Mass Of Target Nucleus Research Articles

Global Microscopic Description of Nucleon-Nucleus Scattering with Quantified Uncertainties.

We develop for the first time a microscopic global nucleon-nucleus optical potential with quantified uncertainties suitable for analyzing nuclear reaction experiments at next-generation rare-isotope beam facilities. Within the improved local density approximation and without any adjustable parameters, we begin by computing proton-nucleus and neutron-nucleus optical potentials from a set of five nuclear forces from chiral effective field theory for 1800 target nuclei in the mass range 12≤A≤242 for energies between 0 MeV<E≲150 MeV. We then parameterize a global optical potential for each chiral force that depends smoothly on the projectile energy as well as the target nucleus mass number and isospin asymmetry. Uncertainty bands for elastic scattering observables are generated from a full covariance analysis of the parameters entering in the description of our global optical potential and benchmarked against existing experimental data for stable target nuclei. Since our approach is purely microscopic, we anticipate a similar quality of the model for nucleon scattering on unstable isotopes.

Photoneutron reaction kinematics and error of commonly used approximations

An exact closed-form classical equation and a transcendental relativistic equation for the energy-angle relationship of the neutrons produced from the photoneutron reaction are derived in the laboratory coordinate system. Additional formulas are derived to describe the restriction on scattering angle in the double-valued photoneutron energy regime for incident photon energies near the kinematic threshold energy of the target nucleus. The full range of photoneutron reaction independent variables (target nucleus mass number, neutron separation energy, and photon energy) encountered in practical photoneutron production applications are explored to give the applicable range of classical kinematics and other approximations in the calculation of the photoneutron energy-angle relationship. A six-way comparison study of classical, relativistic, and approximation equations presented in this work and those implemented in radiation transport codes is performed. The well-known and widely-used approximations presented without derivation by Wattenberg and Hanson in the late 1940s are only applicable to energy spread of neutrons produced from gamma-ray photoneutron sources, the intended application of the approximations. The Wattenberg and Hanson approximations are inappropriate for general purpose radiation transport simulation and give unphysical negative photoneutron energies for incident photon energies near the kinematic threshold. Recent versions of the MCNP code appear to use erroneous equations related to inelastic neutron scattering to describe photoneutron kinematics resulting in the overestimation of photoneutron energy. Simulated photoneutron spectra are significantly hardened and cannot be used in contemporary nuclear science applications such as characterization of accelerator-driven photoneutron sources. The Monte-Carlo code developer and user communities need to exhaustively review, correct, document, verify, and validate photoneutron physics implementations in the codes that are in common use.

Projectile fragment emission in the fragmentation of 20Ne on C, Al and CH2 targets at 400 MeV/u

The emission angle distributions of projectile fragments (PFs) and the temperature of PFs emission source for fragmentation of 20Ne on C, Al and CH2 targets at 400 MeV/u are investigated. It is found that the averaged emission angle increase with the decrease of the charge of PF for the same target, and no obvious dependence of angular distribution on the mass of target nucleus is found for the same PF. The cumulated squared transverse momentum distribution of PF can be well explained by a single Rayleigh distribution, the temperature parameter of PFs emission source is obtained, which is about 2.0 MeV and do not depend on the size of PF and mass of target for PF with charge of 5⩽Z≤9.

Projectile fragment emission in the fragmentation of silicon on carbon and polyethylene targets at 775 A · MeV

The emission angle and the transverse momentum distributions of projectile fragments (PFs) produced in fragmentation of 28Si on C and CH2 targets at 775 A. MeV are measured. It is found that the mean emission angle and the mean transverse momentum increase with the decrease of the charge of PFs for the same target, and no obvious dependence of angular and transverse momentum distribution on the mass of target nucleus are found for the same PF. The cumulative squared transverse momentum distribution of PF can be well explained by a single Rayleigh distribution. The temperature of PF emission source do not depend on the size of PF and mass of target for PF with charge 5 ≤ Z < 13.

Description of elastic polarized-deuteron scattering in the optical model with Skyrme forces

Microscopic deuteron-nucleus optical potential was constructed on the basis of the nucleon-nucleus optical potentials recently obtained by the authors from approximate calculations of the mass operator of the single-particle Green function using the Skyrme forces, which in general involve additional density- and momentum-dependent terms. Both the nucleon- and deuteron-nucleus elastic scattering processes are described in a self-consistent approach using the effective nucleon-nucleon forces, which simultaneously provide a satisfactory description of nuclear structure. The calculations performed using the Watanabe-type approximation have made it possible to obtain reasonable results for describing differential cross sections and polarization observables for the elastic deuteron scattering in a wide range of target-nucleus mass numbers at different incident deuteron energies, when using several Skyrme-force variants both from literature and proposed by the authors. Contributions to elastic deuteron-nucleus scattering cross sections coming from the effects of deuteron virtual breakup have been estimated in the continuum-discretized coupled channels approach.

