Cascade Calculations Research Articles

Baryon spectra and mean elasticities in proton-nucleus inclusive reactions

A Glauber-type multiple collision model for proton-nucleus inclusive reactions is used in intranuclear cascade calculations to derive the inelastic spectra and the integrated cross section of leadin baryons. Both flat and realistic elasticity distributions are considered in nucleon-nucleon interactions. Model predictions are compared with experimental p-A inclusive cross section data at 100 GeV/c and show satisfactory agreement for a wide range of target nuclei. The dependence of the mean elasticity of the leading nucleon on the final isospin state and on the target mass is also obtained and compared with available data.

Angular distributions in Auger-electron-cascade coincidence measurements.

A formalism is developed for the angular distribution of two electrons in an Auger cascade. The formalism is applied to a coincidence measurement on the ${L}_{1}$-${L}_{2}$,3${\mathrm{M}}_{\mathrm{i}}$-${M}_{i}$${M}_{J}$Mk cascades in argon. The motivation for this study is the possibility of using such a cascade measurement in ${}^{1}$${}_{67}^{63}$Ho to detect a nonzero neutrino mass. The cascade calculation in Ho is currently sufficiently unmanageable that a simpler calculation in Yb was performed. The latter calculation indicates that the angular anisotropy is on the order of 25% when reasonable assumptions on experimental detector parameters are made. This is comparable to the angular anisotropy calculated for a similar transition in Ar with similar experimental detector parameters.

Inclusive pion production in 330, 400, and 500 MeV proton-nucleus collisions.

We present measurements of the inclusive ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$ momentum distributions and total pion production cross sections for 330, 400, and 500 MeV protons incident on $^{12}\mathrm{C}$ and $^{238}\mathrm{U}$. The ${\ensuremath{\pi}}^{+}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ cross section ratio is seen to increase sharply with decreasing projectile energy for the light nucleus. Comparisons are also presented of the projectile energy systematics of data and intranuclear cascade calculations in the intermediate energy region.

Do nuclei flow inside the intranuclear cascade model?

An intranuclear cascade calculation of Ca + Ca and Nb + Nb at 400 MeV/ A is performed and analysed in terms of global variables. Our results are in qualitative agreement with the recent plastic ball data. The ability of the cascade dynamics to generate a collective flow and the effects of the fluctuations are underlined.

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation—Part I: Inelastic Hadron/Nucleon Collisions at Energies Below 5 GeV

A model for sampling inelastic hadron/nucleon interactions at energies below 5 GeV is described. The model describes the total hadronic cross section as a sum of quasi-two-body reaction channels. Inelastic events are sampled by first selecting one of these reaction channels and the subsequent decay of all resonances produced. Comparison with exclusive and inclusive data indicates very good agreement. The model is very well suited for hadron cascade calculations, detector simulation, and as input for models of hadron/nucleus interactions.

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation—Part II: Inelastic Hadron/Nucleus Collisions at Energies Below 5 GeV

Hadronic Event Generation for Hadron Cascade Calculations and Detector Simulation—Part II: Inelastic Hadron/Nucleus Collisions at Energies Below 5 GeV

The electron screening effect in muonic 28Si

We have measured the wavelengths of the 4 f 7 2 -3 d 5 2 and the 4 f 5 2 -3 d 3 2 X-ray transitions in μ- 28Si with the bent-crystal spectrometer at the SIN muon channel. The results are compared to the calculated transition wavelengths which include radiative corrections (QED). The differences in the corresponding transition energies are attributed to the electron screening shift. Combining the results from both transitions, we obtain ΔE ES(4f-3d) = −1.66±0.20 eV. This corresponds to (83±11)% of the electron-screening shift calculated for a neutral atom with the muon and Z − 1 electrons. These results are in moderate agreement with cascade calculations constrained to reproduce measured muonic X-ray intensities.

Transport properties of excited nuclear matter and the shock-wave profile

Shear viscosity and heat conduction coefficients of nuclear matter are derived from the Uhlenbeck-Uehling equation. The calculated coefficients exceed by a factor of two or more those used until now in hydrodynamic calculations of nuclear collisions. When applied to study a shock profile in nuclear matter, the coefficients yield results that are roughly consistent with cascade calculations. The study reveals that shock phenomena are not possible at energies E lab≲100 MeV/nucleon, while at higher energies a fully developed shock wave requires heavy nuclei ( A≳100).

