Energetic Particle Fluxes Research Articles

ATEP: an advanced transport model for energetic particles

In this paper we report on the implementation and verification of a phase-space resolved energetic particle (EP) transport model. It is based on a first-principle theoretical framework, i.e. the system of non-linear gyrokinetic equations and the related transport equations. Its focus is primarily directed toward understanding the meso-scale character of EPs and its consequences. Compared to the conventional description of thermal radial transport via a one-dimensional radial diffusion equation, the newly developed model is three-dimensional using canonical constants-of-motion (CoM) variables. The model does not assume diffusive processes to be dominant a priori, instead the EP fluxes are self-consistently calculated and directly evolved in CoM space. We use the EP-Stability workflow and the HAGIS code to determine the phase space fluxes explicitly either in the limit of constant mode amplitudes or an energy-conserving quasi-linear model. As an application of the model the transport of neutral-beam-generated EPs due to a toroidal Alfvén eigenmode in an ITER plasma is investigated. As there are no sources and collisions taken into account so far (for an extension of the model see the companion paper (Meng et al 2024 Nucl. Fusion accepted)), the results cannot be considered as an exhaustive study, but rather as a practical demonstration of the conceptual framework on the way to a comprehensive reduced description of burning plasmas.

IMF Bx, By, and Bz dependence of energetic particle precipitation in the magnetosphere

The orientation of Interplanetary Magnetic Field (IMF B) components plays a major role in magnetospheric Energetic Particles Precipitation (EPP). This is because the IMF B components in the Geocentric Solar Magnetospheric (GSM) coordinate system control magnetic reconnection at the subsolar magnetopause. This study intends to unravel the dependence of the preceding conditions of the orientations of IMF B components that drove geomagnetic storms on the EPPs produced in the Van Allen radiation belt. We classified the geomagnetic storms based on their drivers and IMF Bz orientations prior to the storms’ onset. Energetic particle fluxes, IMF B, and solar wind data were used. The study showed that electrons are more reactive to solar wind speed than protons. Additionally, storms with southward IMF Bz orientation caused more EPP enhancement than with northward orientation. Our results also showed that protons are more influenced by magnetospheric compression than electrons at the northward orientation of IMF Bz. In fact, at this point, the proton’s motion violates adiabatic invariants. As particles interact with electric fields, a significant population of EPPs is produced by pitch angle diffusion. Generally, IMF Bx and IMF By are often anticorrelated. The preceding conditions of orientations of the IMF Bx indicated weaker dependence on auroral indices, and invariably on energetic particles precipitation than the IMF By.

Parker Solar Probe Observations of Energetic Particles in the Flank of a Coronal Mass Ejection Close to the Sun

We present an event observed by Parker Solar Probe (PSP) at ∼0.2 au on 2022 March 2 in which imaging and in situ measurements coincide. During this event, PSP passed through structures on the flank of a streamer blowout coronal mass ejection (CME) including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging observations and in situ helicity and principal variance signatures consistently show the presence of flux ropes internal to the CME. In both the sheath and the CME interval, the distributions are more isotropic, the spectra are softer, and the abundance ratios of Fe/O and He/H are lower than those in the isolated flux tube, and yet elevated relative to typical plasma and solar energetic particle abundances. These signatures in the sheath and the CME indicate that both flare populations and those from the plasma are accelerated to form the observed energetic particle enhancements. In contrast, the isolated flux tube shows large streaming, hard spectra, and large Fe/O and He/H ratios, indicating flare sources. Energetic particle fluxes are most enhanced within the CME interval from suprathermal through energetic particle energies (∼keV to >10 MeV), indicating particle acceleration, as well as confinement local to the closed magnetic structure. The flux-rope morphology of the CME helps to enable local modulation and trapping of energetic particles, in particular along helicity channels and other plasma boundaries. Thus, the CME acts to build up energetic particle populations, allowing them to be fed into subsequent higher-energy particle acceleration throughout the inner heliosphere where a compression or shock forms on the CME front.

