Charge-changing Cross Sections Research Articles

Charge radii of 11−16C, 13−17N and 15−18O determined from their charge-changing cross-sections and the mirror-difference charge radii

Charge-changing cross-sections (CCCSs) of 11−16C, 13−17N and 15−18O on a carbon target have been determined at energies around 300 MeV/nucleon. A nucleon separation energy-dependent correction factor has been introduced to the Glauber model calculation for extracting the nuclear charge radii from the experimental CCCSs. The charge radii of 11C, 13,16N and 15O thus were determined for the first time. With the new radii, we studied the experimental mirror-difference charge radii (ΔRchmirror) of 11B-11C, 13C-13N, 15N-15O, 17N-17Ne pairs for the first time. We find that the ΔRchmirror values of 13C-13N and 15N-15O pairs follow well the empirical relation to the isospin asymmetry predicted by the abinitio calculations, while ΔRchmirror of 11B-11C and 17N-17Ne pairs deviate from such relation by more than two standard deviations.

The total and the partial charge-changing cross sections of 28Si fragmentation on C, CH2 and H targets at 500-800 A MeV

The total and the partial charge-changing cross sections of ²⁸Si fragmentation on C, CH₂ and H targets at 500-800 A MeV

Charge-changing cross sections and charge radii of B, C, and N isotopes

Charge-changing cross sections and charge radii of B, C, and N isotopes

A new approach for deducing rms proton radii from charge-changing reactions of neutron-rich nuclei and the reaction-target dependence

We report the charge-changing cross sections (σcc) of 24 p-shell nuclides on both hydrogen and carbon at about 900A MeV, of which 8,9Li, 10–12Be, 10,14,15B, 14,15,17–22N and 16O on hydrogen and 8,9Li on carbon are for the first time. Benefiting from the data set, we found a new and robust relationship between the scaling factor of the Glauber model calculations and the separation energies of the nuclei of interest on both targets. This allows us to deduce proton radii (Rp) for the first time from the cross sections on hydrogen. Nearly identical Rp values are deduced from both target data for the neutron-rich carbon isotopes; however, the Rp from the hydrogen target is systematically smaller in the neutron-rich nitrogen isotopes. This calls for further experimental and theoretical investigations.

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.

Charge-changing cross section measurements of 300 MeV/nucleon 28Si on carbon and data analysis* *Supported by the National Natural Science Foundation of China (U1832211, 11961141004, 11922501, 11475014, 11905260), the Western Light Project of Chinese Academy of Sciences, and the Natural Science Foundation of Anhui Province, China (2008085MA17)

Charge-changing cross section () measurements via the transmission method have recently seen significant progress with the aim of determining the charge radii of exotic nuclei. In this work, we report a new measurement of 304(9) MeV/nucleon Si on carbon at the second Radioactive Ion Beam Line in Lanzhou (RIBLL2) and describe the data analysis procedure in detail. This procedure is essential for evaluating the systematic uncertainty in the transmission method. The determined of 1125(11) mb is found to be consistent with the existing data at similar energies. The present work will serve as a reference for determinations at RIBLL2.

Total and partial charge changing cross-sections of 300 A MeV Fe26+ ion beam in different target media

In the present study, the total and partial charge changing cross-sections of 300 A MeV Fe26+ ion beam in CR39 and in combined medium of Al and CR39 were measured. The CR39 nuclear track detectors were used to identify the incident charged particles and their fragments using an automated image analyzing system. The total charge changing cross-section as calculated is (1220 ± 132) mb in CR39 target and (1472 ± 170) mb in combined target of Al and CR39. The total charge changing cross-section was fitted to the Bradt-Peters geometrical cross-section and compared with earlier results. For calculating the partial charge changing cross-sections for ΔZ = -1, −2, −3,….…,–23, the number of events corresponding to each fragment were determined from multiple Gaussian fitting of the diameter distributions within ±2σ confidence levels and the number of incident and survived beam ions were counted within ±3σ confidence levels. Some beam contaminated events were observed and presented.

Nuclear fragmentation reactions as a probe of neutron skins in nuclei

We investigate the contributions of various reaction channels to the interaction, reaction, charge-changing and neutron-changing cross sections. The goal is to investigate the relation between microscopic interactions and the symmetry energy component of the equation of state (EoS) of interest for the structure of neutron stars. We have made a comparison of the neutron skins extracted from diverse experimental techniques with those obtained with Hartree-Fock-Bogoliubov calculations with 23 Skyrme and with 8 density-dependent interactions used in the relativistic mean field method. We have shown that no particular conclusion can be drawn on the best EoS in view of the wide range of uncertainty in the experimental data. We have further investigated the prospects of using neutron-changing reactions to assess the isospin dependence of the neutron-skin in neutron-rich nuclei.

