Collisional Fragmentation Research Articles

Nuclear dynamics and particle production near threshold energies in heavy-ion collisions

Recent progress of the quantum molecular dynamics model for describing the dynamics of heavy-ion collisions is viewed, in particular the nuclear fragmentation, isospin physics, particle production and in-medium effect, hadron-induced nuclear reactions, hypernucleus etc. The neck fragmentation in Fermi-energy heavy-ion collisions is investigated for extracting the symmetry energy at subsaturation densities. The isospin effects, in-medium properties and the behavior of high-density symmetry energy in medium and high energy heavy-ion collisions are thoroughly discussed. The hypernuclide dynamics formed in heavy-ion collisions and in hadron induced reactions is analyzed and addressed in the future experiments at the High-Intensity heavy-ion Accelerator Facility (HIAF).

Metabolomic spectral libraries for data-independent SWATH liquid chromatography mass spectrometry acquisition.

High-quality mass spectral libraries have become crucial in mass spectrometry-based metabolomics. Here, we investigate a workflow to generate accurate mass discrete and composite spectral libraries for metabolite identification and for SWATH mass spectrometry data processing. Discrete collision energy (5-100eV) accurate mass spectra were collected for 532 metabolites from the human metabolome database (HMDB) by flow injection analysis and compiled into composite spectra over a large collision energy range (e.g., 10-70eV). Full scan response factors were also calculated. Software tools based on accurate mass and predictive fragmentation were specially developed and found to be essential for construction and quality control of the spectral library. First, elemental compositions constrained by the elemental composition of the precursor ion were calculated for all fragments. Secondly, all possible fragments were generated from the compound structure and were filtered based on their elemental compositions. From the discrete spectra, it was possible to analyze the specific fragment form at each collision energy and it was found that a relatively large collision energy range (10-70eV) gives informative MS/MS spectra for library searches. From the composite spectra, it was possible to characterize specific neutral losses as radical losses using in silico fragmentation. Radical losses (generating radical cations) were found to be more prominent than expected. From 532 metabolites, 489 provided a signal in positive mode [M+H]+ and 483 in negative mode [M-H]-. MS/MS spectra were obtained for 399 compounds in positive mode and for 462 in negative mode; 329 metabolites generated suitable spectra in both modes. Using the spectral library, LC retention time, response factors to analyze data-independent LC-SWATH-MS data allowed the identification of 39 (positive mode) and 72 (negative mode) metabolites in a plasma pool sample (total 92 metabolites) where 81 previously were reported in HMDB to be found in plasma. Graphical abstract Library generation workflow for LC-SWATH MS, using collision energy spread, accurate mass, and fragment annotation.

Determining Linear Free Energy Relationships in Peptide Fragmentation Using Derivatization and Targeted Mass Spectrometry.

The sequence complexity of a proteome is utilized with rational chemical derivatization to establish the linear free energy relationship (LFER) in order to investigate the collision-induced dissociation (CID) of peptides. The derivatization produces groups of peptides that have varying designer residues of aliphatic amino acids at the N-terminus but stay invariable for the rest of sequences, which are naturally occurring and uncontrolled. Collisional fragmentation of the derivatized peptides is advantageously monitored by liquid-chromatography multiple-reaction-monitoring mass spectrometry. Systematically tuning the gas-phase basicity of the N-termini of peptides establishes LFERs that report the structural similarities and differences in CID of all the backbone amides of doubly protonated tryptic peptides. For the cleavage of an internal or C-terminal amide, the peptide N-terminus mainly affects the mobility of the N-terminal proton instead of directly participating in the amide cleavage. In contrast, the terminal residue plays more pronounced roles in the cleavage of the first and second amide bonds. LFERs for the competition between the symmetric and asymmetric cleavage of the second amide bond support the protonated oxazolone structure for N-terminal fragments. This competition is affected locally by the chemistry of the first three residues and remotely by charge repulsion between the two protonation sites.