Further Study of the Relationship between Transient Effects in Energetic Proton and Cosmic Ray Fluxes Induced by Coronal Mass Ejections

The study and better understanding of energetic transient phenomena caused by disturbances occurring on our Sun are of great importance, primarily due to the potential negative effects those events can have on Earth’s environment. Here, we present the continuation of our previous work on understanding the connection between disturbances in the flux of energetic particles induced in the near-Earth environment by the passage of interplanetary coronal mass ejections and related Forbush decrease events. The relationship between the shape of fluence spectra of energetic protons measured by the instruments on the SOHO/ERNE probe at Lagrange point L1, Forbush decrease parameters measured by the worldwide network of neutron monitors, and coronal mass ejection parameters measured in situ is investigated. Various parameters used to characterize transient phenomena and their impact on the heliosphere, provided by the WIND spacecraft, were utilized to improve the accuracy of the calculation of the associated energetic proton fluence. The single and double power laws with exponential rollover were used to model the fluence spectra, and their effectiveness was compared. Correlation analysis between exponents used to characterize the shape of fluence spectra and Forbush decrease parameters is presented, and the results obtained by the two models are discussed.

Relationship Between NM Data and Radiation Dose at Aviation Altitudes During GLE Events

AbstractGround‐level enhancements (GLEs) are sporadic events that signal the arrival of high fluxes of solar energetic particles (SEPs) that have been produced by solar eruptions. Ground‐level enhancement events are characterized by a significant increase in the count rate of ground‐based neutron monitors (NMs). The arrival of high‐energy SEPs in the atmosphere leads to an enhancement of the radiation environment, with the enhancement at aviation altitudes being particularly hazardous to human health as pilots, crew, and airline passengers can be subjected to dangerous levels of radiation during a GLE. Through the use of a currently expanding library of analyzed GLEs and the application of a newly developed atmospheric radiation model, both of which have been created in‐house, we found a strong statistically significant relationship between real‐time NM data during GLE events and the radiation doses at aviation altitudes. This result provides a strong scientific basis for the use of real‐time NM data as a proxy for radiation dose estimates during GLE events and aids in the development of future nowcasting models to help mitigate the dangerous impacts of future GLEs.

Sulfur Implantation into Water Ice with Propane: Implications for Organic Chemistry on the Surface of Europa

We performed experiments of implantation of energetic sulfur ions (105 keV) into 2:1 water:propane ices at 80 K and analyzed the resulting refractory organic matter with ultrahigh-resolution mass spectrometry. Our goal was to characterize the organic matter processed in the surface conditions of Europa, where it would receive a heavy flux of energetic particles, including sulfur ions, and determine whether organosulfurs could be formed in these conditions, using the simplest alkane that can exist in solid form on Europa’s surface. We find that the produced organic matter contains a large variety of both aliphatic and aromatic compounds (several thousand unique formulae), including polycyclic aromatic hydrocarbons (PAHs), with masses up to 900 amu. A large number of aromatic hydrocarbons is found along with oxygenated, mostly aliphatic, compounds. Organosulfurs are found in both CHS and CHOS form, demonstrating they can be formed from any organic compound through sulfur implantation. These organosulfurs’ properties (aromaticity, mass) appear similar to the rest of the organic matter, albeit their low quantity does not allow for a thorough comparison. Our results have implications for the type of refractory organic matter that could be observed by the JUICE and Europa Clipper space missions and how the surface of Europa could generate complex organics, including PAHs and organosulfurs, that could then enrich the subsurface ocean. In particular, they indicate that a large diversity of organic matter, including organosulfurs, can be formed from simple precursors in a geologically short time frame under the ion flux that reaches Europa.

