Proton Angles Research Articles

Amplitudes of 3H, 3He Two-Particle Photo-Breakup in Non-Local QED Approach

Three-nucleon systems are essential for the investigation of many-body forces in nuclear physics. Well-grounded parametrization of their vertex functions with further application for the calculation of cross-sections in nonlocal QED approach provides the ground for investigation of the variety of multi-particle systems. In present paper we describe the process of parametrization of two-particle photo-breakup amplitudes of three-nucleon systems (3H, 3He). We provide the general description of the wave function construction for three-nucleon systems as well as the parametrization of their vertex functions accounting two- and three-nucleon interactions based on meson exchange current formalism. In our calculations we account first and second order one-pion exchange terms and the term related to the exchange of ω and ρ mesons. The three-nucleon interaction potential is given as a sum of attraction (two-pion exchange) term andappropriate repulsive part. Based on the variational ”Urbana + Model VII” amplitudes we provide the results for energy dependence of differential cross-section of 3He(γ, p)d reaction at proton angle θ = 90◦ from the threshold up to Eγ = 40 MeV and compare theoretical predictions with the available experimental data. The investigation is also provided for angular cross-section distributions at high photon energies (Eγ = 305 ± 5 MeV; 365 ± 5 MeV; 450 ± 10 MeV and 675 ± 50 MeV). Correct description of 3H, 3He photo-disintegration processes in a unified approach based on the gauge nature of the electromagnetic field implies application of this model for other multi-particle systems.

Polarized fusion and potential in situ tests of fuel polarization survival in a tokamak plasma

The use of spin-polarized fusion fuels would provide a significant boost towards the ignition of a burning plasma. The cross section for D + T → α + n, would be increased by 1.5 if the fuels were injected with parallel polarization. Furthermore, our simulations demonstrate additional non-linear power gains in large-scale machines such as ITER, due to increased alpha heating. Such benefits require the survival of spin polarizations for periods comparable to the particle confinement time. During the 1980s, calculations predicted that polarizations could survive a plasma environment, although concerns persisted regarding the cumulative impacts of wall recycling. In that era, technical challenges prevented direct tests and left the large scale fueling of a power reactor beyond reach. Over the last decades, this situation has changed dramatically. Detailed simulations of ITER have predicted negligible wall recycling in a high-power reactor, and recent advances in laser-driven sources project the capability of producing large quantities of ∼100% polarized D and T. The remaining crucial step is an in-situ demonstration of polarization survival in a plasma. For this, we outline a measurement strategy using the isospin-mirror reaction, D + 3He → α + p. Polarized 3He avoids the complexities of handling tritium, while encompassing the same spin-physics. We evaluate two methods of delivering deuterium, using dynamically polarized Lithium-Deuteride (with vector polarization PV D of 70%) or frozen-spin Hydrogen-Deuteride (with PV D of 40%), together with a method of injecting optically-pumped 3He (with 65% polarization). Pellets of these materials all have long polarization decay times (∼6 min for LiD at 2 K, ∼2 months for HD at 2 K, and ∼3 d for 3He at 77 K), all far greater than a plasma shot in a research tokamak such as DIII-D (∼20 s). Both species can be propelled from a single cryogenic injection gun. We review plasma requirements and strategies for detecting polarization survival. Polarization alters both fusion yields and the angular distribution of fusion products, and each of these provides a potential signal. In this paper we simulate a selection of shots with similar characteristics in a future high-Tion H plasma, and find ratios of yields from shots with fuel spins parallel and antiparallel reaching 1.3 (HD + 3He) to 1.6 (LiD + 3He) over a wide range of poloidal angles. (A companion paper finds sensitivity to fusion product angular distributions as reflected in the pitch angles of protons and alphas reaching the plasma facing wall.)

