Pickup Cross Sections Research Articles

Neutron transfer in 7Li+205Tl system

Neutron transfer cross sections for 7Li+205Tl system were measured near Coulomb barrier energies using online γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray detection technique. One neutron stripping, two neutron stripping, and one neutron pickup cross sections have been extracted and are compared with the Coupled Reaction Channel (CRC) calculations. The systematics of one and two neutron stripping and pickup cross sections with a 7Li projectile on several targets show an approximate universal behaviour. A comparison of integrated neutron transfer cross sections with complete and incomplete fusion cross sections available with 7Li projectile is presented to understand the systematic behaviour. The neutron transfer along with cumulative sum of complete and incomplete fusion was found to explain the estimated reaction cross section in 7Li+205Tl system.

Understanding the Formation and Growth of New Atmospheric Particles at the Molecular Level through Laboratory Molecular Beam Experiments.

Atmospheric new particle formation (NPF), which exerts comprehensive implications for climate, air quality and human health, has received extensive attention. From molecule to cluster is the initial and most important stage of the nucleation process of atmospheric new particles. However, due to the complexity of the nucleation process and limitations of experimental characterization techniques, there is still a great uncertainty in understanding the nucleation mechanism at the molecular level. Laboratory-based molecular beam methods can experimentally implement the generation and growth of typical atmospheric gas-phase nucleation precursors to nanoscale clusters, characterize the key physical and chemical properties of clusters such as structure and composition, and obtain a series of their physicochemical parameters, including association rate coefficients, electron binding energy, pickup cross section and pickup probability and so on. These parameters can quantitatively illustrate the physicochemical properties of the cluster, and evaluate the effect of different gas phase nucleation precursors on the formation and growth of atmospheric new particles. We review the present literatures on atmospheric cluster formation and reaction employing the experimental method of laboratory molecular beam. The experimental apparatuses were classified and summarized from three aspects of cluster generation, growth and detection processes. Focus of this review is on the properties of nucleation clusters involving different precursor molecules of water, sulfuric acid, nitric acid and NxOy, respectively. We hope this review will provide a deep insight for effects of cluster physicochemical properties on nucleation, and reveal the formation and growth mechanism of atmospheric new particle at the molecular level.

Properties of water and argon clusters developed in supersonic expansions.

Using adiabatic molecular dynamics coupled with the fluid dynamics equations, we model nucleation in an expanding beam of water vapor and argon on a microsecond scale. The size distribution of clusters, their temperature, and pickup cross sections in dependence on velocity are investigated and compared to the geometric cross sections and the experiment. The clusters are warmer than the expanding gas because of the time scale of relaxation processes. We also suggest that their translational and rotational kinetic energies are modified due to evaporative cooling. The pickup cross sections determined for the final clusters using molecules of the same kind increase with decreasing velocity, still obeying the (a+bN1/3)2 law.

Investigating neutron transfer in the Li6+Sn124 system

One-neutron stripping and pickup cross sections in the $^{6}\mathrm{Li}+^{124}\mathrm{Sn}$ system have been investigated through coupled-channel calculations by using a reliable global set of potentials. The systematics of one-neutron stripping and pickup cross sections with $^{6}\mathrm{Li}$ projectiles on several targets have been presented. An approximate universal behavior is seen, which has been explained by a model based on barrier penetration. The neutron transfer along with cumulative sum of complete and incomplete fusion was found to explain most of the reaction cross section in the $^{6}\mathrm{Li}+^{124}\mathrm{Sn}$ system.

Investigation of neutron transfer in Li7+Sn124 system

The relative importance of neutron transfer and breakup process in a reaction around Coulomb barrier energies has been studied for the $^{7}\mathrm{Li}+^{124}\mathrm{Sn}$ system. Coupled channel calculations have been performed to understand the one neutron stripping and pickup cross sections along with the breakup in the $^{7}\mathrm{Li}+^{124}\mathrm{Sn}$ system. The systematics of one and two neutron stripping and pickup cross sections with a $^{7}\mathrm{Li}$ projectile on several targets show an approximate universal behavior, which has been explained by a simple model based on barrier penetration. Complete reaction mechanism have been studied by comparing the reaction cross sections with the measured total fusion and one neutron transfer cross sections.

