Longitudinal Momentum Transfer Research Articles

Target residues from the interaction of copper with 90 MeV/nucleon 6Li ions.

Target residues from the interaction of copper with 90 MeV/nucleon [sup 6]Li ions have been studied utilizing thick-target, thick-catcher recoil range techniques. Cross sections, average forward ranges, and forward-to-backward ratios have been measured. Isobaric and mass yield distributions have been constructed from the cross section data. Longitudinal momentum transfer information has been obtained. Comparison with a variety of lighter and heavier projectiles interacting with copper have been made. Comparisons of the data with initial interaction-evaporation models ISABELLE-EVA, BUU-GEMINI, and BUU-PACE are presented.

Measurements of recoil ion longitudinal momentum transfer in multiply ionizing collisions of fast heavy ions with multielectron targets.

The longitudinal momentum transfer to the recoil ion in collisions of 1 MeV/amu bare F ions with Ne are resolved for final charge states of both projectile and recoil ions. We observe the recoil to be thrown backwards in electron-capture events, reflecting the physical impact of the electron translation factor. The size of the momentum transfer is in agreement with classical trajectory Monte Carlo calculations for low charge state recoil ions but not for high charge state recoil ions.

Color transparency and Fermi motion.

It is argued that color transparency in quasi elastic scattering of electrons and hadrons on nuclei is possible only due to Fermi-motion. We found a strong dependence of nuclear transparency on Bjorken x in (e,e'p), it is close to the Glauber model expectations at $x>1$, but increases and even exceeds one at $x<1$. It is argued that color transparency is accompanied by large longitudinal momentum transfer to nuclear matter during the passage of the small size wave packet. \vspace{\fill}

Evolution of the reaction dynamics in the interaction of copper with 15-90 MeV/nucleon 12C ions.

Target residues from the interaction of copper with 90 MeV/nucleon [sup 12]C ions have been studied using thick-target, thick-catcher recoil range techniques. Cross sections, average ranges, and forward-to-backward ratios have been measured. Isobaric and mass yield distributions, along with mean longitudinal momentum transfer and mean excitation energy, have been obtained from these data. Comparisons with previous 15--45 MeV/nucleon [sup 12]C+Cu results and with intranuclear cascade and evaporation models are presented.

Longitudinal-momentum transfer from thick-target recoil studies of intermediate-energy heavy-ion reactions

The longitudinal velocity ν | of the composite system formed in intermediate-energy heavy-ion reactions is frequently obtained from the mean forward recoil range, FW, of evaporation residues, a procedure that neglects the effect of evaporation. The validity of this approach is examined with the help of the cascade-evaporation code ISABEL-EVA. The results for 45–90 MeV/nucleon 12C on copper and silver indicate that ν | is overestimated by at most (6 ± 3)%. The magnitude of this is related to the experimentally observable ratio of forward and backward ranges.

Soft charge form factor of the pion.

We identify the source of a discrepancy between ${F}_{\ensuremath{\pi}}^{\mathrm{soft}}|\mathrm{long}$ and ${F}_{\ensuremath{\pi}}^{\mathrm{soft}}|\mathrm{trans}$ found by Isgur and Llewellyn Smith. We find that the discrepancy disappears when virtual $q\overline{q}$ pair production for longitudinal-momentum transfers is included. Our result rectifies the discussion by Isgur and Llewellyn Smith of soft nonperturbative effects at presently available values of ${Q}^{2}$.

Note on a narrow peak at 1170 MeV/c2 in neutral three-pion systems produced in the reaction pp→pp→π+π-π0 at 19 GeV/cat 19 GeV/c

A narrow peak is seen at about 1170 MeV/c2 in three-pion systems selected by restrictions on longitudinal momentum and four-momentum transfers in the reaction pp→pp→π+π-π0 at 19 GeV/c,i.e. in the region of the oldA1.5(1170).

The role of quantum effects and non-equilibrium transport coefficients for relativistic heavy ion collisions

Stopping power and thermalization in relativistic heavy ion collisions is investigated employing the quantum molecular dynamics approach. For heavy systems stopping of the incoming nuclei is predicted, independent of the energy. The influence of the quantum effects and their increasing importance at low energies, is demonstrated by inspection of the mean free path of the nucleons and the n-n collision number. Classical models, which neglect these effects, overestimate the stopping and the thermalization as well as the collective flow and squeeze out. The sensitivity of the transverse and longitudinal momentum transfer to the in-medium cross section and to the pressure is investigated.

Target residues from the interaction of silver with 15–45 MeV/nucleon 12C ions

Target residues from the interaction of silver with 15, 25, 35, and 45 MeV/nucleon 12C ions have been studied by off-line γ-ray spectroscopy. Cross sections, average forward ranges, and forward-to-backward ratios were measured for approximately 70 products. The data were used to obtain the isobaric yield distribution, the mass yield distribution, the mean longitudinal momentum transfer, and the mean excitation energy. The results are compared with other studies of the interaction of medium- A targets with intermediate-energy heavy-ion projectiles.

