Proton Distribution Research Articles

Coulomb and symmetry-energy effects on proton and neutron density-distributions in central heavy-ion collisions, across beam energies and system masses

In this contribution, we review our current and previous investigations of total, proton, and neutron particle number densities and the asymmetry of proton and neutron density distributions achievable in central heavy-ion collisions at beam energy below 800 MeV/nucleon. Furthermore, the effects of the Coulomb interaction and the dependence on a system size in three representative symmetric and asymmetric Ca, Sn and Pb systems are studied. The Boltzmann-Uhlenbeck-Uehling (pBUU) transport and Time-Dependent Hartree-Fock (TDHF) models, employing the SVbas, SkT3 and SVsym Skyrme interactions, are used in these simulations. We find that (i) the highest total densities predicted at Ebeam = 800 MeV/nucleon are on the order of ∼ 2.5ρ0 (ρ0 = 0.16 fm−3), (ii) the proton-neutron asymmetry for maximal densities, δ = (ρnmax−ρpmax)/(ρnmax+ρpmax) do not generally exceed the asymmetry in the initial state of the collision at all beam energies and tend to decrease during the reaction, and (iii) a significant portion of this asymmetry has its microscopic origin in Coulomb forces, masking the pure nuclear contribution. In addition, the evolution of normalized maximal proton, neutron, and total nucleon number density with increasing beam energy, the impact of correlations in the reaction, and the time evolution of the proton and neutron density distributions in the plane transverse to the beam direction are illustrated and discussed.

Inelastic scattering reaction as a probe for monopole, dipole and quadrupole excitations

The study of collective motions within atomic nuclei, such as monopole, dipole, and quadrupole excitations, is crucial for understanding nuclear structure and properties, which provide insights into the spatial distribution and dynamic nature of protons and neutrons in nuclei. By analyzing the angular distributions of these modes excited via inelastic scattering reactions, we can determine the transition characteristics and deformation lengths of nuclei. Specific case studies, including quadrupole excitations and dipole excitations indicating exotic cluster structures in light nuclei, highlight the utility of modern experimental setups like the solenoidal spectrometer and the active target detector.

Probing the nature of the QCD phase transition with higher-order net-proton number fluctuation and local parton density fluctuation measurements at RHIC-STAR

The moments of proton and net-proton multiplicity distributions are observables expected to be sensitive to the QCD critical point and the nature of the QCD phase transition from QGP to hadron gas. Hyper-order cumulants are measured in wide centrality bins in STAR BES-I data and found to be qualitatively consistent with trends predicted by lattice QCD which finds a cross-over phase transition at low μB. Data collected at √SNN = 3 GeV in BES-II exhibit trends opposite of those observed in higher energy collisions which may suggest the dominance of hadronic interactions at this energy. The variance of proton multiplicity distributions in azimuthal partitions is measured to search for signals of clustering indicative of a first-order phase transition. A strong dependence on the event multiplicity is observed. This dependence is independent of energy in AMPT while in STAR data a significant trend with energy is observed.

Design of synchrotron for proton FLASH radiotherapy

Proton FLASH, which combines the advantages of a better spatial dose distribution of protons with the unique temporal effect of FLASH radiotherapy, is currently a hot topic of international research. In this study, a series of innovative methods are proposed to manipulate the beam with the longitudinal dynamics and to extract particles from the synchrotron, thus meeting the dose rate requirements for proton FLASH point scanning radiotherapy in a 1L volume in the target area.

Effect of washing on nickel-rich NCMs: methodology to quantify the lithium/proton-exchange kinetics, the inserted protons, and the structural changes

This study quantifies the lithium/proton exchange by five independent techniques, also characterizing proton distribution, inflicted structural changes, and thermal stability.

