Relative Cross Sections Research Articles

Hard exclusive $\pi^{+}n$ electro production beam spin asymmetries off the proton in the GPD and TDA regimes

Hard exclusive \pi^{+}π+n electro-production can be used to gain access to the 3D nucleon structure. The QCD factorisation mechanism in the “nearly forward region” (t/Q^{2}t/Q2 small) allows a description by Generalized Parton Distributions (GPDs), while for the “nearly backward” kinematic region (u/Q^{2}u/Q2 small) a description based on nucleon to pion transitions (TDAs) is available. The paper presents a measurement of single beam spin asymmetries to extract the A^{\sin\phi}_{LU}ALUsinϕ moments and the related cross section ratio \sigma_{LT^\prime}/\sigma_{0}σLT′/σ0 from the hard exclusive \pi^{+}π+ channel off the unpolarized hydrogen target in a wide range of kinematics based on data taken with the CLAS spectrometer at Jefferson Lab. In addition, under forward angles a detailed multidimensional study will be presented based on CLAS12 data and compared to theoretical predictions.

Measurement of n- and l-resolved State-selective Charge Exchange in Ar8+ Collision with He

The state-resolved capture cross sections for principal n and orbital angular momentum l play an important role in modeling soft X-ray emissions induced by charge exchange for many astrophysical environments. However, the empirical and semiclassical theories used to produce these data of n- and l-resolved state-selective capture have not been well tested. Using the cold target recoil ion momentum spectroscopy apparatus at Fudan University, we perform a series of measurements of Ar8+ ion charge exchange with He in the collision energy range from 1.4 to 20 keV u−1. We find that electrons are mainly captured in the n = 4 state of Ar7+ ions. This agrees with the prediction of the scaling law for n capture. Moreover, the relative cross sections are reported for 4s-, 4p-, 4d-, and 4f-resolved state-selective capture. The often used analytical l distributions in the astrophysical literature are evaluated by comparing to the measurements.

Comparative Study on the Impact of endf/b-vii.1 Nuclear Library Uncertainty on the CERCER and CERMET Fueled Accelerator-Driven System Calculation Results Using Monte Carlo Method Codes

Abstract A new design of a small power accelerator-driven system (ADS) using inert matrix fuel—ceramic–ceramic matrix (CERCER) and ceramic-metallic matrix (CERMET) was proposed in our previous work for high transmutation rate, small reactivity loss due to burnup, and enhanced safety features. The fast neutron spectrum in the ADS showed a benefit for reducing minor actinides inventories in the fuel cycle. However, the reliability of the nuclear cross section data of evaluated libraries, especially at high energy, needs to be investigated and its impact on CERCER and CERMET fueled ADS calculation results needs to be assessed. In this study, the impact of endf/b-vii.1 nuclear library uncertainty on the CERCER and CERMET fueled ADS reactivity calculation are evaluated using the Monte Carlo method (scale6.2 and whisper-1.1). The sensitivity coefficients and uncertainty obtained by the two codes show a good agreement. The results reveal the uncertainty of the endf/b-vii.1 nuclear data caused significant uncertainty in the reactivity calculations (about 1000 pcm) and it is particularly higher in the CERMET fueled core due to a harder neutron spectrum. The paper identifies the major contributes—isotopes and related cross sections—to the core reactivity uncertainty by suggesting the enhancement of these nuclear data.

In-plane modal behavior of a single shallow flexible cable with an intermediate transverse elastic support

