Interaction Cross Sections Research Articles

Helium radiography with a digital tracking calorimeter—a Monte Carlo study for secondary track rejection

Radiation therapy using protons and heavier ions is a fast-growing therapeutic option for cancer patients. A clinical system for particle imaging in particle therapy would enable online patient position verification, estimation of the dose deposition through range monitoring and a reduction of uncertainties in the calculation of the relative stopping power of the patient.Several prototype imaging modalities offer radiography and computed tomography using protons and heavy ions. A Digital Tracking Calorimeter (DTC), currently under development, has been proposed as one such detector. In the DTC 43 longitudinal layers of laterally stacked ALPIDE CMOS monolithic active pixel sensor chips are able to reconstruct a large number of simultaneously recorded proton tracks.In this study, we explored the capability of the DTC for helium imaging which offers favorable spatial resolution over proton imaging. Helium ions exhibit a larger cross section for inelastic nuclear interactions, increasing the number of produced secondaries in the imaged object and in the detector itself. To that end, a filtering process able to remove a large fraction of the secondaries was identified, and the track reconstruction process was adapted for helium ions.By filtering on the energy loss along the tracks, on the incoming angle and on the particle ranges, 97.5% of the secondaries were removed. After passing through 16 cm water, 50.0% of the primary helium ions survived; after the proposed filtering 42.4% of the primaries remained; finally after subsequent image reconstruction 31% of the primaries remained. Helium track reconstruction leads to more track matching errors compared to protons due to the increased available focus strength of the helium beam. In a head phantom radiograph, the Water Equivalent Path Length error envelope was 1.0 mm for helium and 1.1 mm for protons. This accuracy is expected to be sufficient for helium imaging for pre-treatment verification purposes.

Radiation shielding characteristics of selected ceramics using the EPICS2017 library

In this paper, the investigation of the Electron-Photon Interaction Cross Sections 2017 (EPICS2017) library on the shielding properties of several ceramics is presented. The EPICS2017 library was used to calculate the mass attenuation coefficients of different ceramic samples. The results from EPICS2017 were compared with values from several experimental and theoretical methods used in characterizing the photon shielding properties. The experimental mass attenuation coefficient values agreed well with the EPICS2017 evaluations, with relative differences ranging from 0.04–6.58%. The mass attenuation coefficient values derived using MCNP5 simulations agreed with EPICS2017 with a reasonable deviation. XCOM values for mass attenuation coefficients strongly agreed with EPICS2017. The obtained results dictate that EPICS2017 can be used to evaluate the MACs for ceramic systems for which no experimental values are available at various energies. From these findings, the EPICS2017 library can be an important alternative for the future photon shielding research and development of ceramic materials.

Pair productions from gauge bosons collisions

Pair production is a process of creating a particle and its antiparticle from two gauge bosons collision. In this work, we suppose the pair production can occur from the collision between a spin-two graviton and a spin-one gauge boson. We focus on the electron-positron pair production between gravitons which is determined from the vielbein field and coupling to a photon in minimal coupling scheme. The collision cross section is evaluated and compared to those of the same creation types at the energy 0.71 MeV. We found that the total cross section of the graviton-photon interaction is less than that of photon-photon about 1041 times but that is greater than that of graviton-graviton about 1042 times.

The Size of a Photon

This paper begins by exploring a useful and neglected detail of a photon—its physical size perpendicular to the direction of propagation in the same way as an atom or neutron has a physical size. Such a photon size would be quite separate from the cross-section of a photonic interaction, which depends on the material interacting. Such a perpendicular dimension of a photon will be invariant under Lorentz transform parallel to the light propagation direction and will thus be the same for all frequencies of light. This study also leads to new details about how a photon interacts, offering an explanation for the familiar physics where light slightly above and below the mean frequency of an excited state can still excite the same state without violation of conservation of energy—a mystery explored thoroughly in a previous paper without finding the solution offered here. As usual, a better elucidation of the details of light interaction also leads to new insights—especially about the vacuum field. The Appendix summarizes some previous research relevant to this discussion

Electric dipole response of low-lying excitations in the two-neutron halo nucleus F29