Molecular‐level insight on CO2 electroreduction to formate facilitated by triazole ionic liquid interfacial microhabitat

AbstractThe interfacial microhabitat induced by functionalized ionic liquid (IL) electrolyte can effectively improve product selectivity for CO2 electroreduction. The multiple interactions in IL electrolytes affect the ions, CO2, proton distribution, and the protonation reaction, which are relevant to product selectivity. However, the specific effects are still unclear. Herein, molecular dynamics simulation and density functional theory were combined to reveal the regulatory mechanisms. The results showed that the dipolar interaction between CO2 and [124Triz]− cooperating the hydrogen bonds between [124Triz]− and H2O facilitates the accumulation of H atoms around C atoms of CO2. Moreover, the strong polar [124Triz]− induces protons to attack the C atoms of CO2, which results in lower free energy (−0.10 eV) for the formation of *HCOO intermediate and promotes the formation of formate, compared with the free energy of 0.43 eV for [NTf2]−. This work reveals the [124Triz]− regulatory mechanism for high formate selectivity.

Simulating Crystal Structure, Acidity, Proton Distribution, and IR Spectra of Acid Zeolite HSAPO-34: A High Accuracy Study.

It is a challenge to characterize the acid properties of microporous materials in either experiments or theory. This study presents the crystal structure, acid site, acid strength, proton siting, and IR spectra of HSAPO-34 from the SCAN + rVV10 method. The results indicate: the crystal structures of various acid sites of HSAPO-34 deviate from the space group of R3¯; the acid strength inferred from the DPE value likely decreases with the proton binding sites at O(2), O(4), O(1),and O(3), contrary to the stability order in view of the internal energy; the calculated ensemble-averaged DPE is about 1525 kJ/mol at 673.15 K; and the proton siting and the proton distribution are distinctly influenced by the temperature: at low temperatures, the proton is predominantly located at O(3), while it prefers O(2) at high temperatures, and the proton at O(4) assumedly has the least distribution at 273.15-773.15 K. In line with the neutron diffraction experiment, a correction factor of 0.979 is needed to correct for the calculated hydroxyl stretching vibration (ν(O-H)) of HSAPO-34. It seems that the SCAN meta-GGA method, compensating for some drawbacks of the GGA method, could provide satisfying results regarding the acid properties of HSAPO-34.

Least-squares analysis of the moments of the charge distribution in the mean-field models

Abstract The nth moment, $R^{(n)}_c$, of the charge distribution is composed of not only the m(≤ n)th moments, $R^{(m)}_p$, of the point proton distribution, but also the m(≤ (n − 2))th ones, $R^{(m)}_n$, of the point neutron distribution. The experimental value of $R^{(n)}_c(R^{(n)}_{c,{\rm exp}})$ observed through electromagnetic interaction makes it possible to investigate the point proton and neutron distributions together on the same basis. In order to estimate $R^{(m)}_\tau (\tau =p,n)$ from $R^{(n)}_{c,{\rm exp}}$, however, nuclear models are required. The structure of the least-squares analysis (LSA) between $R^{(n)}_c$ and $R^{(m)}_\tau$ is investigated within the mean-field framework. The LSA reveals constraints inherent in the model framework through the least-squares lines (LSL) and determines the value of $R^{(m)}_\tau$ of $R^{(n)}_{c,{\rm exp}}$ uniquely as a result of the sum rule with respect to the coefficients of the LSL equations. The n-dependence of the values of $R^{(m)}_\tau$ in the LSA is examined numerically by using the moments calculated up to n = 6 for 40Ca, 48Ca, and 208Pb.

A Comparative Study of Ground-level Enhancement Events of Solar Energetic Particles

Major solar eruptions can accelerate protons up to relativistic energies. Solar relativistic ions arriving at 1 au may cause a solar particle event detectable by the worldwide network of neutron monitors (NMs), a ground-level enhancement (GLE) event. Using the newly computed NM yield function, we have fitted the 15 historic GLEs. Moments of the fitted proton distributions are used for the analysis. Profiles of the proton net flux are very diverse, while some profiles are similar. For this study, we select two events with similar time profiles, GLE 60 (2001 April 15) and GLE 65 (2003 October 28), and ask what makes these GLEs similar. We compare the GLEs with their progenitor solar flares and coronal mass ejections (CMEs). We find a close relationship between the rise and peak of the GLE, on the one hand, and the solar flare and the metric radio emissions from extended coronal sources at the base of the CME, on the other hand. The GLE decay time, the rate of the proton spectrum evolution, and the CME speed are proportional to the duration of the soft X-ray flare. We compare the two GLEs with GLE 59 (2000 July 14) analyzed by Klein et al. and with the deka-MeV nucleon−1 proton and helium data from the ERNE instrument on the Solar and Heliospheric Observatory spacecraft. The comparison indicates that a single solar eruption can produce more than one component of solar energetic particles, differently contributing at different energies and locations.

