Studying of the neutron halo structure in quasi-free proton scattering from 6He Halo nucleus

An experimental method based on an analysis of the neutron-neutron correlations in reactions induced by halo nuclei in nuclear photoemulsion is proposed for studying the two-neutron halo structure. Photoemulsion stacks were exposed to a beam of radioactive ⁶He nuclei. Preliminary data on interaction of the ⁶He halo nucleus to hydrogen are compared with the results of the kinematic calculation for the reaction of quasi-free proton scattering from clusters making up the ⁶He halo nucleus. A fraction of quasi-free scattering events with “survival” of the dineutron is evaluated for scattering of protons by the dineutron configuration of the ⁶He nucleus.     

Spin-alignment and g-factor measurement of the I^{\pi} = 12+ isomer in 192Pb produced in the relativistic-energy fragmentation of a 238U beam

Reactions of a 16.8 MeV ⁶He beam with a ⁹Be target have been investigated using highly segmented detector setup covering a large solid angle. Data on elastic and quasi-free scattering, as well as two-neutron transfer, are reported. The results for elastic scattering are fairly well reproduced by a CDCC calculation, in agreement with the interpretation of a breakup effect already observed for the scattering of ⁶He on other light targets. Exotic quasi-free scattering of ⁶He on $ \alpha$ -cluster in ⁹Be is clearly observed. Inclusive and coincident events were used to extract information on the two-neutron transfer reaction ⁹Be(⁶He, $ \alpha$ )¹¹Be . Sequential decay of the ¹¹Be state at the excitation energy $\ensuremath E_x = 10.6$ MeV through different channels is discussed.     

Quasi-free scattering of pions on 3, 4He

Differential cross sections for ^{3, 4}He(π, π') are presented for angles of 60° and 120° at 200 MeV and 120° at 295 MeV. The momentum spectra for the scattered pions are dominated by a peak attributed to quasi-free scattering from individual nucleons. There are significant differences between the scattering on ³He and ⁴He as well as between the scattering of π⁺ and π^? on ³He. The data are compared to a simple model incorporating the free π+N scattering amplitudes. Modifications for the structure and dynamics of the target nucleus are discussed.     

Investigation of the <Superscript>6</Superscript>He structure in quasi free scattering reactions

Momentum correlations inherent to the ⁶He constituents in the ground state of this nucleus were studied in the quasi-free scattering (QFS) reaction ⁴He(⁶He, 2α)2n at ⁶He beam energy of 25 MeV/nucleon. A detailed study of nucleus structure was performed for the first time in QFS reactions with an unbound spectator. The Plane Wave Impulse Approximation was used in analyzing the experimental data. It was shown that the experimental data are described by model calculations in which the two neutron final state interaction is taken into account. t + t and t + d + n configurations were also studied in the ⁴He(⁶He, tα)t and ⁴He(⁶He, tα)dn QFS reactions.     

Quasi-free scattering in 7(p,pd)5He and 12C(p,pd)10B reactions at 670 MeV

The reactions ⁷Li(p, pd)⁵He and ¹²C(p, pd)¹⁰ were investigated at 670 MeV in quasi-free scattering geometry at large angles. In transitions to low-lying as well as to highly excited states of the residual nuclei the energy distributions of the scattered protons are in agreement with the mechanism of quasi-free scattering on quasi-deuterons in the p- and s-shells of ⁷Li and ¹²C.     

Quasi-free contributions in the6Li(d,tp)4He-reaction atE d =0.465 MeV

The⁶Li(d, tp)⁴He reaction was investigated at a bombarding energy ofE _d =0.465 MeV in a kinematically complete experiment. Evidence was found for a quasi-free reaction.     

