Search

An intense solar energetic particle (SEP) event was observed on 2021 October 9 by multiple spacecraft distributed near the ecliptic plane at heliocentric radial distances R ≲ 1 au and within a narrow range of heliolongitudes. A stream interaction region (SIR), sequentially observed by Parker Solar Probe (PSP) at R = 0.76 au and 48° east from Earth (ϕ = E48°), STEREO-A (at R = 0.96 au, ϕ = E39°), Solar Orbiter (SolO; at R = 0.68 au, ϕ = E15°), BepiColombo (at R = 0.33 au, ϕ = W02°), and near-Earth spacecraft, regulated the observed intensity-time profiles and the anisotropic character of the SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at the onset of the SEP event, which resulted from the fact that PSP and STEREO-A were in the declining-speed region of the solar wind stream responsible for the SIR and from the passage of a steady magnetic field structure by SolO during the onset of the event. By contrast, the intensity-time profiles observed near Earth displayed a delayed onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV protons between the SIR and the shock driven by the parent coronal mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were nominally connected to the same region of the Sun, the intensity-time profiles at BepiColombo resemble those observed near Earth, with the bulk of low-energy ions also confined between the SIR and the CME-driven shock. This event exemplifies the impact that intervening large-scale interplanetary structures, such as corotating SIRs, have in shaping the properties of SEP events., Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. The STEREO SECCHI data are produced by a consortium of RAL (UK), NRL (USA), LMSAL (USA), GSFC (USA), MPS (Germany), CSL (Belgium), IOTA (France), and IAS (France). SOHO is a mission of international cooperation between ESA and NASA. The SDO/AIA data are provided by the Joint Science Operations Center (JSOC) Science Data Processing (SDP). Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins University Applied Physics Laboratory as part of NASA's LWS program (contract NNN06AA01C). We thank the German Federal Ministry for Economic Affairs and Energy and the German Space Agency (Deutsches Zentrum für Luft- und Raumfahrt, e.V., (DLR)) for their unwavering support of STEP, EPT, and HET under grants Nos. 50OT0901, 50OT1202, 50OT1702, and 50OT2002. N.W. acknowledges funding from the Research Foundation—Flanders (FWO–Vlaanderen, fellowship No. 1184319N). This project has received funding from the European Union's Horizon 2020 research and innovation programs under grant agreement No. 870405 (EUHFORIA 2.0). These results were also obtained in the framework of the ESA project "Heliospheric modeling techniques" (contract No. 4000133080/20/NL/CRS) and the projects C14/19/089 (C1 project Internal Funds KU Leuven), G.0D07.19N (FWO–Vlaanderen), SIDC Data Exploitation (ESA Prodex-12), and Belspo project B2/191/P1/SWiM. E.P. acknowledges support from NASA's PSP-GI (grant No. 80NSSC22K0349) and O2R (grant No. 80NSSC20K0285) programs. B.S.-C. acknowledges support through UK-STFC Ernest Rutherford Fellowship ST/V004115/1 and STFC grants ST/W00089X/1 and ST/V000209/1. R.G.H. acknowledges the financial support by the Spanish MICIU (project PID2019-104863RB-I00/AEI/10.13039/501100011033). R.V. and N.D. acknowledge funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004159 (SERPENTINE). N.D. also acknowledges support from the Turku Collegium for Science, Medicine and Technology of the University of Turku, Finland. A.A. acknowledges the support by the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant PID2019-105510GB-C31 and through the "Centre of Excellence María de Maeztu 2020-2023" award to the ICCUB (CEX2019-000918-M). D.L. and I.G.R. acknowledge support from NASA Living With a Star (LWS) programs NNH17ZDA001N-LWS and NNH19ZDA001N-LWS, the Goddard Space Flight Center Internal Scientist Funding Model (competitive work package) program, and the Heliophysics Innovation Fund (HIF) program. I.G.R. also acknowledges support from the ACE mission. The data used in this paper can be downloaded from spdf.gsfc.nasa.gov, www.srl.caltech.edu/ACE/ASC/, soar.esac.esa.int/soar/, stereo.gsfc.nasa.gov, gong.nso.edu/data/magmap/, sdo.gsfc.nasa.gov/data/aiahmi/. See also 10.48322/7gr7-1791, 10.48322/97te-0132, 10.48322/wpk2-yq48, and 10.48322/c0zj-xf76. BepiColombo data used in Figures 11 and 12 can be downloaded from 10.25392/leicester.data.19447259.v1.