Measurements of jets in heavy ion collisions

The Quark Gluon Plasma (QGP) is created in high energy heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). This medium is transparent to electromagnetic probes but nearly opaque to colored probes. Hard partons produced early in the collision fragment and hadronize into a collimated spray of particles called a jet. The partons lose energy as they traverse the medium, a process called jet quenching. Most of the lost energy is still correlated with the parent parton, contributing to particle production at larger angles and lower momenta relative to the parent parton than in proton-proton collisions. This partonic energy loss can be measured through several observables, each of which give different insights into the degree and mechanism of energy loss. The measurements to date are summarized and the path forward is discussed.

Strange and heavy hadrons production from coalescence plus fragmentation in AA collisions at RHIC and LHC

In a coalescence plus fragmentation approach we study the pT spectra of charmed hadrons D0, Ds up to about 10 GeV and the Λ+c /D0 ratio from RHIC to LHC energies. In this study we have included the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence. The pT dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass. In particular we found that the Λc/D0 is much flatter than the one for light baryon/meson ratio like p/π and Λ/K.

Fragments in heavy ion collisions in a hydrodynamic approach with a nonequilibrium equation of state

A hydrodynamic approach with a nonequilibrium equation of state is used to describe heavy ion collisions at medium energies. This approach includes describing the compression, dilution, and freeze-out stages of a hot spot formed during a heavy ion collision. The calculated energy spectra of protons and light 4He, 7Li, 9Be fragments produced in the 14N + 124Sn reaction at a 14N ion energy of 32 MeV/nucleon are compared to experimental data.

Estimates of the Size Distribution of Meteoric Smoke Particles From Rocket‐Borne Impact Probes

AbstractIce particles populating noctilucent clouds and being responsible for polar mesospheric summer echoes exist around the mesopause in the altitude range from 80 to 90 km during polar summer. The particles are observed when temperatures around the mesopause reach a minimum, and it is presumed that they consist of water ice with inclusions of smaller mesospheric smoke particles (MSPs). This work provides estimates of the mean size distribution of MSPs through analysis of collision fragments of the ice particles populating the mesospheric dust layers. We have analyzed data from two triplets of mechanically identical rocket probes, MUltiple Dust Detector (MUDD), which are Faraday bucket detectors with impact grids that partly fragments incoming ice particles. The MUDD probes were launched from Andøya Space Center (69°17'N, 16°1'E) on two payloads during the MAXIDUSTY campaign on 30 June and 8 July 2016, respectively. Our analysis shows that it is unlikely that ice particles produce significant current to the detector, and that MSPs dominate the recorded current. The size distributions obtained from these currents, which reflect the MSP sizes, are described by inverse power laws with exponents of k∼ [3.3 ± 0.7, 3.7 ± 0.5] and k∼ [3.6 ± 0.8, 4.4 ± 0.3] for the respective flights. We derived two k values for each flight depending on whether the charging probability is proportional to area or volume of fragments. We also confirm that MSPs are probably abundant inside mesospheric ice particles larger than a few nanometers, and the volume filling factor can be a few percent for reasonable assumptions of particle properties.

