Target Mass Number Research Articles

Compound multiplicity in the collisions of 4.1 A GeV/c 22Ne nuclei with nuclear emulsion

This work displays a study of the compound multiplicity characteristics of 4.1 A GeV/c 22Ne–emulsion interactions, where the number of shower and grey particles taken together is termed as compound multiplicity, Nc. The present data are compared with the corresponding ones obtained for other projectiles at nearly the same momentum per nucleon. It is observed that while the average compound multiplicity depends on the mass number of the projectile, Ap, the value of the ratio <Nc>/D(Nc) seems to be independent of Ap. The impact parameter is found to affect the shape of the compound multiplicity distribution. A positive linear dependence of the compound multiplicity on both the black and heavy charged particles is also noted. Finally, the results indicate that the value of <Nc> depends also on the target mass number. PACS No.: 25.70

Fusion Mechanism in Superheavy Mass Region

58 Fe + 248 Cm were carried out. 2 The mass and the total kinetic energy distributions of fission fragments of these reactions were measured. In this paper, we focus on the fusion-fission process and try to reproduce the experimental data by using a fluctuation-dissipation model taking into account the competition between the fusion and quasi-fission. We estimate the fusion-fission cross section σCN as σCN = π¯ h 2 2µ0Ecm ∞ ∑=0 (2l+ 1)TlPCN , (1) where µ0 denotes the reduced mass in the entrance channel and Ecm denotes the incident energy in center-of-mass frame. Tl is the barrier penetration coefficient of the lth partial wave through the potential barrier. Tl is calculated with parabolic approximation of the combined Coulomb potential and proximity potential. PCN is the probability of forming a compound nucleus in the competition with quasi-fission. In this work, we employ the Langevin equation. 3 We adopt the three-dimensional nuclear deformation space with the twocenter parametrization. As the three collective parameters to be described by the Langevin equation, we treat z0 (distance between two potential centers), δ (deformation), and α (mass asymmetry of the colliding partner); α =( A1 − A2)/(A1 + A2), where A1 and A2 denote the mass number of target and projectile, respectively. Hydrodynamical inertia tensor is adopted with the Werner-Wheeler approximation for the velocity field, and the wall-and-window one-body dissipation is adopted for the dissipation tensor. For the purpose of the calibration of our calculation, firstly we analyze the fusion-fission cross section for the 48 Ca + 208 Pb reaction, where we can utilize the enough data of fusion-fission cross section. 2 The calculation results of the mass distribution of the fission fragments and the excitation function of the fusionfission cross section give a good agreement with the experimental data beyond the Bass barrier region. 4 Next, we present the analysis of the 48 Ca + 244 Pu reaction. We assume that both shapes of the target and the projectile are spherical at touching point of the colliding system. We also take into account the temperature dependent shell correction energy for the potential energy surface. 3, 4 For example, at T = 0, the potential energy surface in the reaction 48 Ca + 244 Pu is shown in Figure 1. z = δ = α = 0 corresponds to a spherical compound nucleus. The contact point in the reaction and saddle points are denoted by (+) point and (×) points, respectively. The shadow box denotes the fusion box which is defined as the inside of the fission saddle point, {z< 0.6, δ< 0.2, |α|< 0.25}. We can see

Antineutron–nucleus annihilation cross sections below 400 MeV/ c

Antineutron annihilation cross sections on C, Al, Cu, Ag, Sn and Pb targets were measured in the momentum range 50–400 MeV/ c. The full set of data is very well described by a parameterization in which the target mass number and momentum dependence are factorized. The A dependence is, within 2%, consistent with a A 2/3 scaling law, indicating a pure surface process. The momentum dependence is, within 20%, consistent with that expected from a properly averaged contribution of the elementary cross section for n ̄ p and n ̄ n annihilation, indicating that the process is due to the interaction with single nucleons on the surface.

Parameterization of Proton-induced Neutron Production Double Differential Cross Section up to 3 GeV in Terms of Moving Source Model

The parameterization of double differential cross sections is made for the neutron emission from proton- induced spallation reaction. The emitted neutron data for incident proton energies of 0.8 to 3 GeV are analyzed by the three-component moving source model based on the Maxwell-like energy distribution. In addition, a Gaussian-shaped term is utilized for reproducing the neutron spectrum originating from the quasi-elastic- and quasi-inelastic-like scattering. The systematics of parameters is obtained in the target mass number region from C to Pb.