Kollhoff, A., et al., Context. On 2020 November 29, the first widespread solar energetic particle (SEP) event of solar cycle 25 was observed at four widely separated locations in the inner (≲ 1 AU) heliosphere. Relativistic electrons as well as protons with energies > 50 MeV were observed by Solar Orbiter (SolO), Parker Solar Probe, the Solar Terrestrial Relations Observatory (STEREO)-A and multiple near-Earth spacecraft. The SEP event was associated with an M4.4 class X-ray flare and accompanied by a coronal mass ejection and an extreme ultraviolet (EUV) wave as well as a type II radio burst and multiple type III radio bursts. Aims. We present multi-spacecraft particle observations and place them in context with source observations from remote sensing instruments and discuss how such observations may further our understanding of particle acceleration and transport in this widespread event. Methods. Velocity dispersion analysis (VDA) and time shift analysis (TSA) were used to infer the particle release times at the Sun. Solar wind plasma and magnetic field measurements were examined to identify structures that influence the properties of the energetic particles such as their intensity. Pitch angle distributions and first-order anisotropies were analyzed in order to characterize the particle propagation in the interplanetary medium. Results. We find that during the 2020 November 29 SEP event, particles spread over more than 230° in longitude close to 1 AU. The particle onset delays observed at the different spacecraft are larger as the flare-footpoint angle increases and are consistent with those from previous STEREO observations. Comparing the timing when the EUV wave intersects the estimated magnetic footpoints of each spacecraft with particle release times from TSA and VDA, we conclude that a simple scenario where the particle release is only determined by the EUV wave propagation is unlikely for this event. Observations of anisotropic particle distributions at SolO, Wind, and STEREO-A do not rule out that particles are injected over a wide longitudinal range close to the Sun. However, the low values of the first-order anisotropy observed by near-Earth spacecraft suggest that diffusive propagation processes are likely involved., The CAU Kiel team acknowledges support from the German Federal Ministry for Economic Affairs and Energy, the German Space Agency (Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR) under grants 50OT0901, 50OT1202, 50OT1702, and 50OT2002. A.K. acknowledges financial support from the ANR COROSHOCK project (ANR-17-CE31-0006-01). D.L. acknowledges support from NASA-HGI grant NNX16AF73G and the NASA Program NNH17ZDA001N-LWS. This study has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004159 (SERPENTINE). The U. Turku team acknowledges funding by the Academy of Finland (Grant No. 336809). The UAH team acknowledges financial support by the Spanish Ministerio de Ciencia, Innovación y Universidades FEDER/MCIU/AEI Projects ESP2017-88436-R and PID2019-104863RB-I00/AEI/10.13039/501100011033. [...] The Swedish National Space Agency, ESA-PRODEX and all the participating institutes. I.G.R. acknowledges support from NASA programs NNH19ZDA001N-HSR and NNH19ZDA001N-LWS, and the STEREO mission. IRFU team acknowledges support from the Swedish National Space Agency grant 20/136. A.A. acknowledges the support of the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant PID2019- 105510GB-C31 and through the ‘Center of Excellence María de Maeztu 2020-2023’ award to the ICCUB (CEX2019-000918- M). F.C. acknowledges the financial support by the Spanish MINECO-FPI-2016 predoctoral grant with FSE. E.A. would like to acknowledge the financial support by the Academy of Finland (Postdoctoral Grant No 322455). V.K. acknowledges the support by NASA under grants 18-2HSWO218_2-0010 and 19-HSR-19_2-0143. Solar Orbiter magnetometer operations are funded by the UK Space Agency (grant ST/T001062/1). T.S.H. is supported by STFC grant ST/S000364/1. T.L. and S.D. acknowledge support from the UK Science and Technology Facilities Council (STFC; grant ST/R000425/1).

Aran, A., et al., [Context] In mid-June 2020, the Solar Orbiter (SolO) mission reached its first perihelion at 0.51 au and started its cruise phase, with most of the in situ instruments operating continuously. [Aims] We present the in situ particle measurements of the first proton event observed after the first perihelion obtained by the Energetic Particle Detector (EPD) suite on board SolO. The potential solar and interplanetary (IP) sources of these particles are investigated. Methods. Ion observations from ∼20 keV to ∼1 MeV are combined with available solar wind data from the Radio and Plasma Waves (RPW) instrument and magnetic field data from the magnetometer on board SolO to evaluate the energetic particle transport conditions and infer the possible acceleration mechanisms through which particles gain energy. We compare > 17-20 MeV ion count rate measurements for two solar rotations, along with the solar wind plasma data available from the Solar Wind Analyser (SWA) and RPW instruments, in order to infer the origin of the observed galactic cosmic ray (GCR) depressions. [Results] The lack of an observed electron event and of velocity dispersion at various low-energy ion channels and the observed IP structure indicate a local IP source for the low-energy particles. From the analysis of the anisotropy of particle intensities, we conclude that the low-energy ions were most likely accelerated via a local second-order Fermi process. The observed GCR decrease on 19 June, together with the 51.8-1034.0 keV nuc-1 ion enhancement, was due to a solar wind stream interaction region (SIR). The observation of a similar GCR decrease in the next solar rotation favours this interpretation and constitutes the first observation of a recurrent GCR decrease by SolO. The analysis of the recurrence times of this SIR suggests that it is the same SIR responsible for the He events previously measured in April and May. Finally, we point out that an IP structure more complex than a common SIR cannot be discarded, mainly due to the lack of solar wind temperature measurements and the lack of a higher cadence of solar wind velocity observations., EPD was built with funding from Ministerio de Ciencia e Innovación (Spain), Deutsches Zentrum für Luft- und Raumfahrt (Germany), and the European Space Agency (ESA); operations are funded by FEDER/MCI/AEI Projects ESP2017-88436-R and PID2019-104863RBI00/AEI/10.13039/501100011033 (Spain), 50OT 2002 (DLR, Germany), and NASA contract 80MSFC19F0002. The UB team acknowledges the support by the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant PID2019-105510GB-C31 and through the “Center of Excellence María de Maeztu 2020-2023” award to the ICCUB (CEX2019-000918-M). The CAU Kiel team acknowledges support by the German Federal Ministry for Economic Affairs and Energy, the German Space Agency (Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR) under grants 50OT0901, 50OT1202, 50OT1702, 50OT2002, and 50OC1702. The Solar Orbiter magnetometer was funded by the UK Space Agency (grant ST/T001062/1). M.L. and S.B. acknowledge financial support by the Italian MIUR-PRIN grant 2017APKP7T on Circumterrestrial Environment: Impact of Sun-Earth Interaction. N.W. acknowledges funding from the Research Foundation – Flanders (FWO – Vlaanderen, fellowship no. 1184319N). D.L. acknowledges the support from the NASA-HGI grant NNX16AF73G and the NASA Programs NNH17ZDA001N-LWS. I.G.R. and D.L. acknowledge support from NASA program NNH19ZDA001N-LWS. E.S. was supported by a PhD grant awarded by the Royal Observatory of Belgium. V.K. acknowledges the support by NASA under grants 18-2HSWO218_2-0010 and 19-HSR-19_2-0143. S.P. is supported by the projects C14/19/089 (C1 project Internal Funds KU Leuven), G.0D07.19N (FWO-Vlaanderen), SIDEX (ESA Prodex-12), and EUHFORIA 2.0 (funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405). IRFU team acknowledges support from the Swedish National Space Agency grant 20/136. F.C. acknowledges the financial support by the Spanish MINECO-FPI-2016 predoctoral grant with FSE. The JHU/APL team is supported under NASA contract NNN06AA01C and thanks NASA headquarters and the NASA/GSFC Solar Orbiter project office for their continuing support. Solar Orbiter Solar Wind Analyser (SWA) data are derived from scientific sensors which have been designed and created, and are operated under funding provided in numerous contracts from the UK Space Agency (UKSA, most recently grant ST/T001356/1), the UK Science and Technology Facilities Council (STFC), the Agenzia Spaziale Italiana (ASI), the Centre National d’Etudes Spatiales (CNES, France), the Centre National de la Recherche Scientifique (CNRS, France), the Czech contribution to the ESA PRODEX programme and NASA.

