Cascade Code Research Articles

Femtoscopy in relativistic heavy ion collisions and its relation to bulk properties of QCD matter

By using a viscous hydrodynamic model coupled to a hadronic cascade code, numerous features of the dynamics and equilibrium properties are explored for their impact on femtoscopic measurements. The equation of state, viscous parameters, and initial conditions are investigated. We find that femtoscopy is affected by numerous model features at the 10% level and that by including features and adjusting unknown parameters, one can explain experimental source size measurements to better than 10%.

MEASUREMENT AND ANALYSIS OF EXCITATION FUNCTIONS AND FORWARD RECOIL RANGE DISTRIBUTIONS IN 12C + 59Co SYSTEM

With the motivation of studying complete and incomplete fusion reactions in a 12 C +59 Co projectile target system, the excitation functions for ( C , p3n ), ( C , 2p2n ), ( C , αn ), ( C , α2n ), ( C , αp3n ) and ( C , 2α2n ) reactions have been measured up to 80 MeV. The well-known activation technique followed by offline high purity Ge γ-ray spectroscopy was used. The measured experimental values were compared with the statistical model calculations by using the ALICE-91 and CASCADE codes. For the calculations obtained by CASCADE, the variation of parameter Fθ, which is the ratio of actual moment of inertia to the rigid body value have also been studied. Considerable enhancement of the measured excitation functions compared to theoretical predictions for some channels clearly indicates the presence of incomplete fusion with complete fusion in the present projectile energy range. The measurements of forward recoil range distribution of evaporation residues at 80 MeV projectile energy confirm these observations.

Intra-Nuclear Cascade (INC) code for simulation of meson photoproduction in nuclei

η meson photoproduction in the 14N nucleus was studied using simulations done with INC (Intra-Nuclear Cascade) code. The probability for mesons and nucleons to escape the nucleus on different steps of the reaction was evaluated. These results predict the possibility of studying elastic and inelastic η meson interactions with intra-nuclear nucleons using the recoil proton as a tag for the case of slow η meson and fast recoil proton.

Improvements of INCL4 in view of more reliable predictions for RIB facilities

Some improvements of the Intra-Nuclear Cascade code INCL4 for low energy projectiles are presented and discussed.

Measurement of neutron-induced activation cross-sections using spallation source at JINR and neutronic validation of the Dubna code

A beam of 1 GeV proton coming from Dubna Nuclotron colliding with a lead target surrounded by 6 cm paraffin produces spallation neutrons. A Th-foil was kept on lead target (neutron spallation source) in a direct stream of neutrons for activation and other samples of 197Au, 209Bi, 59Co, 115In and 181Ta were irradiated by moderated beam of neutrons passing through 6 cm paraffin moderator. The gamma spectra of irradiated samples were analyzed using gamma spectrometry and DEIMOS software to measure the neutron cross-section. For this purpose neutron fluence at the positions of samples is also estimated using PREPRO software. The results of cross-sections for reactions 232Th(n, γ), 232Th(n, 2n), 197Au(n, γ), 197Au(n, α), 197Au(n, xn), 59Co(n, α), 59Co(n, xn), 181Ta(n, γ) and 181Ta(n, xn) are given in this paper. Neutronics validation of the Dubna Cascade Code is also done using cross-section data by other experiments.

Role of (n, xn) reactions in ADS, IAEA-benchmark and the Dubna Cascade Code

Dubna Cascade Code (version-2004) has been used for the Monte Carlo simulation of the 1500 MWt accelerator driven sub-critical system (ADS) with 233U + 232Th fuel using the IAEA benchmark. Neutron spectrum, cross-section of (n, xn) reactions, isotopic yield, heat spectra etc. are simulated. Many of these results that help in understanding the IAEA benchmark are presented. It is revealed that the code predicts the proton beam current required for the 1500 MWt ADS for K eff = 0.98 to be 11.6 mA. Radial distribution of heat is fairly in agreement with other codes like the EA-MC and it needs nearly 1% less enrichment than given by other codes. This may be because the code takes care of the role of larger order of the (n, xn) reactions. It is emphasized that there is a strong need to study (n, xn) reactions both theoretically and experimentally for better design.