Measurement of cross sections for charge pickup by 40Ar on elemental targets at 500 MeV/n

The nuclear charge pickup cross sections of 40Ar on polyethylene(CH2), carbon, aluminum, copper and lead targets at the highest energy of 495 MeV/n were measured using CR-39 nuclear track detector. The cross sections for H were calculated from those measured on C and CH2 targets. The dependence of charge pickup cross section on target mass was studied, it was found that the nuclear charge pickup cross section exhibits a linear dependence on the target mass.

Measurement of cross sections for charge pickup by 12C on elemental targets at 400 MeV/n

The nuclear charge pickup cross sections of 12C on CH2, C, Al, Cu, and Pb targets at the highest energy of 398 MeV/n were investigated using CR-39 nuclear track detector. The cross section for H was calculated from those measured on C and CH2 targets. The dependence of charge pickup cross section on target mass was investigated, it was found that the nuclear charge pickup cross section is linearly depended on the target mass. This linear dependence is consistent with the prediction of nuclear peripheral and surface collision of charge pickup.

Measurement of cross-sections for charge pickup by 12C on elemental targets at 290MeV/n

The nuclear charge pickup cross-sections of [Formula: see text]C on CH2, C, Al, Cu and Pb targets at the highest energy of 288[Formula: see text]MeV/n were investigated using CR-39 nuclear track detector. The cross-section for H was calculated from those measured on C and CH2 targets. The dependence of charge pickup cross-section on target mass was investigated. It was found that the nuclear charge pickup cross-section of [Formula: see text]C at our studied beam energies seems to exponentially depend on the target mass with the fitting exponent [Formula: see text], which can be well explained by the peripheral and the surface collisions of the nuclear charge pickup reactions.

Investigating neutron transfer in the Be9+Au197 system

In this work $\textit{n}$-transfer and incomplete fusion cross sections for $^{9}$Be + $^{197}$Au system are reported over a wide energy range, E$_{c.m.}$ $\approx$ 29-45 MeV. The experiment was carried out using activation technique and off-line gamma counting. The transfer process is found to be the dominant mode as compared to all other reaction channels. Detailed coupled reaction channel (CRC) calculations have been performed for $\textit{n}$-transfer stripping and pickup cross sections. The measured 1$\textit{n}$-stripping cross sections are explained with CRC calculations by including the ground state and the 2$^{+}$ resonance state (E = 3.03 MeV) of $^{8}$Be. The calculations for 1$\textit{n}$-pickup, including only the ground state of $^{10}$Be agree reasonably well with the measured cross sections, while it overpredicts the data at subbarrier energies. For a better insight into the role of projectile structure in the transfer process, a comprehensive analysis of 1$\textit{n}$-stripping reaction has been carried out for various weakly bound projectiles on $^{197}$Au target nucleus. The transfer cross sections scaled with the square of total radius of interacting nuclei show the expected Q-value dependence of 1$\textit{n}$-stripping channel for weakly bound stable projectiles.

One-neutron transfer, complete fusion, and incomplete fusion from the Be9 + Au197 reaction

In this work, one-neutron transfer (pickup and stripping), complete and incomplete fusion cross sections for the $^{9}\mathrm{Be}+^{197}\mathrm{Au}$ system were measured over a wide range of energies around the Coulomb barrier by the offline $\ensuremath{\gamma}$-ray detection method. Coupled-channel calculations were used to determine the elastic, inelastic, and transfer cross sections. Coupled reaction channel calculations were performed to derive the one-neutron stripping and pickup cross sections. Three-body continuum discretized coupled-channel calculations were used to determine the effect of the breakup channel on the other reaction mechanisms. The reduced complete and total fusion were found to be hindered above and enhanced below the Coulomb barrier compared with the universal fusion function due to the breakup plus transfer effects.

Measurement of cross sections for charge pickup by $$^{\textbf {{84}}}\textbf {Kr}$$ on Al, C and $$\textbf{CH}_{{\textbf{2}}}$$ targets at 400 MeV/u

The nuclear charge pickup cross sections of $$^{84}\hbox {Kr}$$ on $$\hbox {CH}_{{2}}$$, C, and Al targets are investigated using CR-39 nuclear track detector at the highest energy of 395 MeV/u. The cross sections for H are calculated from those measured on C and $$\hbox {CH}_{{2}}$$ targets. The dependence of the charge pickup cross section on target mass is studied.