Cross-tie solution has been successfully applied in field to mitigate undesirable bridge stay cable vibrations, especially for cables on modern long-span cable-stayed bridges which typically have long length and relative thick cross section. In evaluating the effectiveness of the cross-tie solution and analyzing dynamic response of the formed cable network, the taut cable assumption has been used in most existing studies. Nevertheless, cable sag and bending stiffness could have non-negligible influence in networks consisting of long cables with relatively large diameter. Since a transverse cross-tie provides an elastic constraint to a vulnerable cable by connecting it with its neighbors, to fully comprehend the impact of cable sag and bending stiffness on the dynamic behavior of shallow-cable networks, it is imperative to scrutinize their effect on the behavior of a shallow cable with a transverse elastic constraint within the span. In the current study, by using the linear theory of shallow cables, an analytical model for the in-plane dynamics of a single flexible low-sag cable with an intermediate transverse elastic support is proposed. The impact of the intermediate support stiffness, location, cable bending stiffness, and sag on the in-plane modal response of the studied cable system are examined. Results show that the presence of an intermediate transverse elastic support breaks the symmetry and anti-symmetry of the original cable mode shapes, which renders the influence of sag extends to all cable modes. Further, the level of such a mode shape distortion would determine whether or not modal cross-over would occur. For any given intermediate support location, it is found that there always exists a specific level of intermediate support stiffness of which the cable sag corresponding to the occurrence of modal cross-over would be independent of cable bending stiffness. By reducing or increasing the intermediate support stiffness to be lower or higher than this specific level, the increase of cable bending stiffness would either delay modal cross-over to occur at a larger cable sag or advance its occurrence at a smaller cable sag. Reducing the intermediate support stiffness would render a local mode to evolve into a global mode, and the presence of cable bending stiffness and sag is found to allow this mode evolution to occur when a more flexible intermediate support is used.

Method for the definitive detection of orbital angular momentum states in neutrons by spin-polarized 3He.

A standard method to detect thermal neutrons is the nuclear interaction 3He(n,p)3H. The spin dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized 3He. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross sections for neutrons in an OAM state. The absorption of those neutrons results in compound states , , and . Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of 4He after absorption, taking account of the odd parity of the compound state. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross sections and new channels of radioactive decay.

Electron ionisation of cyanoacetylene: ionisation cross sections and dication formation

Cyanoacetylene (HC3N) is an important trace species in the atmosphere of Titan. We report, for the first time, absolute partial electron ionisation cross sections and absolute precursor-specific partial electron ionisation cross sections for cyanoacetylene, following an experimental and computational investigation. Our methodology involves using 2D ion–ion coincidence mass spectrometry to generate relative cross sections, over the electron energy range 50–200 eV. These relative values are then normalised to an absolute scale, using a binary encounter-Bethe (BEB) calculation of the total ionisation cross section. The BEB calculation agrees well with previous determinations in the literature. The mass spectrometric observations of HC2N+ and HCN+, ions with a connectivity markedly different to that of the neutral molecule, point towards a rich cationic energy landscape possessing several local minima. Indeed, [HC3N]2+ minima involving a variety of cyclic configurations are revealed by a preliminary computational investigation, along with two minima with linear and bent geometries involving H atom migration (CCCNH2+). Determination of the energy of a transition state between these local minima indicates that the dication is able to explore the majority of this rich conformational landscape at our experimental energies. This investigation of the energetics also determines an adiabatic double ionisation energy of 30.3 eV for the lowest lying singlet state of HCCCN2+, and 30.1 eV for the lowest-lying triplet state. The bulk of the cation pairs detected in the coincidence experiment appear to originate from markedly excited dication states, not the ground state. We observe 5 two-body dissociations of HCCCN2+, and subsequent decay of one of the ions generated in such two-body processes accounts for the majority of three-body dissociations we observe.

Evolution of the xenon ( e,2e ) differential cross section from a coplanar geometry to the perpendicular plane in the intermediate-energy regime

New ($e,2e$) differential cross-section measurements from xenon are presented as the scattering geometry changes from coplanar to the perpendicular plane. Measurements were taken at energies of 60 eV, 80 eV, and 100 eV above the ionization potential. These new data are compared to measurements collected for the first four noble gases and to that from xenon at lower energies. The ratio of relative cross sections between xenon and helium have been measured using a xenon-helium mixture. With this data absolute differential cross sections of xenon can be determined once the helium cross sections have been calculated.