A new ground level neutron monitor for space weather assessment

We report on a new ground-level neutron monitor design for studying cosmic rays and fluxes of solar energetic particles at the Earth’s surface. The first-of-its-kind instrument, named the NM-2023 after the year it was standardised and following convention, will be installed at a United Kingdom Meteorological Office observatory (expected completion mid 2024) and will reintroduce such monitoring in the UK for the first time since ca. 1984. Monte Carlo radiation transport code is used for the development and application of parameterised models to investigate alternative neutron detectors, their location and bulk material geometry in a realistic cosmic ray neutron field. Benchmarked against a model of the current and most widespread design standardised in 1964 (the NM-64), two main parameterisation studies are conducted; a simplified standard model and a concept slab parameterisation. We show that the NM-64 standard is well optimised for the intended large-diameter boron trifluoride (BF3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}) proportional counters but not for multiple smaller diameter counters. The new design (based on a novel slab arrangement) produces comparable counting efficiencies to an NM-64 with six BF3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document} counters and has the added advantage of being more compact, lower cost and avoids the use of highly toxic BF3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}.

Ground Electric Field, Atmospheric Weather and Electric Grid Variations in Northeast Greece Influenced by the March 2012 Solar Activity and the Moderate to Intense Geomagnetic Storms

In a recent paper, we extended a previous study on the solar solar influence to the generation of the March 2012 heatwave in the northeastern USA. In the present study we check the possible relationship of solar activity with the early March 2012 bad weather in northeast Thrace, Greece. To this end, we examined data from various remote sensing instrumentation monitoring the Sun (SDO satellite), Interplanetary space (ACE satellite), the Earth’s magnetosphere (Earth-based measurements, NOAA-19 satellite), the top of the clouds (Terra and Aqua satellites), and the near ground atmosphere. Our comparative data analysis suggests that: (i) the winter-like weather (rainfall, fast winds, decreased temperature) in Thrace started on 6 March 2012, the same day as the heatwave started in USA, (ii) during the March 2012 winter-like event in Thrace (6–15 March), the ACE satellite recorded enhanced fluxes of solar energetic particles (SEPs), while SOHO and PAMELA recorded solar protons at very high energies (>500 MeV), (iii) Between 3–31 March, the temperature in Alexandoupoli and the ACE/EPAM solar high energy (1.88–4.70 MeV) proton flux were strongly anticorelated (r = −0.75, p = 0.5). (iv) Thrace experienced particularly intense cyclonic circulation, during periods of magnetic storms on 8–10 and 12–13 March, which occurred after the arrival at ACE of two interplanetary shock waves, on March 8 and March 11, respectively, (v) at the beginning of the two above mentioned periods large atmospheric electric fields were recorded, with values ranging between ~−2000 V/m and ~1800 V/m on 8 March, (vi) the winter-like weather on 8–10 March 2012 occurred after the detection of the main SEP event related with a coronal mass ejection released in interplanetary space as a result of intense solar flare activity observed by SDO on 7 March 2012, (vi) the 8–10 March weather was related with a deep drop of ~63 °C in the cloud top temperature measured by MODIS/Terra, which favors strong precipitation. Finally, we analyzed data from the electric power network in Thrace (~41°N) and we found, for the first time sudden voltage changes of ~3.5 kV in the electric grid in Greece, during the decay phase of the March 2012 storm series. We discuss the winter-like March 2012 event in Thrace regarding the influence of solar cosmic rays on the low troposphere mediated by positive North Atlantic Oscillation (NAO). Finally, we infer that the novel finding of the geomagnetic effects on the electric power grid in Thrace may open a new window into space weather applications research.

Investigation of a Magnetic Reconnection Event with Extraordinarily High Particle Energization in Magnetotail Turbulence