Prediction of charge-changing cross sections of low-charged 88Sr, 138Ba and 142Nd ions in a He-gas target at collision energies 50 eV/u–10 GeV/u

Electron-loss (EL) and electron-capture (EC) cross sections of neutral and low-charged heavy Srq+, Baq+ and Ndq+ ions with charges q = 0, 1 and 2 in collisions with He atoms are predicted in the energy range E = 50 eV/u–10 GeV/u. Experimental data on EL and EC cross sections of these particles colliding with He atoms are practically absent. At relatively low energies E = 8–30 keV, EL cross sections σ12 of Sr1+, Ba1+ and Nd1+ ions are predicted from new experimental equilibrium charge-state fractions F1 and F2 and calculated EC cross sections. Predicted value for Ba1+ ions, σ12=6.8⋅10−18cm2, is in a good agreement with the one available experimental point σ12exp=5.7⋅10−18cm2 at E = 20 keV (Fedorenko, 1954). Calculations of EL and EC cross sections are performed by available computer codes shortly described in the paper. Theoretically estimated neutral-atom fractions F0 are found much smaller than the measured F1, F2, and F3 charge-state fractions.

Proton Distribution Radii of ^{16-24}O: Signatures of New Shell Closures and Neutron Skin.

The root mean square radii of the proton density distribution in ^{16-24}O derived from measurements of charge changing cross sections with a carbon target at ∼900A MeV together with the matter radii portray thick neutron skin for ^{22-24}O despite ^{22,24}O being doubly magic. Imprints of the shell closures at N=14 and 16 are reflected in local minima of their proton radii that provide evidence for the tensor interaction causing them. The radii agree with abinitio calculations employing the chiral NNLO_{sat} interaction, though skin thickness predictions are challenged. Shell model predictions agree well with the data.

Charge-changing cross sections for Ca42–51 and effect of charged-particle evaporation induced by neutron-removal reactions

Charge-changing cross sections $\sigma_\mathrm{CC}$ for $^{42\textrm{--}51}$Ca on a carbon target at around 280~MeV/nucleon have been measured. The measured $\sigma_\mathrm{CC}$ values differ significantly from the previously developed calculations based on the Glauber model. However, through introduction of the charged-particle evaporation effect induced by the neutron-removal reaction in addition to the Glauber-model calculation, experimental $\sigma_\mathrm{CC}$ values on $^{12}$C at around 300~MeV/nucleon for nuclides from C to Fe isotopes are all reproduced with approximately 1\% accuracy. This proposed model systematically reproduces $\sigma_\mathrm{CC}$ data without phenomenological corrections, and can also explain experimental $\sigma_\mathrm{CC}$ values obtained in other energy regions.

Constraining equation of state of nuclear matter by charge-changing cross section measurements of mirror nuclei

The nuclear symmetry energy plays a key role in determining the equation of state (EoS) of dense, neutron-rich matter, which connects the atomic nuclei with the hot and dense matter in universe, thus has been the subject of intense investigations in laboratory experiments, astronomy observations and theories. Various probes have been proposed to constrain the symmetry energy and its density dependence. Currently, the extensive data yield already a good and consistent constraint to the symmetry energy (Esym(ρ)) at saturation density, but do not yet give a consistent result of one critical EoS parameter, L, the density dependence of the symmetry energy. In this work, we report a new probe of L at saturation density. A good linear correlation is found between L and the charge changing cross section difference (Δσcc) of mirror nuclei 30Si-30S for both the Skyrme-Hartree-Fock theory (SHF) and covariant (relativistic) density functionals (CDF). We found that the pairing effect for this mirror pair is essential to get a consistent correlation between L and Δσcc in both the SHF and CDF. Here, the cross sections are calculated on the same target and at the same energy using the zero-range optical-limit Glauber model. The linearity is found to be in the same precision as those found between L and neutron skin thickness or proton radius difference.

The total and the partial charge-changing cross sections of 40Ar fragmentation on elemental targets at 500 A MeV

The total and the partial charge-changing cross sections of 40Ar fragmentation on CH2, C, Al, Cu and Pb targets at the highest energy of 495 A MeV were investigated using CR-39 plastic nuclear track detector. The total charge-changing cross-section for hydrogen target was calculated based on the results of polyethylene and carbon targets. It was found that the total charge-changing cross sections for fragmentation of 40Ar on H, C, Al, Cu and Pb targets were independent on the beam energy in our studied energies, and were consistent with the predictions of Bradt-Peters semi-empirical formula. Nilsen semi-empirical formula, NUCFRG2 and PHITS simulation codes given an underestimation of experimental data. The partial cross sections for projectile fragment production were independent on the beam energy in our studied energies for each target and do not show a significant odd-even effect. The partial cross sections for projectile fragment production were also compared with different empirical parametrization formulas, such as different version of Cummings, Nilsen, FRACS and EPAX3. Generally, EPAX3 and FRACS empirical parametrization can give a reasonable estimation of data within 25% relative errors.

