Distributions Of Projectile-like Fragments Research Articles

Kinetic energy spectra and angular distributions of projectile-like fragments in C12,13+Nb93 reactions

Kinetic-energy spectra and angular distributions of the projectile-like fragments were measured in $^{12,13}\mathrm{C}+^{93}\mathrm{Nb}$ reactions at ${E}_{\mathrm{lab}}=65\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ to investigate the reaction mechanisms involving the role of projectile and target structures. It has been observed that one-nucleon pick-up reactions lead to the formation of target-like fragments predominantly in the ground state, whereas nucleon transfer to the target occurs predominantly in the excited states for both $^{12}\mathrm{C}+^{93}\mathrm{Nb}$ and $^{13}\mathrm{C}+^{93}\mathrm{Nb}$ reactions. In the case of $^{93}\mathrm{Nb}(^{12}\mathrm{C}, ^{15}\mathrm{N})^{90}\mathrm{Zr}$ reactions, a significant yield was observed for $^{15}\mathrm{N}$ (``$1p+2n$'' pick-up) indicating the role of the $N=50$ shell in $^{90}\mathrm{Zr}$. Observation of a systematic increase in the forward peaking of the angular distributions of projectile-like fragments with an increasing number of nucleon transfers indicates an increase in the projectile-target overlap with increasing mass transfer. Angular distributions for inelastic scattering as well as transfer channels populating various states of projectile-like fragments and/or target-like fragments were calculated simultaneously by using the coupled reaction channels code fresco and were in reasonable agreement with the experimental data. New (modified) spectroscopic amplitudes have been proposed for some of the unknown (known) overlapping states for calculating transfer cross sections. In the case of $^{13}\mathrm{C}+^{93}\mathrm{Nb}$, the transfer channels corresponding to ``$2n$'' and ``$1p+1n$'' pick-up channels were not observed. This may be due to the higher N/Z ratio of the projectile, highlighting the importance of projectile structure in addition to that of the target.

Momentum peak shift and width of longitudinal momentum distribution of projectilelike fragments produced at E=290MeV/nucleon

Longitudinal momentum (${P}_{\mathrm{L}}$) distributions of projectilelike fragments produced at $E=290\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}/\mathrm{nucleon}$ are investigated. ${P}_{\mathrm{L}}$ distributions of fragments produced by Ar and Kr beams with a wide variety of targets (C, Al, Nb, Tb, and Au) were measured using the fragment separator at HIMAC. ${P}_{\mathrm{L}}$ distributions observed for fragments with a wide range of mass losses $\mathrm{\ensuremath{\Delta}}A$ (1--30 for Ar beam and 1--64 for Kr beam), show a slightly, but definitely asymmetric nature. The peak shift and width were obtained from the observed ${P}_{\mathrm{L}}$ distributions. No significant target dependence was found in either the peak shift or width. For the practical application, the variation in momentum peak shift with fragment mass (${A}_{\mathrm{F}}$) was represented by a parabolic function. The width on the high-${P}_{\mathrm{L}}$ side (${\ensuremath{\sigma}}_{\mathrm{High}}$) is well reproduced by the Goldhaber formula, which is obtained from the contribution of the Fermi momentum. The behavior of the reduced width, ${\ensuremath{\sigma}}_{0}$, obtained from ${\ensuremath{\sigma}}_{\mathrm{High}}$ via the Goldhaber formulation, is consistent with the mass-dependent Fermi momentum of a nucleon. The width on the low-${P}_{\mathrm{L}}$ side (${\ensuremath{\sigma}}_{\mathrm{Low}}$) is markedly larger than ${\ensuremath{\sigma}}_{\mathrm{High}}$ and exhibits a clear ${A}_{\mathrm{F}}$ dependence.

Angular distributions and cross-sections of projectile-like fragments in the 19F + 159Tb reaction

The angular distribution of projectile-like fragments (PLFs) in the 19F + 159Tb reaction have been measured at beam energy equal to 98MeV. Angular distributions of PLFs showed a systematic change with increasing mass transfer, starting from the peaking at grazing angle for heavier PLFs to very forward peaked angular distributions for lighter PLFs. Cross-sections of the different PLFs were obtained by integrating their centre-of-mass angular distributions. The PLF cross-sections have been compared with the incomplete fusion cross-sections obtained from the earlier measurement of the evaporation residue cross-section. Reduced cross-sections for lighter PLFs were observed to be higher compared to those observed in 19F + 66Zn reaction at similar values of Ecm/Vb. Also, elastic scattering measurements were carried out to get information about the grazing angle and total reaction cross-section.

Cross sections of projectile-like fragments in the reactionF19+Zn66in the beam energy range of 3–6 MeV/nucleon

Angular distributions of projectile-like fragments (PLFs) have been measured in the reaction $^{19}\mathrm{F}+^{66}\mathrm{Zn}$ at ${E}_{\mathrm{lab}}=61,82,92$, and 109 MeV to understand their formation in the low energy domain ($ \ensuremath{\lesssim}7$ MeV nucleon). In this energy range, maximum angular momentum `${l}_{\mathrm{max}}$' in the reaction is lower than or close to the critical or limiting angular momentum for complete fusion `${l}_{\mathrm{lim}}$(CF).' The sum-rule model was modified to explain the cross sections of PLFs in the present study. For the first time, the modified sum-rule model, with a competition of incomplete fusion (ICF) reaction with complete fusion below ${l}_{\mathrm{lim}}$(CF) reasonably reproduced the cross sections of PLFs in the beam energy range of the present study. It was observed that the cross sections of lighter PLFs fall more rapidly with decreasing beam energy compared to those of heavier PLFs, suggesting a change in the reaction mechanism from heavier to lighter PLFs. Transfer probabilities for peripheral collisions were calculated within the framework of a semiclassical formalism. The parameters of the nuclear potential required for the calculation of transfer probability were obtained by fitting the elastic scattering data measured in the present work. Calculated transfer probabilities were significantly lower compared to the corresponding experimental values, suggesting a significant overlap of the projectile and the target nuclei in incomplete fusion reactions. The present analysis showed that the overlap of the projectile and the target nuclei increases with increasing mass transfer at a given beam energy and for a given PLF, overlap increases with increasing beam energy.