EFFECT OF THE COULOMB INTERACTION TO THE PROCESSES OF INELASTIC DEUTERON SCATTERING ON NUCLEI AND THE STRUCTURE OF DEUTERON

The available experimental data on the interaction of polarized and unpolarized deuterons with a large deuteron momentum transfer require their theoretical description and interpretation. At the same time, further experimental studies require theoretical predictions in turn. In particular, there is a need to develop a theoretical model that makes it possible to smoothly connect available experimental data obtained at low-energy region, at which the nucleon-meson structure of the deuteron appears, with data obtained at high-energy region. The latter are related to the structure of the deuteron at small distances. Approaches based on the quark description of the deuteron structure are more adequate for their interpretation. The creation of such a model is an urgent task of modern nuclear physics, since it will allow one to reliably compare the asymptotic predictions of perturbative quantum chromodynamics and other quark approaches with the available experimental data. This will also make it possible to develop the theoretical approaches necessary for planning future experimental studies of elastic and inelastic deuteron scattering at high energies. In the framework of the Glauber–Sitenko model, the contribution of the Coulomb interaction to the reaction cross section A(d,p) at high energies and zero proton angle is calculated. The effect of taking into account the Coulomb interaction for the cross section in a wide inter-nuclear region is evaluated. The present calculations are compared with experiment. One fines that the Coulomb interaction gives a sizable contribution in the observables only at a peak, where the proton momentum is near half of the deuteron momentum in the lab. frame. But it does not change the results in the high momentum region, where quark effects should be taken into account.

Estimation of energy and angle of incident protons from three-dimensional track profiles on CR-39 detectors

The aim of this study was to establish a new method for estimating the energy and angle of incident protons based on the three-dimensional profile of nuclear tracks. An inverse growth approach was developed to obtain the latent track from the etched track pit. The energy and angle of the incident protons can be estimated by determining the critical point (end point of the particle trajectory). The estimated incident energies and angles were in good agreement with the pre-set values for the simulated and experimental data. Compared with the pre-set values, the deviation of the energies and angles for 1–3 MeV protons were within ±0.3 MeV and ±5.0°, respectively. This study provides a valuable reference for extracting energy and angle information from 3-D profiles of a nuclear track, and is expected to be beneficial in reconstruction of energy spectra.

A detailed simulation study on the effect of energy and angle of incidence for low energy protons on Single Event Upsets induced in nanometer CMOS SRAM

Low-energy proton-induced single event upsets (SEUs) are a significant threat to the reliability of nanometer technologies, which are used in radiation environments. In this paper, through a developed program using Geant4 simulation toolkit, the effect of proton energies (<10 MeV) and angles of incidence (0∘ to 60∘), as well as isotropic radiation field on the SEU cross-section in a 65 nm CMOS SRAM, is studied. Furthermore, we have investigated the role of dominant physical mechanisms contributing to inducing SEUs. To analyze the responsible mechanisms for the upsets, proton interactions with BEOL of the device are considered to determine which particles could cause the upsets.The results show that for all investigated cases, the SEU cross-sections first increase for protons with incident energies of less than about 1 MeV and then decrease for higher energy protons. It is also observed that with increasing the tilt angle up to 45∘, the SEU cross-section increases, and the SEU peak shifts to higher energies, while for larger angles, the cross-section decreases. The results for the isotropic proton field show that the SEU peak occurs in lower energies compared to the fixed angle cases. We have also observed that for the proton energies corresponding to the SEU cross-section peak, the energy spectrum of the protons entering the sensitive volume confirms the occurrence of the Bragg peak inside the sensitive volume. Regarding the physical mechanisms responsible for SEU, the results show that for protons with energies of less than 1 MeV, direct ionization and for energies between 2 MeV and 10 MeV, recoiled Si ions due to elastic scattering of protons in the sensitive volume are dominant in inducing upsets. Our findings have also revealed that for proton energies of more than 5 MeV, other particles produced in BEOL such as oxygen and alpha particles also play a role to induce upsets, but have less contribution. These results indicate that the structures of the BEOL in advanced CMOS technologies can play an important role in inducing upsets for the upper limit of low energy protons. These considerations can be useful for designing advanced technologies more hardened against radiation. In general, we have found that for low energy protons, the proton-induced SEU cross-section of the device is a strongly correlated function of energy and direction of the incident protons.