Elucidation of Protonation Cooperativity of a STING-Activating Polymer.

Stimuli-responsive nanomaterials have the potential to improve the performance and overcome existing barriers of conventional nanotherapeutics. Molecular cooperativity design in stimuli-responsive nanomedicine can amplify physiological signals, enabling a cooperative response for improved diagnostic and therapeutic precision. Previously, this work reported an ultra-pH-sensitive polymer, PEG-b-PC7A, that possesses innate immune activating properties by binding to the stimulator of interferon genes (STING) through polyvalent phase condensation. This interaction enhances STING activation and synergizes with the endogenous STING ligand for robust cancer immunotherapy. Despite its successes in innate immune activation, the fundamental physicochemical and pH-responsive properties of PC7A require further investigation. Here, this study elucidates the protonation cooperativity driven by the phase transition of PC7A copolymer. The highly cooperative system displays an "all-or-nothing" proton distribution between highly charged unimer (all) and neutral micelle (nothing) states without gradually protonated intermediates. The binary protonation behavior is further illustrated in pH-precision-controlled release of a representative anticancer drug, β-lapachone, by PC7A micelles over a noncooperative PE5A polymer. Furthermore, the bimodal distribution of protons is represented by a high Hill coefficient (nH >9), featuring strong positive cooperativity. This study highlights the nanoscale pH cooperativity of an immune activating polymer, providing insights into the physicochemical characterization and design parameters for future nanotherapeutics development.

Simulations of two-temperature jets in galaxy clusters

Context. Non-radiating protons in the radio lobes play an essential role in shaping the jet morphology, as demonstrated in recent radio and X-ray observations. However, since protons and electrons are not always in energy equilibrium due to weak Coulomb coupling, it is difficult to estimate the energy contribution of protons for the inflation of radio lobes. Aims. The focus of this study is to examine the effect of the variable model for electron heating by turbulence and shock waves on the thermal energy distribution of electrons and protons. Methods. We performed two-temperature three-dimensional magnetohydrodynamic (3D MHD) simulations of sub-relativistic jets in the galaxy cluster, while varying the jet magnetization parameters. Because the energy partition rate between electrons and protons in shock and turbulence is determined by plasma kinetic scale physics, our global simulations include electron instantaneous heating sub-grid models for shock waves and turbulence. Results. We find that most of the bulk kinetic energy of the jet is converted into the thermal energy of protons through both shocks and turbulence. Thus, protons are energetically dominant. Meanwhile, thermal electrons stored in the lobe evolve toward energy equipartition with magnetic energy through turbulent dissipation. We further estimated the radio power and the mechanical jet power of radio lobes following the same method used for radio and X-ray observations, then we compared these powers with that of the observed radio jets. The two-temperature model quantitatively explains the radiatively inefficient radio cavities, but it cannot reproduce the radiatively efficient cavity, even for strongly magnetized jets. This implies that a significant population of pair-plasma is needed to explain radiatively efficient radio cavities.

Isospin-dependence of the charge-changing cross-section shaped by the charged-particle evaporation process

We present the charge-changing cross sections (CCCS) of 11−15C, 13−17N, and 15,17−18O at around 300 MeV/nucleon on a carbon target, which extends to p-shell isotopes with N<Z for the first time. The Glauber model, which considers only the proton distribution of projectile nuclei, underestimates the cross sections by more than 10%. We show that this discrepancy can be resolved by considering the contribution from the charged-particle evaporation process (CPEP) following projectile neutron removal. Using nucleon densities from the deformed relativistic Hartree-Bogoliubov theory in continuum, we investigate the isospin-dependent CPEP contribution to the CCCS for a wide range of neutron-to-proton separation energy asymmetry. Our calculations, which include the CPEP contribution, agree well with existing systematic data and reveal an “evaporation peak” at the isospin symmetric region where the neutron-to-proton separation energy is close to zero. These results suggest that analysis beyond the Glauber model is crucial for accurately determining nuclear charge radii from CCCSs.

