Energy Differential Cross Sections Research Articles

Ion molecule reaction dynamics for disentangling competing reactive pathways

Ion molecule reaction dynamics for disentangling competing reactive pathways

Methodology for physics-informed generation of synthetic neutron time-of-flight measurement data

Accurate neutron cross section data are a vital input to the simulation of nuclear systems for a wide range of applications from energy production to national security. The evaluation of experimental data is a key step in producing accurate cross sections. There is a widely recognized lack of reproducibility in the evaluation process due to its artisanal nature and therefore there is a call for improvement within the nuclear data community. This can be realized by automating/standardizing viable parts of the process, namely, parameter estimation by fitting theoretical models to experimental data. There are numerous candidate methods to approach this type of problem, but many rely on large, labeled datasets that are not accessible to the nuclear data evaluator. For a reaction cross-section, there are usually just a handful of datasets, none of which can be considered labeled because evaluators never have access to the exact solution (cross section). This work leverages problem-specific physics, Monte Carlo sampling, and a general methodology for data synthesis to generate unlimited, labeled experimental cross-section data of high-utility. The synthesized data is said to be of high-utility because it is statistically similar to the observed data. Heuristic and, where applicable, rigorous statistical comparisons to observed data support this claim. The methodology is split into two generative models. The first generates a realization of an energy-differential cross section for a given isotope. The second takes the output from the first as a determined input and generates noisy experimental observables (radiation detector signals) from the determined cross section realization. The latter is the primary development of this article and is based/limited to transmission measurements at Rensselaer Polytechnic Institute (RPI). The former leverages an existing method for model parameter sampling in the resolved resonance region (RRR), thus limiting the current demonstration to the RRR of incident neutron energies. An open-source software is published alongside this article that executes the complete methodology to produce high-utility synthetic datasets. The goal of this work is to provide an approach and corresponding tool that will allow the evaluation community to begin exploring more data-driven, ML-based solutions to long-standing challenges in the field.

Cross sections, penetrating range and stopping power for charge particles emission from n + 52Cr

In a fusion reactor, DT reactions produce huge amount of neutrons which hit the structure material and produce heat and damages. To understand the production of nuclear heating and material damages, study of double differential cross section (DDX), energy differential cross section (EDX), penetrating range of incident particles and stopping power of target element was calculated for 52Cr(n, p) and 52Cr(n, a) reactions. The calculated data have been compared with the suitable experimental data collected from EXFOR and other. The contribution of compound, pre-equilibrium and direct reaction processes has been analyzed for the entire cross section calculation. The emission of charged particles at different angles has been discussed based on the reaction processes. Parameter adjustment has been applied to fit the experimental data.

Dynamics of the Oxygen Atom Transfer Reaction between Carbon Dioxide and the Tantalum Cation.

The understanding of fundamental atomic-level processes often requires well-defined model systems. The oxygen atom transfer from CO2 to a transition metal cation in the gas phase presents such a model system. We investigate the reaction of Ta+ + CO2 for which the formation of TaO+ is highly efficient and attributed to multistate reactivity. Here, we study the atomistic dynamics of the oxygen atom transfer reaction by recording experimental energy and angle differential cross sections by crossed beam velocity map imaging supported by ab initio quantum chemical calculations. Product ion velocity distributions are dominated by signatures for indirect dynamics, despite the reaction being highly exothermic. Product kinetic energy distributions show little dependence on additional collision energy even with only four atoms involved, which hints at dynamical trapping behind a submerged barrier.

New determination of the production cross section for γ rays in the Galaxy

The flux of $\gamma$ rays is measured with unprecedented accuracy by the $\textit{Fermi}$ Large Area Telescope from 100 MeV to almost 1 TeV. In the future, the Cherenkov Telescope Array will have the capability to measure photons up to 100 TeV. To accurately interpret this data, precise predictions of the production processes, specifically the cross section for the production of photons from the interaction of cosmic-ray protons and helium with atoms of the ISM, are necessary. In this study, we determine new analytical functions describing the Lorentz-invariant cross section for $\gamma$-ray production in hadronic collisions. We utilize the limited total cross section data for $\pi^0$ production channels and supplement this information by drawing on our previous analyses of charged pion production to infer missing details. In this context, we highlight the need for new data on $\pi^0$ production. Our predictions include the cross sections for all production channels that contribute down to the 0.5% level of the final cross section, namely $\eta$, $K^+$, $K^-$, $K^0_S$, and $K^0_L$ mesons as well as $\Lambda$, $\Sigma$, and $\Xi$ baryons. We determine the total differential cross section $d\sigma(p+p\rightarrow \gamma+X)/dE_{\gamma}$ from 10 MeV to 100 TeV with an uncertainty of 10% below 10 GeV of $\gamma$-ray energies, increasing to 20% at the TeV energies. We provide numerical tables and a script for the community to access our energy-differential cross sections, which are provided for incident proton (nuclei) energies from 0.1 to $10^7$ GeV (GeV/n).