Characterization of Energetic Protons Generated in the ShenGuang-II UP Petawatt Laser Interactions with Foil Targets

The characterization of energetic protons generated in the ShenGuang-II UP petawatt laser interactions with foil targets has been systematically studied. The proton energy spectra and angular distributions are measured with a radiochromic film stack. It shows that the proton energy spectra have a Boltzmann distribution with temperature of about 2.8 MeV and cutoff energy of about 20 MeV. The divergence angles of protons vary from 10° to 60°, dependent on the proton energy. The proton source size and location are investigated via the proton point-projection mesh imaging. The proton virtual sources are found to locate tens to hundreds of microns in front of the foil target, depending on the proton energies. A Monte Carlo simulation estimates the diameter of the virtual proton source to be about 12 μm for the protons with energy of 16.8 MeV, which is much smaller than the laser focus size of about 50 μm. The spatial resolution of the 16.8 MeV proton imaging is quantified with the point spread function to be about 15 μm, which is consistent with the proton virtual source size. These results will be important for the users conducting experiments with the protons as a backlighting source on the ShenGuang-II UP petawatt laser.

Proton and Hydrogen Transport through Hydrogen Environments: Ionization and Stripping

Abstract Data are presented over a wide range of impact energies describing the ionization or stripping probability, projectile energy loss, and ejected electron and recoiling target energies and angles for proton and hydrogen passage through hydrogen astrophysical environments. These kinematic and reaction data are tabulated at three levels of detail for use in heavy-particle (H+, H) and secondary-electron transport simulations: (1) the integral scattering cross section and average values of the distributions of energy and angle of the particles, (2) the singly differential cross sections as a function of particle energy and angle, and (3) a subset of the many possible doubly differential cross sections as functions of the particle energy and angle chosen to be most relevant to transport simulations.

Imaging with Ion Beams at MedAustron

MedAustron is an Austrian cancer treatment facility using protons in the energy range from 62.4MeV to 252.7MeV and carbon ions with energies up to 400MeV/u for external beam radiotherapy. The facility features a unique beam line exclusively for non-clinical research, which will be commissioned for even higher proton energies of up to 800MeV.A demonstrator of a proton computed tomography system consisting of a tracking telescope and a residual energy detector is being developed and will be tested in beam at MedAustron. Currently, this demonstrator consists of a beam telescope composed of four double-sided silicon-strip detectors. A rotating table serving as sample holder is placed between the second and third detector. The tracking telescope is triggered by two scintillation detectors operated in coincidence and is placed downstream behind the silicon detectors. This telescope was tested in beam to obtain a radiography of an aluminium sample. Additionally, the tracking telescope was modelled in Geant4 to simulate particle tracks.An image reconstruction method exploiting material dependent variations of the scattering angle of protons was used to obtain a three dimensional image of an irradiated sample.

A comprehensive theoretical comparison of proton imaging set-ups in terms of spatial resolution

We present a comprehensive analytical comparison of four types of proton imaging set-ups and, to this end, develop a mathematical framework to calculate the width of the uncertainty envelope around the most likely proton path depending on set-up geometry, detector properties, and proton beam parameters. As a figure of merit for the spatial resolution achievable with each set-up, we use the frequency at which the modular transfer function of a density step decreases below 10%. We verify the analytical results with Monte Carlo simulations.We find that set-ups which track the angle and position of individual protons in front of and behind the phantom would yield an average spatial resolution of 0.3–0.35 lp mm−1 assuming realistic geometric parameters (i.e. 30–40 cm distance between detector and phantom, 15–20 cm phantom thickness). For set-ups combining pencil beam scanning with either a position sensitive detector, e.g. an x-ray flat panel, or with a position insensitive detector, e.g. a range telescope, we find an average spatial resolution of about 0.1 lp mm−1 for an 8 mm FWHM beam spot size. The pixel information improves the spatial resolution by less than 10%. In both set-up types, performance can be significantly improved by reducing the pencil beam size down to 2 mm FWHM. In this case, the achievable spatial resolution reaches about 0.25 lp mm−1. Our results show that imaging set-ups combining double scattering with a pixel detector can provide sufficient spatial resolution only under very stringent conditions and are not ideally suited for computed tomography applications. We further propose a region-of-interest method for set-ups with a pixel detector to filter out protons which have undergone nuclear reactions and discuss the impact of tracker detector uncertainties on the most likely path.