Parameterization of Proton-induced Neutron Production Double Differential Cross Section up to 3 GeV in Terms of Moving Source Model.

The parameterization of double differential cross sections is made for the neutron emission from proton- induced spallation reaction. The emitted neutron data for incident proton energies of 0.8 to 3 GeV are analyzed by the three-component moving source model based on the Maxwell-like energy distribution. In addition, a Gaussian-shaped term is utilized for reproducing the neutron spectrum originating from the quasi-elastic- and quasi-inelastic-like scattering. The systematics of parameters is obtained in the target mass number region from C to Pb.

Inclusive features of neutral strange particles in $$\overline p $$ A interactions at 40 GeV/c

Mean inclusive features of neutral strange particles produced in antiproton interactions with D, Li, C, S, Cu, and Pb nuclei at an incident momentum of 40 GeV/c are found as functions of the target mass number.

Calculation of hadron yields around thick targets and doses behind concrete shielding of high-energy electron accelerators

The field of neutrons, protons, and pions produced by high-energy electrons hitting thick targets is studied by means of the FLUKA Monte Carlo code. Particle spectra and dependences of fluences on primary energy (1–250 GeV), on angle (20–150°) and on target mass number are given, together with the total number of low-energy neutrons and of high-energy neutrons per electron. The attenuation of the total hadron dose equivalent in concrete and dose ratios of the main components are calculated. All results are parametrized and expressed by simple formulae. In addition, the hadron field behind copper and lead absorbers (beam shutters) in beam direction, its composition and its dependence on primary energy (1–50 GeV), on distance, and on absorber type are studied. Again the total hadron dose equivalent can be expressed by a simple equation. The dose attenuation by an additional concrete shield behind an absorber is examined.

Density-independent folding analysis of the [formula omitted] Li elastic scattering at intermediate energies

The differential cross sections of 6,7 Li elastic scattering from 12 C, 28 S, 40 Ca, 58 Ni, 90 Zr and 208 Pb targets at E/A P =12.5 –53 MeV / u have been analyzed using density-independent double folding optical potentials. The calculations are built upon a very simple phenomenological nucleon–nucleon effective interaction, which is represented by a single Yukawa term with a complex strength. The complex microscopic potentials have successfully reproduced the elastic scattering data for most of the analyzed sets. However, more success has been obtained when the single Yukawa term was considered for the real part only while the imaginary part was formulated in a phenomenological Woods–Saxon form. The predictions of the calculated potentials are compared with those obtained by the phenomenological and the M3Y double folded optical potentials. The effects of the knock-on exchange contribution, the variation of the range of the interaction and the target density uncertainty have been investigated. Also, the target mass number dependence in the real volume integrals and the total reaction cross sections has been studied.

Study of collective matter flow in central C-Ne and C-Cu collisions at 3.7 GeV/nucleon

The transverse momentum technique is used to analyse charged particle exclusive data in the central C-Ne and C-Cu interactions at the energy of 3.7 Gev per nucleon. Clear evidence of in-plane and out-of-plane (squeeze-out) flow effects for protons and π − mesons have been obtained. In C-Ne interactions in-plane flow of π − mesons is in the same direction as for the protons, while in C-Cu collisions pions show antiflow behaviour. From the transverse momentum and azimuthal distributions of protons and π − mesons with respect to the reaction plane, the flow F (the measure of the collective transverse momentum transfer in the reaction plane) and the parameter a 2 (the measure of the anisotropic emission strength) have been extracted. The flow effects increase with the mass of the particle and the mass number of target A T . The comparison of our in-plane flow results with flow data for various projectile/target configurations was made using the scaled flow F S = F/( A P 1/3+ A T 1/3). F S demonstrates a common scaling behaviour for flow values from different systems.

