Target Mass Dependence Research Articles

Information depth in Auger electron spectroscopy

The depth from where the information comes in electron based spectroscopies is still a matter of controversy. In spite of having different physical meanings, inelastic mean free path, attenuation length, escape and information depths are parameters often taken as synonymous. In this work we analyze from the point of view of the Monte Carlo simulation the use of these parameters in Auger electron spectroscopy. We present results about the angular dependence of the electron yield, the in-depth contribution of the different layers to the total yield, and the electron energy and target mass dependence of the information depth. We found that the elastic scattering has two important effects on the electron transport: (i) the normal effect: the increase of the electron path inside the solid decreasing both the electron yield and the information depth, and (ii) the surface effect: the elastic scattering and the break of the isotropy of the medium due to the presence of a surface lowers the information depth, through the mechanism of increasing the electron yield coming from the near surface layers.

Bose-einstein correlations in the target fragmentation region in 200A GeV16O+nucleus collisions

Correlations between positive pions are investigated in the target fragmentation region of 200A GeV16O+nucleus collisions. The pions are measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The target mass dependence of the radii and the correlation strength extracted by interferometry is studied. A new approach to the fit of the correlation function is introduced. The correlation strength and both invariant and transverse radii increase with decreasing target mass. The transverse radius for16O+C reactions appears to be much larger than the geometrical radius of the nuclei involved. For the Au target only a small fraction of the measured pions contributes to the apparent correlation. Hints for a much larger second component in16O+Au reactions are observed. Rescattering phenomena may provide a clue to understand these phenomena.

Target-charge dependence of the Coulomb dissociation cross section of 11Li

Dissociation cross sections are calculated for the reaction 11 Li + Target → 9 Li + X within the Glauber approximation. The present Glauber calculation well reproduces experimental cross sections: the nuclear dissociation cross section has a target-mass dependence quite similar to the one obtained by Kobayashi et al. based on the factorization model and the Coulomb dissociation cross section has a target-charge dependence of Z 1.74, close to the experimentally deduced one. The suppression of the Coulomb dissociation cross section, compared with the normal Z 2 dependence, comes from the effect of finite q ⊥, the transverse component of momentum transfer.

Forward and transverse energies in relativistic heavy ion collisions at 14.6 GeV/c per nucleon.

Forward and transverse energy spectra and the correlation between these two global variables have been measured for the interaction of 14.6{ital A} GeV/{ital c} {sup 28}Si ions with {sup 27}Al and {sup 197}Au. The energy in produced particles near midrapidity is observed to be negatively correlated with forward energy. There is minimal target mass dependence of this correlation for peripheral and semicentral interactions (forward energies{gt}80 GeV). However, the fact that transverse energies for more central collisions in Au become increasingly larger than those in Al ({similar to}50% greater in the limit of zero forward energy), provides evidence for multiple interactions of projectile nucleons in the larger target. The experimental results are discussed in terms of calculations based on a model for nucleus-nucleus interactions.

Target mass dependence and intranuclear cascade in high energy nucleus-nucleus collisions

Intranuclear cascade, one of the most important non-linear effects in high energy nucleus-nucleus collisions, is investigated, its influence on the target mass dependence of the distributions of final state particles is discussed. Using hydrodynamical model to treat non-linear effects, the main features of the rapidity distributions and their dependence on the target mass are naturally explained. The results of numerical calculation for16O-A central collisions at 60 and 200A GeV agree with the existing data.

Pion charge exchange to the isovector giant dipole state at energies above the 3-3 resonance

Small-angle differential cross sections for the (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{0}$) reaction have been measured at energies of 300, 425, and 500 MeV for the isovector giant dipole resonance in a range of targets. Peak differential cross sections are inferred by extrapolation in angle. The target-mass dependence of these cross sections, normalized to the expected sum rule, shows the same mass dependence at 425 MeV that is observed for isobaric analog state transitions.

Unique 6Li-nucleus optical potentials from elastic scattering of 210 MeV 6Li ions by 28Si, 40Ca, 90Zr, and 208Pb.

Differential cross sections for the elastic scattering of /sup 6/Li ions have been measured at a bombarding energy of 210 MeV. Angular distributions for /sup 28/Si (3.6/sup 0/--45.9/sup 0/), /sup 40/Ca (4.6/sup 0/--43.5/sup 0/), and /sup 90/Zr (4.0/sup 0/--43.6/sup 0/) extend sufficiently into the rainbow region to enable the extraction of unique /sup 6/Li potentials. For the /sup 208/Pb target (3.1/sup 0/--36.0/sup 0/), Coulomb scattering dominates with only a slight evidence of nuclear diffraction at the largest angles. The data were analyzed in terms of a six-parameter phenomenological optical-model potential with Woods-Saxon form factors. The unique potentials obtained show a weak target-mass dependence, which allowed the prediction of /sup 208/Pb potential parameters. Using the present results and lower energy analyses, an energy dependence for the /sup 6/Li-nucleus potentials was derived. For all targets, the volume integral per nucleon pair of the real potential seems to satisfy a logarithmic energy dependence of the form J/sub R//6A = J/sup 0//sub R//6A-..beta.. ln E/sub lab/ with J/sub R//sup 0//6A = 830 +- 30 MeV fm/sup 3/ and ..beta.. = 105 +- 5 MeV fm/sup 3/. This result is consistent with elastic scattering of other light ions. By truncating the angular distributions for themore » lighter targets up to the rainbow angle, several discrete potentials, corresponding to the different families found at lower energies, were obtained.« less