Recoil and charged particle energy spectra from the natSi(n,x) reaction and the Si semiconductor detector response to the 14 MeV neutrons

The energy spectra of light and heavy charged particles generated by the 14 MeV neutrons in silicon nuclei and in the Si semiconductor detector (SSD) were analysed. The existing measurements were used to validate the corresponding energy differential cross sections from major evaluations ENDF/B-VIII.0 and JEFF-3.3. The required data were extracted by the various codes: NJOY21, SPKA and MCNP6. It was shown that both evaluations underestimate the high energy part of the 28Si(n,x)p- and α-particle spectra by ≤50%, whereas at smaller emission energies no experimental data even exist. The calculation of the atom displacement damage in SSD reveals that the secondary protons produce additionally ≈15% of damage, whereas the contribution from secondary alphas is impossible to estimate since the Si(α,x) recoil data are not available.The single experiment, carried out by K. Yageta and co-workers in 1988, reported the energy spectra in the Si semiconductor down to the rather low energy of ≈0.3 MeV, at which the production of reaction recoils dominates over the light ions. The Monte Carlo simulation of this experiment was performed by MCNP6. The generation and transport of all relevant ions were taken in account. The energy depositions from protons or alphas were summed with their associated recoils after correction for non-ionization losses. The neutron reactions in the dead layer of the SSD were shown to increase the counts in active layer by (1–20)% depending on sort of ions. The impact of the field funneling effect was studied. Consideration of all these underlying processes has eventually allowed a reasonable reproduction of this experiment.

New determination of the production cross section for secondary positrons and electrons in the Galaxy

The cosmic-ray fluxes of electrons and positrons ($e^{\pm}$) are measured with high precision by the space-borne particle spectrometer AMS-02. To infer a precise interpretation of the production processes for $e^{\pm}$ in our Galaxy, it is necessary to have an accurate description of the secondary component, produced by the interaction of cosmic-ray proton and helium with the interstellar medium atoms. We determine new analytical functions of the Lorentz invariant cross section for the production of $\pi^\pm$ and $K^\pm$ by fitting data from collider experiments. We also evaluate the invariant cross sections for several other channels, involving for example hyperon decays, contributing at the few \% level on the total cross section. For all these particles, the relevant 2 and 3 body decay channels are implemented, with the polarized $\mu^\pm$ decay computed with next-to-leading order corrections. The cross section for scattering of nuclei heavier than protons is modeled by fitting data on $p+C$ collisions. The total differential cross section $d\sigma/dT_{e^\pm}(p+p\rightarrow e^\pm+X)$ is predicted from 10 MeV up to 10 TeV of $e^\pm$ energy with an uncertainty of about 5-7\% in the energies relevant for AMS-02 positron flux, thus dramatically reducing the precision of the theoretical model with respect to the state of the art. Finally, we provide a prediction for the secondary Galactic $e^\pm$ source spectrum with an uncertainty of the same level. As a service for the scientific community, we provide numerical tables and a script to calculate energy-differential cross sections.

Tau longitudinal and transverse polarizations from visible kinematics in (anti-)neutrino nucleus scattering

Since the ντ(ν¯τ)AZ→τ∓X reaction is notoriously difficult to be directly measured, the information on the dynamics of this nuclear process should be extracted from the analysis of the energy and angular distributions of the tau decay visible products. These distributions depend, in addition to d2σ/(dEτdcos⁡θτ), on the components of the tau-polarization vector. We give, for the first time, the general expression for the outgoing hadron (pion or rho meson) energy and angular differential cross section for the sequential ντAZ→τ−(π−ντ,ρ−ντ)X and ν¯τAZ→τ+(π+ν¯τ,ρ+ν¯τ)X reactions. Though all possible nuclear reaction mechanisms contribute to the distribution, it may be possible to isolate/enhance one of them by implementing appropriate selection criteria. For the case of the quasi-elastic reaction off oxygen and neutrino energies below 6 GeV, we show that the pion distributions are quite sensitive to the details of the tau-polarization components. We find significant differences between the full calculation, where the longitudinal and transverse components of the tau polarization vector vary with the energy and the scattering angle of the produced tau, and the simplified scheme in which the polarizations are set to one and zero, being the latter their respective asymptotic values reached in the high energy regime. In addition to its potential impact on neutrino oscillation analyses, this result can be used to further test different nuclear models, since these observables provide complementary information to that obtained by means of the inclusive nuclear weak charged-current differential cross section. We also study the effects on the cross section of the W4 and W5 nuclear structure functions, which contributions are proportional to the charged lepton mass, and therefore difficult to constrain in muon and electron neutrino experiments.