Spin-isovector giant resonances induced by(n,p)reactions on heavy nuclei

Double differential cross sections from the ${}^{120}\mathrm{Sn}{(n,p)}^{120}\mathrm{In}$ and ${}^{181}\mathrm{Ta}{(n,p)}^{181}\mathrm{Hf}$ reactions at 298 MeV and the ${}^{238}\mathrm{U}{(n,p)}^{238}\mathrm{Pa}$ reaction at 318 MeV have been measured for excitation energies up to 50 MeV in the residual nucleus. These data, together with the previously published data from the ${}^{90}\mathrm{Zr}{(n,p)}^{90}\mathrm{Y}$ and ${}^{208}\mathrm{Pb}{(n,p)}^{208}\mathrm{Tl}$ reactions at 198 MeV, have been analyzed for spin-isovector resonances of multipolarities less than 7, using the multipole decomposition method. The strengths due to spin-isovector excitations of multipolarity less than 4 have been extracted. The anomalous behavior of the extracted spin-isovector quadrupole strength with target mass number is discussed with reference to the calculations of Leonardi et al. The cross section due to quasifree processes was calculated and subtracted from the data. The data after this subtraction were reanalyzed for spin-isovector resonances and the strengths due to multipolarities up to 3 were extracted. The strengths due to spin-isovector dipole and octupole excitations were compared to values calculated, for 1\ensuremath{\Elzxh}\ensuremath{\omega} transitions only, using the sum rules of Macfarlane. The behavior with target mass number is well represented by these sum rules.

Transfer and surface vibration couplings in the fusion of40Ca+46,48,50Tiat near-barrier energies

Fusion and quasielastic excitation functions were measured for {sup 40}Ca+{sup 46,48,50}Ti at energies close to the Coulomb barrier. The interest in these systems lies in the opposite target-mass dependence of surface vibration couplings and neutron-transfer couplings. The cross sections were measured at small energy steps and with high precision, so that the structure in the excitation functions (barrier distributions) could be revealed through a differentiation process. The subbarrier fusion data show a larger enhancement with increasing target mass number, which clearly indicates the importance of transfer couplings. The agreement between the fusion and quasielastic barrier distributions is quite good. Simplified coupled-channel calculations were performed to reproduce the fusion data. A very good agreement is obtained by coupling to low lying excited states (2{sup +} and 3{sup {minus}}) and to the most positive neutron-transfer Q value (two-neutron projectile pickup channel). {copyright} {ital 1998} {ital The American Physical Society}

Nucleon and deuteron induced spallation reactions

The intranuclear cascade (INC)+evaporation model is used to display the gross features of proton, neutron and deuteron induced spallation reactions between 200 MeV and 2 GeV incident energy per nucleon. Particular attention is focused on average particle multiplicities and their dependencies upon target mass number and incident energy. Simple formulae are derived to allow an easy use of these results. They are expected to provide a rapid survey of the gross features of spallation reactions. The decomposition of particle multiplicities and of cross-sections into cascade and evaporation components is performed and discussed. The impact parameter dependence is investigated. The excitation energy left in the target at the end of the cascade step is also studied, as well as the gross properties of the subsequent evolution of the target remnant. It is shown that neutron differential cross-sections can be split into components with reasonably identified physical origin, which exhibit simple power laws as functions of the target mass number.

Computer simulation of high-energy proton-nucleus fragmentation cross-section

A computer simulation code is designed to imitate the mass yield fragmentation cross-section as a result of high energy P-N interaction, as well as other effective distributions influencing it. The Monte-Carlo fragmentation is discussed in the framework of an equilibrium macrocanonical statistical model. The code is used to investigate the mass yield cross-section of U238 as well as the Coulomb potential distributions of U238, Au190, Ta181, Xe127, Cu64 nuclei. The comparison of predicted yield cross-section with experimental measurements exhibited tolerable agreement, furthermore, the binary fisson cross-section is formulated in terms of target and fragment mass numbers as well as the expectation values of Coulomb potential are formulated in terms of target and fragment atomic numbers,Z t andZ f, respectively.

Reaction and fission cross-sections of 750 A·MeV238U ions on Pb, Cu and Al-targets

Charge-loss and fission cross-sections of238U at 750 A·MeV were measured on Al, Cu and Pb targets. The charge-loss rate was obtained by the attenuation method. Fission was selected by detecting the pair of highly ionizing fragments. Since the neutron-loss cross sections were measured in a parallel experiment for the same projectiles, all cross sections contributing to238U collisions on nuclei are available now as function of the target mass number and can be compared with current models.