Concentration and heat transfer in nonlinear Gortler vortex flow and the analogy with longitudinal momentum transfer

The similarity between heat, mass and streamwise-momentum transfer for the nonlinear Gortler vortex problem is pointed out. Quantitative interpretation of enhanced surface heat and mass transfer rates for unity Prandtl and Schmidt numbers are given. The relation between the visualized mushroomlike concentration distribution and the similar streamwise velocity development is also quantitatively interpreted.

Recoil momenta in proton-induced spallation reactions.

The cascade-evaporation model of proton-induced spallation reactions is used to study the relationship between the recoil momentum of the target residue in the cascade stage and the mass loss in the evaporation stage. The intranuclear cascade is treated by using a simplified version of Glauber's multiple scattering theory. The evaporation stage is treated as a Poisson random process. An analytical expression is obtained for the longitudinal momentum transfer to the target residue in the first stage of the reaction that involves no free parameters. This expression is found to be in reasonable agreement with the experimental data for the interaction of protons with gold at incident energies ranging from 1 to 300 GeV.

Impact parameter and energy dependence of observables in intermediate energy heavy-ion reactions.

The dependence of various measurable properties of heavy-ion collisions is calculated with the Boltzmann equation, in an attempt to find the best observables to determine the impact parameter in a collision. The observables considered are multiplicity of fast nucleons longitudinal momentum transfer, angular momentum transfer, projectile mass loss, and projectile energy loss. Systems studied in detail include the {sup 14}N+{sup 154}Sm reaction at {ital E}/{ital A}=35 MeV, the {sup 40}Ar+{sup 197}Au reaction at {ital E}/{ital A}=60 MeV, and the {sup 16}O+{sup 197}Au reaction at {ital E}/{ital A}=90 MeV where some experiments have been performed with reaction filters. The energy and impact parameter dependence of nucleon multiplicity distributions have also been studied for the mass symmetric {sup 40}Ar+{sup 40}Ar and asymmetric {sup 16}O+{sup 197}Au systems at energies ranging from {ital E}/{ital A}=35 to 400 MeV. These calculations suggest that the mean multiplicity of fast nucleons and the linear momentum transferred to the target residue are relatively insensitive to the impact parameter at small impact parameters and incident energies below {ital E}/{ital A}{le}60 MeV. These nucleon multiplicity distributions become more sensitive to impact parameters with increasing incident energy and may provide rather accurate impact parameter information for incident energies as large asmore » {ital E}/{ital A}{approx}90 MeV.« less

QMD versus BUU/VUU. Same results from different theories

We demonstrate that the predictions of the n-body quantum molecular dynamics (QMD) approach to heavy-io n collisions does indeed agree with those of the well-established one-body VUU/BUU theory, as far as single-particle observables are concerned. We find in particular good agreement of the longitudinal and transverse momentum transfer, the particle multiplicities and the double differential cross section in the two approaches. These predictions could be checked experimentally via exclusive 4π measurements. Omitting collisions, QMD results agree with that of TDHF and of the Vlasov equation. Thus neither the details of the TDHF wave function (which are not reproduced in Vlasov and QMD) nor the parametrization of the single-particle Wigner densities as gaussians with a constant width (which is employed in QMD) do play a decisive role for intermediate-energy heavy-ion collisions.

Target residues from the interaction of copper with 15-45 MeV/nucleon 12C ions.

Target residues from the interaction of copper with 15, 25, and 45 MeV/nucleon $^{12}\mathrm{C}$ ions have been studied by off-line \ensuremath{\gamma}-ray spectroscopy. Cross sections, average ranges, and forward-to-backward ratios were measured for some 35 products. The data were used to obtain the isobaric yield distribution, the mass yield distribution, the mean longitudinal momentum transfer, and the mean excitation energy. The evolution of these quantities with energy is examined in conjunction with our previous results for 35 MeV/nucleon $^{12}\mathrm{C}$ ions.

Target fragmentation in proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon

Target remnants withZ<3 from proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon were measured in the angular range from 30° to 160° (−1.7<η<1.3) employing the Plastic Ball detector. The excitation energy of the target spectator matter in central oxygen-induced collisions is found to be high enough to allow for complete disintegration of the target nucleus into fragments withZ<3. The average longitudinal momentum transfer per proton to the target in central collisions is considerably higher in the case of16O-induced reactions (≈300 MeV/c) than in proton-induced reactions (≈130 MeV/c). The baryon rapidity distributions are roughly in agreement with one-fluid hydrodynamical calculations at 60 GeV/nucleon16O+Au but are in disagreement at 200 GeV/nucleon, indicating the higher degree of transparency at the higher bombarding energy. Both, the transverse momenta of target spectators and the entropy produced in the target fragmentation region are compared to those attained in head-on collisions of two heavy nuclei at Bevalac energies. They are found to be comparable or do even exceed the values for the participant matter at beam energies of about 1–2 GeV/nucleon.

Target residues from the interaction of copper with 35 MeV/nucleon 12C ions.