Simple structural elucidation of ostreocin-B, a new palytoxin congener isolated from the marine dinoflagellate Ostreopsis siamensis, using complementary positive and negative ion liquid chromatography/quadrupole time-of-flight mass spectrometry.

Ostreocin-B is a new palytoxin congener of comparable complexity. Elucidation of the chemical structure by nuclear magnetic resonance has been hampered due to limited sample availability. More importantly, the dihedral angles of protons at the base of the hydroxyl groups on the ring structures are predicted to produce little couplings and thus disrupt connectivity. The present investigation solved the problem through mass spectrometry. Structural elucidation was performed by high-performance liquid chromatograph coupled to a quadrupole time-of-flight mass spectrometer equipped with an electrospray ionization source operated in positive and negative ion mode. Measurement parameters were optimized to achieve high sensitivity and a high ratio of singly charged ions. Ostreocin-D (C127 H219 N3 O53 ), another palytoxin congener possessing an unambiguously determined structure, was used as a template. The molecular formula of ostreocin-B, C127 H219 N3 O54 , indicates that it has one more oxygen atom than ostreocin-D. Comparison of the product ion spectra in negative ion mode indicates the occurrence of hydroxyl substitution at C44 in ostreocin-B, unlike in ostreocin-D. Positive ion spectra also support the 44-OH substructure by producing conjugated polyenes ascribable to the sequential loss of hydroxyls on the cyclic hemiacetal. The planar structure of ostreocin-B is assigned to 42-hydroxy-3,26-didemethyl-19-deoxypalytoxin (=44-hydroxyostreocin-D). The method used in this study is an excellent tool to obtain structural information on interspecies and intrastrain variation of palytoxin congeners in marine organisms.

Halo structure of 8B determined from intermediate energy proton elastic scattering in inverse kinematics

The absolute differential cross section for small-angle proton elastic scattering on the proton-rich 8B nucleus has been measured in inverse kinematics for the first time. The experiment was performed using a secondary radioactive beam with an energy of 0.7 GeV/u at GSI, Darmstadt. The active target, namely hydrogen-filled time projection ionization chamber IKAR, was used to measure the energy, angle and vertex point of the recoil protons. The scattering angle of the projectiles was simultaneously determined by the tracking detectors. The measured differential cross section is analyzed on the basis of the Glauber multiple scattering theory using phenomenological nuclear-density distributions with two free parameters. The radial density distribution deduced for 8B exhibits a halo structure with the root-mean-square (rms) matter radius Rm=2.58(6) fm and the rms halo radius Rh=4.24(25) fm. The results on 8B are compared to those on the mirror nucleus 8Li investigated earlier by the same method. A comparison is also made with previous experimental results and theoretical predictions for both nuclei.

Geant4 simulations of soft proton scattering in X-ray optics

Low energy protons (< 300 keV) can enter the field of view of X-ray space telescopes, scatter at small incident angles, and deposit energy on the detector, causing intense background flares at the focal plane or in the most extreme cases, damaging the X-ray detector. A correct modelization of the physics process responsible for the grazing angle scattering processes is mandatory to evaluate the impact of such events on the performance of future X-ray telescopes as the ESA ATHENA mission. For the first time the Remizovich model, in the approximation of no energy losses, is implemented top of the Geant4 release 10.2. Both the new scattering physics and the built-in Coulomb scattering are used to reproduce the latest experimental results on grazing angle proton scattering. At 250 keV multiple scattering delivers large proton angles and it is not consistent with the observation. Among the tested models, the single scattering seems to better reproduce the scattering efficiency at the three energies but energy loss obtained at small scattering angles is significantly lower than the experimental values. In general, the energy losses obtained in the experiment are higher than what obtained by the simulation. The experimental data are not completely representative of the soft proton scattering experienced by current X-ray telescopes because of the lack of measurements at low energies (< 200 keV) and small reflection angles, so we are not able to address any of the tested models as the one that can certainly reproduce the scattering behavior of low energy protons expected for the ATHENA mission. We can, however, discard multiple scattering as the model able to reproduce soft proton funneling, and affirm that Coulomb single scattering can represent, until further measurements, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.