Measurement of cross sections for charge pickup reaction by 56Fe on Al, C and CH2 targets at 500 MeV/n

The nuclear charge pickup cross sections of 56Fe on polyethylene (CH2), carbon and aluminum targets at an energy of 497 MeV/n were investigated using CR-39 nuclear track detector. The dependence of charge pickup cross section on target mass was studied.

Fusion reaction studies for the Li6+Sn124 system at near-barrier energies

The complete and incomplete fusion along with one neutron stripping and pickup cross sections for the $^{6}\mathrm{Li}+^{124}\mathrm{Sn}$ system are measured using online and offline characteristic $\ensuremath{\gamma}$-ray detection techniques. The complete fusion (CF) cross sections at energies above the Coulomb barrier are found to be suppressed by $\ensuremath{\sim}34%$ compared to the coupled channel calculations. This suppression observed in complete fusion cross sections is found to be commensurate with the measured total incomplete fusion (ICF) cross sections. There is a distinct feature observed in the ICF cross sections, i.e., $d$ capture is found to be dominant than $\ensuremath{\alpha}$ capture at all the measured energies, contrary to the data available for $^{6}\mathrm{Li}+^{209}\mathrm{Bi},^{197}\mathrm{Au}$ systems. The total fusion cross section ratio between $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ induced reactions shows an increasing trend as the energy decreases below the barrier while it remains unity at above-barrier energies. A simultaneous explanation of complete, incomplete, and total fusion (TF) data is also obtained from the calculations based on the continuum discretized coupled channel method with short-range imaginary potentials. The cross section ratios of CF/TF and ICF/TF obtained from the data as well as the calculations shows the dominance of ICF at below-barrier energies and CF at above-barrier energies.

Uptake of methanol on mixed HNO3/H2O clusters: An absolute pickup cross section

The uptake of atmospheric oxidized organics on acid clusters is relevant for atmospheric new particle formation. We investigate the pickup of methanol (CH3OH) on mixed nitric acid-water clusters (HNO3)M(H2O)N by a combination of mass spectrometry and cluster velocity measurements in a molecular beam. The mass spectra of the mixed clusters exhibit (HNO3)m(H2O)nH+ series with m = 0-3 and n = 0-12. In addition, CH3OH·(HNO3)m(H2O)nH+ series with very similar patterns appear in the spectra after the methanol pickup. The velocity measurements prove that the undoped (HNO3)m(H2O)nH+ mass peaks in the pickup spectra originate from the neutral (HNO3)M(H2O)N clusters which have not picked up any CH3OH molecule, i.e., methanol has not evaporated upon the ionization. Thus the fraction of the doped clusters can be determined and the mean pickup cross section can be estimated, yielding σs¯≈ 20 Å2. This is compared to the lower estimate of the mean geometrical cross section σg¯≈ 60 Å2 obtained from the theoretical cluster geometries. Thus the "size" of the cluster corresponding to the methanol pickup is at least 3-times smaller than its geometrical size. We have introduced a method which can yield the absolute pickup cross sections relevant to the generation and growth of atmospheric aerosols, as illustrated in the example of methanol and nitric acid clusters.

Imaging of hydrogen halides photochemistry on argon and ice nanoparticles.

The photodissociation dynamics of HX (X = Cl, Br) molecules deposited on large ArN and (H2O)N, N̄ ≈ 10(2)-10(3), clusters is investigated at 193 nm using velocity map imaging of H and Cl photofragments. In addition, time-of-flight mass spectrometry after electron ionization complemented by pickup cross section measurements provide information about the composition and structure of the clusters. The hydrogen halides coagulate efficiently to generate smaller (HX)n clusters on ArN upon multiple pickup conditions. This implies a high mobility of HX molecules on argon. On the other hand, the molecules remain isolated on (H2O)N. The photodissociation on ArN leads to strong H-fragment caging manifested by the fragment intensity peaking sharply at zero kinetic energy. Some of the Cl-fragments from HCl photodissociation on ArN are also caged, while some of the fragments escape the cluster directly without losing their kinetic energy. The images of H-fragments from HX on (H2O)N also exhibit a strong central intensity, however, with a different kinetic energy distribution which originates from different processes: the HX acidic dissociation followed by H3O neutral hydronium radical formation after the UV excitation, and the slow H-fragments stem from subsequent decay of the H3O. The corresponding Cl-cofragment from the photoexcitation of the HCl·(H2O)N is trapped in the ice nanoparticle.