Large-angle quasi-free scattering in 6Li(p,pd)4He at 670 MeV

The ⁶Li(p, pd)⁴He reaction was investigated at 670 MeV by a coincidence experiment with a large-angle scattering geometry. The energy sharing and angular correlation of the reaction products were measured and the momentum distribution of the recoil nucleus was determined for transitions leading to residual nuclei in the ground and excited states. Results were analysed in terms of a simplified distorted-wave impulse approximation using cluster-model and three-body wave functions. The observed momentum distribution of the p-n pair in the p-shell of ⁶Li is in agreement with three-body calculations, while the spectroscopic factor is larger than predicted by theory. Transitions to breakup states of the α-particle also have the characteristics of quasi-free scattering on deuteron clusters.     

Scattering of radioactive nuclei 6He and 3H by protons: Effects of neutron skin and halo in 6He, 8He,and 11Li

In an experimental study of ⁶He+p and ³H+p collisions at ∼70 A MeV, the elastic scattering angular distributions were measured and the known excited state ⁶He_1.8¹ was observed. Comparative analysis of existing experimental data on proton elastic scattering by ⁴He, ⁶He, ⁶Li, ⁸He, ⁹Li, and ¹¹Li was performed. Effects of valence neutrons were investigated using the eikonal approach. A difference between ¹¹Li and ^6,8He was found.     

Manifestations of a dineutron cluster in elastic α 6He scattering

A consistent theoretical analysis of elastic α ⁶He scattering is performed with allowance for the correction associated with the exchange of a dineutron cluster. It is shown that the inclusion of the exchange mechanism, along with that of potential scattering, makes it possible to reproduce the measured cross section over the entire range of the ⁶He scattering angle. Concurrently, one can also obtain information about the spatial distribution of the dineutron cluster and the α particle in the ground state of the ⁶He nucleus.     

Scattering theory for quasi-free time automorphisms of C1-algebras and von Neumann algebras

Relations between scattering theory in L² space, for quasi-free automorphism groups of C¹-algebras and for those of their representations are established and it is shown that wave operators as time limits do not exist in these representations. Finally, the connection of scattering theory and dynamical stability is discussed.     

Research on glass cells for He neutron spin filters

Glass cells play an important role in polarized ³He neutron spin filters. To evaluate the scattering and absorption contribution from glass cells during neutron scattering experiments, we measured small-angle scattering and neutron transmission in GE180 and other glasses. The small-angle neutron scattering measurements revealed that the glasses used for ³He spin filters have acceptably lower scattering: dΣ(Q)/dΩ=4-7×10⁻⁴ cm⁻¹ at Q=0.03-0.12 Å⁻¹. The transmission measurement was performed at J-PARC. Neutron transmission of about 92% through empty GE180 cells was observed over a wide wavelength range 0.014-7.0 Å. To pursue the possibility of being a structural influence on ³He spin relaxation in GE180 glass cells, we performed precise X-ray diffraction measurement using synchrotron radiation at SPring-8. From these measurements, a structural difference was observed among GE180 glasses with different thermal treatments.     

Mechanism of independent neutron transfer in elastic <Emphasis Type="Italic">α</Emphasis><Superscript>6</Superscript>He scattering and structure of the <Superscript>6</Superscript>He nuclear wave function

The presence of two topologically different configurations, a dineutron and a cigar-like one, in the spatial wave function for the neutron-rich nucleus ⁶He is predicted. In elastic α ⁶He scattering, the dineutron configuration leads to the appearance of backward maxima in the cross section for elastic α ⁶He scattering. The cigar-like configuration is responsible for the scattering mechanism involving independent sequential neutron transfer and the formation of the ⁵He-⁵He virtual system. In order to estimate the contribution of this mechanism, the matrix element for the two-step sequential particle transfer is calculated by a method that takes into account delay in the interaction and which is realized in the QUADRO code. Calculations performed on this basis make it possible to estimate the weight of the cigar-like component in the wave function for the ⁶He nucleus.     