PRE-EQUILIBRIUM FRACTION IN ALPHA INDUCED REACTIONS FROM THRESHOLD TO 40 MeV

α-particle induced excitation functions for the reactions 55Mn (α, n), 63Cu (α, n), 65Cu (α, n), 107Ag (α, n), 121Sb (α, n), 123Sb (α, n), 165Ho (α, n), 197Au (α, n), in a number of target nuclei from A=55 to 197(Z=25 to 83) have been calculated using the Statistical Model with and without inclusion of pre-equilibrium particle emission in the energy from threshold to 40 MeV. It is found that without consideration of pre-equilibrium decay, the data are not reproducible. As expected, inclusion of pre-equilibrium emission in compound nucleus calculation agree well with the experimental excitation functions. The pre-equilibrium fraction (FR) is found to be dependent on excitation energy, target mass number, neutron number, atomic number and, asymmetry parameter (N−Z).

Proton-nucleus scattering based on the relativistic Brueckner-Hartree-Fock model.

Nucleon-nucleus scattering is studied with optical potentials derived from solutions of the relativistic Brueckner-Bethe-Goldstone (RBBG) equation using the Bonn interaction. The complex effective mass is determined phenomenologically by a fit to 200 MeV proton-nucleus scattering data. Calculations with this effective mass are made and compared with elastic scattering data for p${\mathrm{\ensuremath{-}}}^{16}$O, $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, $^{208}\mathrm{Pb}$ in the energy range from 160 to 500 MeV. Predictions for the differential scattering cross section, analyzing power, and spin rotation functions are compared with elastic proton-nucleus scattering data over a wide range of projectile energies and target mass number.

Centrality dependence of pion and proton spectra in C+C and C+Ta interactions at 4.2 GeV/c per nucleon.

Target and centrality dependence of pion and proton distributions is studied in C+C and C+Ta collisions at 4.2 GeV/c per nucleon using the 2-m propane bubble chamber. The experimental data are compared with the predictions of the Monte Carlo quark-gluon string model (QGSM). The pion and proton transverse momentum spectra at midrapidity are well described by the two-component thermal model. The shape of the proton rapidity distribution strongly depends on the collision centrality and reflects the stopping power of colliding nuclei. The pion rapidity distribution is Gaussian in shape regardless of the target mass number and collision centrality. The QGSM completely reproduces main features of pion and proton rapidity spectra as well as pion transverse momentum spectra. The model does not fully reproduce the features of the proton transverse momentum spectra.

Target mass dependence of Λ4H formation mechanism from K− absorption at rest

Formation probabilities of Λ 4H from K − absorption at rest on light nuclear targets are investigated employing antisymmetrized molecular dynamics combined with multi-step binary statistical decay. Calculated results show that as the target mass number decreases from 16O, 12C to 9Be, the main formation mechanism varies from statistical decay, followed by dynamical fragmentation, to direct formation in nuclear environment.

Anomalous Mass Number Dependence of Nuclear Transparency

Abstract We examine the target mass number ( A ) dependence of the nuclear transparency calculated for ( e , e ′ p ) reactions. Generally, the transparency is proportional to A − 1 3 for large A 's and has weaker A -dependence as A decreases. The conventional nuclear physics calculation yields a transparency whose A − 1 3 dependence is reached in rather light nuclei (around A = 20). If either the proton mean-free path in nuclei becomes substantially longer, or the internal structure of the proton is explicitly incorporated in the calculation, however, the A − 1 3 dependence is reached only in extremely heavy nuclei. The A -dependence should thus serve as a signature of the so-called color-transparency phenomenon.

Anomalous mass number dependence of nuclear transparency

We examine the target mass number ( A) dependence of the nuclear transparency calculated for ( e, e′ p) reactions. Generally, the transparency is proportional to A − 1 3 for large A's and has weaker A-dependence as A decreases. The conventional nuclear physics calculation yields a transparency whose A − 1 3 dependence is reached in rather light nuclei (around A = 20). If either the proton mean-free path in nuclei becomes substantially longer, or the internal structure of the proton is explicitly incorporated in the calculation, however, the A − 1 3 dependence is reached only in extremely heavy nuclei. The A-dependence should thus serve as a signature of the so-called color-transparency phenomenon.