Magnetic reconnection and plasma turbulence are ubiquitous and key processes in the Universe. These two processes are suggested to be intrinsically related: magnetic reconnection can develop turbulence, and, in turn, turbulence can influence or excite magnetic reconnection. In this study, we report a rare and unique electron diffusion region (EDR) observed by the Magnetospheric Multiscale mission in the Earth’s magnetotail with significantly enhanced energetic particle fluxes. The EDR is in a region of strong turbulence within which the plasma density is dramatically depleted. We present three salient features. (1) Despite the turbulence, the EDR behaves nearly the same as that in 2D quasi-planar reconnection; the observations suggest that magnetic reconnection continues for several minutes. (2) The observed reconnection electric field and inferred energy transport are exceptionally large. However, the aspect ratio of the EDR (one definition of reconnection rate) is fairly typical. Instead, extraordinarily large-amplitude Hall electric fields appear to enable the strong energy transport. (3) We hypothesize that the high-energy transport rate, density depletion, and the strong particle acceleration are related to a near-runaway effect, which is due to the combination of low-plasma-density inflow (from lobes) and possible positive feedback between turbulence and reconnection. The detailed study on this EDR gives insight into the interplay between reconnection and turbulence, and the possible near-runaway effect, which may play an important role in other particle acceleration in astrophysical plasma.

Energetic Particle Injection During Short Isolated Bubble as Seen in RCM Simulation and Spacecraft Observations in the Flow Braking Region

AbstractAlthough energetic particle (EP) injections are commonly thought to be formed by the flow burst intrusion from the magnetotail, important details and quantitative aspects of their transport, acceleration and flow braking need further investigation and understanding. Motivated by frequent observations of short transient EP injections being not associated with substorms, we analyze high‐resolution Rice Convection Model simulations of a short (5‐min long) localized (∼3RE width) density depletion (evacuating 90% of flux tube content) initiated at the tailward simulation boundary (∼18RE) and allowed to evolve within an otherwise typical plasma sheet environment. We note that, driven by betatron‐like acceleration, the peak EP flux at fixed energy dramatically increases in a couple of minutes when the bubble head enters the inner magnetosphere at r < 8–10 RE giving rise to a localized injection of subsequently drifting EP clouds. Here the 50–200 keV electron flux reaches values as high as #105 (cm2 s sr keV)−1, and even higher energies (up to 1 MeV) may briefly appear. Surprisingly, at a later stage of bubble penetration, after termination of bubble jet from the tail, the injection boundary of high energy (HE) particles detaches from the bubble earthward boundary while the latter continues moving inward. Time History of Events and Macroscale Interactions during Substorms multi‐spacecraft mission observations of a short bubble‐like flow burst at the spacecraft cluster located near the flow stopping point, show much similarity with simulation results but also reveal important differences between responses of HE protons and electrons attributed to the finite gyroradius effect.

No Response of Surface-Level Atmospheric Electrical Parameters in Israel to Severe Space Weather Events

We report ground-based measurements of the atmospheric electric field (Ez = −potential gradient (PG)) and current density (Jz) that were conducted at two locations in Israel. One is at the Emilio Segre cosmic ray station located on Mt. Hermon (34.45° N, 2020 m AMSL) in northern Israel near the Syrian-Lebanon border, and the other is at the Wise astronomical observatory in the Negev desert highland plateau of southern Israel (31.18° N, 870 m AMSL). We searched for possible effects of strong, short-term solar events on the potential gradient and the vertical current density, as disruptions to the global electric circuit are often observed following strong solar events. The first case study (St. Patrick’s Day, 17 March 2015) was classified as the strongest event of 2015. The second case study (8 September 2017) was categorized as the strongest event of 2017 and one of the twenty strongest events on record to date. The results show that the electrical parameters measured at ground level at both stations were not affected during the two massive proton events and the ensuing geomagnetic storms. The magnetospheric shielding in lower latitudes is strong enough to shield against the flux of energetic particles from solar events, obscuring any impact that may be noticeable above the local daily variations induced by local meteorological conditions (aerosol concentrations, clouds, high humidity, and wind speed), which were investigated as well.

The First Ground Level Enhancement Seen on Three Planetary Surfaces: Earth, Moon, and Mars

AbstractOn 28 October 2021, solar eruptions caused intense and long‐lasting solar energetic particle (SEP) flux enhancements observed by spacecraft located over a wide longitudinal range in the heliosphere. SEPs arriving at Earth caused the 73rd ground level enhancement (GLE) event recorded by ground‐based neutron monitors. In particular, this is also the first GLE event seen on the surface of three planetary bodies, Earth, Moon, and Mars, by particle and radiation detectors as shown in this study. We derive the event‐integrated proton spectrum from measurements by near‐Earth spacecraft and predict the lunar and martian surface radiation levels using particle transport models. Event doses at the lunar and martian surfaces of previous GLE events are also modeled and compared with the current event. This statistical and comparative study advances our understanding of potential radiation risks induced by extreme SEP events for future human explorations of the Moon and Mars.