Study for magnets and electronics protection in the LHC Betatron-cleaning insertion

The collimation system of the future LHC at CERN is a challenging project, since the transverse energy intensities of the LHC beams are three orders of magnitude greater than at other current facilities. The two cleaning insertions (IR3 and IR7) housing the collimators will be among the most radioactive areas of LHC. The 1.5 km long IR7 insertion was fully implemented with the Monte Carlo cascade code FLUKA. Extensive simulations were performed to estimate the radiation level along the tunnel, as well as the energy deposition in the most critical elements. In particular, this paper discusses the latest results of the FLUKA studies, including the design of passive absorbers (to protect warm magnets) and a comparison of W and Cu as material for the active absorber jaws (to protect cold magnets). Any electronic device operating in strong radiation fields such as those expected for the LHC tunnel will undergo degradation. A shielding study was done to reduce radiation damage to the electronics.

Prompt radiation, shielding and induced radioactivity in a high-power 160 MeV proton linac

CERN is designing a 160 MeV proton linear accelerator, both for a future intensity upgrade of the LHC and as a possible first stage of a 2.2 GeV superconducting proton linac. A first estimate of the required shielding was obtained by means of a simple analytical model. The source terms and the attenuation lengths used in the present study were calculated with the Monte Carlo cascade code FLUKA. Detailed FLUKA simulations were performed to investigate the contribution of neutron skyshine and backscattering to the expected dose rate in the areas around the linac tunnel. An estimate of the induced radioactivity in the magnets, vacuum chamber, the cooling system and the concrete shield was performed. A preliminary thermal study of the beam dump is also discussed.

Theoretical simulation of residual nuclide products in 208,207,206Pb, NATPb and 209Bi (P,X) reactions at intermediate and high energies

The independent and cumulative measured yields of residual products in thin lead and bismuth targets irradiated with 0.04-2.6 GeV protons are compared with results by the LAHET, CEM03, LAQGSM03, INCL+ABLA, CASCADE and YIELDX codes, in order to evaluate the predictive power of the codes in this energy region. We found that the predictive power of the tested codes is different but is satisfactory for most of the nuclides in the spallation region, though none of the codes agree well with the data in the whole-mass region of product nuclides and all should be improved further. On the whole, the predictive power of all codes for the data in the fission and fragmentation product regions and, especially, at the borders between spallation and fission and between fission and fragmentation regions is much worse than in the spallation region; therefore, development of better evaporation/fission/fragmentation models is of first priority.

Charged-particle evaporation and pre-equilibrium emission in 1.2 GeV proton-induced spallation reactions

Absolute cross sections, energy spectra, and angular distributions have been measured for 1,2,3H, 3,4,6He, 6,7,8,9Li and 7,9,10Be isotopes produced in 1.2 GeV proton-induced spallation reactions with targets between Al and Th. Results of simulation calculations with the intra-nuclear cascade code INCL2.0 coupled to the statistical model GEMINI are in good agreement with these data, as to charged-particle evaporation, mean excitation energy, and mean linear momentum transfer. The pre-equilibrium emission of composite particles, not accounted for in these simulations, however, typically contributes to the total production of composite particles by 40–60% for 2H and 3He, 20–40% for 3H, 5–20% for 4He, and about 15–25% for Li and Be. The composite pre-equilibrium particles together carry off a mean energy of up to 50 MeV, i.e., about 30% compared to the mean energy released by particle evaporation. For deuterons, pre-equilibrium emission is shown to be well described by surface coalescence while definitely other mechanisms are required for 4He and heavier clusters.

Measurement of the neutron fluence on the spallation source at Dubna

Abstract A 232Th activation sample was exposed directly to the spallation neutrons produced by 1GeV proton colliding with a lead target and other samples of 197Au, 209Bi, 59Co, 115In and 181Ta were irradiated by moderated neutrons after passing through 6 cm of paraffin. Different (n, γ) and (n, xn) reaction products in 232Th, 197Au and 209Bi samples are analyzed by gamma-ray spectrometry to measure the neutron fluence at the positions of the samples. For this purpose a histogram of ‘flat’ spectrum averaged neutron cross-sections in over thirty given energy groups was determined from the PREPRO-2000 software. Results of measurements are compared with Monte-Carlo simulations by the Dubna CASCADE code. Experimental values for both spallation and moderated neutron fluences are in reasonable agreement with the CASCADE code. Thus, the experimentally measured fluence of moderated neutrons was used to infer the ‘one group’ reaction cross-sections of 209Bi (n, xn) reactions for x = 6 to 9.