Differential Ionization Cross Sections of HCl Molecule

In this article, the differential ionization cross-sections of the HCl molecule in the gas phase is investigated. The single differential ionization cross-section (SDCS) as a function of loss of incident electron energy and Double Differential Cross Section (DDCS) as a function of energy loss of incident electron and incident angle, is calculated. To reach exact values of differential ionization cross sections for HCl molecule, a modified semi-empirical approach of Jain and Khare is used. Partial and total absolute ionization cross-section of HCl is available but there is no data for differential ionization crosssections. So, first time, the results for single and double differential ionization cross-sections for HCl molecule is investigated.

Production yields at the distal fall-off of the β+ emitters 11C and 13N for in-vivo range verification in proton therapy

In proton therapy, Positron Emission Tomography (PET) range verification relies on the comparison of the measured and estimated activity distributions from β+ emitters produced by the proton beam in the patient. The accuracy of the estimated activity distributions is basically that of the underlying reaction cross section data. In this context, we have developed a new method for measuring β+ production yields combining the multi-foil technique with a clinical PET scanner, resulting in energy differential cross sections from a single irradiation. The method has been applied to the production of C11 (t1/2 = 20.36 min) and Ny13 (t1/2 = 9.97 min), the main candidates for off-line PET range verification, in carbon, nitrogen and oxygen, the main elements of the human body. The energy range studied with the 18 MeV CNA cyclotron corresponds to the distal fall-off of the activity curve, i.e. near the Bragg peak.

Impact of laser polarization on q -exponential photon tails in nonlinear Compton scattering

Non-linear Compton scattering of ultra-relativistic electrons traversing high-intensity laser pulses generates also hard photons. These photon high-energy tails are considered for parameters in reach at the forthcoming experiments LUXE and E-320. We consider the invariant differential cross sections $d \sigma / du$ between the IR and UV regions and analyze the impact of the laser polarization and find q-deformed exponential shapes. (The variable $u$ is the light-cone momentum-transfer from initial electron to final photon.) Optical laser pulses of various durations are compared with the monochromatic laser beam model which uncovers the laser intensity parameter in the range $\xi = 1 \cdots 10$. Some supplementary information is provided for the azimuthal final-electron/photon distributions and the photon energy-differential cross sections.

Three-body breakup of 6He and its halo structure

The Borromean halo nucleus 6He has been studied by a kinematically complete measurement of Coulomb and nuclear breakup into α + 2n on Pb and C targets at 70 MeV/nucleon. Fully quantum-mechanical four-body breakup calculations reproduce the energy and angular differential cross sections below Erel∼1 MeV for both targets. The model used here reproduces the 6He ground-state properties as well as α-n and n-n scattering data and predicts an average opening angle 〈θnn〉 of 68∘ between the two halo neutrons. However, the model underestimates the breakup cross sections for higher Erel, indicating a possible contribution from the inelastic breakup. Alternatively, we examine the empirically modified calculations that reproduce the energy-differential cross sections for a wide range of scattering angles for both targets. The extracted B(E1) peaks at Erel∼1.4 MeV and amounts to 1.6(2) e2fm2 for Erel ≤ 20 MeV, resulting 〈θnn〉 = 56−10+9 degrees. In either interpretation, the current results show evidence of the dineutron spatial correlation in 6He.

Measurement of the energy-differential cross-section of the 12C(n,p)12B and 12C(n,d)11B reactions at the n_TOF facility at CERN

Although the 12C(n,p)12B and 12C(n,d)11B reactions are of interest in several fields of basic and applied Nuclear Physics the present knowledge of these two cross-sections is far from being accurate and reliable, with both evaluations and data showing sizable discrepancies. As part of the challenging n_TOF program on (n,cp) nuclear reactions study, the energy differential cross-sections of the 12C(n,p)12B and 12C(n,d)11 B reactions have been measured at CERN from the reaction thresholds up to 30 MeV neutron energy. Both measurements have been recently performed at the long flight-path (185 m) experimental area of the n_TOF facility at CERN using a pure (99.95%) rigid graphite target and two silicon telescopes. In this paper an overview of the experiment is presented together with a few preliminary results.

Two-center electron-impact ionization via collisional excitation-autoionization

Electron-impact ionization of an atom or ion in the presence of a neighboring atom is studied. The latter is first collisionally excited by the incident electron, whose energy is assumed to be high but nonrelativistic. Afterwards, the excitation energy is transferred radiationlessly via a two-center Auger process to the other atom or ion, leading to its ionization. We show that the participation of the neighboring atom manifests in a very pronounced resonance peak in the energy-differential cross section and can substantially enhance the total cross section of electron-impact ionization. We also discuss the influence of the neighbouring atom on the angular distribution of the ejected electron.