Model studies for flocculation of sand-clay mixtures

Results are presented from a combined experimental and numerical study aimed at comparing the flocculation behaviour of purely-cohesive (clay) and mixed (sand-clay) sediment suspensions under equivalent controlled hydrodynamic conditions. The experiments were conducted in a grid-stirred settling column and focussed on measuring the parametric influences of grid-generated shear rate and local suspended sediment concentrations on the time-evolution of the micro- and macrofloc size distributions generated in the column, as well as representative maximal and root-mean-square floc sizes. The results indicate that for kaolin clay suspensions under low-medium shear rates, initial aggregation rates and the peak or quasi-equilibrium floc sizes attained increase with the clay input concentration; this latter effect due to the larger proportion of macroflocs generated within these runs. By contrast, under high shear rates, representative floc sizes for kaolin clay suspensions remain largely unchanged over the experimental duration, with little influence from clay input or in-situ concentrations, and no macroflocs present in the resulting floc size distributions. The addition of the fine sand fraction to the kaolin clay suspensions is shown to reduce both initial aggregation rates and the representative floc sizes attained in the column for runs under low-medium shear rates, whilst having negligible effect on the flocculation behaviour for the sand-clay mixtures under high shear rates. These results suggest that the sand fraction inhibits flocculation at lower shear rates due to an additional floc break-up mechanism resulting from direct sand-clay interactions (e.g. particle-floc collisions). The importance of these inter-fractional (sand-clay) interactions diminishes, in comparison to shear-induced floc break-up, under higher shear conditions. A one dimensional vertical (1DV) model incorporating a population balance equation (PBE) that includes new representation of these multi-fractional (sand-clay) collisions is applied to simulate the kaolin clay and sand-clay settling column tests. In general, the 1DV PBE model predictions provide good agreement with the measured in-situ concentrations and quasi-equilibrium floc sizes attained, but under-predict floc sizes during the initial aggregation phase due to uncertainty with the upper boundary condition in the 1DV model domain. Furthermore, the reliance of the 1DV PBE model predictions on empirical floc break-up rates associated with shear-induced floc fragmentation and multi-fractional (sand-clay) collisions warrants further attention to better define the microscale dynamics of these processes for their improved representation in the PBE model. It is anticipated that this multi-fractional approach represents an improved basis for modelling flocculation processes within natural sedimentary environments, such as estuaries and tidal inlets, where bed sediments often consist of interacting cohesive (i.e. muds) and non-cohesive (i.e. silts, sands) fractions.

Classical molecular dynamics simulations of fusion and fragmentation in fullerene-fullerene collisions

We present the results of classical molecular dynamics simulations of collision-induced fusion and fragmentation of C60 fullerenes, performed by means of the MBN Explorer software package. The simulations provide information on structural differences of the fused compound depending on kinematics of the collision process. The analysis of fragmentation dynamics at different initial conditions shows that the size distributions of produced molecular fragments are peaked for dimers, which is in agreement with a well-established mechanism of C60 fragmentation via preferential C2 emission.Atomic trajectories of the colliding particles are analyzed and different fragmentation patterns are observed and discussed. On the basis of the performed simulations, characteristic time of C2 emission is estimated as a function of collision energy.The results are compared with experimental time-of-flight distributions of molecular fragments and with earlier theoretical studies. Considering the widely explored case study of C60–C60 collisions, we demonstrate broad capabilities of the MBN Explorer software, which can be utilized for studying collisions of a broad variety of nanoscale and biomolecular systems by means of classical molecular dynamics.

Geology of the Campanian M1 sandstone oil reservoir of eastern Ecuador: A delta system sourced from the Amazon Craton

The Campanian M1 sandstone Member of the Napo Formation is one of the main reservoirs of the Capiron-Tiputini oil play system of the eastern part of the Oriente Basin of Ecuador. This study presents a geological model for this reservoir at the Apaika and Nenke oil fields included within the Block 31, and the Eden Yuturi oil field, operated by PETROAMAZONAS EP. The geological characterization of the M1 sandstone is based on an integrated study, which includes core description, electric log analyses and seismic data interpretation.The sedimentological descriptions from available cored sections show that M1 sandstone records a variety of fluvial to shallow marine processes, including mass flow and delta-front turbidity currents not previously documented. The stratal stacking pattern interpreted from electric logs indicates that the succession reflects deltaic progradation rather than the backstepping pattern typically displayed by the underlying Albian to Santonian sediments of the Napo Formation. Seismic RMS amplitude defines clinoform geometries with sigmoidal sand body architecture prograding from east to west. Correlation with neighboring regions in Colombia suggest that the M1 sandstone was probably part of a large river-dominated delta system sourced from the east during major Campanian progradation.The location of the source area of sediment was determined using U-Pb detrital zircon dating. Provenance ages are uniform within the M1 Sandstone cluster in a population that ranges from 1.4 to 1.6 billion years. These ages indicate that sands were derived mostly from erosion of the lithotectonic Rio Negro-Jurena province, located to the northeast of the studied area. Detrital ages from the overlying Maastrichtian Tena Formation include ages between 80 and 200 Ma pointing to an important change in the source areas, located in the Eastern Cordillera of Ecuador. The change in sediment supply from east to west recorded in the Tena Formation coincide with the initial episodes of the Andean orogeny, and may be driven by the collision of fragments of the Caribbean large igneous province (CLIP) against the continental margin of northwestern South America.