Collective flow in relativistic heavy-ion collisions: A confirmation of hydrodynamics

Abstract We focus on the fluid dynamical description of nuclear collisions in the energy range 100 MeV n to 1 GeV n . They seem well suited to study bulk properties of nuclear matter at high densities and temperatures. Experimental data from Elab = 400 MeV n to 800 MeV/n are compared with our calculations and a reasonable agreement is found. The experimental data strongly support the existence of collective flow as predicted by the hydrodynamic model but not appearing in cascade calculations.

Measurement of the K-line intensity ratios in muonic hydrogen between 0.25 and 150 torr gas pressures

Precise measurements of the K X-ray energy spectrum of muonic hydrogen ( μ −p) were made at H 2 gas pressures between 0.25 and 150 torr ( T = 300 K). The measured intensity ratios I( K α) I( K tot) and I ( K β) I( K γδ…) are compared with the results of new cascade calculations. The pressure dependence of the relative ( μp) 2 s population was investigated. Its value is (4.24 ± 0.14)% at 10 torr and (2.21 ± 0.22)% at 0.25 torr.

Inclusive measurement of quasifree (p,xn) charge exchange reactions on bismuth from 62 to 800 MeV

The total inclusive (p,$x\mathrm{n}$) charge exchange reaction cross section on bismuth from 62 to 800 MeV was measured using activation and radiochemical techniques. These data for products with as many as 14 neutrons removed from the coherent product display the simple ${E}^{\ensuremath{-}1}$ dependence of the total cross section with incident projectile energy. The distribution of charge exchange products is discussed in terms of quasifree processes in (p,n) reactions. A model comparison between the data and an intranuclear cascade calculation was satisfactory as evidenced by reproducing the energy dependence, cross section magnitude, and mass yields for products up to 14 neutrons removed. Better agreement between the model and data were obtained with mean-free paths of nucleons in nuclear matter twice as long as the one derived from nucleon-nucleon scattering.

Causality and relativistic effects in intranuclear cascade calculations

Two main goals are pursued in this work. The first one is concerned with the relativistic effects in high energy nuclear collisions, when noninvariance of simultaneity is taken into account. It is shown that the time ordering of nucleon-nucleon collisions is quite different for different observers, giving in some cases noninvariant final results for intranuclear cascade calculations. In particular, we have shown an example of such a case, in which the intranuclear cascade simulation, depending on the reference frame, presents a kind of density instability caused by a specific time ordering of collision events. The second one is to propose a new intranuclear cascade calculation, using a causality preserving scheme, which minimizes this kind of relativistic effect. It is verified that the causality preserving intranuclear cascade prescription essentially recovers the relativistic invariance.

Two-pion correlations in heavy ion collisions

An application of intensity interferometry to relativistic heavy ion collisions is reported. The correlation between two like-charged pions is used to study the reactions Ar+KC1..-->..2..pi../sup + -/+X and Ne+NaF..-->..2..pi../sup -/+X, both at an incident beam energy of 1.8A GeV. Source sizes and lifetimes are measured and compared to the predictions of simple geometric models and of Monte Carlo cascade calculations. There appears to be a substantial coherent component of the pion source, although measurement is complicated by the presence of final state interactions. A detailed discussion of the techniques of intensity interferometry is also presented. The generation of uncorrelated background events is discussed, along with the influence of the correlation on the background and the prescription for its removal. The statistical errors in the background spectrum are examined and found to have nontrivial implications for the analysis. The effect of the mutual Coulomb repulsion of the two pions, and of the pion-nuclear Coulomb interaction, on the two-pion correlation function is analyzed. The impact parameter bias resulting from a two-pion trigger is calculated and found to be substantial. Finally, a simple model for the interpretation of Gaussian source parameters is presented and compared to the predictions of Monte Carlo cascade calculations.

Momentum transfer in light-ion-induced fission reactions

Angular correlations and angular distributions of the fission fragments produced in the bombardment of a 232Th target with protons, deuterons and α-particles in the energy range between 35 and 1000 MeV/nucleon have been measured. From these measurements, the distributions of linear momentum imparted to fissioning nuclei have been deduced in the various energy regimes; dominating reaction mechanisms are classified according to the fraction of the available incident momentum transferred to the target. The experimental results are compared to the predictions of intra-nuclear cascade calculations. An optimum excitation energy supported by the fissioning nuclei could be the dominant limitation to momentum transfer at high incident energies. The angular distributions of the fission fragments were used to extract fission cross sections and upper limits of the angular momentum imparted to the fissioning nuclei.