Statistical Study of the Correlation between Solar Energetic Particles and Properties of Active Regions

The flux of energetic particles originating from the Sun fluctuates during the solar cycles. It depends on the number and properties of active regions (ARs) present in a single day and associated solar activities, such as solar flares and coronal mass ejections. Observational records of the Space Weather Prediction Center NOAA enable the creation of time-indexed databases containing information about ARs and particle flux enhancements, most widely known as solar energetic particle (SEP) events. In this work, we utilize the data available for solar cycles 21–24 and the initial phase of cycle 25 to perform a statistical analysis of the correlation between SEPs and properties of ARs inferred from the McIntosh and Hale classifications. We find that the complexity of the magnetic field, longitudinal location, area, and penumbra type of the largest sunspot of ARs are most correlated with the production of SEPs. It is found that most SEPs (≈60%, or 108 out of 181 considered events) were generated from an AR classified with the “k” McIntosh subclass as the second component, and these ARs are more likely to produce SEPs if they fall in a Hale class containing a δ component. The resulting database containing information about SEP events and ARs is publicly available and can be used for the development of machine learning models to predict the occurrence of SEPs.

Ion Implantation and Chemical Cycles in the Icy Galilean Satellites

An essential requisite for the appearance and permanence of life on Earth is the onset of a continuous “cycling” of some key atoms and molecules. Cycling of elements probably also occurs on other objects and is driven by biological or a-biological processing. Here we investigate the cycling of some species in the icy Galilean satellites that are exposed to the intense fluxes of energetic particles coming from the Jupiter magnetosphere. Among the most studied effects of particle bombardment, there is the production of molecules not originally present in the sample. These newly synthesized species are irradiated as well and in some circumstances can re-form the original species, giving rise to a “cycle”. Here we discuss the cycling of some atoms (C, N, O, S) incorporated in molecules observed on the surface of the icy Galilean satellites.The results indicate that cycling of carbon atoms starts with solid elemental carbon. Irradiated in the presence of water ice, carbon dioxide is produced and forms carbonic acid and other organics whose irradiation re-produces carbon dioxide and solid carbon. The effect on nitrogen atoms is limited to a continuous cycle among nitrogen oxides (e.g. NO2 produces NO, and N2O).Oxygen is mostly incorporated in water ice. When irradiated, the large majority of the water molecular fragments recombine to re-form water molecules.The sulfur cycle occurs among SO2 (that cannot be produced by ion irradiation only), sulfuric acid and elemental sulfur.The results are discussed in view of their relevance to the expected space observations of the JWST telescope (NASA, ESA, CSA) and the JUICE (ESA) spacecraft.

Hybrid monitoring and measurement of concrete shielding activation at the ProtherWal proton therapy centre

Proton therapy systems produce large fluxes of energetic secondary particles when tailoring the beam energy and transverse profile to the specificities of each irradiation plan. A Low Activation Concrete (LAC) mix is foreseen for parts of the shielding of the Ion Beam Applications (IBA) Proteus® One (P1) compact system at the ProtherWal proton therapy centre in Charleroi, Belgium, to limit the long-term activation of the concrete shielding. To experimentally monitor the long-term activation and validate the beneficial impact of the LAC mix, a setup of four removable cores to be placed at critical locations in the cyclotron vault is optimised. We report on the experimental and simulation monitoring setup design. Our validated BDSIM/FISPACT-II methodology combines particle tracking and Monte-Carlo particle-matter interactions simulations using Beam Delivery Simulation (BDSIM) and the computation of the activation using FISPACT-II. We show that the evaluation of the short-term activation of the cores is essential to the measurement analysis. We detail a hybrid workflow based on numerical simulations that uses logging data of the workloads of the clinical and research beam production and experimental measurements to evaluate and monitor the short- and long-term activation at any point during the centre lifetime and decommissioning period. The activation of the cores using a realistic foreseen irradiation pattern is studied, allowing for the characterisation of the measurement process and radiation protection considerations related to the measurement campaign. The final experimental setup and the supporting online simulation tools are discussed in detail.