Medium effects in pion production

Pion production is studied in the framework of the intranuclear cascade model, for three different systems: proton-nucleus, heavy-ion and pion-nucleus collisions. The aim of this work is to investigate the sensitivity of the pion yield to modifications of the input data describing the properties of the delta and pion formation, destruction and propagation due to the surrounding nuclear medium. For these systems both the target mass dependence at one incident energy and the energy dependence for few selected targets have been considered. It is found that the three systems behave quite differently. The sensitivity of the heavy-ion case is rather large and medium corrections can remove the original discrepancy between standard cascade results and experiments. The possible lack of absorption in the standard model for pion production is also discussed.

Charged pion production and projectile breakup cIN 85A MeV 12C-induced heavy-ion reactions

Charged pions have been measured at 70° in coincidence with projectile-like fragments in 12C + 12C, 12C + 116Sn and 12C + 124Sn reactions at 85A MeV. Neither the π + emission nor the π −/π + ratio exhibit differences for 124Sn and 116Sn targets outside those expected from the isospin difference. Inconsistencies in the target mass dependence of the pion yield disappear if a correction for reabsorption is included. After this correction, we observe a strong, ~ A 1.1, mass dependence. The projectile breakup is significantly stronger for pion-producing collisions than for the average collision indicating a much stronger abundance of central collisions.

Multiplicity distribution in hadron-nucleus collision and its A-dependence

The multiplicity distribution in the hadron-nucleus collision is investigated and its target mass dependence is established empirically. It is seen that if the multiplicity distribution in the nucleon-nucleon collision follows a gamma distribution, the same distribution is followed in the nucleon-nucleus collision also. However, the parameter K describing the gamma distribution decreases with the target mass. It is conjectured that the parameter K depends inversely on the nucleon size. A simple explanation is then given in terms of increase in the bound-nucleon radius.

Neutral transverse momentum spectra in 60 and 200A·GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (p T ) distributions of inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in 60 and 200 A GeV 16O+nucleus and proton + nucleus reactions. Inclusive photon distributions are compared for central and peripheral reactions. The degree of centrality is determined either from the charged particle multiplicity or from the remaining projectile energy in the forward direction. Deviations from a nucleus + nucleus interaction model based upon linear extrapolation from p + p reactions are observed in central 16O + Au data. The variation of the average transverse momentum is investigated as function of centrality. The target-mass and energy dependence of π°p T distributions are presented. For 16O + Au a change of slope in these distributions is observed at p T ≈0.8 GeV/c compatible with hydrodynamic expansion models.

Target/projectile mass dependence of light ion yields from heavy ion collisions

Differential cross sections for emission of Z=1 and 2 particles are measured for $^{16}\mathrm{O}$, $^{32}\mathrm{S}$, and $^{58}\mathrm{Ni}$ projectiles, with energies between 15 and 25 MeV/nucleon, incident on Al, Ti, Ni, Sn, and Au targets. Integral yields are found to have a complex target mass dependence which, for protons, is consistent with model predictions.

Pion and photon bremsstrahlung in a heavy ion reaction model with friction

Based on a classical dynamical model of nuclear motion with a velocity dependent friction force we calculate pionic and electromagnetic bremsstrahlung emitted in heavy ion collisions with bombarding energies between 20 and 84 MeV/n. For arbitrary projectile-target combinations and with a fixed value of the only parameter of the model, the friction coefficientκ, our calculations reproduce the observed beam energy and target mass dependence for pions. The gamma yields, calculated with the same value ofκ, reproduce the measured dependence of the cross-section on energy and target mass, but underestimate the published data by a factor two. This is a good agreement in view of the discrepancies between different experimental groups.

Target mass dependence of the average linear momentum transfer

The average transferred linear momentum in nuclear reactions induced by 3He, 4He, 14N, and 20Ne projectiles on Co, Cu and Ag targets was determined by thick-target-thick-catcher recoil range techniques for bombarding energies between 10 AMeV and 90 AMeV. A comparison with results obtained from fission fragment angular correlations indicates a strong target mass dependence of the linear momentum transfer.

TARGET MASS DEPENDENCE AND SCALING OF THE CHARGED PARTICLE MULTIPLICITY

Target mass dependence of multiplicity distribution of particles produced in hadron-nucleus interactions is exhibited by a new kind of empirical relation through the study of the mean number of wounded quarks. Scaling in proton-nucleus as well as proton-proton collisions is studied and is extrapolated to see its applicability to the data at the highest energy available.