SU‐C‐207A‐01: A Novel Maximum Likelihood Method for High‐Resolution Proton Radiography/proton CT

Purpose:Multiple Coulomb scattering is the largest contributor to blurring in proton imaging. Here we tested a maximum likelihood least squares estimator (MLLSE) to improve the spatial resolution of proton radiography (pRad) and proton computed tomography (pCT).Methods:The object is discretized into voxels and the average relative stopping power through voxel columns defined from the source to the detector pixels is optimized such that it maximizes the likelihood of the proton energy loss. The length spent by individual protons in each column is calculated through an optimized cubic spline estimate. pRad images were first produced using Geant4 simulations. An anthropomorphic head phantom and the Catphan line‐pair module for 3‐D spatial resolution were studied and resulting images were analyzed. Both parallel and conical beam have been investigated for simulated pRad acquisition. Then, experimental data of a pediatric head phantom (CIRS) were acquired using a recently completed experimental pCT scanner. Specific filters were applied on proton angle and energy loss data to remove proton histories that underwent nuclear interactions. The MTF10% (lp/mm) was used to evaluate and compare spatial resolution.Results:Numerical simulations showed improvement in the pRad spatial resolution for the parallel (2.75 to 6.71 lp/cm) and conical beam (3.08 to 5.83 lp/cm) reconstructed with the MLLSE compared to averaging detector pixel signals. For full tomographic reconstruction, the improved pRad were used as input into a simultaneous algebraic reconstruction algorithm. The Catphan pCT reconstruction based on the MLLSE‐enhanced projection showed spatial resolution improvement for the parallel (2.83 to 5.86 lp/cm) and conical beam (3.03 to 5.15 lp/cm). The anthropomorphic head pCT displayed important contrast gains in high‐gradient regions. Experimental results also demonstrated significant improvement in spatial resolution of the pediatric head radiography.Conclusion:The proposed MLLSE shows promising potential to increase the spatial resolution (up to 244%) in proton imaging.

Scattering characteristics and imaging of energetic neutral atoms from the Moon in the terrestrial magnetosheath

AbstractWe study hydrogen energetic neutral atom (ENA) emissions from the lunar surface, when the Moon is inside the terrestrial magnetosheath. The ENAs are generated by neutralization and backscattering of incident protons of solar wind origin. First, we model the effect of the increased ion temperature in the magnetosheath (&gt;10 times larger than that in the undisturbed solar wind) on the ENA scattering characteristics. Then, we apply these models to ENA measurements by Chandrayaan‐1 and simultaneous ion measurements by Kaguya at the Moon, in the magnetosheath. We produce maps of the ENA scattering fraction, covering a region at the lunar near‐side that includes mare and highland surfaces and several lunar magnetic anomalies. We see clear signatures of plasma shielding by the magnetic anomalies. The maps are made at different lunar local times, and the results indicate an extended influence and altered morphology of the magnetic anomalies at shallower incidence angles of the magnetosheath protons. The scattering fraction from the unmagnetized regions remains consistent with that in the undisturbed solar wind (10%–20%). Moreover, the observed ENA energy spectra are well reproduced by our temperature‐dependent model. We conclude that the ENA scattering process is unchanged in the magnetosheath. Similarly to the undisturbed solar wind case, it is only magnetic anomalies that provide contrast in the ENA maps, not any selenomorphological features such as mare and highland regions.

