A. V. Shvedchikov

Polarization effects in the quasielastic (p, 2p) reaction with the nuclear S-Shell Protons at 1 GeV

The polarization of the secondary protons in the (p, 2p) reaction with the S-shell protons of nuclei 4He, 6Li, 12C, 28Si, 40Ca was measured at 1 GeV unpolarized proton beam. The spin correlation parameters Cij for the 4He and 12C targets also were for the first time obtained as well. The polarization measurements were performed by means of a two-arm magnetic spectrometer, each arm of which was equipped with the multiwire-proportional chamber polarimeter. This experiment was aimed to study a modification of the proton-proton scattering matrix in the nuclear medium.

Polarization in quasielastic (p, 2p) scattering on a 4He nucleus at 1 GeV

The polarization of secondary protons from the (p, 2p) reaction induced by 1-GeV protons incident to a 4He nucleus was measured in a kinematically complete experiment. By using a two-arm magnetic spectrometer, two secondary protons from this reaction were recorded in coincidence at unequal scattering angles of Θ1 = 18°−24.21° and Θ2 = 53.22° over a broad range of the recoil-nucleus momentum KB between 0 and 150 MeV/c. It was found that the measured polarization of either secondary proton is less than that observed in free elastic proton-proton scattering. The magnitude of this difference is determined by the mean binding energy of s-shell protons rather than by the effective nuclear density. The polarizations measured in inclusive quasielastic and elastic scattering of 1-GeV protons on 4He nuclei are presented for scattering angles in the range Θ1 = 18° − 24.21°.

Total cross sections for fission of heavy nuclei by intermediate-energy protons

The results of measuring total cross sections for proton-induced fission of natPb, 209Bi, 232Th, 233U, 235U, 238U, 237Np, and 239Pu nuclei at proton energies from 200 to 1000 MeV are reported. The measurements were carried out in steps of ≈100 MeV. Complementary fission fragments were detected in coincidence by two parallel-plate avalanche gas counters placed in the beam line on both sides of the thin target close to it. Energy and isotope dependences of the fission cross sections are analyzed.

Measurement of the spin rotation parameters R and A in πp elastic scattering and a test of πN partial-wave analyses in the region of low-lying P11, S11 and D13 resonances

Abstract This paper presents the results of an experiment in which the spin rotation parameters R and Ain π − p elastic scattering have been measured at energies 450, 530, 560 and 600 MeV. The experiment was performed on a pion channel of the PNPI synchrocyclotron. The main parts of the setup were a polarized proton target with horizontal spin orientation and a carbon-plate polarimeter consisting of multigap optical spark chambers with television read-out. A comparison of the obtained results with partial-wave analyses is given.

Measurement of the polarization parameterP inπ+p elastic scattering in the region of low-lying pion-nucleon resonances

This paper presents the results of an experiment in which the polarization parameterP in π+p elastic scattering has been measured in the energy range from 335 to 580 MeV. The experiment was performed on a pion channel of the LNPI synchrocyclotron using a polarized proton target and wire spark chambers with magnetostrictive read-out. The results have substantially higher precision in comparison with the most of other experiments in this energy range and allow to determine unambiguously the shape of angular dependenceP(θ*) in the whole investigated region. New phase-shift analysis of π+p scattering data has been performed. The results of this experiment were used also to check isospin invariance.

Energy dependence of the spin-spin correlation parameter CNN at 50° and 90° c.m. for pp-elastic scattering in the energy range 0.69–0.95 GeV

Abstract The spin-spin correlation parameter C NN at 50° and 90° c.m. for elastic pp-scattering has been obtained in the energy range 0.69–0.95 GeV. It was found that the parameter C NN (90°) shows resonance-like structure at energies near 700 MeV. Its energy dependence does not agree with Hoshizakis phase-shift analysis predictions. C NN (50°) agrees well with these predictions and does not show any structure within the accuracy of the measurements.

Investigation of near-threshold eta-meson production in the reaction π − p→ ηn

Differential and total cross sections for eta-meson production in the reaction π−p → ηn were measured within the experimental program eta-meson physics implemented in the pion channel of the synchrocyclotron of the Petersburg Nuclear Physics Institute (PNPI, Gatchina). These measurements were performed at incident-pion momenta (700, 710, 720, and 730 MeV/c) in the vicinity of the threshold for the process under study by using the neutral-meson spectrometer designed and created at the Meson Physics Laboratory of PNPI. It is shown that, in the immediate vicinity of the threshold (685 MeV/c), the process of eta-meson production proceeds predominantly via S11(1535)-resonance formation followed by the decay S11(1535) → ηn (the respective branching fraction is Br ≈ 60%), but that, as the momentum of incident pions increases, the role of the D wave becomes ever more important. A detailed analysis of this effect indicates that it is due to the increasing contribution of the D13(1520) resonance. Although the branching fraction of the decay of this resonance through the ηn channel is assumed to be very small (BR ≈ 0.24%), the effect is enhanced owing to the interference between the D wave and the dominant resonance S11(1535).

New approximations to the energy dependences of the total cross sections for the proton-induced fission of 197Au, 203Tl, natPb, and 209Bi nuclei

The total cross sections for 197Au and 203Tl fission induced by protons of energy varied from about 200 to 1000 MeV with a step of about 100 MeV are measured. New approximations to the energy dependences of the cross sections for the proton-induced fission of 197Au, 203Tl, natPb, and 209Bi nuclei are presented and discussed. For all of these nuclei, exponential functions are used as approximations.

Isotopic effect in the energy dependence of the total fission cross section of lead and 209Bi nuclei for protons with energies up to 1 GeV

The results from measurements of the total fission cross sections of 206Pb, 207Pb, and 208Pb nuclei for protons with energies from 207 to 1000 MeV and a step of ≈100 MeV. These results complemented by our data for 209Bi and the data of the EXFOR world base allow determination of absolute and relative contributions of the isotopic effect.

Measurement of the spin rotation parameters R and A in π‐p‐elastic scattering in the region of pion‐nucleon resonances

First measurement of the spin rotation parameters R and A in {pi}-p elastic scattering in the region of pion-nucleon resonances has been performed at the Leningrad Nuclear Physics Institute. The experiment was carried out on a pion channel of the LNPI synchrocyclotron using a polarized target with LNPI synchrocyclotron using a polarized target with horizontally oriented polarization vector and a multi-plate carbon polarimeter consisting of optical spark chambers with television read-out. Results at the energies 450 and 560 MeV are given in comparison with the predictions of phase-shift analyses.