The neutron-rich $^{28,29}$F isotopes have been recently studied via knockout and interaction cross-section measurements. The $2n$ halo in $^{29}$F has been linked to the occupancy of $pf$ intruder configurations. We investigate bound and continuum states in $^{29}$F, focusing on the $E1$ response of low-lying excitations and the effect of dipole couplings on nuclear reactions. $^{29}\text{F}$ ($^{27}\text{F}+n+n$) wave functions are built within the hyperspherical harmonics formalism, and reaction cross sections are calculated using the Glauber theory. Continuum states and $B(E1)$ transition probabilities are described in a pseudostate approach using the analytical THO basis. The corresponding structure form factors are used in CDCC calculations to describe low-energy scattering. Parity inversion in $^{28}$F leads to a $^{29}$F ground state characterized by 57.5% of $(p_{3/2})^2$ intruder components, a strong dineutron configuration, and an increase of the matter radius with respect to the core radius of $\Delta R=0.20$ fm. Glauber-model calculations for a carbon target at 240 MeV/nucleon provide a total reaction cross section of 1370 mb, in agreement with recent data. The model produces also a barely bound excited state corresponding to a quadrupole excitation. $B(E1)$ calculations into the continuum yield a total strength of 1.59 e$^2$fm$^2$ up to 6 MeV, and the $E1$ distribution exhibits a resonance at $\approx$ 0.85 MeV. Results using a standard shell-model order for $^{28}$F lead to a considerable reduction of the $B(E1)$ distribution. The four-body CDCC calculations for $^{29}\text{F}+^{120}\text{Sn}$ around the Coulomb barrier are dominated by dipole couplings, which totally cancel the Fresnel peak in the elastic cross section. These results are consistent with a two-neutron halo and may guide future experimental campaigns.

Calculations of electronic excitation by protons and α particles in silicon

This paper presents a method of calculating the valence electron contribution to the stopping and interaction cross sections of swift ions in matter using linear response calculations of the dielectric function in crystals. The ab initio response function is used to calculate excitations at low energy and momentum transfers to account for material-specific effects, while higher energy and momentum transfers use a free electron gas response for increased computational efficiency. The ECPSSR method for computing core cross sections is modified to allow predictions of the core contribution to electronic stopping. The charge distribution by entrained electrons is explicitly modeled to account for the additional screening beyond linear response. We use the methods developed to predict the electronic stopping of protons and $\ensuremath{\alpha}$ particles in silicon and compare to measured values.

Adjusting neutrino interaction models and evaluating uncertainties using NOvA near detector data

The two-detector design of the NOvA neutrino oscillation experiment, in which two functionally identical detectors are exposed to an intense neutrino beam, aids in canceling leading order effects of cross-section uncertainties. However, limited knowledge of neutrino interaction cross sections still gives rise to some of the largest systematic uncertainties in current oscillation measurements. We show contemporary models of neutrino interactions to be discrepant with data from NOvA, consistent with discrepancies seen in other experiments. Adjustments to neutrino interaction models in GENIE are presented, creating an effective model that improves agreement with our data. We also describe systematic uncertainties on these models, including uncertainties on multi-nucleon interactions from a newly developed procedure using NOvA near detector data.

Theoretical uncertainties of muon transport calculations for very large volume neutrino telescopes

Underground cosmic-ray experiments, including very large volume neutrino telescopes, depend on a precise description of the interaction cross sections of muons, which can travel large distances before reaching the detector. High-energy muons lose their energy almost exclusively via four processes: ionization, electron-positron pair production, bremsstrahlung and inelastic interaction with nuclei. At low energies, ionization is the dominant process, while above energies of about a TeV, the three other processes dominate the energy loss. We discuss the uncertainties of the cross sections of the energy loss processes used in the simulation chain of current very large volume neutrino telescopes and review recent theoretical improvements.