Updated results on the cosmic ray energy spectrum and composition from the GRAPES-3 experiment

Here, we present the updated results on the cosmic ray energy spectrum and composition analysis from the GRAPES-3 experiment over the energy range of 50 TeV to 1000 TeV since ICRC 2021. The simulation of cosmic ray showers was performed using the post-LHC high energy hadronic interaction model QGSJetII-04 and low energy hadronic model FLUKA. A detailed GEANT4 simulation of the GRAPES-3 muon telescope was performed. The composition was obtained by fitting simulated muon multiplicity distributions for proton, helium, nitrogen, aluminium, and iron primaries to the observed data. The energy spectrum connects to the direct measurements with a fairly good agreement in flux.

Outcomes after Proton Beam Irradiation in Patients with Choroidal Melanoma Eligible for Investigational AU-011 Treatment

Introduction: Vision loss is common in patients treated with radiotherapy for uveal melanoma. With proton beam irradiation (PBI), the prescribed dose is delivered to the tumor with a sharp dose reduction outside the target volume. However, radiation complications are likely to develop when tumors are located near the optic nerve or fovea. Treatment with light-activated AU-011 (belzupacap sarotalocan), an investigational drug which specifically targets tumor cells, may avoid these complications. We evaluated outcomes in a historical group of patients who fit eligibility criteria for AU-011 therapy and were treated with PBI. Methods: A consecutive series of patients who received PBI for small choroidal melanoma at a single center between 1986 and 2016 were identified. Consistent with eligibility criteria in clinical trials of AU-011, patients were included when tumor dimensions did not exceed 2.5 mm in maximum thickness and 10.0 mm in largest basal diameter (LBD). Snellen visual acuities were converted to logMAR for analysis. Visual acuity outcomes were analyzed in patients with an initial acuity of logMAR 0.7 or better (equivalent to Snellen 20/100). Rates of visual acuity loss and mortality were calculated using the Kaplan-Meier method. Acuity loss by tumor location was compared using log-rank testing. Rates of tumor recurrence, neovascular glaucoma (NVG), and eye loss were also described. Results: Two hundred and 22 patients were included in the study. The median age was 60.7 years (range 21.3–94.8 years). Median tumor thickness was 2.0 mm (range 1.2–2.5 mm), and median LBD was 8.0 mm (range 4.0–10.0 mm). Median follow-up was 6.9 years (range 1.0–30.2 years). In 204 patients with a baseline logMAR visual acuity of 0.7 or better, the mean baseline acuity was 0.15 (equivalent to Snellen 20/25), which decreased to 0.52 (approximately Snellen 20/70) by 5 years after PBI. Visual outcomes were significantly worse for patients with tumors located within 3 mm of the optic disc and/or fovea. Tumor recurrence (1.4%), NVG (4.5%), and eye loss (2.7%) were uncommon. Discussion: Despite the advantageous dose distribution of protons, over half of patients with small choroidal melanomas located near the optic disc or fovea had a visual acuity equivalent to 20/80 or worse at 5 years after PBI. Treatment with AU-011 may allow better vision preservation in small tumors that carry a high risk of vision loss with radiotherapy.

Acute normal tissue responses in a murine model following fractionated irradiation of the head and neck with protons or X-rays

Background The purpose of this study was to investigate acute normal tissue responses in the head and neck region following proton- or X-irradiation of a murine model. Materials and methods Female C57BL/6J mice were irradiated with protons (25 or 60 MeV) or X-rays (100 kV). The radiation field covered the oral cavity and the major salivary glands. For protons, two different treatment plans were used, either with the Bragg Peak in the middle of the mouse (BP) or outside the mouse (transmission mode; TM). Delivered physical doses were 41, 45, and 65 Gy given in 6, 7, and 10 fractions for BP, TM, and X-rays, respectively. Alanine dosimetry was used to assess delivered doses. Oral mucositis and dermatitis were scored using CTC v.2.0-based tables. Saliva was collected at baseline, right after end of irradiation, and at day 35. Results The measured dose distribution for protons (TM) and X-rays was very similar. Oral mucositis appeared earlier, had a higher score and was found in a higher percentage of mice after proton irradiation compared to X-irradiation. Dermatitis, on the other hand, had a similar appearance after protons and X-rays. Compared to controls, saliva production was lower right after termination of proton- and X-irradiation. The BP group demonstrated saliva recovery compared to the TM and X-ray group at day 35. Conclusion With lower delivered doses, proton irradiation resulted in similar skin reactions and increased oral mucositis compared to X-irradiation. This indicates that the relative biological effectiveness of protons for acute tissue responses in the mouse head and neck is greater than the clinical standard of 1.1. Thus, there is a need for further investigations of the biological effect of protons in normal tissues.

