Fragmentation Cross Sections Research Articles

Mechanisms of lipid preservation in archaeological clay ceramics revealed by mass spectrometry imaging

Traces of lipids, absorbed and preserved for millennia within the inorganic matrix of ceramic vessels, act as molecular fossils and provide manifold information about past people's subsistence, diet, and rituals. It is widely assumed that lipids become preserved after adsorption into nano- to micrometer-sized pores, but to this day the distribution of these lipids in the ceramics was virtually unknown, which severely limits our understanding about the process of lipid preservation. Here we use secondary ion mass spectrometry (SIMS) imaging for direct in situ analysis of lipids absorbed in 700- to 2,000-y-old archaeological pottery. After sectioning from larger sherds, wall cross-sections of smaller fragments were used for SIMS analysis. Lipids were found in relatively large zones of 5- to 400-µm diameter, which does not support the notion of absorption only into individual nanometer-scale pores but indicates that more macroscopic structures in the ceramics are involved in lipid preservation as well. Furthermore, lipids were found concentrated on calcium carbonate inclusions in the ceramics, which suggests that precipitation of fatty acids as calcium salts is an important aspect of lipid preservation in archaeological samples. This has important implications for analytical methods based on extraction of lipids from archaeological ceramics and needs to be considered to maximize the yield and available information from each unique sample.

Investigation of shielding material properties for effective space radiation protection

Geant4 Monte Carlo simulations were carried out to investigate the possible shielding materials of aluminum, polyethylene, hydrides, complex hydrides and composite materials for radiation protection in spacecraft by considering two physical parameters, stopping power and fragmentation cross section. The dose reduction with shielding materials was investigated for Fe ions with energies of 500 MeV/n, 1 GeV/n and 2 GeV/n which are around the peak of the GCR energy spectrum. Fe ions easily stop in materials such as polyethylene and hydrides as opposed to materials such as aluminum and complex hydrides including high Z metals with contain little or no hydrogen. Attenuation of the primary particles in the shielding and fragmentation into more lightly charged and therefore more penetrating secondary particles are competing factors: attenuation acts to reduce the dose behind shielding while fragmentation increases it. Among hydrogenous materials, 6Li10BH4 was one of the more effective shielding materials as a function of mass providing a 20% greater dose reduction compared to polyethylene. Composite materials such as carbon fiber reinforced plastic and SiC composite plastic offer 1.9 times the dose reduction compared to aluminum as well as high mechanical strength. Composite materials have been found to be promising for spacecraft shielding, where both mass and volume are constrained.

Ionization and electron capture for H+ collisions at low keV energy with CCl4 molecules

Relative total ionization cross sections and fragment target ions have been measured for proton impact on CCl4 molecules for the first time, namely associated with the formation of CCl3+, CCl2+, CCl+, Cl2+, Cl+ and C+ ions. The experiment was conducted by crossing a proton beam of 2.5 to 10 keV with a CCl4 vapor target where the fragment ions were measured employing the time of flight technique. Relative fragment cross sections were added leading to the total relative cross section. All relative cross sections seem to be independent of the collisional energy. A qualitative comparison was conducted with previous measurements of electron impact experiments. Ratios of CCl3+/CCl2+, CCl3+/CCl+, CCl3+/C+ and CCl3+/Cl+ were compared to those obtained from electron impact experiments.

The Foot Experiment: Measuring Proton and Light Nuclei Fragmentation Cross Sections up to 700 MeV/A

FOOT is a nuclear physics experiment which aims to fill the gap in experimental data on the differential cross sections for the production of secondary fragments induced by proton and ion beam interactions with energies up to 700 MeV/A. These data are necessary for correct medical applications and calculations of radiation doses in different conditions, for the design and optimization of spacecrafts for cosmic flights.