Neutron Stars and Dark Matter

Neutron stars change their structure with accumulation of dark matter. We study how their mass is influenced from the environment. Close to the sun, the dark matter accretion from the neutron star does not have any effect on it. Moving towards the galactic center, the density increase in dark matter results in increased accretion. At distances of some fraction of a parsec, the neutron star acquire enough dark matter to have its structure changed. We show that the neutron star mass decreases going towards the galactic centre, and that dark matter accumulation beyond a critical value collapses the neutron star into a black hole. Calculations cover cases varying the dark matter particle mass, self-interaction strength, and ratio between the pressure of dark matter and ordinary matter. This allow us to constrain the interaction cross section, σdm, between nucleons and dark matter particles, as well as the dark matter self-interaction cross section.

On-shell mediator dark matter models and the Xenon1T excess * *Supported in part by the National Natural Science Foundation of China (U1738134, 11775109)

We present a dark matter model to explain the excess events in the electron recoil data recently reported by the Xenon1T experiment. In our model, dark matter annihilates into a pair of on-shell particles , which subsequently decay into the final state; interacts with electrons to generate the observed excess events. Because of the mass hierarchy, the velocity of can be rather large and can have an extended distribution, providing a good fit to the electron recoil energy spectrum. We estimate the flux of from dark matter annihilations in the galaxy and further determine the interaction cross section, which is sizable but sufficiently small to allow to penetrate the rocks to reach the underground labs.

Self-generated ultraviolet radiation in molecular shock waves

Context. Shocks are ubiquitous in the interstellar and intergalactic media, where their chemical and radiative signatures reveal the physical conditions in which they arise. Detailed astrochemical models of shocks at all velocities are necessary to understand the physics of many environments including protostellar outflows, supernova remnants, and galactic outflows. Aims. We present an accurate treatment of the self-generated ultraviolet (UV) radiation in models of intermediate velocity (VS = 25–60 km s−1), stationary, weakly magnetised, J-type, molecular shocks. We show how these UV photons modify the structure and chemical properties of shocks and quantify how the initial mechanical energy is reprocessed into line emission. Methods. We develop an iterative scheme to calculate the self-consistent UV radiation field produced by molecular shocks. The shock solutions computed with the Paris–Durham shock code are post-processed using a multi-level accelerated Λ-iteration radiative transfer algorithm to compute Lyman α, Lyman β, and two-photon continuum emission. The subsequent impacts of these photons on the ionisation and dissociation of key atomic and molecular species as well as on the heating by the photoelectric effect are calculated by taking the wavelength dependent interaction cross-sections and the fluid velocity profile into account. This leads to an accurate description of the propagation of photons and the thermochemical properties of the gas in both the postshock region and in the material ahead of the shock called the radiative precursor. With this new treatment, we analyse a grid of shock models with velocities in the range VS = 25–60 km s−1, propagating in dense (nH ≥ 104 cm−3) and shielded gas. Results. Self-absorption traps Lyα photons in a small region in the shock, though a large fraction of this emission escapes by scattering into the line wings. We find a critical velocity VS ~ 30 km s−1 above which shocks generate Lyα emission with a photon flux exceeding the flux of the standard interstellar radiation field. The escaping photons generate a warm slab of gas (T ~ 100 K) ahead of the shock front as well as pre-ionising C and S. Intermediate velocity molecular shocks are traced by bright emission of many atomic fine structure (e.g. O and S) and metastable (e.g. O and C) lines, substantive molecular emission (e.g. H2, OH, and CO), enhanced column densities of several species including CH+ and HCO+, as well as a severe destruction of H2O. As much as 13–21% of the initial kinetic energy of the shock escapes in Lyα and Lyβ photons if the dust opacity in the radiative precursor allows it. Conclusions. A rich molecular emission is produced by interstellar shocks regardless of the input mechanical energy. Atomic and molecular lines reprocess the quasi totality of the kinetic energy, allowing for the connection of observable emission to the driving source for that emission.