Radiological considerations on multi-MW targets. Part I: Induced radioactivity

CERN is designing a Superconducting Proton Linac (SPL) to provide a 2.2 GeV, 4 MW proton beam to feed facilities like, for example, a future Neutrino Factory or a Neutrino SuperBeam. The material activation in such facilities is an important aspect that has to be taken into account at an early design stage. In particular, the choice of the target has consequences on the induced radioactivity and dose rates in the target itself and in its surroundings. In the present work, the radiological aspects of a stationary target made up of small tantalum pellets are compared to those of a free-surface jet of mercury. An estimation of the hadronic inelastic interactions and the production of residual nuclei in the target, the magnetic horn, the decay tunnel, the surrounding rock and a downstream dump were performed for both targets by the Monte Carlo hadronic cascade code FLUKA. The aim was to assess the dose equivalent rate to be expected during maintenance work and to evaluate the amount of residual radioactivity, which will have to be disposed of after the facility has ceased operation.

Pre-equilibrium and equilibrium emission of neutrons inCd114(α,xn)reactions

The $^{114}\mathrm{Cd}(\ensuremath{\alpha},\mathit{xn})$ reaction has been studied for ${E}_{\ensuremath{\alpha}}=35\text{\ensuremath{-}}55\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ following neutron emission and $\ensuremath{\gamma}$-ray deexcitation. Excitation functions of various $(\ensuremath{\alpha},\mathit{xn})$ channels measured from $\ensuremath{\gamma}$-ray yields have been compared with theoretical calculations based on ALICE-91 and CASCADE codes. Neutron energy spectra were generated from $\ensuremath{\gamma}$-gated neutron time of flight spectra. Neutron energy spectra corresponding to $(\ensuremath{\alpha},3n)$ and $(\ensuremath{\alpha},4n)$ reactions at ${E}_{\ensuremath{\alpha}}=50\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ have been theoretically reproduced taking into account the contributions of equilibrated source with level density parameter $a=A/11$, along with the contributions from the pre-equilbrium process.

Asymmetries in the Nonmesonic Weak Decay of PolarizedΛHypernuclei

The nonmesonic weak decay of polarized $\ensuremath{\Lambda}$ hypernuclei is studied for the first time by taking into account, with a Monte Carlo intranuclear cascade code, the nucleon final state interactions. A one-meson-exchange model is employed to describe the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\Lambda}}N\ensuremath{\rightarrow}nN$ processes in a finite nucleus framework. The relationship between the intrinsic $\ensuremath{\Lambda}$ asymmetry parameter ${a}_{\ensuremath{\Lambda}}$ and the asymmetry ${a}_{\ensuremath{\Lambda}}^{\mathrm{M}}$ accessible in experiments is discussed. A strong dependence of ${a}_{\ensuremath{\Lambda}}^{\mathrm{M}}$ on nucleon final state interactions and detection threshold is obtained. Our results for ${a}_{\ensuremath{\Lambda}}^{\mathrm{M}}$ are consistent with $_{\ensuremath{\Lambda}}^{11}\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ and $_{\ensuremath{\Lambda}}^{12}\stackrel{\ensuremath{\rightarrow}}{\mathrm{C}}$ data but disagree with observations in $_{\ensuremath{\Lambda}}^{5}\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}\mathrm{e}$.

Non-mesonic weak decay of Λ-hypernuclei: a new determination of the [formula omitted] ratio

Theoretical descriptions of the non-mesonic weak decay of Λ-hypernuclei are unable to reproduce the experimental values of the ratio Γ n / Γ p ≡ Γ ( Λ n → n n ) / Γ ( Λ p → n p ) . In this contribution we discuss a new approach to this problem. We have incorporated a one-meson-exchange model for the Λ N → n N transition in finite nuclei in an intranuclear cascade code for the calculation of double-coincidence nucleon distributions corresponding to the non-mesonic decay of 5 Λ He and 12 Λ C. The two-nucleon induced decay mechanism, Λ n p → n n p , has been taken into account within a local density approximation scheme using a one-pion-exchange model supplemented by short range correlations. A weak decay model independent analysis of preliminary KEK coincidence data for 5 Λ He allows us to extract Γ n / Γ p = 0.39 ± 0.11 when the two-nucleon induced channel is neglected (i.e., Γ 2 = 0 ) and Γ n / Γ p = 0.26 ± 0.11 when Γ 2 / Γ 1 = 0.2 .