Characterization of high-energy quasi-monoenergetic neutron energy spectra and ambient dose equivalents of 80–389 MeV 7Li(p,n) reactions using a time-of-flight method

We completed a series of measurements on mono-energetic neutron energy spectra of the 7Li(p,n) reaction with 80–389-MeV protons in the 100-m time-of-flight (TOF) tunnel at the Research Center for Nuclear Physics cyclotron facility. For that purpose, we measured neutron energy spectra of the 80-, 100- and 296-MeV proton incident reactions, which had not been investigated in our previous studies. The neutron peak intensity was 0.9–1.1×1010neutrons/sr/µC in the incident proton energy region of 80–389MeV, and it was almost independent of the incident proton energy. The contribution of peak intensity of the spectrum to the total intensity integrated with energies above 3MeV varied between 0.38 and 0.48 in the incident proton energy range of 80–389MeV. To consider the correction required to derive a response in the peak region from the measured total responses of neutron monitors in the 100-m TOF tunnel, we proposed the subtraction method using energy spectra between 0° and 25°. The normalizing factor k against 25° neutron fluence to equalize it to 0° neutron fluence in the continuum region ranges from 0.74 to 1.02 depending on the incident proton energy and angle measured. Even without the TOF method, the subtraction method with the k factor almost decreases the response in the continuum region of a neutron spectrum against the total response of neutron monitors.

SU‐C‐204‐04: Patient Specific Proton Stopping Powers Estimation by Combining Proton Radiography and Prior‐Knowledge X‐Ray CT Information

Purpose:The material relative stopping power (RSP) uncertainty is the highest contributor to the range uncertainty in proton therapy. The purpose of this work is to develop a robust and systematic method that yields accurate, patient specific, RSP by combining 1) pre‐treatment x‐ray CT and 2) daily proton radiograph of the patient.Methods:The method is formulated as a linear least‐square optimization problem (min||Ax‐B||2). The parameter A represents the pathlength crossed by the proton in each material. The RSPs for the materials (water equivalent thickness (WET)/physical thickness) are denoted by x. B is the proton radiograph expressed as WET crossed. The problem is minimized using a convex‐conic optimization algorithm with xi&lt;xi+1 constraint. The Gammex RMI‐465 phantom, with 13 material inserts, is used to investigate the optimal RSPs. The proton radiograph (B) is produced using Geant4 simulation. The matrix A is computed by calculating proton trajectories through the CT with the cubic‐spline approach. Geant4 RSPs are used as reference and the clinical HU‐RSP calibration curve is used as comparison. The convergence is investigated as a function of the number of angles and protons used. The radiographs angle which yield the most accurate RSPs are investigated.Results:Optimization with 9 angles and 104 protons/angle yields precise RSP (&lt;0.75%) for all materials, except plastic lung (1.5%). Average deviation relative to Geant4 RSP is 0.5% and 3.5% using HU‐RSP. Using more than two angles or more than 4×103 proton does not further increase the RSP estimate accuracy. The insert distance to the beam initial plane is related to the RSP error for this insert material. Specific filters are applied on the proton angle and energy loss to remove nuclear interaction artefacts.Conclusion:The proposed formulation of the problem with prior knowledge x‐ray CT demonstrates serious potential to increase the accuracy of present RSP estimates.

Determination of the beam-spin asymmetry of deuteron photodisintegration in the energy regionEγ=1.1–2.3 GeV

The beam-spin asymmetry, $\Sigma$, for the reaction $\gamma d\rightarrow pn$ has been measured using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility (JLab) for six photon-energy bins between 1.1 and 2.3 GeV, and proton angles in the center-of-mass frame, $\theta_{c.m.}$, between $25^\circ$ and $160^\circ$. These are the first measurements of beam-spin asymmetries at $\theta_{c.m.}=90^\circ$ for photon-beam energies above 1.6 GeV, and the first measurements for angles other than $\theta_{c.m.}=90^\circ$. The angular and energy dependence of $\Sigma$ is expected to aid in the development of QCD-based models to understand the mechanisms of deuteron photodisintegration in the transition region between hadronic and partonic degrees of freedom, where both effective field theories and perturbative QCD cannot make reliable predictions.