Image sorting of nuclear reactions recorded on CR-39 nuclear track detector using deep learning

Deep learning has been utilized to trace nuclear reactions in the CR-39 nuclear track detector. Etch pit images on front and back surfaces of the CR-39 detector were obtained sequentially by moving the objective lens of a microscope, and merged to one image. This image merging makes it possible to combine information on the displacement of the position of the etch pits produced by single particle traversals through a CR-39 layer in a single image, thereby making it easier to recognize corresponding nuclear fragmentation reactions. Object detection based on deep learning has been applied to the merged image to identify nuclear fragmentation events for measurement of the total charge changing cross-section based on the number of incident particles (Nin) and the number of particles that passed through target without any nuclear reaction (Nout). We verified the accuracy (correct answer rate) of algorithms for extracting the two patterns of etch pit in merged images which corresponds to Nin and Nout using the learning curves expressed as a function of the number of trainings. Accuracy of Nin and Nout were found to be 97.3 ± 4.0% and 98.0 ± 4.0%, respectively. These results show that the object detection algorithm based on the deep learning can be a strong tool for CR-39 etch pit analysis.

Empirical method evaluation of charge – Changing cross sections

A method based on experimental data, theoretical models, and the empirical estimation of experimental parameters in the equilibrium charge distribution of ions is proposed to evaluate charge changing cross sections. This method makes it possible to obtain cross sections for loss and capture of one or several electrons in gaseous and solid targets with the inclusion of the influence of excited states of ions and target atoms.

Applicability of composite materials for space radiation shielding of spacecraft

Energetic ion beam experiments with major space radiation elements, 1H, 4He, 16O, 28Si and 56Fe, have been conducted to investigate the radiation shielding properties of composite materials. These materials are expected to be used for parts and fixtures of space vehicles due to both their mechanical strength and their space radiation shielding capabilities. Low Z materials containing hydrogen are effective for shielding protons and heavy ions due to their high stopping power and large fragmentation cross section per unit mass. The stopping power of the composite materials used in this work is intermediate between that of aluminum and polyethylene, which are typical structural and shielding materials used in space. The total charge-changing cross sections per unit mass, σUM, of the composite materials are 1.3–1.8 times larger than that of aluminum. By replacing conventional aluminum used for spacecraft with commercially available composite (carbon fiber / polyether ether ketone), it is expected that the shielding effect is increased by ∼17%. The utilization of composite materials will help mitigate the space radiation hazard on future deep space missions.

Dynamic charge-changing processes in highly charged ions colliding with Ar atoms near the Bohr velocity

The average charge states of $^{20}\mathrm{Ne}^{7+}$ and $^{131}\mathrm{Xe}^{20+}$ ions penetrating through the gaseous argon targets with different areal densities are measured, and the velocities of projectile is close to the Bohr velocity regime ($v\ensuremath{\sim}1$ a.u.). The results show that, with the increase of target density, the dynamic evolution of average charge occurs in three different stages. The dependence of the average charge state on the charge-changing cross section from the nonequilibrium stage to the equilibrium stage is revealed by the theoretical predictions that consider single-electron and additional double-electron processes. It is found that the multi-electron charge-changing process needs to be properly considered in the equilibrium stage. In addition, an analysis model is proposed to predict the average charge state of the projectile in the event of significant energy loss and to quantitatively evaluate the dependence of energy loss on the charge-changing cross section.

Empirical relations for heavy-ion equilibrated charges and charge-changing cross sections in diluted $$\hbox {H}_{{2}}$$ with application

Highly ionized heavy evaporation residues (ERs) resulting from heavy-ion (HI) fusion–evaporation reactions are knocked out from solid targets to rarefied gas of gas-filled recoil separators. In gas, these ERs undergo charge-changing collisions on their way to a detection system. An equilibrium between the loss of charge (electron capture) and the gain of charge (electron loss) for ionized ERs allows one to use equilibrated charge-state distributions in trajectory calculations for ERs moving through a magnetic field. The distance from a target to the point where the ER charge-state distributions become to be the equilibrated one is essential for such calculations. This distance can be estimated in simulations based on electron capture and loss cross sections for energetic HIs. Reasonable approximations of available experimental data have provided these cross sections, which were applied to the Monte Carlo simulations of the ionic charge evolution for highly ionized heavy ERs. The results of these simulations demonstrate the setting of charge equilibration close to the target.

Fragmentation of carbon on elemental targets at 290AMeV

The total charge-changing cross-sections and the partial cross-sections for projectile fragments (PFs) production for the fragmentation of 12C on C, Al, Cu, Pb and CH2 targets at the highest energy of 290[Formula: see text]A[Formula: see text]MeV were studied. It was found that the total charge-changing reaction cross-sections and the partial reaction cross-sections of PFs production were independent of the beam energy, and increased with increase of mass of target for the same beam energy. The total charge-changing reaction cross-section was the same as the prediction of Bradt–Peters semi-empirical formula, PHITS and NUCFRG2 simulation models. The partial cross-section of PFs production increased with the increase of the mass of target, and it was the same as the prediction of NUCFRG2 models. The mean scattering angle of projectile particle was smaller than the average emission angle of PF, and the width of scattering angle distribution of projectile particle was smaller than that of emission angle distribution of PFs. The mean emission angle of PFs does not obviously depend on the target mass and beam energy in our studied beam energy regions.

Evaluation of the Charge-Changing Cross Sections for Ion—Atom Collisions

Evaluation of the Charge-Changing Cross Sections for Ion—Atom Collisions