Projectile Fragment Emission in the Fragmentation of Silicon on Carbon and Polyethylene Targets at 800 A MeV

The emission angle and the transverse momentum distributions of projectile fragments (PFs) produced in fragmentation of silicon on carbon and polyethylene targets at 800 A MeV are measured. It is found that the angular and transverse distribution of PFs do not evidently depend on the mass of target nucleus, the averaged emission angle and transverse momentum decrease with increase of the charge of PF for the same target, and no obvious dependence on the target mass is found for the same PF. The cumulated squared transverse momentum distribution of PF can be well explained by a single Rayleigh distribution. The temperature parameter of PF emission source is determined, which is about 2-4 MeV and independent of the target and PF size.

Fragmentation 56Fe on C, Al and CH2 targets at 471 A MeV

The emission angle and the transverse momentum distributions of projectile fragments (PFs) produced in fragmentation of 56Fe on CH2, C, and Al targets at 471AMeV are measured. It is found that the angular and transverse momentum distribution of all PFs do not evidently depend on the mass of target nucleus, the average value and width of angular distribution decrease with increase of the charge of PF for the same target, and no obvious dependence of angular distribution on the mass of target nucleus is found for the same PF. The transverse momentum distribution of PF can be explained by a single Gaussian distribution and the averaged transverse momentum decreases with the increase of the charge of PF. The cumulated squared transverse momentum distribution of PF can be well explained by a single Rayleigh distribution. The temperature parameter of PF emission source decreases with the increase of the size of PF.

Extended Skyrme interaction in the microscopic optical model of nucleon-nucleus scattering

The microscopic optical potential model based on calculations of the mass operator of the single-particle Green function has been refined by using the extended Skyrme-force variant, which involves additional both density- and momentum-dependent terms, and is employed for describing simultaneously properties of nuclei, nuclear-matter characteristics, and the nucleon-nucleus scattering observables in a self-consistent approach. From analyzing a differential cross section and polarization for a chosen case of the elastic neutron-nucleus scattering while controlling the characteristics of nuclear matter and finite-nuclei structure, a few sets of parameters have been determined for new variants of the extended Skyrme forces. It has been shown that the allowance for both the density- and momentum-dependent terms makes it possible to significantly improve the agreement with experimental data. The proposed extended Skyrme-force variants provide a satisfactory description for cross sections and analyzing powers of the neutron and proton scattering in a wide range of the target-nucleus mass numbers at different incident nucleon energies, as well as for a variety of nuclear structure characteristics.

Phenomenological analysis of elastic scattering reactions using different models

McIntyre and Frahn-Venter three-parameter models are used to analyze the experimental data of three elastic scattering reactions α+ 58Ni, α+ 116Sn and α+ 197Au at the same incident energy of 240MeV. The different α-scattering cases have the same number of minima and maxima in their oscillatory structures of angular distribution. The increase in the mass of target nucleus leads to a smaller nuclear deflection minimum and causes the corresponding angular distribution to become smoother and with steeper slope. The Coulomb damping of Fraunhofer oscillations has an effect accompanied with the increase of mass of target nucleus. The presence of semi-classical phenomena such as Fresnel and Fraunhofer diffraction patterns etc., has been found by analyzing the experimental data of elastic scattering reactions, 16O + 64Zn, 32S + 64Ni, and 58Ni + 27Al at several laboratory energies. The generalised Fresnel model can fairly reproduce the angular distribution of these reactions. Excellent fitting can be obtained using Regge pole model, especially at backward angles where the data can not be recovered by the other three models. The adopted theoretical models can reasonably account for the general pattern of the data, thus allowing us to extract important parameters from elastic scattering processes. The analysis also shows that the total reaction cross section has an energy-dependent trend similar to that found by other models.

Single-spin asymmetry for charged hadrons produced in proton-nucleus collisions at 40 GeV for c.m. production angles in the range 40°–79°

The transverse single-spin asymmetry for charged hadrons ({pi}{sup {+-}}, K{sup {+-}}, p, p-bar) produced in proton-nucleus collisions was measured for c.m. production angles in the range 40{sup o}-79{sup o}. The measurements were performed with the FODS-2 setup by using a 40-GeV polarized proton beam originating from the accelerator of the Institute for High Energy Physics (Protvino) and hitting carbon and copper nuclear targets. The data in question were obtained in the polarized-proton-fragmentation region (0.0 < x{sub F} < 0.7, 0.6 < pT < 2.5 GeV/c). In agreement with data obtained at other energies, the single-spin asymmetry for {pi}{sup {+-}} mesons is significant at high x{sub F}. For the first time, a sizable analyzing power, which changes sign at x{sub F} = 0.43, is observed for protons. The dependence of the analyzing power on the target-nucleus mass is insignificant.