Reconstructing the EUV Spectrum of Star-forming Regions from Millimeter Recombination Lines of H i, He i, and He ii

Abstract The extreme ultraviolet (EUV) spectra of distant star-forming regions cannot be probed directly using either ground- or space-based telescopes due to the high cross section for interaction of EUV photons with the interstellar medium. This makes EUV spectra poorly constrained. The millimeter/submillimeter recombination lines of H and He, which can be observed from the ground, can serve as a reliable probe of the EUV. Here we present a study based on ALMA observations of three Galactic ultracompact H ii regions and the starburst region Sgr B2(M), in which we reconstruct the key parameters of the EUV spectra using millimeter recombination lines of H i, He i, and He ii. We find that in all cases the EUV spectra between 13.6 and 54.4 eV have similar frequency dependence: We compare the inferred values of the EUV spectral slopes with the values expected for a purely single stellar evolution model (Starburst99) and the Binary Population and Spectral Synthesis code (BPASS). We find that the observed spectral slope differs from the model predictions. This may imply that the fraction of interacting binaries in H ii regions is substantially lower than assumed in BPASS. The technique demonstrated here allows one to deduce the EUV spectra of star-forming regions, providing critical insight into photon production rates at , and can serve as calibration to starburst synthesis models, improving our understanding of star formation in the distant universe and the properties of ionizing flux during reionization.

Implications of baryon–dark matter interaction on IGM temperature and tSZ effect with magnetic field

ABSTRACT We show that the combined effect of cosmic magnetic field and a possible non-standard interaction between baryons and dark matter (DM) has interesting consequences on the thermal Sunyaev−Zel’dovich (tSZ) effect depending on the temperature and the ionization state of the intergalactic medium. The drag force between the baryons and DM due to the relative velocity between them, and their temperature difference results in heat transfer between these two species. At the same time, the ambipolar diffusion and the decaying magnetic turbulence tends to heat up the baryons. This interplay of these two processes give rise to different evolution histories of the thermal and ionization state of the universe and hence influences the cosmic microwave background (CMB) spectrum at small scales through the tSZ effect. In this work, we have computed the evolution of the temperature, ionization fraction, and the y-parameter of the CMB for different strengths of the magnetic field and the interaction cross-section. We note that the y-parameter can be significantly enhanced with the inclusion of magnetic field and baryon–DM interaction as compared to the case when these are absent. The enhancement depends on the strength of the magnetic field.

Measurement of the Low-Energy Antideuteron Inelastic Cross Section.

In this Letter, we report the first measurement of the inelastic cross section for antideuteron-nucleus interactions at low particle momenta, covering a range of 0.3≤p<4 GeV/c. The measurement is carried out using p-Pb collisions at a center-of-mass energy per nucleon-nucleon pair of sqrt[s_{NN}]=5.02 TeV, recorded with the ALICE detector at the CERN LHC and utilizing the detector material as an absorber for antideuterons and antiprotons. The extracted raw primary antiparticle-to-particle ratios are compared to the results from detailed ALICE simulations based on the geant4 toolkit for the propagation of (anti)particles through the detector material. The analysis of the raw primary (anti)proton spectra serves as a benchmark for this study, since their hadronic interaction cross sections are well constrained experimentally. The first measurement of the inelastic cross section for antideuteron-nucleus interactions averaged over the ALICE detector material with atomic mass numbers ⟨A⟩=17.4 and 31.8 is obtained. The measured inelastic cross section points to a possible excess with respect to the Glauber model parametrization used in geant4 in the lowest momentum interval of 0.3≤p<0.47 GeV/c up to a factor 2.1. This result is relevant for the understanding of antimatter propagation and the contributions to antinuclei production from cosmic ray interactions within the interstellar medium. In addition, the momentum range covered by this measurement is of particular importance to evaluate signal predictions for indirect dark-matter searches.

Excitation of a layered medium by 𝑁 sources: Scattering relations, interaction cross sections and physical bounds

A layered medium is excited by N N external or internal point sources. Boundary-value problems for the generated acoustic waves are formulated. General scattering and optical theorems are established relating the involved fields and far-field patterns due to groups of sources. Interaction scattering cross sections are defined and associated physical bounds are derived. The large- N N behavior of these cross sections is also investigated. Numerical results are presented demonstrating the variations of the interaction cross sections and their physical bounds.