SOLIS

Context. The study of the early phases of star and planet formation is important to understand the physical and chemical history of stellar systems such as our own. In particular, protostars born in rich clusters are prototypes of the young Solar System. Aims. In the framework of the Seeds Of Life In Space (SOLIS) large observational project, the aim of the present work is to investigate the origin of the previously inferred high flux of energetic particles in the protocluster FIR4 of the Orion Molecular Cloud 2 (OMC-2), which appears asymmetric within the protocluster itself. Methods. Interferometric observations carried out with the IRAM NOEMA interferometer were used to map the silicon monoxide (SiO) emission around the FIR4 protocluster. Complementary archival data from the ALMA interferometer were also employed to help constrain excitation conditions. A physical-chemical model was implemented to characterise the particle acceleration along the protostellar jet candidate, along with a non-LTE analysis of the SiO emission along the jet. Results. The emission morphology of the SiO rotational transitions hints for the first time at the presence of a collimated jet originating very close to the brightest protostar in the cluster, HOPS-108. Conclusions. The NOEMA observations unveiled a possible jet in the OMC-2 FIR4 protocluster propagating towards a previously measured enhanced cosmic-ray ionisation rate. This suggests that energetic particle acceleration by the jet shock close to the protostar might be at the origin of the enhanced cosmic-ray ionisation rate, as confirmed by modelling the protostellar jet.

Consistency of the average flux of solar energetic particles over timescales of years to megayears

Aims. Solar energetic particles (SEPs) have been measured directly in space over the past decades. Rare extreme SEP events are studied based on terrestrial cosmogenic proxy data for the past ten millennia. Lunar rocks record the average SEP fluxes on the megayear timescale. The question of whether the SEP fluxes averaged over different timescales are mutually consistent is still open. Here we analyze these different datasets for mutual consistency. Methods. Using the data from directly measured SEPs over the past decades and reconstructions of extreme SEP events in the past, we built a distribution function of the occurrence of annual SEP fluences for SEPs with energies above 30, 60, 100, and 200 MeV. The distribution function was fit with the Weibull and other types of distributions, and the long-term average SEP flux was computed and compared with the megayear SEP flux estimated from lunar data. Results. In contrast to the current paradigm, the direct space-era data are not representative of the long-term averaged SEP flux because they are only 20–55% of it, while the major fraction was formed by rare extreme SEP events in the past. The combined statistics of direct and proxy data are fully consistent with megayear lunar data, implying that our knowledge of the whole range of the SEP fluxes, from frequent weak to rare extreme events, is now consistent.

Ionization of inner T Tauri star discs: effects ofin situenergetic particles produced by strong magnetic reconnection events

ABSTRACTMagnetic reconnection is one of the major particle acceleration processes in space and astrophysical plasmas. Low-energy supra-thermal particles emitted by magnetic reconnection are a source of ionization for circumstellar discs, influencing their chemical, thermal, and dynamical evolution. The aim of this work is to propose a first investigation to evaluate how energetic particles can propagate in the circumstellar disc of a T Tauri star and how they affect the ionization rate of the disc plasma. To that end, we have collected experimental and theoretical cross sections for the production of H+, H$_2^+$, and He+ by electrons and protons. Starting from theoretical injection spectra of protons and electrons emitted during magnetic reconnection events, we have calculated the propagated spectra in the circumstellar disc considering the relevant energy loss processes. We have considered fluxes of energetic particles with different spectral indices and different disc magnetic configurations, generated at different positions from the star considering the physical properties of the flares as deduced from the observations obtained by the Chandra Orion Ultra Deep point source catalogue. We have then computed the ionization rates for a disc whose structure has been calculated with the radiation thermo-chemical code prodimo. We find that energetic particles are potentially a very strong source of local ionization with ionization rates exceeding by several orders of magnitude the contribution due to X-rays, stellar energetic particles, and radioactivity in the inner disc.