SPATIAL CONFINEMENT OF THEIBEXRIBBON: A DOMINANT TURBULENCE MECHANISM

The narrow ribbon of enhanced energetic neutral atom flux observed by the Interstellar Boundary Explorer (IBEX) spacecraft has prompted numerous ideas to explain its structure and properties. One of these ideas is the "neutral solar wind" scenario, which identifies the source particles as pickup protons in the local interstellar medium originating in solar wind charge-exchange interactions. This scenario has been thought to require unrealistically weak pitch-angle scattering of the pickup protons to explain the narrow structure. Recently, Schwadron & McComas (2013) suggested that this structure could result from a spatial retention of the pickup protons, rather than from a restricted pitch-angle distribution. Here, we present a physically motivated, quantitative mechanism to produce such a spatial configuration. This mechanism is based on the "dominant turbulence" assumption, which can be applied where the production of new pickup protons is slow, and has been used to successfully explain the level of turbulent heating observed in the outer solar wind. This formalism predicts a pickup isotropization process which adds or subtracts energy from the ambient turbulent fluctuations, depending on the initial pitch angle of the pickup protons. We show that a simple model of this process can yield a ribbon structure in qualitative agreement with the observations. The results of this simple model are not yet quantitatively satisfactory, but we suggest several improvements which may reduce the quantitative discrepancy.

Measurement of the structure function of the nearly free neutron using spectator tagging in inelasticH2(e,e′ps)Xscattering with CLAS

Much less is known about neutron structure than that of the proton due to the absence of free neutron targets. Neutron information is usually extracted from data on nuclear targets such as deuterium, requiring corrections for nuclear binding and nucleon off-shell effects. These corrections are model dependent and have significant uncertainties, especially for large values of the Bjorken scaling variable x. The Barely Off-shell Nucleon Structure (BONuS) experiment at Jefferson Lab measured the inelastic electron deuteron scattering cross section, tagging spectator protons in coincidence with the scattered electrons. This method reduces nuclear binding uncertainties significantly and has allowed for the first time a (nearly) model independent extraction of the neutron structure function. A novel compact radial time projection chamber was built to detect protons with momentum between 70 and 150 MeV/c. For the extraction of the free neutron structure function $F_{2n}$, spectator protons at backward angle and with momenta below 100 MeV/c were selected, ensuring that the scattering took place on a nearly free neutron. The scattered electrons were detected with Jefferson Lab's CLAS spectrometer. The extracted neutron structure function $F_{2n}$ and its ratio to the deuteron structure function $F_{2d}$ are presented in both the resonance and deep inelastic regions. The dependence of the cross section on the spectator proton momentum and angle is investigated, and tests of the spectator mechanism for different kinematics are performed. Our data set can be used to study neutron resonance excitations, test quark hadron duality in the neutron, develop more precise parametrizations of structure functions, as well as investigate binding effects (including possible mechanisms for the nuclear EMC effect) and provide a first glimpse of the asymptotic behavior of d/u as x goes to 1.

Collision dynamics of proton with formaldehyde: Fragmentation and ionization

Using time-dependent density functional theory, applied to the valence electrons and coupled non-adiabatically to molecular dynamics of the ions, we study the ionization and fragmentation of formaldehyde in collision with a proton. Four different impact energies: 35 eV, 85 eV, 135 eV, and 300 eV are chosen in order to study the energy effect in the low energy region, and ten different incident orientations at 85 eV are considered for investigating the steric effect. Fragmentation ratios, single, double, and total electron ionization cross sections are calculated. For large impact parameters, these results are close to zero irrespective of the incident orientations due to a weak projectile-target interaction. For small impact parameters, the results strongly depend on the collision energy and orientation. We also give the kinetic energy releases and scattering angles of protons, as well as the cross section of different ion fragments and the corresponding reaction channels.