Clustering effects in the exit channels of C13,12+C12 reactions within the collective clusterization mechanism of the dynamical cluster decay model

From the past few years, increasing experimental evidence has shown that clusters (multiple of $\ensuremath{\alpha}$ particles) of intermediate mass are emitted with quite large cross sections at forward angles in heavy-ion reactions. In the present work a theoretical investigation has been made to explore the role of $\ensuremath{\alpha}$-clustering in $^{13,12}\mathrm{C}+^{12}\mathrm{C}$ reactions populating $^{25,24}\mathrm{Mg}^{*}$ compound nuclei (CN), which results in the enhanced cross sections of intermediate mass fragments (IMFs) within the collective clusterization framework of the dynamical cluster decay model (DCM). With in the formalism the experimental cross sections are reproduced using the spherical as well as deformed configurations effects included up to quadruple deformations (${\ensuremath{\beta}}_{2i}$) for two nuclei having optimum orientations ${\ensuremath{\theta}}^{\mathrm{opt}}$. The ratio of the calculated (fission-like) yields of each isotopic fragment $^{6,7}\mathrm{Li}, ^{7,8,9}\mathrm{Be}$ obtained in the two reactions has been compared with the experimental and statistical model predictions also. The DCM calculated result is in little better comparison to the statistical models due to the inclusion of structure effects in the calculations. In the present calculations, the dynamical yields count for the preformation probability (${P}_{0}$) of the IMFs within the collective clusterization process of DCM, before penetrating the scattering potential barrier. Quite interestingly, the calculated ratio of ${P}_{0}$ of the corresponding IMFs ${P}_{0(\mathrm{IMFs})}^{^{25}\mathrm{Mg}^{*}}/{P}_{0(\mathrm{IMFs})}^{^{24}\mathrm{Mg}^{*}}$ for the CN $^{25,24}\mathrm{Mg}^{*}$ shows the trend of ratio of experimental cross sections, i.e., ${\ensuremath{\sigma}}_{\mathrm{IMFs}}^{^{25}\mathrm{Mg}^{*}}/{\ensuremath{\sigma}}_{\mathrm{IMFs}}^{^{24}\mathrm{Mg}^{*}}$. It is found that $\ensuremath{\alpha}$-cluster structure of complimentary fragments of the IMFs under investigation plays quite a significant role in their decays.

Measurement of 12C Fragmentation Cross Sections on C, O, and H in the Energy Range of Interest for Particle Therapy Applications

In a carbon ion treatment the nuclear fragmentation of both target and beam projectiles impacts on the dose released on the tumor and on the surrounding healthy tissues. Carbon ion fragmentation occurring inside the patient body has to be studied in order to take into account this contribution. These data are also important for the development of the range monitoring techniques with charged particles. The production of charged fragments generated by carbon ion beams of 115–353 MeV/u kinetic energy impinging on carbon, oxygen, and hydrogen targets has been measured at the CNAO particle therapy center (Pavia, Italy). The use of thin targets of graphite (C), PMMA (C2O5H8) and polyvinyl-toluene [plastic scintillator (PS), ${\text{C}}_{b}{\text{H}}_{a}$ ] allowed to measure fragments production cross sections, exploiting a time-of-flight (ToF) technique. PS detectors have been used to perform the ToF measurements, while LYSO crystals have been used for the deposited energy measurement and to perform particle identification. Cross sections have been measured at 90° and 60° with respect to the beam direction. The measured proton, deuteron, and triton differential production cross sections on C, O, and H, obtained exploiting the target subtraction strategy, are presented here as a function of the fragment kinetic energy.

Timing performances of a Time-Of-Flight detection system for the FRACAS large acceptance mass spectrometer

In this work, we report on the timing performances of the Time-Of-Flight (TOF) apparatus of the FRACAS large acceptance mass spectrometer designed to measure the fragmentation cross sections of a 12C beam in hadrontherapy. The TOF system is composed of a Parallel Plate Avalanche Counter and scintillating detectors to create so-called ΔE—TOF maps used in the fragment charge identification process. From tests with an alpha source and a 12C beam experiment, we measured a coincidence resolving time for the apparatus below 300 ps. Those results should lead in the final design to the identification of all the fragments produced by the interaction of 12C ions with thin targets for energies up to 400 MeV/nucleon.

GENERAL CHARACTERISTICS OF INTERMEDIATE MASS FRAGMENT INCLUSIVE CROSS SECTIONS IN 20Ne INDUCED INTERACTIONS

Inclusive integrated cross sections of intermediate mass fragments have been measured in 20Ne induced reactions on silver and gold targets at 20, 30, 40, 50 and 60 MeV/nucleon incident energies. Whereas the production yields remain approximately constant for the Ne+Ag system, for incident energies greater than 30 MeV/nucleon, they increase by a factor of 3.5 for the Ne+Au system over the full energy range studied.

