, in comparison to pure Ni. It is also known that the production of such extend defect structures results from the formation of subcascades by high-energy recoils and their subsequent interaction. A detailed analysis of the ballistics of 40 keV cascades in Ni and NiFe is performed to identify the formation of such subcascades and to assess their spatial distribution. It is found that subcascades in Ni and NiFe are created with nearly identical energies and distributed similarly in space. This suggests that the differences in production of extended defect structures is not related to processes taking place in the ballistic phase of the collision cascade. These results can be generalized to other, more chemically complex, concentrated alloys where the elements have similar atomic numbers, such as many high-entropy alloys.

Modulation effects in dark matter-electron scattering experiments

One of the next frontiers in dark-matter direct-detection experiments is to explore the MeV to GeV mass regime. Such light dark matter does not carry enough kinetic energy to produce an observable nuclear recoil, but it can scatter off electrons, leading to a measurable signal. We introduce a semi-analytic approach to characterize the resulting electron-scattering events in atomic and semiconductor targets, improving on previous analytic proposals that underestimate the signal at high recoil energies. We then use this procedure to study the time-dependent properties of the electron-scattering signal, including the modulation fraction, higher-harmonic modes and modulation phase. The time dependence can be distinct in a non-trivial way from the nuclear scattering case. Additionally, we show that dark-matter interactions inside the Earth can significantly distort the lab-frame phase-space distribution of sub-GeV dark matter.

Energy spectra of primary knock-on atoms under neutron irradiation

Materials subjected to neutron irradiation will suffer from a build-up of damage caused by the displacement cascades initiated by nuclear reactions. Previously, the main “measure” of this damage accumulation has been through the displacements per atom (dpa) index, which has known limitations. This paper describes a rigorous methodology to calculate the primary atomic recoil events (often called the primary knock-on atoms or PKAs) that lead to cascade damage events as a function of energy and recoiling species. A new processing code SPECTRA-PKA combines a neutron irradiation spectrum with nuclear recoil data obtained from the latest nuclear data libraries to produce PKA spectra for any material composition. Via examples of fusion relevant materials, it is shown that these PKA spectra can be complex, involving many different recoiling species, potentially differing in both proton and neutron number from the original target nuclei, including high energy recoils of light emitted particles such as α-particles and protons. The variations in PKA spectra as a function of time, neutron field, and material are explored. The application of PKA spectra to the quantification of radiation damage is exemplified using two approaches: the binary collision approximation and stochastic cluster dynamics, and the results from these different models are discussed and compared.

7Be-recoil radiolabelling of industrially manufactured silica nanoparticles.

Radiolabelling of industrially manufactured nanoparticles is useful for nanoparticle dosimetry in biodistribution or cellular uptake studies for hazard and risk assessment. Ideally for such purposes, any chemical processing post production should be avoided as it may change the physico-chemical characteristics of the industrially manufactured species. In many cases, proton irradiation of nanoparticles allows radiolabelling by transmutation of a tiny fraction of their constituent atoms into radionuclides. However, not all types of nanoparticles offer nuclear reactions leading to radionuclides with adequate radiotracer properties. We describe here a process whereby in such cases nanoparticles can be labelled with 7Be, which exhibits a physical half-life of 53.29 days and emits γ-rays of 478 keV energy, and is suitable for most radiotracer studies. 7Be is produced via the proton-induced nuclear reaction 7Li(p,n)7Be in a fine-grained lithium compound with which the nanoparticles are mixed. The high recoil energy of 7Be atoms gives them a range that allows the 7Be-recoils to be transferred from the lithium compound into the nanoparticles by recoil implantation. The nanoparticles can be recovered from the mixture by dissolving the lithium compound and subsequent filtration or centrifugation. The method has been applied to radiolabel industrially manufactured SiO2 nanoparticles. The process can be controlled in such a way that no alterations of the 7Be-labelled nanoparticles are detectable by dynamic light scattering, X-ray diffraction and electron microscopy. Moreover, cyclotrons with maximum proton energies of 17–18 MeV that are available in most medical research centres could be used for this purpose.

A Deep Level Transient Spectroscopy Study of Electron and Proton Irradiated ${\hbox {p}} ^{+} {\hbox {n}}$ GaAs Diodes

Defects produced by 0.6 MeV, 1 MeV, and 5 MeV electrons are compared with those produced by 2 MeV proton irradiations in p+n GaAs diodes using Deep Level Transient Spectroscopy (DLTS). The introduction rates are determined as a function of electron energy and compared with the nonionizing energy loss (NIEL). It has been determined that a majority of the electron-induced defects (E-traps) are similar to those observed following proton irradiation (PR-traps). However, a new defect emerges in the 5 MeV electron DLTS spectrum with a peak maximum occurring at ∼ 163 K which is not observed at the other electron energies. It has been determined that this new electron-induced defect which has previously not been detected is the proton-induced PR4'' defect. This defect emerges as the incident electron energy is increased suggesting it is formed by higher energy recoils and may be a complex defect. The recoil spectra are analyzed.

Dark matter direct detection with non-Maxwellian velocity structure

The velocity distribution function of dark matter particles is expected to show significant departures from a Maxwell-Boltzmann distribution. This can have profound effects on the predicted dark matter - nucleon scattering rates in direct detection experiments, especially for dark matter models in which the scattering is sensitive to the high velocity tail of the distribution, such as inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for experiments that require high energy recoil events, such as many directionally sensitive experiments. Here we determine the velocity distribution functions from two of the highest resolution numerical simulations of Galactic dark matter structure (Via Lactea II and GHALO), and study the effects for these scenarios. For directional detection, we find that the observed departures from Maxwell-Boltzmann increase the contrast of the signal and change the typical direction of incoming DM particles. For iDM, the expected signals at direct detection experiments are changed dramatically: the annual modulation can be enhanced by more than a factor two, and the relative rates of DAMA compared to CDMS can change by an order of magnitude, while those compared to CRESST can change by a factor of two. The spectrum of the signal can also change dramatically, with many features arising due to substructure. For LDM the spectral effects are smaller, but changes do arise that improve the compatibility with existing experiments. We find that the phase of the modulation can depend upon energy, which would help discriminate against background should it be found.