Total Cross Section Phenomenological Formulas for X-Ray and Gamma Radiation Interaction With Matter for Different Energies and Absorber Types

Abstract The in-function log-polynomial regression method for empirical approximations of physical relationships was presented and applied in practice. Thanks to that the single phenomenological equation for the total cross section for X-ray and gamma radiation interaction with matter was presented. The proposed equation depends on the photon energy (from 1 keV to 100 GeV) and absorber type (atomic number from Z = 1 to 100) and takes into considerations all important physical effects of photon interaction, namely, coherent (Rayleigh) and incoherent (Compton) scattering, photo-electric effect and pair/triplet production. Finally, the single formula for the total cross section of photon interaction with matter was presented in the simple form easy to apply in practice, e.g., in radiation protection or in radiation shields designing.

СОЦИАЛЬНЫЕ ОСНОВАНИЯ ПОЛИТИЧЕСКОЙ КОНФЛИКТНОСТИ

The article deals with the sociological aspects of the analysis of political conflict related to the socio-structural and subjective foundations of political processes and relations. It is shown that many problems and contradictions in the social sphere, such as social polarization, excessive inequality, poverty and violation of the principles of social justice, deprivation of basic needs and interests, unstable labor employment significantly determine the field of politics and are projected on the object and subject of political conflict, weighing down their course and positive outcomes. The insolubility of social problems and contradictions, their encapsulation cause either a decrease in the population's interest in politics, in the effectiveness of democratic institutions, con- tribute to the widening of the gap between "private" and "public", generate a sense of political alienation and powerlessness, or push to meet basic needs beyond the existing social norms and political institutions, to destructive forms of resolving political conflicts, which leads to a loss of control of society and social catastrophe. Sociological analysis of the subject cross-section of conflict interaction shows that a conflict based on group interests (in comparison with class and elitist) contributes more to maintaining a dynamic balance in society and realizing the positive potential of political conflict, since it is characterized by flexible intra-group connections and mobile inter-group barriers in the socio-political system. Class and elitist models of conflict tend more to vertical polarization of society, which strengthens the "discontinuous" lines of interaction between the "top" and "bottom", makes the dichotomy "rule-submission" rigid, and reduces the possibilities of dialogical plasticity and flexibility of the political system.

Charge-changing cross section measurements of atomic nuclei and charge radii

<p indent=0mm>The atomic nucleus is a finite open quantum many-body system that is composed of two basic building blocks, proton and neutron. Like many systems governed by the laws of quantum mechanics, a nucleus is an object full of mysteries. Nuclear properties and structure are much more difficult to characterize than those of macroscopic objects and it is almost impossible to build an exact replica of this Fermi-scale nuclear system. In reality, physicists have developed an approach to reveal nature by collisions of two atomic nuclei, i.e., nuclear reactions, since the very beginning of nuclear physics. One famous example is the Rutherford scattering experiment performed at around 1910, in which the nuclide as a core of atom was discovered. Since the late 1980s, precision measurements of reaction cross section or interaction cross sections played a crucial role in nuclear size determination. This was entwined with the realization of radioactive ion beams (RIB). Such measurements contributed to discovering, for example, the neutron skin and neutron halo, when moving far away from the stability line. The new phenomena and properties found along the experimental advance are meanwhile among the strongest motivations for initiating, constructing, and operating the new generations of nuclear physics facilities worldwide. HIAF, the High-Intensity heavy-ion Accelerator Facility, is now under construction in Huizhou, China. In the last few years, systematic measurements of charge-changing cross sections (CCCS) of exotic nuclei have attracted much attention. It offers a complementary way to study exotic structures that could exist in exotic nuclei. By definition, CCCS refers to the total probability of removing at least one proton from the projectile nuclide. It reflects the geometric overlapping area during the collision. In particular, by combining with the Glauber-type model calculations, precise CCCS data have been used as an effective probe to investigate the proton density distribution of unstable atomic nuclei. This method is suitable for the investigation of exotic nuclei with low production yields, and the measurements accordingly were proposed in almost all the major nuclear physics facilities in the last years. In this paper, we first attempted to give a review on the progress of CCCS worldwide, from the pioneering work of RIB physics in the 1980s to the recent advances towards neutron-rich nuclei. Then we introduced the experimental work performed at the Heavy Ion Research Facility at Lanzhou (HIRFL). So far, CCCSs of more than 30 light nuclei have been determined and most of them are along the β-stability line. Based on the same setup, the Beihang group will focus on the CCCS measurements of sd-shell nuclei, aiming to study the (sub-)shell structure at 14 and 16. After surveying the existing CCCS data worldwide, it is found that there are often large deviations among various measurements in different laboratories even for the simplest reaction system. Precision data are therefore urgently called to clarify the deviations in existing data and to constrain the reaction mechanism on hydrogen targets. From my point of view, simultaneous measurements of both CCCS and reaction cross section in particular on hydrogen targets, the simplest target composed of only protons, are expected to enhance dramatically the journey to reveal the nature of very exotic nuclei. In the last part of this paper, perspectives at the High-energy FRagment Separator (HFRS) at HIAF are discussed. After a careful design of the detector setup and data taking system, it is possible to open a new era of nuclear physics experiments, in which various types of experiments can be carried out simultaneously.