The α-<Superscript>12</Superscript>C scattering studied via the Trojan-Horse method

The Trojan-horse method has been suggested as a means to study a two-body reaction at astrophysical energies via a three-body breakup reaction. In order to test this method the ⁶Li(¹²C,α¹²C)²H reaction was studied in a kinematically complete experiment at an incident energy of 18 MeV. Coincidence spectra show the presence of the quasi-free α-¹²C scattering process. The excitation function of the three-body reaction is calculated in the plane wave impulse approximation assuming quasi-free scattering and is compared with the experimental data. Also, the excitation function of the virtual α-¹²C elastic scattering is extracted from the three-body reaction cross section at low deuteron momenta and compared with the behaviour of the free scattering cross section. Received: 4 June 1999 / Revised version: 15 November 1999     

Analyzing Power in Elastic Scattering of Polarized Protons from Neutron-rich Helium Isotopes

The vector analyzing power has been measured for the elastic scattering of neutron-rich ⁶He from polarized protons at 71 MeV/nucleon. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a ⁶He nucleus. An optical model analysis revealed that the spin-orbit potential for ⁶He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semi-microscopic analysis with a α + n + n cluster folding model suggests that the inclusion of realistic interaction between a proton and the α core is important in describing the p-⁶He elastic scattering.     

The reaction 3He + p → p + p + d studied with BOL at 69 MeV 3He incoming energy

The proton-induced ³He breakup into p and d has been studied in a kinematically complete way at 69 MeV ³He-incoming (23 MeV p-incoming) lab energy, using the spherical multi-detector array BOL.The four-dimensional cross-section data cover most of the three-body final-state phase space. By slicing and integrating the data, they have been brought into suitable one- and two-dimensional representations to reveal different aspects of the reaction process. Based on these, this paper presents information on the interplay between the different reaction modes occurring in the p³He breakup process. In particular, pp final-state interaction, pp and pd quasi-free scattering and nucléon transfer have been studied here.Anomalous effects, probably due to interference between these processes, show up in the data.     

Excitation function of quasi-free processes in the6Li+6Li → 3α reaction

The⁶Li+⁶Li → 3α reaction was studied at energies around the Coulomb barrier. Excitation functions of the quasi-free processes⁶Li(d,α)⁴ He with an α-particle spectator either in the target or in the beam were measured.     

The 2H(p, 2p)n reaction at Einc = 45 MeV and its sensitivity to various separable S-wave N-N potentials

This paper presents and analyses the data for the ²H(p, pp)n reaction at E_inc = 44.9 MeV. Kinematic conditions including the quasi-free scattering region and the regions far from quasi-two-body processes are considered. The experimental results are compared with the predictions of several separable S-wave models of the N-N interaction. Potential models that differ only off-shell, as well as models that predict different N-N scattering results are included to help to isolate aspects of the break-up reaction sensitive to off-shell and on-shell differences. The regions far from quasi-free scattering are generally much more sensitive to the off-shell features of the interaction than are quasi-free scattering results. On-shell differences in the potential affect predictions in all regions of phase space with the potentials best representing the free N-N data giving the best overall fit to the data over most regions of phase space.     

Mechanisms in d + 6Li three-body reactions at low bombarding energies

The three-body reactions induced by low energy deuterons on ⁶Li have been studied. The contributions from the sequential processes through the excited states of the intermediate ⁴He, ⁵Li, ⁶Li and ⁷Li nuclei dominate the coincidence spectra. The quasi-free d + d → d + d, d + α → d + α, and d + d → p + t reactions have been observed and compared with plane wave impulse approximation (PWIA) calculations.     

Optical model analysis of p+6He scattering over a wide range of energy

Optical-model analysis of proton elastic scattering from ⁶He has been carried out for eight sets of elastic scattering data at energies, 24.5, 25.0, 36.2, 38.3, 40.9, 41.6, 71.0 and 82.3 MeV/n respectively. The vector analyzing power and differential cross section for the elastic scattering of ⁶He nucleus from polarized protons at 71 MeV have been analyzed in the framework of the optical model potentials. The data are, first, analyzed in term of phenomenological potentials using the Woods-Saxon form for the real and imaginary parts supplemented by a spin-orbit potential of Thomas form. The analysis has been also performed using microscopic complex potentials.