Delayed fission and multifragmentation in sub-keV C60 – Au(0 0 1) collisions via molecular dynamics simulations: Mass distributions and activated statistical decay

We have recently observed, both experimentally and computationally, the phenomenon of postcollision multifragmentation in sub-keV surface collisions of a C60 projectile. Namely, delayed multiparticle breakup of a strongly impact deformed and vibrationally excited large cluster collider into several large fragments, after leaving the surface. Molecular dynamics simulations with extensive statistics revealed a nearly simultaneous event, within a sub-psec time window. Here we study, computationally, additional essential aspects of this new delayed collisional fragmentation which were not addressed before. Specifically, we study here the delayed (binary) fission channel for different impact energies both by calculating mass distributions over all fission events and by calculating and analyzing lifetime distributions of the scattered projectile. We observe an asymmetric fission resulting in a most probable fission channel and we find an activated exponential (statistical) decay. Finally, we also calculate and discuss the fragment mass distribution in (triple) multifragmentation over different time windows, in terms of most abundant fragments.

Production of exotic nuclei in heavy ion collisions at Fermi energies

Isotopic distributions of projectile fragmentation in peripheral heavy ion collisions of 86Kr on 124Sn are calculated within the statistical multifragmentation model. Obtained data are compared to the experimental cross section measurements. We show the enhancement in the production of neutron-rich isotopes close to the projectile, observed in the experiments. The universality of the limitation of the excitation energy induced in the projectile residues is also demonstrated.

Neoproterozoic eclogite- to high-pressure granulite-facies metamorphism in the Mozambique belt of east-central Tanzania: A petrological, geochemical and geochronological approach

This study investigated Neoproterozoic (Pan-African) eclogite- and high-pressure-granulite (E-HPG) facies rocks from the Mozambique belt of east-central Tanzania, collected close to the town of Ifakara and the adjacent Furua area from different tectonic settings, the Palaeoproterozoic Usagaran and the Neoproterozoic Mozambique belt. The studied rocks are E-HPG facies granite- and diorite-gneisses and a meta-gabbroic rock, which are retrogressed to amphibolite- and greenschist-facies conditions. Four different clockwise P-T paths were constructed. The first P-T path for a granodioritic gneiss displays peak metamorphic conditions at ~830°C and ~13.0kbar. The second P-T path for a quartz dioritic gneiss shows peak metamorphic conditions of ~920°C and ~14.9kbar. The third P-T path for a mafic granulite shows peak metamorphic conditions of ~820°C and ~13.2kbar. A fourth P-T path for a monzodioritic gneiss also displays peak metamorphic conditions of up to ~810°C and ~14.9kbar. Evidence for all four P-T paths is provided by mineral chemical and modal abundance calculations in combination with textural observations in thin sections. Zircon ages indicate that the east-central part of the Mozambique belt in Tanzania consists of granite-, granodiorite- and monzodiorite gneisses with Mesoarchaean (~2915Ma), Neoarchaean (~2637–2676Ma) and Palaeoproterozoic (~1873–1926Ma) protolith ages. Early Neoproterozoic (Tonian) igneous zircons were found in the mafic granulite with an age of ~989Ma. Late Neoproterozoic (Cyrogenian) igneous zircons were found in a dioritic and monzodiorite gneiss with ages of ~748Ma and ~718Ma, respectively. Metamorphic zircons extracted from Qtz-monzodiorite and granodiorite gneisses yielded ages of ~640Ma and are considered to approximate the peak of regional E-HPG metamorphism. We suggest that this high-grade metamorphic event was caused by the collision of fragments of East and West Gondwana during the Pan-African orogeny, associated with ocean closure and the formation of Andean-type continental arc domains, which ended in the formation of a collisional belt.

Comets as a possible source of nanodust in the Solar System cloud and in planetary debris discs.