Fast Neutron Imaging with Semiconductor Nanocrystal Scintillators.

Fast neutrons offer high penetration capabilities for both light and dense materials due to their comparatively low interaction cross sections, making them ideal for the imaging of large-scale objects such as large fossils or as-built plane turbines, for which X-rays or thermal neutrons do not provide sufficient penetration. However, inefficient fast neutron detection limits widespread application of this technique. Traditional phosphors such as ZnS:Cu embedded in plastics are utilized as scintillators in recoil proton detectors for fast neutron imaging. However, these scintillation plates exhibit significant light scattering due to the plastic-phosphor interface along with long-lived afterglow (on the order of minutes), and therefore alternative solutions are needed to increase the availability of this technique. Here, we utilize colloidal nanocrystals (NCs) in hydrogen-dense solvents for fast neutron imaging through the detection of recoil protons generated by neutron scattering, demonstrating the efficacy of nanomaterials as scintillators in this detection scheme. The light yield, spatial resolution, and neutron-vs-gamma sensitivity of several chalcogenide (CdSe and CuInS2)-based and perovskite halide-based NCs are determined, with only a short-lived afterglow (below the order of seconds) observed for all of these NCs. FAPbBr3 NCs exhibit the brightest total light output at 19.3% of the commercial ZnS:Cu(PP) standard, while CsPbBrCl2:Mn NCs offer the best spatial resolution at ∼2.6 mm. Colloidal NCs showed significantly lower gamma sensitivity than ZnS:Cu; for example, 79% of the FAPbBr3 light yield results from neutron-induced radioluminescence and hence the neutron-specific light yield of FAPbBr3 is 30.4% of that of ZnS:Cu(PP). Concentration and thickness-dependent measurements highlight the importance of increasing concentrations and reducing self-absorption, yielding design principles to optimize and foster an era of NC-based scintillators for fast neutron imaging.

Searching for Sub-GeV dark matter in the galactic centre using Hyper-Kamiokande

Indirect detection of dark matter via its annihilation products is a key technique in the search for dark matter in the form of weakly interacting massive particles (WIMPs). Strong constraints exist on the annihilation of WIMPs to highly visible Standard Model final states such as photons or charged particles. In the case of s-wave annihilation, this typically eliminates thermal relic cross sections for dark matter of mass below \U0001d4aa(10) GeV . However, such limits typically neglect the possibility that dark matter may annihilate to assumed invisible or hard-to-detect final states, such as neutrinos. This is a difficult paradigm to probe due to the weak neutrino interaction cross section. Considering dark matter annihilation in the Galactic halo, we study the prospects for indirect detection using the Hyper-Kamiokande (HyperK) neutrino experiment, for dark matter of mass below 1 GeV . We undertake a dedicated simulation of the HyperK detector, which we benchmark against results from the similar Super-Kamiokande experiment and HyperK physics projections. We provide projections for the annihilation cross-sections that can be probed by HyperK for annihilation to muon or neutrino final states, and discuss uncertainties associated with the dark matter halo profile. For neutrino final states, we find that HyperK is sensitive to thermal annihilation cross-sections for dark matter with mass around 20 MeV, assuming an NFW halo profile. We also discuss the effects of neutron tagging, and prospects for improving the reach at low mass.