Positron Emitter Depth Distribution in PMMA Irradiated With 130-MeV Protons Measured Using TOF-PET Detectors

Proton therapy for cancer treatment has a precise dose deposition capability owing to the nature of the interactions of heavy charge particles with matter resulting in a Bragg Peak. Uncertainties in the proton range can limit the scope of proton therapy. Academia Sinica PET employs a modular design for In-beam detection using SiPMs and crystals read out by STiC asic for range verification. In this work we report the depth distribution of the positron emitters from a PMMA sample irradiated with 130 MeV protons at the Chang Gung Memorial Hospital measured using a compact 32-channel setup. The timing capabilities of this system are assessed and presented. The depth dependence of the positron activity measured using coincidences agrees well with the Geant4 simulated distributions. Using a multi-exponential fit function we estimate and compare the relative amounts of different positron emitting isotopes with the relative cross sections. The application of this method can be useful to estimate the anatomical changes between different treatment sessions. The modular design of the AS-PET currently under development at Academia Sinica is presented and the simulated images of the reconstructed positron activity for the palm sized modules are used to assess the range verification capability.

Impact of intrinsic charm amount in the nucleon and saturation effects on the prompt atmospheric nu _{mu } flux for IceCube

The predictions for the atmospheric neutrino flux at high energies strongly depend on the contribution of prompt neutrinos, which are determined by the production of charmed mesons in the atmosphere at very forward rapidities. In this paper we estimate the related cross sections taking into account the presence of an intrinsic charm (IC) component in the proton wave function and the QCD dynamics modified by the onset of saturation effects. The impact on the predictions for the prompt neutrino flux is investigated assuming different values for the probability to find the IC in the nucleon (P_{ic}). We demonstrate that for P_{ic} sim 1%, the IC component dominates the high-energy prompt neutrino flux. A first comparison with the IceCube data is performed and upper limits on the amount of IC are obtained for the linear and nonlinear descriptions of the QCD dynamics.

Development and application of CATCH: A cylindrical active tracker and calorimeter system for hyperon–proton scattering experiments

In this study, we developed a new proton detector system called CATCH, which was designed for a scattering experiment involving a Σ hyperon and a proton (J-PARC E40). CATCH is a cylindrical detector system covering an inner target that can be used to measure the trajectory and energy of a proton emitted from the target for the kinematic identification of a Σp scattering event. It comprises a cylindrical fiber tracker (CFT), a bismuth germanate (BGO) calorimeter, and a plastic scintillator hodoscope (PiID), which are coaxially arranged from the inner to the outer sides. The CFT is a tracking detector consisting of 5,000 scintillation fibers, and it has two types of cylindrical layers in which the fibers are arranged in straight and spiral configurations. 24 BGO crystals are placed around the CFT to measure the kinetic energy of the recoil proton. The PiID is used to determine whether the recoil proton is stopped in the BGO calorimeter . We performed proton–proton (pp) and proton–carbon (pC) scattering experiments using an 80 MeV proton beam to evaluate the performance of CATCH. The total energy resolution for the recoil proton was 2.8 MeV in σ for the entire angular region after the energy calibrations of the BGO calorimeter and the CFT. The angular resolution of the CFT was 1.27 degrees in σ for the proton, and the time resolution was more than 1.8 ns in σ. We also developed an analysis method for deriving the cross section of the pp scattering using CATCH. The obtained relative differential cross section for the pp elastic scattering was consistent with that obtained by reliable partial wave analysis, and the systematic error was maintained at below 10%. These performance results satisfy our requirements for a reliable detection system for the Σp scattering experiment conducted at J-PARC.

A detailed uncertainty analysis of EI-MBMS data from combustion experiments

Electron ionization molecular-beam mass spectrometry (EI-MBMS) is a widely used analytical method for studying the chemistry of combustion processes and for providing quantitative validation targets for kinetic model development often in form of species mole fraction profiles. The present study focuses on the determination of the uncertainties of such data, which result from the mass spectrometric measurements as well as from the data evaluation procedure, in particular through the use of different calibration methods, i.e., through a direct calibration of the instrument, a convolution procedure, and through the method of Relative Ionization Cross Sections (RICS). A series of calibration experiments were carried out using two independent time-of-flight mass spectrometers in order to check the influence of experimental and instrumental parameters on the uncertainties. The data obtained reveal several key contributors to the uncertainty, which are, among others, the signal intensity of a species in the mass spectrum, the instability of instrumental parameters, the species itself, and the calibration method.The propagation of these uncertainties from the different calibration methods as well as from the instrumental inconstancies into the final uncertainties of the mole fractions is further demonstrated using a gaussian error propagation and provision of sensitivities for different uncertainty sources is given. It was found that most of the uncertainties of the mole fractions reported in the literature are smaller than those reported here and presumably only consider the reproducibility of the signal.The use of two independent mass spectrometers for the experiments also revealed that the uncertainties determined for one instrument cannot be directly transferred to another especially for the method of direct calibration due to differences in the signal reproducibility, but that the uncertainties only change marginal for the semi-theoretical approaches.