The properties of the suprathermal particle distributions observed upstream of interplanetary shocks depend not only on the properties of the shocks but also on the transport conditions encountered by the particles as they propagate away from the shocks. The confinement of particles in close proximity to the shocks, as well as particle scattering processes during propagation to the spacecraft, lead to the common observation of upstream diffuse particle distributions. We present observations of a rare extended anisotropic low-energy (≲30 keV) proton beam together with a trapped ≳500 keV proton population observed in association with the arrival of an oblique interplanetary shock at the Advanced Composition Explorer, the Interplanetary Monitoring Platform-8, and the Wind spacecraft on 2001 January 31. Continuous injection of particles by the traveling shock into a smooth radial magnetic field region formed in the tail of a modest high-speed solar wind stream produced an extended foreshock region of energetic particles. The absence of enhanced magnetic field fluctuations upstream of the shock results in the observation of a prolonged anisotropic field-aligned beam of ≲30 keV protons as well as a population of higher-energy (≳500 keV) protons with small pitch-angle cosine (μ ∼ 0) extending far from the shock.

The purpose of this study was to investigate the effects of age on calcium silicate hydrate (C–S–H) present in two cement pastes: one in which the C–S–H at a younger age had a high Ca/Si ratio and another that had a low ratio. The study involved characterising a 20 year old neat ordinary Portland cement (OPC) paste (high Ca/Si) and a blend of the OPC with 90% ground granulated blast furnace slag (GGBS; low Ca/Si); the results are compared with data on the same mixes at 14 months old. The morphology of the outer product (Op) C–S–H in the blend was essentially the same as at 14 months, whereas that in the neat OPC paste appeared to be finer. The mean aluminosilicate chain length of the C–S–H was considerably longer in both pastes than in similar systems at younger ages. The chemical composition of the C–S–H in both pastes was significantly different than at 14 months: in the neat OPC paste, the Ca/Si ratio of the outer product C–S–H had increased with age, whereas that of the inner product C–S–H had...

The C-S-H gels present in both water- and alkali-activated hardened pastes of white Portland cement/blast-furnace slag blends have been studied by solid-state 29Si magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and analytical transmission electron microscopy (TEM). Structural data are obtained by NMR for the semi-crystalline C-S-H gels in the alkali-activated systems and extended to the nearly amorphous gels in the water-activated systems by peak broadening; unambiguous chemical analyses are determined in the TEM. The following conclusions apply to both the semi-crystalline and nearly amorphous C-S-H gels: (1) aluminium substitutes for silicon at tetrahedral sites; (2) aluminium only substitutes for silicon in the central tetrahedron of pentameric silicate chains; (3) the results strengthen confidence in dreierkette-based models for the structure of C-S-H. Compositional similarities suggest that these conclusions will be true for OPC/slag blends, and possibly also for OPC/pulverized fuel ash blends indicating that the same structural model applies to C-S-H gels in a wide range of hardened cement pastes.