Possible evidence of nonstatistical properties in the Cl35(n, p)S35 cross section

Author(s): Batchelder, JC; Chong, SA; Morrell, J; Unzueta, MA; Adams, P; Bauer, JD; Bailey, T; Becker, TA; Bernstein, LA; Fratoni, M; Hurst, AM; James, J; Lewis, AM; Matthews, EF; Negus, M; Rutte, D; Song, K; Van Bibber, K; Wallace, M; Waltz, CS | Abstract: The Cl35(n,p) and Cl35(n,α) cross sections at incident neutron energies between 2.42 and 2.74 MeV were measured using the Berkeley High Flux Neutron Generator. The cross sections for Cl35(n,p) were more than a factor of 3 to 5 less than all of the values in the neutron absorption data libraries, while the Cl35(n,α) cross sections are in reasonable agreement with the data libraries. The measured energy-differential cross section is consistent with a single resonance with a width of 293(46) keV. This result suggests that, despite the high incident neutron energy, any attempt to model (n,x) cross sections in the vicinity of the N=Z=20 shell gap requires a resolved resonance approach rather than a Hauser-Feshbach approach.

Reproduction of true energy spectrum of charged particles with Monte Carlo method

To measure the energy differential cross section of charged particles, it is essential to correct the energy loss of charged particles in the target foil due to nuclear scattering. In the present work, a Monte Carlo method based on the transport of charged particles to reproduce the true energy spectrum of charged particles has been developed. In the proposed method, charged particles are generated randomly throughout the foil and transported to the exit of the target foil. At their exit, each particle is weighted with the measured spectrum, and transported back to their origin to reproduce the true energy spectrum. Proposed method has been validated with Geant-4.1 which transports charged particle dynamics within the foil while TALYS-1.8 code is used to produce the true energy spectrum of charged particles in the foil. This proposed method has also been compared with other published methods to obtain the true energy spectrum and differences in their results have been discussed.

Inclusive Photoproduction of Υ(1s) and J/ψ in Ultra-peripheral p-Pb Collisions at TeV**Supported by the National Natural Science Foundation of China under Grant Nos. 11465021, 11065010

With a photon spectrum of high energy charged partons, both differential and total cross sections of J/ψ and Υ(1s) inclusive photoproduction in ultra-peripheral p-Pb Collisions (UPCs) at TeV are given. A direct photon process and a resolved photon process including fragment and non-fragment contributions are considered. The total cross section is compared to the inelastic production results in coherent p-Pb collisions at the same center-of-mass energy. Our results seem non-negligible.

Calculated differential and double differential cross section of DT neutron induced reactions on natural chromium (Cr)

Chromium is an important alloying element of stainless steel (SS) and SS is the main constituent of structural material proposed for fusion reactors. Energy and double differential cross section data will be required to estimate nuclear responses in the materials used in fusion reactors. There are no experimental data of energy and double differential cross section, available for neutron induced reactions on natural chromium at 14 MeV neutron energy. In this study, energy and double differential cross section data of (n,p) and (n,α) reactions for all the stable isotopes of chromium have been estimated, using appropriate nuclear models in TALYS code. The cross section data of stable isotopes are later converted into the energy and double differential cross section data of natural Cr using the isotopic abundance. The contribution from compound, pre-equilibrium and direct nuclear reaction to total reaction have also been calculated for 52,50Cr(n,p) and 52Cr(n,α). The calculation of energy differential cross section shows that most of emitted protons and alpha particles are of 3 and 8 MeV respectively. The calculated data is compared with the data from EXFOR data library and is found to be in good agreement.

Magnetic Moments of Excited Baryons

In project A.3, the reaction γ p → π 0 γ ’ p has been studied using the TAPS photon spectrometer in the energy range √s= 1221-1331 MeV. Energy tagged photon beams have been produced with the Glasgow tagging spectrometer from electron beams provided by the MAMI-B accelerator. Angle and energy differential cross sections have been measured and compared to theoretical calculations. This comparison allows the magnetic moment of the Δ + isobar to be extracted for the first time to μ Δ+ = [2.7 +1.3 −1.0 (stat)±1.5(syst)±3(theo)] μ N . In an extension of the A3 project to the meson sector, the time-like transition form factor of the η meson has been measured with the Crystal Ball/TAPS detector system at MAMI-C.

Double photoionization of helium from the 1s2p excited state

Time-dependent close-coupling (TDCC) calculations are carried out for the double photoionization of Helium in the excited state. TDCC results are presented for the total and energy differential cross sections for the term. TDCC results are presented for the total and energy differential cross sections for the levels. Differences found between the level resolved double photoionization cross sections are due to varying degrees of continuum correlation found in the outgoing two electrons.