Total Electron Detachment and Induced Cationic Fragmentation Cross Sections for Superoxide Anion (O2-) Collisions with Benzene (C6H6) Molecules.

In this study, novel experimental total electron detachment cross sections for O2− collisions with benzene molecules are reported for the impact energy range (10–1000 eV), as measured with a transmission beam apparatus. By analysing the positively charged species produced during the collision events, relative total ionisation cross sections were derived in the incident energy range of 160–900 eV. Relative partial ionisation cross sections for fragments with m/z ≤ 78 u were also given in this energy range. We also confirmed that heavier compounds (m/z > 78 u) formed for impact energies between 550 and 800 eV. In order to further our knowledge about the collision dynamics governing the fragmentation of such heavier molecular compounds, we performed molecular dynamics calculations within the framework of the Density Functional Theory (DFT). These results demonstrated that the fragmentation of these heavier compounds strongly supports the experimental evidence of m/z = 39–42, 50, 60 (u) cations formation, which contributed to the broad local maximum in the total ionisation observed from 550 to 800 eV. This work reveals the reactivity induced by molecular anions colliding with hydrocarbons at high energies, processes that can take place in the interstellar medium under various local conditions.

Interaction of evaporated glycine and dipeptide derivatives of glycine with He2+ ions

In this paper we have studied a mechanism for radiation damage of gas phase molecules of glycine [Gly] and dipeptide derivatives of glycine, such as diglycine [Gly-Gly], cyclo(glycylglycyl) [cyclo(Gly-Gly)] and glycyl-leucine [Gly-Leu] by the impact of He2+ ions with energy Ep = 4 keV/u. Relative cross sections of different elementary processes occurring in single collisions between dipeptide derivatives of glycine and ions have been measured for the first time. The fragmentation channels of both singly and multiply charged molecular ions have been studied experimentally. It has been shown that in the process of Gly-Gly sublimation, cyclization in the crystalline sample takes place, which results in formation of cyclo(Gly-Gly). Using the DFT method, the geometry of molecules and singly charged ions of glycine dipeptide derivatives has been calculated, as well as energies of different experimentally observed fragmentation channels of these ions.

Фрагментация ионов циклического дипептида 2,5-дикетопиперазина

The mechanism of radiation damage to 2,5-diketopiperazine (DKP, C4H6N2O2) molecules in the gas phase upon interaction with He2+ ions with an energy Ep = 4 keV/u has been investigated. The relative cross sections of various elementary processes occurring in single collisions of DKP with ions have been measured for the first time. The channels of fragmentation processes of singly charged ions have been studied experimentally. The DFT method was used to calculate the geometry of molecules and singly charged DKP ions, as well as the energies of the main experimentally observed channels of fragmentation of these ions.

Fragmentation of 2,5-diketopiperazine cyclic dipeptide ions

The mechanism of radiation damage to 2,5-diketopiperazine (DKP, C4H6N2O2) molecules in the gas phase upon interaction with He2+ ions with an energy Ep = 4 keV/u has been investigated. The relative cross sections of various elementary processes occurring in single collisions of DKP with ions have been measured for the first time. The channels of fragmentation processes of singly charged ions have been studied experimentally. The DFT method was used to calculate the geometry of molecules and singly charged DKP ions, as well as the energies of the main experimentally observed channels of fragmentation of these ions. Keywords: electron capture, dipeptides, molecular ion fragmentation.

Dissociative Excitation of Nitromethane Induced by Electron Impact in the Ultraviolet - Visible Spectrum.