In the alkaline environment of concretes, silica can react in two ways. In the pozzolanic reaction, it combines with free lime to generate additional CSH binding phase. Alternatively reaction with alkali (ASR) can form a potentially expansive alkali silicate gel. 29Si enrichment enabled a series of 29Si MAS and CP MAS NMR spectra to be acquired in situ from a single sample. The hydrate from pozzolanic reaction of lime with silica was relatively crystalline and had long silicate chains. It was similar to the hydrate formed around silica in blended cements. Without lime, silica reacted with alkali solution to give a highly cross linked gel with a range of silicate mobilities. Tri-calcium silicate hydration was accelerated by high levels of alkali (KOH) in solution; shorter silicate chains and a more crystalline hydrate was produced than for hydration in water. Hydration in alkali solution of a model blended cement comprising a mixture of tri-calcium silicate and silica gave two products, a long chain relatively crystalline CSH and an alkali silicate of low rigidity. The alkali silicate gradually polymerized; at later ages it underwent a phase change.

The hydration of a mixture of tricalcium silicate and silica has been studied by 29Si solid-state nuclear magnetic resonance, using selective enrichment of the reactants with 29Si in order to follow and compare the behaviour of the silicon nuclei originating from either source. This approach shows for the first time that the silicon atoms from the two components are not equilibrated throughout the hydration products but are preferentially located in distinct species. In particular, from the distinctive spectra observed when the silica only is enriched, it is concluded that the part of the calcium silicate hydrate gel formed which incorporates silicon from this source has a longer chain length and a slightly better-ordered structure than the remainder. The spectra obtained with selective enrichment are interpreted in terms of a model based on a dreierkette chain structure for C-S-H.

In the current paradigm for the modulation of galactic cosmic rays (GCRs), diffusion is taken to be the dominant process during solar maxima while drift dominates at minima. Observations during the recent solar minimum challenge the pre-eminence of drift at such times. In 2009, the 2 GV GCR intensity measured by the Newark neutron monitor increased by 5% relative to its maximum value two cycles earlier even though the average tilt angle in 2009 was slightly larger than that in 1986 ( 20 vs. 14 ), while solar wind B was significantly lower ( 3.9 nT vs. 5.4 nT). A decomposition of the solar wind into high-speed streams, slow solar wind, and coronal mass ejections (CMEs; including postshock flows) reveals that the Sun transmits its message of changing magnetic field (diffusion coefficient) to the heliosphere primarily through CMEs at solar maximum and high-speed streams at solar minimum. Long-term reconstructions of solar wind B are in general agreement for the 1900-present interval and can be used to reliably estimate GCR intensity over this period. For earlier epochs, however, a recent 10Be-based reconstruction covering the past 104 years shows nine abrupt and relatively short-lived drops of B to _0 nT, with the first of these corresponding to the Sp rer minimum. Such dips are at variance with the recent suggestion that B has a minimum or floor value of 2.8 nT. A floor in solar wind B implies a ceiling in the GCR intensity (a permanent modulation of the local interstellar spectrum) at a given energy/rigidity. The 30 40% increase in the intensity of 2.5 GV electrons observed by Ulysses during the recent solar minimum raises an interesting paradox that will need to be resolved.

The local site symmetry of aluminium in Al-substituted calcium silicate hydrate phases, similar to those found in hardened Portland cement pastes, has been determined by experimental measurement and theoretical modelling of the electron energy loss near-edge structure associated with the aluminium K-edge measured using parallel electron energy loss spectroscopy in the transmission electron microscope. Changes in the local aluminium environment were observed between different regions of the microstructure which are explained in terms of aluminium substitution into both tetrahedral silicon and octahedral magnesium sites. This spatially-resolved information is in excellent agreement with27Al and29Si magic angle spinning nuclear magnetic resonance data on bulk samples as well as the predictions based upon compositional trends derived from the results of energy dispersive X-ray and electron energy loss elemental microanalysis. In a wider context we wish to stress the complementarity of both spatially-resolved and bulk spectroscopic techniques, which possess differing degrees of sensitivity, in the analysis of materials science samples.

29Si isotopic enrichment was used for acquisition of multiple 29Si magic-angle spinning (MAS) and cross-polarization magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra, in situ in an NMR probe, from a single sample of hydrating Ca3SiO5 (C3S). Data with excellent signal-to-noise ratios were obtained at 20, 50 and 75 °C, with minimal use of spectrometer time, and without the need for the quenching of multiple samples. Spectral line widths and polymer-chain lengths derived from the spectra had no detectable differences from experiments in which the quenching was carried out with propan-2-ol. Furthermore, the effects of the MAS technique on the hydration reaction appeared to be minimal. At 20 °C, the bulk hydrate initially produced was dimeric; at later stages of the reaction, polymerization occurred. Arrhenius energies of 35 and 100 kJ mol−1, respectively, were calculated for these two reactions. The cross-polarization (CP) spectra acquired throughout the hydration showed that at 20 °C, 2% of the hydrated monomeric Q o (H) species persisted from after the induction period through to the late stages of the hydration reaction; this indicates that this species is unlikely to result from surface hydroxylation of C3S; an upfield shift of this species occurred with increasing hydration, indicating a possible change of environment for the silicate species. The amount of Q o (H) produced was found to increase at higher temperatures. Potential mechanisms for polymerization were assessed and a model in which dimeric-silicate units are linked together by insertion of monomers (dimer → pentamer → octomer) was found to give the best fit to the observed data; these results support a dreierketten model for the structure of the hydrate.