Two proton emission and other exotic decays in the 48Ni region with ACTAR TPC

Since the first indirect measurements of the two proton radioactivity in 2002 [1], some theoretical descriptions have been able to reproduce experimental results until the 2-proton radioactivity was established for 67Kr at RIKEN [2], with a lifetime about 20 times lower than expected. New theory inputs have recently been developed [3][4], predicting angular distributions of the emitted protons for some of the two proton emitters, that need to be confirmed experimentally. An experiment at GANIL/LISE3 facility was performed in May 2021 aiming to produce one of the 2 proton emitters (48Ni) and measure the angular distribution of the emitted protons. We used the ACTAR TPC detector to implant the ions and perform the tracking of their proton decays. In addition, other exotic nuclei in the 48Ni region were produced. For several of them we have found a first evidence of exotic decays such as β delayed 3- and 2-proton emission or low energy proton branches for β delayed single proton emission. The analysis of this decays will provide helpful experimental information about the structure and the partial decay schemes of these unstable nuclei.

Charge transport in protic ionic liquids: Effect of protonation state in 1-methylimidazolium – acetate/trifluoroacetate mixtures

Despite the potential to overcome slow charge transport in ionic liquids by decoupling charge transport from mass transport in protic ionic liquids (PILs), the average proton distribution and the contribution of proton conduction to the overall charge transport in PILs has not been fully established. To elucidate the predominant underlying molecular species in the PILs and the molecular dynamics of the PILs, we study the dipolar response and conductivity using dielectric relaxation (DR) spectroscopy and the nucleis chemical environment and molecular mobility using nuclear magnetic resonance (NMR) spectroscopy of prototypical PILs based on 1–methylimidazolium as Brønsted base. To elucidate the effect of the acidity of the Brønsted acid we gradually vary the composition of the PILs from 1–methylimidazoliumacetate [MimH][AcO] to 1–methylimidazoliumtrifluoroacetate [MimH][TFA]. Both, 15N-NMR chemical shifts and the sample conductivities suggest that in neat [MimH][AcO] electro-neutral molecular species dominate, consistent with earlier findings. The dipolar response of these molecular species as detected via the DR spectra is stronger than what one would expect based on the molecular dipole moments estimated from density functional theory calculations, which points to the formation of an extended hydrogen-bonded network. Upon addition of [MimH][TFA], this dipolar response is reduced as the degree of protonation of 1–methylimidazolium gradually increases, which is apparent from the conductance and 15N chemical shifts. Interestingly, diffusion ordered NMR spectroscopy indicates protons to become more mobile than the constituting acid and base molecules, consistent with Grotthuss-like proton transport. To vary the immediate environment of the PILs, we study solutions of the PIL mixtures in aprotic dimethylformamide (DMF) and protic methanol (MeOH) as two limiting cases. We find that [MimH][AcO] exclusively forms electroneutral species in DMF, as evident from the negligible conductivity, while with increasing TFA content the fraction of charged molecular species increases. Although these ionic species give rise to a finite conductivity, demonstrating the presence of mobile ions, a large fraction of these ions is bound in [MimH][TFA] ion-pairs, as detected in the DR spectra. Yet, temperature dependent 1H-NMR linewidths of the acidic proton signals suggest proton exchange to occur on the NMR timescale, presumably between [MimH]+ and [Mim]. Conversely, in MeOH we find no evidence for the presence of ion-pairs, while the high conductivity of these solutions shows that MeOH can efficiently solvate ions and may participate in proton transfer. Together, our results highlight the sensitivity of protonation equilibria to the immediate environment and of proton dynamics to these protonation equilibria. Our results show that tuning these equilibria using PIL mixtures can provide routes to tailor the contribution of proton transport to charge transport in PILs.