The excitation of nitromethane (CH3 NO2 ), which is an important propellant and prototypic molecule for large class of explosives, has been investigated by electron impact and subsequent emission of photons in the UV-VIS spectral region between 300 nm and 670 nm. Emission spectrum of nitromethane was recorded at an electron energy of 50 eV. New dissociative excitation channels were observed through the appearance of different CH, CN, NH, OH and NO bands, and the Balmer series of atomic hydrogen. In addition, relative emission cross sections were recorded for the transitions of selected fragments. The emission spectrum was captured with significantly higher resolution in comparison to previous studies.

Measurement of relative differential cross sections of the neutron-deuteron elastic scattering for neutron energy from 13 to 52 MeV

Measurement of relative differential cross sections of the neutron-deuteron elastic scattering for neutron energy from 13 to 52 MeV

State-selective nonradiative electron capture in collisions of 95–197−MeV/uXe54+ with Kr and Xe

Lyman transitions of ${\mathrm{Xe}}^{53+*}$ produced by nonradiative electron capture in collisions of 95, 146, and 197 ${\mathrm{MeV/u}\phantom{\rule{4pt}{0ex}}\mathrm{Xe}}^{54+}$ ions with Kr and Xe atoms have been studied experimentally. It shows that the captured electrons preferentially populate lower states. The intensity ratios $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\beta})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha})$ and $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\gamma})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha})$ are found to decrease with increasing projectile velocity, and the ratios for Xe decrease faster than those of Kr. The obtained results are compared with the relative cross sections calculated with the relativistic eikonal approximation. For both targets, the theoretical results overestimate the experimental ratio $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\beta})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha})$ but underestimate $I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\gamma})/I(\mathrm{Ly}\text{\ensuremath{-}}\ensuremath{\alpha}).$ Moreover, the theory gives parallel decreasing curves for the two targets, which does not agree with the present experiment. In order to well understand the experimental findings, a more sophisticated theoretical approach is urgently required.

Electron loss of CH− and [formula omitted] induced by interactions with N2 and O2 at keV energies

Relative electron detachment cross sections for the projectiles CH− and CH2− colliding with N2 and O2 target gases were measured. Two different methods to measure the cross sections were used, the signal growth rate and the beam attenuation. The cross sections measured with the beam attenuation technique were higher than those measured with the signal growth rate method. An analysis based on the differences of the cross sections measured with the two methods showed consistency with the time-dependent processes of metastable auto-detaching state populations undergoing decay as a function of its time of flight. These metastable processes seem to be target dependent. When the target was O2, a decaying process characterized by a lifetime of the order of 0.40 ± 0.16 μs was found. For the case of the N2 as a target, it was not possible to derive a characteristic lifetime.

Measurement of the relative Bc±/B± production cross section with the ATLAS detector at s=8 TeV

The total cross section and differential cross sections for the production of $B_{c}^{\pm}$ mesons, times their branching fraction to $J/\psi \pi^{\pm}$, are measured relative to those for the production of $B^{\pm}$ mesons, times their branching fraction to $J/\psi K^{\pm}$. The data used for this study correspond to an integrated luminosity of $20.3\,\mathrm{fb}^{-1}$ of $pp$ collisions recorded by the ATLAS detector at the Large Hadron Collider in 2012 at a center-of-mass energy of $\sqrt{s} = 8$ TeV. The measurement is performed differentially in bins of transverse momentum $p_{\mathrm{T}}$ for $13$ GeV $<p_{\mathrm{T}}(B_{c}^{\pm})<22$ GeV and $p_{\mathrm{T}}(B_{c}^{\pm}) > 22$ GeV and in bins of rapidity $y$ for $|y| <0.75$ and $0.75<|y|<2.3$. The relative cross section times branching fraction for the full range $p_{\mathrm T} > 13$ GeV and $|y| < 2.3$ is $(0.34\,\pm\,0.04_{\text{stat}}\,^{+0.06}_{-0.02}\,_{\text{sys}}\,\pm\,0.01_{\text{lifetime}})\%$. The differential measurements suggest that the production cross section of the $B^{\pm}_c$ decreases faster with $p_{\mathrm T}$ than the production cross section of the $B^{\pm}$, while no significant dependence on rapidity is observed.