Comets, comet-like objects and their fragments are the most plausible source for the dust in both the inner heliosphere and planetary debris discs around other stars. The smallest size of dust particles in debris discs is not known and recent observational results suggest that the size distribution of the dust extends down to sizes of a few nanometres or a few tens of nanometres. In the Solar System, electric field measurements from spacecraft observe events that are explained with high-velocity impacts of nanometre-sized dust. In some planetary debris discs an observed mid- to near-infrared emission supposedly results from hot dust located in the vicinity of the star. And the observed emission is characteristic of dust of sizes a few tens of nanometres. Rosetta observations, on the other hand, provide little information on the presence of nanodust near comet 67P/Churyumov-Gerasimenko. This article describes why this is not in contradiction to the observations of nanodust in the heliosphere and in planetary debris discs. The direct ejection of nanodust from the nucleus of the comet would not contribute significantly to the observed nanodust fluxes. We discuss a scenario that nanodust forms in the interplanetary dust cloud through the high-velocity collision process in the interplanetary medium for which the production rates are highest near the Sun. Likewise, fragmentation by collisions occurs near the star in planetary debris discs. The collisional fragmentation process in the inner Solar System occurs at similar velocities to those of the collisional evolution in the interstellar medium. A question for future studies is whether there is a common magic size of the smallest collision fragments and what determines this size.This article is part of the themed issue 'Cometary science after Rosetta'.

The Demographics of Rocky Free-floating Planets and their Detectability by WFIRST

Abstract Planets are thought to form via accretion from a remnant disk of gas and solids around a newly formed star. During this process, material in the disk either remains bound to the star as part of either a planet, a smaller celestial body, or makes up part of the the interplanetary medium; falls into the star; or is ejected from the system. Herein we use dynamical models to probe the abundance and properties of ejected material during late-stage planet formation and estimate their contribution to the free-floating planet population. We present 300 N-body simulations of terrestrial planet formation around a solar-type star, with and without giant planets present, using a model that accounts for collisional fragmentation. In simulations with Jupiter and Saturn analogs, about one-third of the initial (∼5 M ⊕) disk mass is ejected, about half in planets more massive than Mercury but with a mass lower than 0.3 M ⊕, and the remainder in smaller bodies. Most ejections occur within 25 Myr, which is shorter than the timescale typically required for Earth-mass planets to grow (30–100 Myr). When giant planets are omitted from our simulations, almost no material is ejected within 200 Myr and only about 1% of the initial disk is ejected by 2 Gyr. We show that about 2.5 terrestrial-mass planets are ejected per star in the Galaxy. We predict that the space-borne microlensing search for free-floating planets from the Wide-Field Infra-Red Space Telescope will discover up to 15 Mars-mass planets, but few free-floating Earth-mass planets.

Symmetry energy and experimentally observed cold fragments in intermediate heavy-ion collisions**Supported by National Natural Science Foundation of China (U1432247, 11605097), National Basic Research Program of China (973 Program, 2014CB845405), Doctoral Scientific Research Foundation of Inner Mongolia University for the Nationalities (BS365)

An attempt is made to study the symmetry energy at the time of primary fragment formation from the experimentally observed cold fragments for a neutron-rich system of 64Ni + 9Be at 140 MeV/nucleon, utilizing the recent finding that the excitation energy becomes lower for more neutron-rich isotopes with a given Z value. The extracted asym/T values from the cold fragments, based on the Modified Fisher Model (MFM), are compared to those from the primary fragments of the antisymmetrized molecular dynamics (AMD) simulation and become consistent with the simulation when the I = N − Z value becomes larger, indicating that the excitation energy of these neutron-rich isotopes is indeed lower.