Intranuclear cascade and Fermi breakup calculations ofH1- andHe4-induced reactions on light target nuclei

Mass, energy, and angular distribution data for fragments with $A\ensuremath{\ge}6$ produced in intermediate-energy proton- and alpha-particle-induced reactions on $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ nuclei are compared with the results of an intranuclear cascade calculation followed by deexcitation of the residual nuclei via a Fermi breakup mechanism. In this latter step all possible particle-stable exit-channel states are included in the phase space available for decay. The shapes of the angular distributions are reproduced successfully by the calculation, even at relatively low bombarding energies (e.g., ${E}_{\ensuremath{\alpha}}=60$ MeV). The energy spectra are also reproduced qualitatively. The isobaric cross sections of fragments heavier than the target nucleus are underpredicted for alpha-particle-induced reactions, whereas the yields of fragments with $A=6\ensuremath{-}8$ are overpredicted. The former discrepancy is attributed to the importance of alpha-particle breakup during the cascade while the latter may serve as a measure of the relative importance of statistical multibody breakup mechanisms.[NUCLEAR REACTIONS Intranuclear cascade, Fermi breakup model, evaporation model; calculated $\ensuremath{\sigma}(E,\ensuremath{\theta},A)$ for $^{12}\mathrm{C}(\ensuremath{\alpha},\mathrm{HI})$, $^{16}\mathrm{O}$(p,HI), $^{12}\mathrm{C}$(p,HI); HI: $A=6\ensuremath{-}19$.]

Collective Flow Observed in Relativistic Nuclear Collisions

The reactions Ca + Ca and Nb + Nb at 400 MeV/nucleon have been studied at the Bevalac using the "Plastic Ball" spectrometer. A global analysis of the events shows two nontrivial collective flow effects: the bounceoff of the projectile fragments, and the side-splash of the intermediate-rapidity fragments for the higher-multiplicity Nb + Nb events. Neither effect is seen in a knockon cascade calculation. A simulation with an event-generating statistical model has been done in order to extract the magnitudes of the effects.

Hydrodynamics of relativistic nucleus-nucleus collisions

Collisions between relativistic heavy nuclei have been studied in fluid dynamic models. Viscosity and heat conduction do not generate much additional entropy but tend to drive the system from local to global thermal equilibrium. Pion production is a sensitive measure of the partitioning of energy among pion degrees of freedom, local temperature and global collective fluid flow. Experiments now show that nuclei are not as transparent at Bevalac energies as cascade calculations tend to suggest. Preliminary calculations in a two-fluid model indicate that for central collisions between uranium nuclei at a CM energy of 5 GeV per nucleon the central cores rebound, much as in the old Landau picture.

Neutron kerma values above 15 MeV calculated with a nuclear model applicable to light nuclei

Accurate neutron dosimetry is currently dependent on the availability of neutron kerma values (ICRU 1980) to convert absorbed dose as measured with a dosemeter into absorbed dose in tissue. Apart from two experimental determinations at approximately 15 MeV for carbon (Goldberg et al. 1978, De Luca et al. 1983), only calculations based on neutron cross-sections are available. The author has developed a model, applicable to low-mass nuclei, in which experimental nuclear structure information is explicitly included. Details of the model which is based on an intranuclear cascade calculation followed by Fermi breakup (INC/FB) are discussed in Brenner et al. (1981) and Subramanian et al. (1983). The calculations do not include the channel for shape-elastic scattering and this has been separately calculated using an optical potential. Kerma values were calculated for carbon, nitrogen and oxygen at 18 energy points between 16 and 80 MeV, and it was noted that they could be fitted to a simple functional form. The differences between this calculation and others are clearly significant, and ultimately result in significant uncertainties in the calculated absorbed dose delivered during high energy neutron radiotherapy. In principle, the choice of which set of calculations to use should be based on the applicability of the nuclear model to the range of nuclear masses, neutron energies under consideration.

Binary collision cascade calculation of sputtering from Cu-Ni alloys by 90 keV Cu and Ni ions

Total and elemental sputtering yields, and angular and energy distributions of sputtered atoms, are calculated as a function of surface composition for the cases of 90 keV Cu and Ni ions, respectively, normally incident on Cu-Ni binary alloy targets using the binary collision cascade code MARLOWE. The results are compared with experiment.

Proton momentum spectra in high-energy reactions of 9Be and 12C with quasimonochromatic photons

Momentum spectra of protons emitted at three lab angles 23°, 55° and 130° in high-energy photoreactions of 9Be and 12C are studied by using tagged photons in the energy range between 360 and 600 MeV. At 23° and 55°, we observe a structure which may be ascribed to protons from quasifree production of a single pion and those from quasideuteron photodisintegration, while at 130°, the spectra are predominantly due to protons resulting from intranuclear multiple scattering. The results of an intranuclear cascade calculation are compared with the data.