Target effect on fragmentation reaction at E = 290A MeV

The longitudinal and transverse momentum (PL and PYenT) distributions of projectile-like fragments, which were produced with an Ar beam and various targets (C, Al, Nb, Tb, Au), were measured at E=290A MeV. No significant target effects are found in P L distribution. The width of PT distribution increases with target mass. It is plausible that this result is explained by the deflection of orbit arising from Coulomb repulsion. The nuclear structural effects are observed in isotopic and isotonic distributions of production cross-sections of fragments, which are derived from observed momentum distributions.

Azimuthal 2α correlations and projectile-residue distributions selected by neutron and charged-particle multiplicity measurements

The resolution of reaction filters for intermediate-energy heavy-ion collisions based upon charged-particle and neutron multiplicity measurements with 4\ensuremath{\pi} coverage is compared for ${}^{112}\mathrm{Sn}{+}^{112}\mathrm{Sn}$ and ${}^{124}{\mathrm{S}\mathrm{n}+}^{124}\mathrm{Sn}$ collisions at $E/A=40$ MeV. The quality of event characterization is inferred from the azimuthal correlations of \ensuremath{\alpha} particles emitted at intermediate rapidity and from the Z distributions of projectilelike fragments emitted at forward angles. For central and midimpact parameter collisions, the associated charged-particle multiplicity appears to provide better impact-parameter selection than the associated neutron multiplicity.

18O+ 58Ni reaction at 35 MeV/nucleon

Momentum and angular distributions of projectile like fragments were measured in the vicinity of the grazing angle for the reaction 18O+ 58Ni at 35 MeV/nucleon. Mass and charge identification was achieved with the use of a magnetic spectrometer. Momentum spectra were analysed assuming fragmentation of the projectile.

The inelastic reactions induced by32S on58Ni at 125 and 143 MeV

The inelastic reactions induced by 125 and 143 MeV32S on58Ni have been studied by measuring the element, angular and energy loss distributions of projectilelike fragments. A sizeable drift of the element distribution first moment toward asymmetry is evidenced, due to charge equilibration of the dinuclear system. This drift is consistent with the prediction of liquid drop potential energy surfaces only if shell corrections are considered in the evaluation of Qgg. The yield ratio between fragments withZ=15 and 14 shows a linear dependence on the TKEL*, favouring the ΔZ=2 reaction as inelasticity increases. In the quasi-elastic region (TKEL*<10 MeV), this yield ratio shows a clear dependence on the bombarding energy. The relationship between energy loss and angular momentum, as derived from the measured cross-sections, shows features close to the ones obtained from earlier gamma-ray multiplicity measurements.

Angular evolution of peripheral heavy ion reactions at intermediate energies

Energy spectra and angular distributions of projectile-like fragments have been measured in the vicinity of the grazing angle for the 40Ar + 40Ca and 40Ar + 208Pb reactions at 44 MeV/nucleon. Measurements of the 40Ar + 40Ca system at 27 MeV/nucleon and 20Ne + 208Pb reaction at 44 MeV/nucleon at one angle have also been performed. For fragments with charge and mass close to the projectile numerous deviations from the standard fragmentation model have been observed including rapidly changing shapes of the angular distributions with the fragment mass. Moreover the isotopic distributions and mean fragment velocities are strongly dependent on detection angle. A surface transfer reaction component dominant at the grazing angle can be separated from a second component which cannot be entirely accounted for by a simple fragmentation mechanism.

Qualitative properties of the discrete random walk evolution of projectile-like ( N, Z) values on the dinuclear liquid-drop surface

A discrete random walk calculation of the evolution of the ( N, Z) distribution of projectile-like fragments from a nuclear heavy ion collision is presented. It incorporates energy conservation explicitly for each nucleon transfer, utilizing the liquid drop energies of osculating dinuclei to estimate the ( N, Z) dependence of the ground state energy of the system. The results show that energy conservation and the liquid-drop energy surface suffice to prescribe the characteristic shapes in ( N, Z) of the distributions when the transfer probabilities are defined by the total nuclear level densities; the rate at which the distribution spreads, on the other hand, is dominated by the fraction of the kinetic energy which is assumed to be dissipated by mechanisms other than nucleon transfer. Possible alternative prescriptions for the transfer probabilities are considered and shown to be qualitatively in disagreement with the observations at higher total kinetic energy loss (TKEL). Also it is shown that the overall width. σ 2 A , is less sensitive to such variations of the transfer probabilities than σ 2 Z , and how this feature is a natural consequence of the dinuclear energy surface. Finally, a residual discrepancy between calculation and observation at low TKEL values is identified as the most prominent remnant weakness of the description.

Alpha-Particle Emission in Deeply Inelastic Reactions of 204-MeVO16+Nb93

Angular and energy correlations have been measured for ..cap alpha.. particles emitted in coincidence with projectilelike fragments from deeply inelastic collisions of 204-MeV /sup 16/O with /sup 93/Nb. Anisotropic emission of fast ..cap alpha.. particles is observed; however, the main results of this and similar experiments can be reproduced by model calculations which assume the ..cap alpha.. particles are evaporated from fully accelerated fragments and take the angular distribution of projectilelike fragments into account.