INCLUSIVE PRODUCTION OF INTERMEDIATE MASS FRAGMENTS IN 20Ne+Ag,Au INTERACTIONS AT 20-60 MeV/nucleon

Energy spectra and angular distributions of intermediate mass fragments were measured at 20, 30, 40, 50 and 60 MeV/nucleon incident energies. Assuming two prevailing origins, fragmentation and evaporation (or fission), the measured energy spectra and angular distributions are reproduced by emission from two moving sources. The dependence of the parameters extracted for the sources on the fragment charge and on the incident energy is discussed. The distinctive role of fission in the case of the gold target is stressed. Xuclear fragmentation cross sections deduced from the moving source analysis are given and discussed for the two systems.

Strangeness and hypernuclear production in fragmentation reactions induced by antikaons

Formation mechanism of hyperfragments with strangeness s=-1 and s=-2 in collisions of antikaons on nuclei has been investigated within a microscopic transport model. Dynamics of pseudoscalar mesons and hyperons is modeled within the transport model, in which all possible reaction channels for creating hyperons such as the elastic scattering, resonance production and decay, strangeness exchange reaction and direct strangeness production in meson-baryon and baryon-baryon collisions have been included. A coalescence approach is developed for constructing hyperfragments in phase space and the decay process is described with a statistical approach. It is found that the $\Xi^{-}$ production is correlated to the K$^{+}$ formation and the hyperons $\Lambda$ and $\Sigma$ are created within a broad rapidity region. The production cross sections of nucleonic fragments and hyperfragments weakly depends on the incident momentum. The yields of $\Lambda-$ hyperfragments are the six order of magnitude of $\Xi^{-}-$ hyperfragments.

Angular momentum as a probe for the reaction mechanism: The [formula omitted] decay at three excitation energies

The angular momentum effects on the reaction mechanism in the decay of a hot system, formed in 48Ti + 40Ca → Mo⁎88 reaction at three excitation energies, have been studied using the dynamical cluster-decay model based on the quantum mechanical fragmentation theory. Angular momentum windows have been defined for the compound and non-compound nucleus processes (like deep inelastic collisions etc.) with respect to the angular momentum variation of the fission barriers of the incoming channel. First, the angular momentum distributions of the summed up preformation, penetration probabilities and the cross-sections for light particles, intermediate mass fragments and fission fragments have been calculated by considering the angular momentum up to the critical value. Then, the mass and charge distributions (with isotopic compositions) of the cross-sections have been calculated in accordance with the defined angular momentum windows. The cross-sections for fragments coming both from the compound nucleus decay and from other processes have been calculated and the total reaction cross-section is compared with the one presented in the work of Valdré and co-workers. The ratios of the observed fusion-evaporation and total fusion cross-sections to the total reaction cross-sections of (i) our calculation and (ii) presented in the work of Valdré and co-workers, are compared and found comparable. The change of the reaction mechanism has been analyzed as a function of the angular momentum variation of the cross-sections of the fission fragments. Finally, the effect of the incident energy on the compound nucleus formation and survival probabilities has been studied.

Approaching neutron-rich nuclei towards the r-process path in 86Kr-induced collisions at 15 MeV/nucleon

The production cross sections of projectile-like fragments from collisions of 15 MeV/nucleon 86Kr with 64,58Ni and 124,112Sn have been measured using a magnetic separator with emphasis on the neutron-rich isotopes. Neutron pick-up isotopes (with up to 6-8 neutrons picked-up from the target) were observed with large cross sections. The present results were also compared with our previous data of the same reactions at 25 MeV/nucleon. The data at 15 MeV/nucleon show enhanced production of neutron-rich isotopes very close to the projectile, relative to the corresponding data at 25 MeV/nucleon. The large cross sections of such reactions involving peripheral nucleon exchange, indicate that these reactions offer a novel route to access extremely neutron-rich rare isotopes towards the the astrophysical r-process path and the neutron-drip line.