A-dependences of neutral strange particle yields in $\bar p$ -nuclei collisions at 40 GeV $/c$

The interactions of $\bar p$ with $^2$ D, $^7$ Li, $^{12}$ C, $^{32}$ S, $^{64}$ Cu and $^{207}$ Pb nuclei at 40 GeV/c were studied by the RISC-streamer chamber spectrometer. The yields of $K^0$ mesons and $\Lambda$ and $\bar\Lambda$ hyperons as functions of the target nucleus mass number are investigated. The experimental results are compared with model predictions using the FRITIOF-7.02 program package.

Photonuclear K + production calculation near threshold

Photonuclear kaon production near threshold is investigated as a function of incident energy and the target-nucleus mass, by using the intranuclear cascade model. The present calculation shows that the residual nuclei produced in coincidence with kaons are hotter than those obtained by averaging the excitation energy over inclusive γ-nucleus events. We note that the experimental differential cross section for 12C( γ,K +) is well reproduced within the present model.

Coulomb interaction in light-ion fragmentation processes at intermediate energies

The diffraction approach is applied to the investigation of light weakly-bound ion fragmentation to reveal the role of Coulomb effects in the (d, pX) reaction for deuteron energies 56 MeV and 80 MeV and, in particular, to interpret the dependence of proton inclusive cross sections on the target nucleus mass number.

Catastrophic destruction of heavy emulsion nuclei induced by fast hadrons

Photoemulsions were irradiated to 8.4, 9.6, 69 GeV/c protons and 4.2 GeV/c/nucleon12C ions. Large stars, having a number of heavily ionizing particlesn h≧28, were selected for this study. These events represent the catastrophic destruction of AgBr emulsion nuclei. Multiplicity, angular and energy distributions of particles, produced in this case, were studied at different momenta and for different incident particles. It was shown that the products of complete destruction of heavy nuclei are nearly individual nucleons. The probability of this phenomenon increases with the projectile mass number. About half of nuclear matter is knocked out of the target nucleus with energy higher than 30 MeV/nucleon. The average multiplicity ofs-particles¯n s is weakly dependent on the target nucleus mass number whereas the average multiplicity ofg-particles¯n g is strongly dependent on it. The modified pre-equilibrium model gives a satisfactory description for the energy spectrum of the emitted slow protons.

Rapidity distribution of shower particles in proton–nucleus interactions in emulsions at 70 GeV

Nuclear emulsion plates exposed to 70 GeV protons have been scanned for inelastic interactions. The rapidity distribution of the shower particles observed in 132 events are presented. The dependence of rapidity on the target nucleus mass number has been studied and compared with the results for other energies obtained by earlier workers. The individual rapidity of the shower particles observed in some high multiplicity events are also shown. The qualitative features of the observed rapidity distributions are found to agree with the Glauber–Gribov multiperipheral model.

Energy dependence of backward particle emission from high-energy Hadron-nucleus collisions

Angularand kinetic-energy distributions of protons and pious emitted in laboratory backward direction from collisions of 28.5 GeV/c protons with tan ta lum nuclei, were previously reported (1). There, the increase of invariant cross-section of backward emission of protons and pions with incident energy was also reported, comparing with experimental data at lower energies by BAT.DI~ et al. (2) and BAYUKOV et al. (3). However in the case of proton spectrum, we were obliged to compare between results obtained by different nuclei in a wide range of mass number, because the experiments by BAYUKOV cta l . were carried out with carbon, cupper and xenon as target nuclei. Therefore, in the previous paper we discussed incident-energy dependence of proton spectrum (1), assuming the target nucleus mass number dependence of invar iant cross-section being A! obtained by BAYUKOV et aL (s). This assumption made incident-energy dependence of proton spect rum somewhat uncertain. In the case of pion spectrum, this uncertainty is small enough because the experiments with lead target were available to compare with our results. In this paper results obtained for K--Ta collisions are reported. Because the measurements were carried out for 12.6 GeV/c K.Ta interaction under the same experimental conditions as 28.5 GeV/c P-Ta collisions, incident-energy dependence of both pion and proton emission spectra is derived more definitely between 12.6 and 28.5 GeV/e. The difference of incident particles (Kand P) has only little effect for backward particle emission.