Pionic fusion and the clustering correlation.

Pionic fusion reactions $^{4}\mathrm{He}$,${\ensuremath{\pi}}^{+}$${)}^{7}$Li and $^{4}\mathrm{He}$,${\ensuremath{\pi}}^{0}$${)}^{7}$Be at the subthreshold energy are studied theoretically. The cross section is enhanced largely by the clustering correlation. The general trend of target-mass dependence of the A${(}^{3}$He,${\ensuremath{\pi}}^{+}$)C reaction is also studied.

Correlation effects in the relativistic impulse approximation treatment of proton-nucleus elastic scattering.

Target nucleon correlation contributions to intermediate energy proton-nucleus elastic scattering observables are explored within the context of a semirelativistic multiple scattering model. A general, nonlocal expression for this second-order relativistic optical potential model is derived and discussed. Use is made of the local, projectile-target nucleon interaction given by the relativistic impulse approximation together with a shell model target nucleus wave function represented in a suitable, four-component form. For this initial investigation a simplified model is then assumed in which only the scalar and time-like vector components of the projectile-nucleon interaction are retained and in which the lower components of the target wave function are omitted. Intermediate propagation of positive and negative energy projectile states are included, as are important nonlocalities arising from the Dirac propagator for the projectile. Numerical estimates are provided for several cases of interest. Individual terms in the correlation contribution to the optical potential are fairly large; significant cancellations occur, however, resulting in relatively small changes in the calculated proton-nucleus elastic scattering observables. The differential cross section predictions are increased in magnitude at forward angles, although to a lesser degree than in nonrelativistic models of correlation effects. Analyzing powers and spin rotation functions, which are generally described quite well by the first-order relativistic impulse approximation model, are not significantly affected by these corrections, except at large scattering angles. These results indicate that the semirelativistic impulse approximation model considered here is stable with respect to higher-order multiple scattering contributions, at least to the level of two-body target nucleon correlations. The erroneous target mass dependence of the first-order relativistic impulse approximation model is not corrected by these effects, however.

Delta production by pion charge exchange on complex nuclei.

We have used the (..pi../sup -/,..pi../sup 0/) reaction at a beam energy of 475 MeV on targets of /sup 1/H, /sup 2/H, C, and /sup 90/Zr to examine excitations near 300 MeV. At this excitation energy, delta production is expected to occur by charge exchange on a nucleon. Our (..pi../sup -/,..pi../sup 0/) results for delta production in complex nuclei are compared to those for photoabsorption, (p,n), and (/sup 3/He,t) reactions. The target mass dependence of the absorption for the three charge-exchange reactions is found to be similar.

Proton-nucleus interaction at high energy

The interaction of high energy protons (between 100 MeV and 20 GeV incident energy) with nuclei is studied in the frame of an intranuclear cascade (INC) model. Particular attention is paid to the energy loss of the projectile and on the emission patterns. It is shown that, in general, the incident proton has left the nucleus before the emission process starts. The latter proceeds first on a rather short time scale and involves fast particles. Progressively the emission rate slows down and the ejected particles are less rapid. The target mass, energy and impact parameter dependences of the energy loss is displayed. As a by-product, we calculate the nuclear stopping power. We investigate the fluctuations in the number of primary collisions, i.e. those suffered by the incoming nucleon, and in the energy loss. Fluctuations in the number of ejectiles are also studied as well as the relationship between primary collisions and the number of fast (grey) particles. The latter number is tentatively related with the number of site vacancies in percolation models. The entropy created inside the target is also calculated. It is shown that the representative point of the system in the (internal energy, entropy) plane spends a relatively long time in the coexistence zone and even in the instability zone corresponding to gas-liquid transition. Implications for these two models of fragmentation are discussed. A preliminary comparison with energy loss measurements in the 3–4 GeV/ c range is performed.

Low energy pi + inelastic scattering from nuclei to the continuum.

Differential cross sections ${d}^{2}$\ensuremath{\sigma}/d\ensuremath{\Omega} dE have been measured with a germanium telescope for the (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{+\mathcal{'}}$) reaction on C, Ca, Sn, and Pb at incident energies of 67, 85, and 100 MeV. The yields at backward angles along with available information on total reaction cross sections are interpreted in terms of a simple classical model in which it is assumed that free-space pion nucleon interaction parameters prevail inside the nucleus. Among the experimental findings which can be accounted for in terms of the model (to within 10--15 %) are the measured pion reaction cross sections and their dependence on target mass, the energy and mass dependences of the differential scattering cross section at backward angles, and the ratio of normal to charge exchange scattering cross sections. The model appears to overestimate the ratios ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ to ${\ensuremath{\pi}}^{+}$ reaction and scattering cross sections but there appear to be some inconsistencies in the available data.