Elastic scattering of high-energy protons from nuclei

The elastic scattering of high-energy protons from zero-spin nuclei is considered within the framework of Glauber theory. The sensitivity of the cross sections to the nuclear structure and to the proton-nucleon amplitude is studied. Results of calculations demonstrating the investigated effects are presented for the case of 1 GeV proton scattering from ⁴He, ¹⁶O and ⁵⁸Ni.     

Collinear three-body disintegrations of tungsten nuclei by 1-GeV protons

The (2E, 2V) measurement method is applied to analyze the kinematics of the separation of two complementary collinear fragments of the disintegration of tungsten nuclei by 1-GeV protons. In addition to the main process of binary fission, three branches of collinear three-body disintegration, which are associated with various mechanisms of the excitation of a deformed fissioning nucleus, are observed.     

Polarization in the quasielastic scattering of 1-GeV/c protons on light nuclei

Polarization measurements in the A(p, 2p)B reactions on ⁶Li, ⁷Li, and ²⁸Si nuclei at a proton-beam energy of 1 GeV were performed in a kinematically complete experiment. By using a two-arm magnetic spectrometer, two secondary protons were recorded in coincidence at asymmetric scattering angles of θ₁=15°?26° and θ₂=58.6° for residual-nucleus momenta in the range K _B=0–150 MeV/c. Either arm of the spectrometer was equipped with polarimeters based on proportional chambers. The data coming from this experiment are analyzed within the distorted-wave impulse approximation. It is shown that the polarization of recoil protons formed at angle θ₂ in the interaction featuring a proton from the P shell of the ⁷Li nucleus can be described under the assumption of an effective intranuclear-proton polarization by using the single-particle shell-model wave function of the nucleus. Our data on the polarizations of the two protons from the reaction (p, 2p) on a ²⁸Si nucleus also suggest the effective polarization of the protons in the D shell of the ²⁸Si nucleus. It is found that, for high recoil-nucleus momenta of K _B≥90 MeV/c, the effective polarization of the protons in the P shell of the ⁶Li nucleus—this polarization was discovered in studying the polarization of recoil protons in the reaction ⁶Li(p, 2p)⁵He—cannot be described within the shell model assuming LS coupling. As might have been expected, the polarization of recoil protons knocked out from the S shells of the ⁶Li and ⁷Li nuclei comply well with the predictions obtained in the impulse approximation with allowance for the depolarization effect alone.     

Elastic scattering of 800-MeV protons by 20Ne nuclei

The differential cross section and polarization observables are calculated for the elastic scattering of 800-MeV protons by ²⁰Ne nuclei. The assumption that the ²⁰Ne nucleus has an alpha-cluster structure is shown to lead to results that agree with the measured values of observables of the above scattering process.     

Elastic scattering of 1 GeV protons from nuclei as a test for flucton model

Cross sections for elastic scattering of 1 GeV protons from⁴⁰Ca nuclei have been calculated using the flucton model. The influence of the collective flucton nuclaon correlations on the calculated cross sections is examined. The calculated cross sections are in significant disagreement with the experimental data. This may be considered as an argument against the flucton model.     

Formation of 24Mg* in the spallation of 28Si nuclei by 1-GeV protons

The ²⁸Si(p, p′γ₀ X)²⁴Mg reaction has been studied at the ITEP accelerator by the hadron-gamma coincidence method for a proton energy of 1 GeV. Two reaction products are detected: a 1368.6-keV γ-ray photon accompanying the transition of the ²⁴Mg* nucleus from the first excited state to the ground state and a proton p′ whose momentum is measured in a magnetic spectrometer. The measured distribution in the energy lost by the proton in interaction is attributed to five processes: the direct knockout of a nuclear α cluster, the knockout of four nucleons with a total charge number of 2, the formation of the _ΔSi isobaric nucleus, the formation of the Δ isobar in the interaction of the incident proton with a nuclear nucleon, and the production of a π meson, which is at rest in the nuclear reference frame. The last process likely corresponds to the reaction of the formation of a deeply bound pion state in the ²⁸P nucleus. Such states were previously observed only on heavy nuclei. The cross sections for the listed processes have been estimated.     

On high-energy elastic scattering of protons by nuclei

The two coupled channel formalism for high energy elastic scattering [1] is extended to include spin and isospin effects. For a spin and isospin zero nucleus these manifest themselves by additional spin-orbit terms in the potentials. Explicit formulas for these potentials are obtained in terms of the fully spin and isospin dependent nucleon-nucleon scattering amplitude, the ground state nuclear form factor and the state dependent correlation functions. The coupling potential except for a small term arising from double spin and isospin flip process involving nuclear excitation depends only upon the pair correlations.Numerical calculations are performed for the elastic scattering of 1 GeV protons incident on ⁴He. Various phenomenological dynamical two-body correlations as well as correlations generated from the Reid soft-core and Tabakin potentials in an approximate Brueckner-Hartree-Fock calculation are considered. The angular distribution beyond its first diffraction minimum as well as the polarization in the same angular range are shown to be sensitive to these correlations. However, the present accuracy of the experimental data and the lack of knowledge of the nucleon-nucleon scattering amplitude prevent any definitive conclusion about their nature.     