Double-differential cross sections for the production of neutrons from Pb, W, Zr, Cu, and Al targets irradiated with 0.8-, 1.0-, and 1.6-GeV protons

Experimental results obtained by determining the double-differential cross sections for neutron production in Pb, W, Zr, Cu, and Al targets irradiated with 0.8-, 1.0-, and 1.6-GeV protons are presented. The spectra of neutrons were measured at 15°, 30°, 60°, 90°, 120°, and 150° with a time-of-flight spectrometer by using a proton beam extracted from the 10-GeV synchrotron at the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The neutrons are recorded with 5MAB-1F6BC501A/5L liquid scintillation detectors and NE110 solid-state scintillators. The experimental data in question are compared with the results of simulations based on the CEM97, LAHET, and CASCADE codes.

Analysis of Efficiency of the Noise-Immunity Encoding in Channels with Discrete Frequency-Aggregate Signals

Analysis of efficiency of noise immunity coding in channels with discrete frequency-aggregate signals is carried out. It is shown that there exists a possibility to increase efficiency for noise immunity coding in channels with multiple-position signals. Here, presentation of such systems on the basis of cascade codes is a productive tool.

Isotopic and velocity distributions of Bi83 produced in charge-pickup reactions of Pb82208 at 1AGeV

Isotopically resolved cross sections and velocity distributions have been measured in charge-pickup reactions of $1A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$ $^{208}\mathrm{Pb}$ with proton, deuterium, and titanium targets. The total and partial charge-pickup cross sections in the reactions $^{208}\mathrm{Pb}+^{1}\mathrm{H}$ and $^{208}\mathrm{Pb}+^{2}\mathrm{H}$ are measured to be the same within the limits of the error bars. A weak increase in the total charge-pickup cross section is seen in the reaction of $^{208}\mathrm{Pb}$ with the titanium target. The measured velocity distributions show different contributions---quasielastic scattering and $\ensuremath{\Delta}$-resonance excitation---to the charge-pickup production. Data on total and partial charge-pickup cross sections from these three reactions are compared with other existing data and also with model calculations based on the coupling of different intranuclear cascade codes and an evaporation code.

Spallation neutron spectrum on a massive lead/paraffin target irradiated with 1 GeV protons

The gamma-ray spectra emitted by decaying of residual nuclei produced by spallation neutrons in (n, xn), (n, xnyp), (n, p), (n, γ) reactions with activation threshold detectors, i.e. 209Bi, 197Au, 59Co, 115In, 232Th, were measured in the Laboratory of Nuclear Problems (LNP), JINR, Dubna, Russia. Spallation neutrons were generated by bombarding a 20 cm long cylindrical lead target with 8 cm diameter surrounded by a 6 cm thick layer of paraffin moderator with 1 GeV proton beam from the NUCLOTRON accelerator. Reaction rates and a spallation neutron spectrum were measured and compared with CASCADE code calculations.

Nuclide cross-sections of fission fragments in the reaction 208Pb + p at 500 A MeV

The isotopic distributions and recoil velocities of the fission fragments produced in the spallation reaction 208Pb + p at 500 A MeV have been measured using the inverse-kinematics technique, a lead beam onto a liquid-hydrogen target, and the high-resolution spectrometer FRS at GSI. The shapes of the different distributions are found in good agreement with previously published data while the deduced total fission cross-section is higher than expected from existing systematics and some previous measurements. From the experimental data, the characteristics of the average fissioning system can be reconstructed in charge, mass and excitation energy, and the average number of post-fission neutrons can be inferred. The results are also compared to different models describing the spallation reaction. The intranuclear cascade code INCL4 followed by the de-excitation code ABLA is shown to describe reasonably well the evolution of the isotopic distribution shapes between 500 and 1000 A MeV.