Exospheric Solar Wind Model Based on Regularized Kappa Distributions for the Electrons Constrained by Parker Solar Probe Observations

In the present work, the kinetic exospheric model of the solar wind is improved by considering regularized Kappa distributions that have no diverging moments through consideration of a cut-off at relativistic velocities. The model becomes valid even for kappa indices lower than 2, which is important since low values of kappa are observed in the fast solar wind. The exospheric model shows that the electric potential accelerates the wind to supersonic velocities. The presence of suprathermal Strahl electrons at the exobase can further increase the velocity to higher values, leading to profiles comparable to the observations in the fast and slow wind at all radial distances. The kappa index is not the only parameter that influences the acceleration of the wind: the difference in the altitude of the exobase also makes a significant difference between the fast and slow wind. The exobase is located at lower altitudes in the coronal holes where the density is smaller than in the other regions of the corona, allowing the wind originating from the holes to be accelerated to higher velocities. The new observations of Parker Solar Probe are used to constrain the model. The observations at low radial distances show suprathermal electrons already well present in the Strahl in the antisunward direction and a deficit in the sunward direction, confirming the exospheric feature of almost no incoming particles. For proton distributions, we observe that the proton tail parallel to the magnetic field is already present at 17.2 Rs.

Adiabatic energy change in the inner heliosheath: how does it affect the distribution of pickup protons and energetic neutral atom fluxes?

ABSTRACT The hydrogen atoms penetrate the heliosphere from the local interstellar medium, and while being ionized, they form the population of pickup protons. The distribution of pickup protons is modified by the adiabatic heating (cooling) induced by the solar wind plasma compression (expansion). In this study, we emphasize the importance of the adiabatic energy change in the inner heliosheath that is usually either neglected or considered improperly. The effect of this process on the energy and spatial distributions of pickup protons and energetic neutral atoms (ENAs), which originate in the charge exchange of pickup protons, has been investigated and quantified using a kinetic model. The model employs the global distributions of plasma and hydrogen atoms in the heliosphere from the simulations of a kinetic-magnetohydrodynamic model of solar wind interaction with the local interstellar medium. The findings indicate that the adiabatic energy change is responsible for the broadening of the pickup proton velocity distribution and the significant enhancement of ENA fluxes (up to ∼5 and ∼20 times in the upwind and downwind directions at energies ∼1–2 keV for an observer at 1 au). It sheds light on the role of adiabatic energy change in explaining the discrepancies between the ENA flux observations and the results of numerical simulations.

Multiple scattering calculations for proton beams: Comparison of results from the general-purpose Monte Carlo codes penh, fluka and topas

Purpose:To test the multiple Coulomb scattering theories implemented in the Monte Carlo simulation codes penh, fluka and topas. Methods:Simulations with the three codes of proton beams with initial energies between 100 and 220 MeV impinging normally on slabs of 14 different compositions and various thicknesses were performed. The simulated angular distributions of transmitted protons are very approximately Gaussian with a characteristic angle θ0, which measures the spread of the distribution. The characteristic angles resulting from the simulations are compared to experimental data available from two experiments. The degree of agreement is quantified by the χ2 statistic. The 151 cases considered are analyzed by grouping the data in various ways (all together, by experiment, according to the energy of the proton beam or the slab material). Results:In general, penh produced the better description of the experimental data. If all data are included, the χ2 values were 3.7±0.6 for penh, 18.7±0.4 for fluka and 7.4±1.5 for topas. The ranges in the values of χ2 obtained for the various data groups are [0.1±0.2;10.7±4.1] for penh, [0.10±0.03;221.1±7.8] for fluka, and [0.2±0.3;46.2±26.4] for topas. The minimum and maximum values in these ranges occur, in the three codes, for the Zn and the brass slabs, respectively, with 158.6MeV protons. Conclusions:The three codes provide a reasonably accurate description of multiple scattering distributions of protons transmitted through material slabs. Brass is the material whose experimental data are worst described by the three codes analyzed.