Selective isotopic enrichment of SiO 2 with 29 Si in a mixture with tricalcium silicate (C 3 S) has allowed the Si from this phase to be effectively labeled during the course of the hydration reaction, thus isolating its contribution to the reaction. A double Q 2 signal has been observed in 29 Si solid-state MAS NMR spectroscopy of C-S-H gels of relatively low Ca/Si ratio, prepared by hydration or by carbonation of a C 3 S paste. The origin of the weaker, downfield peak is discussed and tentatively attributed to bridging tetrahedra of a dreierkette silicate chain structure

A microcrystalline form of calcium hydroxide consisting of clusters of lamallae, ∼10nm in thickness, intimately mixed with CSH gel, has been observed in a lime-silica cement paste by transmission electron microscopy. The volumes of calcium hydroxide and CSH in the clusters are comparable. The implications of this are discussed.

The C-S-H gels present in commercial blast-furnace slag and synthetic-slag glass pastes produced by hydrating with 5M KOH solution have been studied by a combination of transmission electron microscopy (TEM) and 29 Si and 27 Al nuclear magnetic resonance (NMR) spectroscopy. They are related by both composition and morphology to the C-S-H gels present in slag-OPC pastes but are more crystalline. The inner product C-S-H is intermixed on a fine scale with a Mg,Al-rich phase with a Mg/Al ratio of ≈2.5. The C-S-H in both inner and outer product contains substituted Al in tetrahedral co-ordination sites. The data are analysed in terms of a model for the structure of C-S-H gel.

The local environment of aluminium in Al-substituted calcium silicate hydrate phases in cement pastes has been determined by measurement and modelling Al K-ELNES. The results are in agreement with bulk 27Al and 29Si MAS NMR data and predictions derived from compositional trends.

Solid-state 27 Al and 29 Si magic angle spinning NMR spectroscopy has been combined with electron energy loss spectroscopy carried out in the transmission electron microscope to determine the location of Al substituting in a semicrystalline C-S-H gel present in a hydrated synthetic slag glass. The gel is found to contain mainly pentameric silicate chains in which the central silicon is substituted by aluminum

Slices of hardened pastes of OPC and an OPC/silica fume blend of the same water: solids ratio of 0·5 were carbonated in air for 116 days at a fixed relative humidity. The blended paste slices were found to have carbonated less overall, and to a lesser depth, than the OPC slices. The microstructures of the partially carbonated slices were examined by transmission electron microscopy, and in the case of the OPC the silicate structure was investigated by 29Si NMR.

Hardened ordinary Portland cement pastes of various ages have been examined by analytical transmission electron microscopy (TEM) and electron microprobe analysis (EMPA). The stability of the various hydrate phases in the electron microscope is discussed. Although all are subject to damage in varying degrees, even the least stable phase, AFt, can be recognized in relict form in the TEM. The basic framework of the microstructure and the differentiation into inner and outer hydration product are well-established at 24 h hydration. Although the dominant inner product formed within the boundaries of the original anhydrous grains is C-S-H gel, particles of AFt, AFm, Ca(OH)2, a magnesium-rich phase and an iron-rich phase are occasionally observed within the inner product. The Ca∶Si ratio of the C-S-H gel determined by TEM shows significant variation from one region to another in a given paste. There is no relationship between the average Ca∶Si ratio of the C-S-H and the maturity of the paste, although young pastes appear to show a bimodal distribution. Microanalysis by EMPA gives Ca∶Si ratios in substantial agreement with those found by TEM but it is essentially impossible to obtain by EMPA analyses of outer product C-S-H without admixture of other phases, particularly sulphoaluminate phases. Despite the presence of small amounts of embedded phases as revealed by TEM, single-phase inner product C-S-H can be analysed by EMPA. The compositions of AFt and AFm phases have been obtained by TEM and the results do not require the substitution of silicon in the formulae.

The interstitial phase of an oil-well cement production clinker was examined by analytical transmission electron microscopy. The predominant interstitial component was a ferrite of varying composition, the Fe: Al ratio varying from a low value to 2, and values most commonly in the range O·7-2. A substantial variation in composition sometimes took place over quite short distances. Displacement faults were found in the ferrite, and these appeared to be associated with relatively iron-rich regions of the ferrite. Small regions of C2S, MgO and non-cubic C3A were also found in the interstitial phase of the clinker.

The General model for CSH gel described by Richardson and Groves (1) has been extended to incorporate elements other than Ca, Si, O and H which have been detected by X-ray microanalysis of gels in hardened Portland cement and blended cement pastes.

Models for the structure of CSH gels occuring in hardened C3S cement pastes are considered and compared to some examples in which composition and silicate anion structure have been investigated experimentally.

The microstructure and composition of hardened cement pastes of a wide range of blends of ground granulated blast-furnace slag with ordinary Portland cement have been studied, using techniques of transmission electron microscopy with microanalysis combined with electron microprobe analysis. Throughout the range, a calcium silicate hydrate gel (C-S-H) is the dominant cementing phase, present in the “inner product” within the space originally occupied by either slag grains or alite or belite grains originating from the Portland cement, or in the “outer product” in the originally water-filled spaces. The morphology and composition of the outer product C-S-H and the composition of inner product C-S-H change with blend composition. Inner product of slag grains contains C-S-H of the same composition as the outer product C-S-H, intimately mixed with a Mg, Al-rich hydroxide phase whose fineness shows considerable variation. Inner product C-S-H of alite or belite does not differ significantly in Ca∶Si ratio from that of slag. The reduction of Ca∶Si ratio of all forms of C-S-H with increasing slag loading may have implications for the pH-buffering capacity of blends of large slag loading.