Elastic scattering of electrons by spherical nuclei

The differential effective scattering cross sections of electrons by spherical nuclei are obtained using a proposed density distribution. The analysis is based on the method of the distorted wave high energy approximation. From the comparison of the obtained results with the corresponding experimental data, the parameters of the density distributions of protons, neutrons and nucleons are determined, for which the best agreement is achieved.     

Neutron production in the interaction of 2-GeV protons with nuclei

The double-differential cross sections for neutron production in the interactions of 2-GeV protons with Be, Al, Cu, Cd, and Pb nuclei were measured by the time-of-flight method in the region of angles larger than 30°. The respective experimental data are analyzed within the phenomenological model of four moving sources, including those associated with neutron emission in primary nucleon-nucleon collisions, the decay of a hot source (fireball), the multifragmentation process, and the deexcitation of nuclear fragments via neutron evaporation. Temperature-parameter values are universal for all sources and are virtually independent of the target nucleus and of the projectile energy in the region above 0.5 GeV. It is found that, for all of the above reactions, the relative contribution to the mean neutron multiplicity from the decay of a hot source and multifragmentation is about 41%.     

Volume reflection of 1-GeV protons by a bent silicon crystal

The volume reflection of 1-GeV protons by a bent crystal has been observed. The crystal is made of single crystal silicon. The (111) atomic planes are bent owing to the elastic quasimosaicity effect, which makes it possible to reduce the crystal length for a beam to 30 μm. It is found that the probability of the reflection effect is higher than the probability of the channeling effect (0.71 vs. 0.63), and the deflection angle of the protons reflected inside the crystal is equal to 1.39 ± 0.04 in terms of the critical angle for channeling under the conditions of the experiment (170 μrad). The width of the reflected peak is equal to 1.76 ± 0.04 in the same units. The protons that are not involved in channeling at the angular position of maximum channeling undergo volume reflection and are deflected in the direction opposite to the channeled beam by the angle 1.01 ± 0.05 in terms of the critical angle for channeling. The width of the reflected peak is equal to 1.94 ± 0.08 in the same units. Original Russian Text ? Yu.M. Ivanov, N.F. Bondar’, Yu.A. Gavrikov, A.S. Denisov, A.V. Zhelamkov, V.G. Ivochkin, S.V. Kos’yanenko, L.P. Lapina, A.A. Petrunin, V.V. Skorobogatov, V.M. Suvorov, A.I. Shchetkovsky, A.M. Taratin, W. Scandale, 2006, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 84, No. 7, pp. 445–450.     

Elastic scattering at small angles of protons

Differential cross sections and asymmetries are obtained from elastic scattering, between 0° and 7°, of 36.2 MeV polarized protons by C, Al, Fe and Ni natural targets.     

Quasielastic channel of single-stage nuclear fission induced by 1-GeV protons

Experimental indications that there exists single-stage fission of ²³⁸U and ²³²Th nuclei that is induced by a nearly transverse flux of intranuclear nucleons are obtained from an experiment that employs a two-arm time-of-flight spectrometer exposed to a beam of 1-GeV protons. A nearly transverse flux of mean multiplicity about 10 to 15 nucleons is initiated by a recoil nucleon of mean momentum about 240 MeV/c in the quasielastic scattering of an incident proton.     

Vacuum polarization effects in elastic scattering of protons by nuclei

Sensitivity of spin observables in elastic proton scattering by nuclei to the vacuum polarization correction δϱ_VAC is explored. The Dirac optical potential is calculated from a complete set of Lorentz invariant amplitudes, Dirac-Hartree densities and the existing estimate of δϱ_VAC based on quantum hadrodynamics.     

Elastic scattering of polarized deuterons by protons at intermediate energies

The tensor analyzing power T₂₀(θ) in dp backward scattering has been measured at or near center-of-mass angle θ = 180° in the energy range 0.3–2.3 GeV. A pronounced structure is observed around T_d = 0.5 GeV which is explained by a predominant one-neutron-exchange mechanism. Other structures appear around 1 GeV and higher. They are not explained by calculations which include Δ-excitations in intermediate states. In addition, full angular distributions of vector A_y and tensor A_yy analyzing powers and differential cross sections have been obtained at 1.2 GeV and limited angular ranges explored at 0.5 GeV (back angles) and 1.6 GeV (forward angles).     

Measurement of cross sections for gamma transitions induced in excited nuclei by the interaction of 1.1-GeV protons with silicon nuclei

The cross sections for the production of excited nuclei were measured in the reaction ²⁸Si(p, xpyn)A* followed by a gamma transition to a state of lower excitation energy or to the ground state. The experiment was performed in an extracted proton beam from the accelerator of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The reaction in question was identified by a Ge(Li)-NaI(Tl) anticoincidence spectrometer that recorded prompt gamma radiation emitted by the excited final nucleus. The sensitivity of the experiment was 1.5 mb. The cross-section values were obtained for 24 gamma transitions in 17 nuclear products. The cross sections for spallation reactions were estimated. A comparison was performed with known experimental data and with the results of calculations by a semiempirical formula, as well as with the results obtained by simulating hadron interactions on the basis of the GEANT and INUCL codes.