Dissociative multiple ionization of the H2O molecule induced by ion impact: experimental and theoretical results

SynopsisFragment energy spectra of the water molecule impacted by singly charged (SCI) and highly charged (HCI) ions have been measured in crossed beam experiments. Double differential fragmentation cross sections (DDCS) have been determined. Similarities and differences of the measured DDCSs induced by the medium- and low-energy projectiles have been analyzed. Multiple target ionization cross sections have been deduced and they were further analyzed through the results of the CTMC and CDW-EIS models.

Isotopic cross-sections in proton induced spallation reactions based on the Bayesian neural network method * * Supported by the National Natural Science Foundation of China (11975091, U1732135, 11875070), and Natural Science Foundation of Henan Province (162300410179). This work is also supported by the US Department of Energy (DE-FG02-93ER40773)

The Bayesian neural network (BNN) method is proposed to predict the isotopic cross-sections in proton induced spallation reactions. Learning from more than 4000 data sets of isotopic cross-sections from 19 experimental measurements and 5 theoretical predictions with the SPACS parametrization, in which the mass of the spallation system ranges from 36 to 238, and the incident energy from 200 MeV/u to 1500 MeV/u, it is demonstrated that the BNN method can provide good predictions of the residue fragment cross-sections in spallation reactions.

Computational study of fragmentation cross-sections for 28Si ions in various media using GEANT4

The comparison of simulated data with experimental results is needed for the accuracy and reliability of the transport codes. In this work, we performed a comparative study of simulated results of projectile fragmentation cross-sections (PFXS) for three different models. The obtained results also compared with published experimental data. For simulation purposes, the GEANT4 simulation toolkit based on the Monte Carlo (MC) codes is used. The models in Geant4 employed to compute the PFXS are the Binary Cascade (BIC), the Quantum Molecular Dynamics (QMD), and the Intranuclear cascade (INCL). In the present study we reported the interaction of 28Si ion beam for the energy range 270–1200 A MeV incident on carbon (C), aluminium (Al), copper (Cu), tin (Sn), and lead (Pb) targets. The QMD, the BIC, and the INCL model coupled with the de-excitation models reproduce the results in agreement with experimental fragmentation cross-sections.

Fragment charge identification technique with a plastic scintillator detector using clinical carbon beams

Nuclear physics processes are an important source of uncertainty in dose calculations in particle therapy and radioprotection in space. Accurate cross section measurements are a crucial ingredient in improving the understanding of these processes. The FOOT (FragmentatiOn Of Target) experiment aims at measuring the production cross sections of fragments for energies, beams and targets that are relevant in particle therapy and radioprotection in space. An experimental apparatus composed of several sub-detectors will provide the mass, charge, velocity and energy of fragments produced in nuclear interactions in a thin target. A crucial component of the FOOT apparatus will be the ΔE-TOF detector, designed to identify the charge of the fragments using plastic scintillators to measure the energy deposited and the time of flight with respect to a start counter. In this work, we present a charge reconstruction procedure of produced fragments at particle therapy energies. We validate it by measuring the charges of various fragments at an angle of 3.2°and 8.3°with respect the beam-axis, using a small-scale detector and clinical beams of carbon ions at the CNAO oncology center. Experimental results agree well with FLUKA Monte Carlo simulations.

Charge identification performance of a [formula omitted]E-TOF detector prototype for the FOOT experiment

FOOT (FragmentatiOn On Target) is an applied nuclear physics experiment aimed at measuring the production cross sections of fragments for energies, beams and targets relevant in particle therapy and radioprotection in space. The ΔE-TOF detector will measure the energy deposited by the fragments in a wall of plastic scintillators and the time of flight with respect to a start detector. These two quantities allow to determine the charge Z of the fragment. In this work, we summarize the charge identification procedure of a detector prototype with two scintillator modules.