The structures of partially carbonated hardened C3S cement pastes have been investigated by a combination of 29Si magic angle spinning nuclear magnetic resonance spectroscopy and analytical transmission electron microscopy, supported by X-ray diffraction and thermogravimetric analysis. Progressive changes in structure are reported for thin slices for a paste carbonated in pure CO2 for times from 1 to 16 h, and the results are compared with those for a paste carbonated for 2 months in air. C-S-H gel of reduced Ca:Si ratio and increased silicate polymerization was formed during the early stages of carbonation. The morphology of the original C-S-H was, in the main, retained. A cross-linked silica-rich gel formed at later times in paste carbonated in CO2 but not up to the time of 2 months in air. Calcium carbonate took the form of microcrystals of vaterite and calcite which formed dense masses between gel fibrils and around partially reacted CH crystals, possibly accounting for the observed slowing in the rate of reaction of CH with time.

The microstructure of hardened pastes of C3S and a C3S/silica fume blend have been examined by transmission electron microscopy before and after partial carbonation in pure CO2 at a relative humidity of 72·6%. Fibrillar outer product C-S-H and the outer regions of inner product C-S-H gel carbonate without change of morphology to silica gel. Calcium carbonate is formed mainly in outer product regions as microcrystalline vaterite or calcite. Residual CH embedded in vaterite microcrystals is observed in the carbonated C3S pastes. It is proposed that outer product C-S-H and CH surfaces carbonate relatively rapidly, compared with inner regions of CH or the inner regions of inner product C-S-H, leading to a substantial level of carbonation of thin slices (0·4 mm) of paste within one day, with little further carbonation in the next few days. The implications for the theory of the kinetics of cement paste carbonation are discussed.

29Si enrichment has been used to enable acquisition of multiple 29Si MAS and CP-MAS NMR spectra from samples of C3S hydrating in situ in a MAS NMR probe. Data with excellent signal-to noise ratios were obtained at 20, 50, and 75°C, with minimal use of spectrometer time, and without the need for quenching of multiple samples; the data were however consistent with those obtained conventionally. The bulk hydrate initially produced was dimeric; at later stages of reaction, polymerization occurred. Arrhenius energies of 35 and 100 kJmol−1 were calculated for formation of the two products. A model of hydration in which dimeric silicate units are linked together by monomers was found to be consistent with the observed results. The pozzolanic reaction with C3S and SiO2 has also been studied with enrichment of both starting materials — the hydrate produced is more ordered and of longer chain length than that produced by hydration of C3S alone. By enrichment of the SiO2 only it was possible selectively to observe hydrate which contains silicate species which originate from the SiO2; this material had a much higher degree of order, and a much longer chain length than the remainder of the hydrate. Thus isotopic enrichment and especially selective isotopic enrichment are valuable tools for the study of cementitious systems.

Energetic particles respond to the presence of solar wind disturbances with the signatures depending on the characteristics of the disturbance. Thus by using observations of energetic particles over a wide range of energies, it is possible to elucidate the type of disturbance present. For transient events, energetic particles also supply information about the history of the related solar mass ejection and hence provide a valuable means of relating solar and interplanetary phenomena. We point out that erroneous relationships may have been inferred in previous studies relating magnetic clouds and prominence eruptions which did not take energetic particle data into consideration.

We investigate the solar-cycle dependence of the occurrence rate in the solar wind of regions with abnormally low proton temperatures during the years 1965 to 1990. To identify such regions, we compare the observed temperature with the temperature expected from the proton temperature-solar wind speed correlation found in ‘normal’ solar wind. The occurrence rate of abnormally low temperature plasma is correlated with solar activity levels and in particular with the rate of coronal mass ejections (CMEs) at the Sun. The low temperature regions show higher than chance associations with other signatures of ejecta in the solar wind. However abnormally low temperature plasma is not be a unique signature of ejecta since around 30% of the regions identified are related to encounters with the heliospheric plasma sheet, and the occurrence rate for these events depends more on the tilt angle of the heliospheric current sheet than on the CME rate.

We demonstrate that the anisotropies of energetic particles (>0.2 MeV electrons and >1 MeV protons) can provide information on the magnetic topology of ejecta. In particular, we have examined 38 solar energetic particle events for which the onset phase was observed by ISEE 3 when the spacecraft was located inside an ejecta. Around 30% of these particle events exhibit unusual flows from the east of the Sun at event onset. Such flows are rarely found in 34 events which were observed outside ejecta. The observations are consistent with the presence of looped magnetic structures in ejecta.