Kinetic energy distributions of product ions from singly and multiply ionized C2H2 molecules induced by 0.8 MeV C+ collisions

We measure kinetic energy distributions (KEDs) of product ions from singly and multiply ionized acetylene, C2H2r+∗ (r=1–4), generated as intermediate states prior to fragmentation in collisions between C2H2 and 0.8MeV C+ ions, in single-electron capture conditions. The KEDs are systematically obtained as functions of the charge state r by performing coincidence measurements between momentum imaging of the product ions and counting of the number of emitted electrons. The KEDs of the fragment ions exhibit a variety of dependences on r, reflecting the variation of fragmentation dynamics and dominant fragmentation pathways. In particular, the KEDs of C2+ present a characteristic dependence on r because of the different symmetries of charge distributions in three-body fragmentation.

Is the Eureka cluster a collisional family of Mars Trojan asteroids?

We explore the hypothesis that the Eureka family of sub-km asteroids in the L5 region of Mars could have formed in a collision. We estimate the size distribution index from available information on family members; model the orbital dispersion of collisional fragments; and carry out a formal calculation of the collisional lifetime as a function of size. We find that, as initially conjectured by Rivkin et al. (2003), the collisional lifetime of objects the size of (5261) Eureka is at least a few Gyr, significantly longer than for similar-sized Main Belt asteroids. In contrast, the observed degree of orbital compactness is inconsistent with all but the least energetic family-forming collisions. Therefore, the family asteroids may be ejecta from a cratering event sometime in the past ∼ 1 Gyr if the orbits are gradually dispersed by gravitational diffusion and the Yarkovsky effect (Ćuk et al., 2015). The comparable sizes of the largest family members require either negligible target strength or a particular impact geometry under this scenario (Durda et al., 2007; Benavidez et al., 2012). Alternatively, the family may have formed by a series of YORP-induced fission events (Pravec et al., 2010). The shallow size distribution of the family is similar to that of small MBAs (Gladman et al., 2009) interpreted as due to the dominance of this mechanism for Eureka-family-sized asteroids (Jacobson et al., 2014). However, our population index estimate is likely a lower limit due to the small available number of family asteroids and observational incompleteness. Future searches for fainter family members, further observational characterisation of the known Trojans’ physical properties as well as orbital and rotational evolution modelling will help distinguish between different formation models.

Planetesimal Clearing and Size-dependent Asteroid Retention by Secular Resonance Sweeping during the Depletion of the Solar Nebula

Abstract The distribution of heavy elements is anomalously low in the asteroid main belt region compared with elsewhere in the solar system. Observational surveys also indicate a deficit in the number of small (≲50 km size) asteroids, which is two orders of magnitude lower than what is expected from the single power-law distribution that results from a collisional coagulation and fragmentation equilibrium. Here, we consider the possibility that a major fraction of the original asteroid population may have been cleared out by Jupiter’s secular resonance, as it swept through the main asteroid belt during the depletion of the solar nebula. This effect leads to the excitation of the asteroids’ orbital eccentricities. Concurrently, hydrodynamic drag and planet–disk tidal interaction effectively damp the eccentricities of sub-100 km-size and of super-lunar-size planetesimals, respectively. These combined effects lead to the asteroids’ orbital decay and clearing from the present-day main belt region (∼2.1–3.3 au). Eccentricity damping for the intermediate-size (50 to several hundreds of kilometers) planetesimals is less efficient than for small or large planetesimals. These objects therefore preferentially remain as main belt asteroids near their birthplaces, with modest asymptotic eccentricities. The smaller asteroids are the fragments of subsequent disruptive collisions at later times as suggested by the present-day asteroid families. This scenario provides a natural explanation for both the observed low surface density and the size distribution of asteroids in the main belt, without the need to invoke special planetesimal formation mechanisms. It also offers an explanation for the confined spatial extent of the terrestrial planet building blocks without the requirement of extensive migration of Jupiter, which is required in the grand-tack scenario.

Jet fragmentation and multijet studies in heavy ion collisions at ATLAS

We report on two measurements done by ATLAS in a context of exploring the jet quenching physics at LHC: the jet fragmentation measurement and the measurement of neighbouring jet production. Both of these measurements were done using the data collected in 2011 Pb+Pb run providing Pb+Pb collisions at . These measurements are expected to provide an insight into the modifications of jets initiated by partons passing through hot and dense QCD matter created in heavy ion collisions.