Absolute ionization and dissociation cross sections of tetrahydrofuran: Fragmentation-ion production mechanisms

We report an experimental and theoretical investigation on the absolute ionization and fragmentation cross sections of tetrahydrofuran (THF, C4H8O), a base molecule of the DNA-backbone. The measurements enabled the identification of 50 ionic species produced by 12 eV up to 2000 eV electron impact which allowed us to make a close inspection of the mechanisms of both the primary vacancy production and the postcollisional fragmentation pathways which lead to the fragment ions. The experimental cross sections of the ionic species were examined in the framework of the fragmentation matrix model to attribute from which molecular orbitals (MOs) the electron is removed and find out the relative contribution of up to 15 outer and inner valence MOs in the fragment-ion production. A comparison between measured and calculated dissociative cross sections relative to the molecular parent ion cross section allowed us to clearly identify the prevalence of the single or double ionization in the fragment-ion production. Due to these different production mechanisms, the relative proportion of some ejected fragment-ions strongly depends on the impact energy. The single ionization of the MOs leading to selected fragment ions was compared to those measured at a low electron-impact energy using a reaction microscope with good agreement between the two techniques. The formation of the dications C4HnO2+, excluding the molecular parent dication, is also presented.

Spallation reactions induced by 4.4 GeV deuterons on lead isotopes

Independent and cumulative production cross sections for radioactive nuclear fragments from the deuteron-irradiation of isotopically enriched lead (204Pb, 206Pb, 207Pb, and 208Pb) targets were obtained for the first time. The experiment has been performed with a 4.4 GeV deuteron beam from the Nuclotron of the Laboratory of High Energy Physics (LHE), Joint Institute for Nuclear Research (JINR) at Dubna. The production cross sections of target fragments were determined by off-line γ-ray spectroscopy. Charge dispersion and mass-yield distributions were deduced from these data. The results are discussed in terms of the relative importance of different reaction mechanisms (evaporation–spallation, fission and multifragmentation). Comparison of our results with the data from the reaction induced by protons of about the same kinetic energy per nucleon, has been performed. The coexistence of the different decay modes in the formation of the reaction residues, such as spallation, fission and multifragmentation is suggested.

Microscopic studies of production cross sections in multinucleon transfer reaction Ni58+Sn124

Background: Multinucleon transfer reactions at low-energy collisions are considered to be promising for the production of new exotic nuclei, which are difficult to produce by other methods. Theoretical studies are required to provide reliable predictions for the experiments and to help understand the microscopic mechanism in multinucleon transfer reactions.Purpose: We provide a predictive approach for production cross sections and show how and to what extent the microscopic approach works well in multinucleon transfer reactions.Methods: We employ the $\text{TDHF}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\text{GEMINI}$ approach, which combines the microscopic time-dependent Hartree-Fock (TDHF) model with the state-of-art statistical model $\text{GEMINI}\phantom{\rule{0.16em}{0ex}}++$, to take into account both the multinucleon transfer dynamics and the secondary de-excitation process. The properties of primary products in multinucleon transfer process, such as transfer probabilities and primary cross sections, are extracted from TDHF dynamics using the particle-number projection method. Production cross sections for secondary products are evaluated using the statistical model $\text{GEMINI}\phantom{\rule{0.16em}{0ex}}++$.Results: We investigate the influence of colliding energies and deformation orientations of target and projectile nuclei on multinucleon transfer dynamics in the reaction $^{58}\mathrm{Ni}+^{124}\mathrm{Sn}$. More nucleons are observed to transfer in the tip collision than in the side collision. The production cross sections for secondary fragments with $\text{TDHF}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\text{GEMINI}$ calculations well reproduce the experimental measurements at energies close to the Coulomb barrier. At sub-barrier energy, the theoretical results gradually deviate from the experimental data with the increase of the number of transferred neutrons, showing the limitations of a single mean-field approximation in the TDHF approach. Possible origins for this discrepancy are discussed. The total cross sections integrated over all the neutron transfer channels are in good agreement with the experimental data for all the energies. We compare the production cross sections of $\text{TDHF}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\text{GEMINI}$ calculations with those from GRAZING model and find that our approach gives a description as quantitatively good as the semiclassical model, although there is no adjustable parameters for the reaction dynamics in the microscopic TDHF method.Conclusions: The microscopic $\text{TDHF}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\text{GEMINI}$ approach reasonably reproduces the experimental data at energies close to the Coulomb barrier and well accounts for the multinucleon transfer mechanism. The present studies clearly reveal the applicability of $\text{TDHF}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\text{GEMINI}$ method in multinucleon transfer reactions, which thus is a promising tool for predicting the properties of new reactions.