Burst-like enhancements of energetic ions were observed by the EPAS instrument on the International Cometary Explorer (ICE) during its closest approach to (28 × 106 km upstream of) Comet P/Halley, in late March 1986. The enhancements showed considerable temporal structure and highly anisotropic angular distributions, with strong ion streaming in the antisolar direction. The ion intensity was modulated by the varying solar wind speed (the latter reaching maxima of around 600 km s−1), as was found to be the case for heavy cometary ions accelerated by pick-up in the solar wind flow, during the ICE encounter with Comet P/Giacobini-Zinner (G-Z). We therefore conclude that we observed pick-up ions (most probably ≥ 65 keV oxygen ions) produced by heavy neutrals from Comet Halley. The region of pick-up ions extended to more than 0.2 AU (∼35 × 106 km) from the nucleus at this time, at least three times further than was observed during the Giotto and VEGA encounters. The observations of energetic ions at such large distances suggest the presence, in the neutral atmosphere surrounding the nucleus, of a component with an ionisation scale length of 5-10 million km, resulting from a relatively high expansion speed of a few km s−1 and/or an ionisation time scale of a few times 106s.

Bame et al. (1983) have given plasma measurements for two 12-hour intervals and have identified the plasma regions observed during the January 1-March 30, 1983 traversal by the ISEE-3 spacecraft of a previously unexplored part of the distant geomagnetic tail. Attention is presently given to the 35 keV-1.6 MeV energetic ion and magnetic field measurements made by ISEE-3, relating them to the plasma measurements. The plasma sheet is found to be a region of energetic ion enhanced fluxes, with unidirectionally tailored flow. A characterization accounting for these characteristics involves occurrence of reconnection at a neutral line that lies earthward of the spacecraft.

A general characterization of the early stage hydration behaviour of ground granulated blastfurnace slag/ordinary Portland cement blends reacting in the temperature range 20–60°C has been made by thermal and electron microscopic techniques. In the blends studied, both the silicate and aluminate associated reactions were accelerated by an increase in hydration temperature, although the aluminate acceleration was greatest. The marked effect of thermal activation on the hydration of ground granulated blastfurnace slag is illustrated.

The properties of energetic (65–95 keV) cometary water-group ions in the extended solar wind pick-up region surrounding comet Giacobini-Zinner are examined using data from the EPAS instrument on the ICE spacecraft. In the outer part of this region, extending from cometocentric distances of several hundred thousand to a few million kilometres (the limit of pick-up ion detectability), it is found that large modulations of the ion flux occur (with J MAX J MIN ≅ 10 2 -10 3 ) which are related to the direction of the magnetic field. It is also found that the ions stream in a direction which is intermediate between the directions of the solar wind flow and the E × B drift, and that ions are present at energies somewhat above the local pick-up energy. These properties indicate that the waves which are excited by the unstable “ring-beam” pick-up ion velocity distributions do result in significant scattering of the ions in this region, both in pitch angle and in energy, but that they have insufficient amplitude to scatter the ions into near isotropy in the solar wind frame. Closer to the comet (but still upstream from the bow shock), the ion flux modulations are considerably reduced in amplitude and the ions respond less to the E × B drift, indicating that the ions are scattered nearer to isotropy in this region. Inbound, this transition takes place relatively abruptly at a distance of ∼4 × 10 5 km in association with an increase in the solar wind speed, after which the ion flux increases, and ceases to be modulated by the field direction, while the streaming direction is continuously antisolar and unmodulated by the direction of the E × B drift. Outbound, weak vestiges of the ring-beam ion anisotropy are present in the region immediately upstream from the bow shock (at −1 × 10 5 km), but these become more marked at distances in excess of t4 × 10 5 km, increasing gradually with increasing distance from the comet. It is shown that the evolution of the ion properties is qualitatively consistent with expectations based on quasi-linear diffusion of the ions by the magnetosonic waves observed during the encounter.

Drift mirror waves have been de- encounter. The decrease in density can be ex- tected 207 R e downstream in the distant magneto- plained if IMP-8 has entered a different region sheath by instrumentation onboard ISEE-3. The of the interplanetary event. The densities de- MHD structures have estimated scale sizes of 4.6 crease to ~0.2 cm -3 by 1000 UT, the start of x 104 to 2.3 x 105 km or 130 to 700 proton gyro- the interval of interest. The earth's bow shock radii, assuming 1 keV protons. Simultaneous mea- may have become very weak (or even non-existent) surements on IMP-8 indicate that at the time of at this time. The unusually low density, high the events, the earth's magnetosphere was envel- field plasma has a correspondingly high Alfvn oped by a solar flare-associated interplanetary speed, and therefore the bow shock, a low Alfvn shock and driver gas. The (shocked) driver gas Mach number. was characterized by an unusually low plasma den- The IMP magnetic fields are shown in higher sity with a B (plasma pressure/magnetic pressure) time resolution in the top three panels of fig- of ~ 0.2. From the instability criterion, l/ ure 2. The field has an unusual orientation, 11>l+l/l, the magnetosheath plasma should notSM =45o, SM =30o and there is an absence of dis- go mirror-mode unstable unless the anisotropy, Bl continuities and long period waves. The above / 811 is large, >6. These unusual conditions are field characteristics indicate that this region met by the demonstrated presence of highly aniso- may correspond to the driver gas of the solar tropic, energetic 35-384 keV ions with Pi/Pll=30. flare event (Zwickl et al., 1983; Tsurutani et It is calculated that most of the plasma energy al., 1984). density can be due to >1 keV ions. The source of Figure 2 also shows a comparision between ISEE the ions is not well understood, but an appealing and IMP magnetic fields. The orientation of the possibility is magnetic annihilation of the north- ISEE fields detected 207 R e downstream is almost ward magnetosheath fields with southern hemi- identical to that detected at IMP. The field mag- sphere polar cusp magnetic fields. nitude at ISEE is slightly lower due to the down- stream expansion of the magnetosheath plasma. The plasma velocity of ~550 km/sec detected at ISEE