Growth of ice nanoparticles via uptake of individual molecules: pickup cross sections

We present cross sections for pickup of several atmospherically relevant molecules on ice nanoparticles with the 0.5-3 nm diameter range. The experimental values are supported by molecular dynamics simulations and analytical calculations based on long-range cluster-molecule potentials. The cross sections are all considerably larger than the geometrical cross section of nanoparticle and vary significantly for different guest molecules.

Charge-changing cross sections ofNe30,Na32,33with a proton target

The total charge-changing, charge pick-up, and partial charge-changing cross sections of very neutron-rich nuclei (Ne30, Na32,33) with a proton target have been measured at ∼240A MeV for the first time. We introduced the phenomenological correction factor in Glauber-model calculations for the total charge-changing cross sections with the proton target, and applied it to deduce the proton radii of these nuclei. For Ne30 and Na32, the neutron skin thicknesses of the nuclei were deduced by comparing the proton radii with the matter radii deduced from the interaction cross-section measurements. A significant thick neutron-skin has been observed for the nuclei. We also found that the charge pick-up cross sections are much larger than those in the systematics of stable nuclei.Received 30 January 2014Revised 7 March 2014DOI:https://doi.org/10.1103/PhysRevC.89.044602©2014 American Physical Society

Irregular Shapes of Water Clusters Generated in Supersonic Expansions

We report cross sections for pickup of guest molecules on neutral argon and water clusters with the mean sizes in the range from N = 50 to 600. The experiments are supported by molecular dynamics simulations and analytical models based on the interaction potentials. The cross sections for argon clusters are consistent with their assumed spherical shape and follow approximately the theoretically justified N(1/3) dependence. On the other hand, the cross sections of water clusters depart from this dependence and are considerably larger starting from N ≥ 300. We interpret this increase of cross section by the occurrence of highly irregular shapes of water clusters produced in the supersonic expansion of water vapor under the conditions of the large cluster generation.

Atmospheric processes on ice nanoparticles in molecular beams.

This review summarizes some recent experiments with ice nanoparticles (large water clusters) in molecular beams and outlines their atmospheric relevance: (1) Investigation of mixed water–nitric acid particles by means of the electron ionization and sodium doping combined with photoionization revealed the prominent role of HNO3 molecule as the condensation nuclei. (2) The uptake of atmospheric molecules by water ice nanoparticles has been studied, and the pickup cross sections for some molecules exceed significantly the geometrical sizes of the ice nanoparticles. (3) Photodissociation of hydrogen halides on water ice particles has been shown to proceed via excitation of acidically dissociated ion pair and subsequent biradical generation and H3O dissociation. The photodissociation of CF2Cl2 molecules in clusters is also mentioned. Possible atmospheric consequences of all these results are briefly discussed.

Fragmentation cross-section of 600 A MeV Si14+ ions in thick polyethylene target

Total and partial charge-changing cross-sections of 600 A MeV Si14+ ions in a thick polyethylene target were measured by CR39 track etch detectors using an optical microscope DM 6000 M system installed with Leica QWin Plus software. The CR39 nuclear track detectors were used to identify the incident charged particles and their fragments using the cone-height distribution method. The charge resolution of CR39 detectors was achieved to be 0.17e in the present condition. The value of the total charge-changing cross-section was calculated to be σ tot = (766±17) mb. To calculate the partial charge-changing cross-sections for ΔZ = −11, −10, ..., −1, , number of events corresponding to each fragment were determined from multiple Gaussian fitting of cone-height distributions within 95.5% confidence level and the number of incident and survived beam ions were counted within 99.7% confidence level. Possible odd-even pattern in the values of the partial charge-changing cross-section is also presented. The measured charge pick-up cross-section for ΔZ = +1 is (7.2 ±1.7) mb.