Ambient dose simulation of the ProtherWal proton therapy centre radioactive shielding decay using BDSIM and FISPACT-II

Next-generation proton therapy centres couple treatment and research programs, leading to higher beam currents and longer irradiation times than in clinical conditions. Large fluxes of energetic secondary particles are produced and long- and short-term radioactive nuclides are generated in the concrete shielding of the cyclotron vault. While the overall long-term activation of the centre is well known from the shielding design activation studies, the short-term activation peaks are still of importance when radiation protection studies are involved. The centre shielding design was validated using the BDSIM/FISPACT-II methodology combining particle tracking and Monte Carlo particle-matter interactions simulations using Beam Delivery Simulation (BDSIM) and the computation of the activation using FISPACT-II. We establish, as the next stage of our methodology, the simulation of the decay radiation of the activated concrete shielding and the accurate scoring of the related radiation protection quantities. A single BDSIM simulation per radioactive nuclide is performed based on the nuclide concentration obtained from the prior FISPACT-II activation computations at the start of a given cooling period. The evolution of the radiation protection quantities is obtained by scaling the results with the nuclides activity obtained at later times from fast FISPACT-II computations. We show the evolution of the ambient dose equivalent in the centre vault when considering regular concrete and Low Activation Concrete (LAC) as shielding material to demonstrate the efficiency of LAC mix in mitigating the shielding activation.

Polar particle flux distribution and its spatial extent

Context: The main challenge in atmospheric ionisation modelling is that sparse measurements are used to derive a global precipitation pattern. Typically this requires intense interpolation or scaling of long-term average maps. In some regions however, the particle flux might be similar and a combination of these regions would not limit the results even though it would dramatically improve the spatial and temporal data coverage. Aims: The paper intends to statistically analyse the particle flux distribution close to the geomagnetic poles labelled as Polar Particle Flux Distribution (PPFD) and identify similar distributions in neighbouring bins. Those bins are grouped and the size of the PPFD area is estimated. The benefit is that single measurements within the PPFD area should be able to represent the particle flux for the whole area at a given time. Methods: We use spatially binned energetic particle flux distributions measured by POES and Metop spacecraft during 2001–2018 to identify a Kp-dependent area with a similar flux distribution as the one found close to the geomagnetic poles (|magn.lat| > 86°). First, the particle flux is mapped on a magnetic local time (MLT) vs. magnetic latitude grid. In the second step, the gridded data is split up according to Kp levels (forming the final bins). Third, the particle flux in every bin has been recalculated in order to replace zero-count rates with rates based on longer measurement periods which results in a more realistic low flux end of the particle distribution. Then the binned flux distributions are compared to the PPFD. A “Δ-test” indicates the similarity. A threshold for the Δ-test is defined using the standard deviation of Δ-test values inside the (|magn.lat| > 86°) area. Bins that meet the threshold are attributed as PPFD area. Results: PPFDs and the corresponding PPFD areas have been determined for all investigated particle channels, covering an energy range of 154 eV–300 keV for electrons and 154 eV–2.5 MeV for protons. Concerning low energy channels a gradual flux increase with rising Kp has been identified. High energy channels show a combination of background population and solar particle event (SPE) population that adds up with increasing Kp. The size of the PPFD area depends on particle species, energy and geomagnetic disturbance, as well as MLT. The main findings are: a) There are small but characteristic hemispheric differences. b) Only above a certain energy threshold do the PPFD areas increase with particle energy. c) A clear enlargement with rising Kp is identified – with exceptions for very low Kp. d) The centre of the PPFD area is shifted towards midnight and moves with Kp. Asymmetries of the boundaries could be explained by auroral intensity. e) For low-energy particles the main restriction of the PPFD area seems to be the auroral precipitation.