Ground granulated blast-furnace slag (ggbfs)/OPC blends are among the materials being considered as possible encapsulating matrices for low and intermediate level radioactive wastes. It is therefore desirable to identify any microstructural modifications which may result in these systems frmn exposure to ionizing radiations. In order to investigate this, ggbfs/COC blends were γ-irradiated to >80M3y at 50°C over a period of 2 years. These were examined by electron optical, X-ray and thermal analysis techniques and the results ccmpared with controls subjected to a similar hydration regime. The morphological and ccmpositional similarities and differences revealed between the irradiated and control samples are presented and discussed.

Ground granulated blast-furnace slag (ggbfs) /Ordinary Portland cement (OPC) blends are possible materials for use in intermediate and low-level radioactive waste repositories. The microstructural development in neat OPC is described. The effect of increasing the loading of ggbfs on the composition and microstructure of the hardened paste has been examined by a number of techniques, including transmission electron microscopy. The implications for performance are discussed. A ggbfs/OPC 9:1 blend which had been exposed, after normal hydration to aqueous leaching was also examined. Marked changes in the microstructure and composition were observed.

The application of transmission electron microscope techniques to the study of cement hydration can reveal the nature of the fine pore structure present in dried cement pastes. Studies of OPC cement pastes and OPC/fly ash or blast-furnace slag blends are presented and compared. Preliminary results of a technique which allows effective imaging of the porosity which is important in permeation, and which is involved in mercury porosimetry measurements, are presented.

On March 25, 1986, the ICE spacecraft came within 28 106 km of the nucleus of comet Halley. For several days around this time, bursts of heavy ions were observed by the ICE energetic ion experiment. These bursts were observed only during periods when the solar wind velocity was considerably higher than its nominal value. We examine the characteristics of these ions, in particular their anisotropies. Using the well known formulae for transformation of distributions from the solar wind frame of reference to the spacecraft frame, we examine the angular distributions expected from either protons, or heavy ions from the water group, and show that the measurements are consistent with heavy ions, and not with protons. We discuss other sources of heavy ions and conclude that the most likely source of these ions is comet Halley.

The energy spectrum of water-group pick-up ions with energies > 35 keV observed during the encounter of comet Giacobini-Zinner by the ICE spacecraft is examined using data from the EPAS experiment, combined with published data from the ULECA sensor. In the plasma frame the combined spectra consist mainly of a steeply-falling tail extending to energies of a few hundred keV, but there is also evidence for flattening at speeds somewhat below the local pick-up speed. The latter feature is most evident in the solar wind outside the mass-loaded region of slowed flow, where the local pick-up speed is sufficiently fast that it falls within the range of the combined EPAS and ULECA data. Above the local ion pick-up speed the ion distribution function is well approximated by a decreasing exponential of ion speed. The characteristic speed of this distribution increases (i.e. the spectrum hardens) as the comet is approached. It is demonstrated that EPAS data can give detailed information on this portion of the spectrum with 32 s time resolution.

We demonstrate a close relationship between bidirectional flows of galactic cosmic rays measured by the worldwide neutron monitor network and bidirectional flows of solar/shock-accelerated particles at much lower energies (∼ 1 MeV) observed by near-Earth spacecraft, during January–September 1982. We find that ∼ 80% of bidirectional cosmic ray flows are accompanied by bidirectional low energy ion flows. The observations indicate a close association between BCRFs and interplanetary coronal mass ejections/ejecta. The bidirectional flows suggest that particles of a wide range of energies are trapped on expanding, looped magnetic field lines, providing that their gyroradii are much smaller than the ∼ 0.1 to few AU scale sizes of ejecta. Unidirectional flow components are less well correlated at ∼ 1 MeV and cosmic ray energies, presumably because they reflect gradients in different particle populations. We discuss several events in detail and illustrate how changes in particle flows may be related to substructures within these ejecta.

During a 9-hour period following a storm-sudden commencement, six spacecraft near geosynchronous orbit, one over the pole, and three in the mgnetotail, monitored a complex sequence of magnetospheric variations. Magnetic field compressions associated with the sudden commencement were seen first by the near-earth spacecraft and subsequently by the three down-tail spacecraft with increasing time delays that were consistent with the tailward movement of an interplanetary-shock-associated pressure enhancement. Ground magnetograms and synchronous orbit data are used to identify 7 substorm intensifications during this geomagnetically active period. Six of these intensifications are clearly associated with tail lobe field decreases about 18 R sub E behind the earth. Four of these intensifications are followed by both Bz field increases in the tail lobes at about 18 and about 30 R sub E and by the subsequent observation of rapidly flowing plasma sheet plasma at ISEE 3 about 110 R sub E down the tail. During two substorms where DE 1 was optically observing the auroral oval, the area of the polar cap was observed to decrease as the tail lobe field decreased at 18 R sub E. All these observations are consistent with the substorm associated release of a plasmoid at a neutral line near 20 R sub E.