Target residues from the interaction of copper with 35 MeV/nucleon $^{12}\mathrm{C}$ ions have been studied by off-line \ensuremath{\gamma}-ray spectroscopy. Cross sections, average forward ranges, and forward-to-backward ratios were measured for 35 products. The data were used to obtain the isobaric yield distribution, the mass yield distribution, and the longitudinal momentum transfer. The results are compared with other studies of the interaction of copper with intermediate-energy projectiles and with various models.

Light fragment production in the interaction of 84 MeV/nucleon 12C with 208Pb.

Using a CR-39 plastic track detector, it is proved that the low energy light fragments (5\ensuremath{\le}Z\ensuremath{\le}26) produced in the interaction of 84 MeV/nucleon $^{12}\mathrm{C}$ with a Pb target originate predominantly from the binary breakup. The characteristics of light fragments and their corresponding heavy partners have been determined. The dependence of measured parameters on the atomic numbers of light fragments is observed. The obtained values of the velocity of the c.m. system of fragments indicate that high longitudinal momentum transfer to the target is characteristic for this reaction channel. The data are consistent with the assumption that at the energy used in this experiment the projectile is stopped in the target nucleus.

Recoil range distributions of residues from alpha + 59Co reactions.

The recoil range distributions of /sup 61/Cu, /sup 60/Cu, /sup 58/Co, /sup 57/Co, /sup 56/Co, /sup 54/Mn, and /sup 52/Mn residual nuclei produced in ..cap alpha.. particle bombardment of /sup 59/Co at 38, 50, 65, and 85 MeV have been measured and analyzed. Analysis of these measurements, as well as other recently published measurements of longitudinal linear momentum transfer to residue isobars at energies extending up to roughly-equal200 MeV, in the same reaction, shows that calculations based on the exciton model and a realistic description of the ..cap alpha..-nucleus interaction allow a quantitatively correct description of ..cap alpha..-induced reactions. Contrary to recent suggestions, data of this kind do not seem to indicate a change in the general character of the ..cap alpha..-nucleus interaction for incident energies below roughly-equal50 MeV/nucleon.

Radiation from fast charged particles in crystals: Unified quantal treatment.

We present a unified quantal treatment of the various types of radiation emitted by fast, charged, spin-(1/2) or spinless particles which propagate at small angles relative to a set of principal atomic planes or rows in a crystal. [Henceforth, direction(s) parallel or perpendicular to these rows (planes) will be referred to as longitudinal or transverse, respectively.] We analyze the dependence of the emission frequencies and rates on the energy and transverse momentum of the incident particle, distinguishing between two fundamental emission modes. One is the transverse mode (TM), which unifies all radiative transitions that are characterized only by the projected potential (i.e., the periodic transverse variation of the crystal potential), such as channeling, quasichanneling, and TM coherent bremsstrahlung transitions. The other one is the longitudinal mode (LM), which includes all transitions involving longitudinal momentum transfer to the lattice, with or without a simultaneous projected potential transition.Our treatment reduces the input needed for a comprehensive analysis of both TM and LM emission spectra to the set of Bloch eigenfunctions and quasimomenta of the particle which are obtained on considering its interaction with the projected potential only. The resulting expressions for LM emission rates as a function of the frequency and direction of emission give a considerably more complete and quantitatively correct characterization of this emission mode than previous attempts. Contrary to previous works, we analyze explicitly the effects of quantum recoil ${r}_{q}$, which is the ratio of the photon energy to the incident particle energy. The case of ${r}_{q}$\ensuremath{\sim}1 [which is applicable to LM emission from electrons and positrons (\ensuremath{\beta} particles) with energies as low as few tens of MeV and to TM coherent bremsstrahlung from \ensuremath{\beta} particles with energies in the GeV range] is shown to correspond to frequencies, linewidths, and directional distribution of the emission that differ strongly from those obtained in the more familiar limit of ${r}_{q}$\ensuremath{\simeq}0. Quantum-recoil corrections to emission frequencies given by extant theories are shown to be significant even for ${r}_{q}$ considerably smaller than 1.

Recoil of products from reactions of20,22Ne withNb93at 100 and 142 MeV

The recoil properties of thirty-five nuclides produced in reactions of 100 and 142 MeV $^{20}\mathrm{Ne}$ and $^{22}\mathrm{Ne}$ with $^{93}\mathrm{Nb}$ have been measured. A thick-target/thick-catcher technique was used, with the foils mounted at 45\ifmmode^\circ\else\textdegree\fi{} to the beam axis so as to provide information on the transverse as well as the longitudinal momentum transfer. Relationships have been derived to extract values, from the resulting data, for the average longitudinal component of recoil velocity and the average recoil angle. The experimental results show, in almost all cases, mean recoil velocities less than the compound nuclear velocity. For products with near-target mass, transverse momentum transfers greater than those along the axis were observed. For heavier products, the momentum transfer increases with the product mass. The results from the $^{22}\mathrm{induced}$ reactions are significantly different from those of $^{20}\mathrm{Ne}$. The results are interpreted mainly in terms of two competing mechanisms: complete fusion/evaporation and a class of process involving varying degrees of mass transfer between projectile and target.