The elastic scattering of polarized 3He by 3He and excitation in the 6Be system

Angular distributions of the polarization in the elastic scattering of ³He by ³He have been measured at eight energies between 18 and 33 MeV, corresponding to excitation of ⁶Be between 20.5 and 28 MeV. The measurements were made using the 33 MeV polarised ³He beam at the University of Birmingham Radial Ridge cyclotron and a small gas target. The data have been analysed in terms of real and complex phase shifts. The deduced phase shift energy dependence cannot be associated with a single isolated level in ⁶Be, however an application of the two-level R-matrix formula reveals some broad L = 3 structures around E_x = 25 MeV.     

Elastic scattering of vector polarized deuterons by 4He

The vector analyzing power iT₁₁ for deuterons elastically scattered by ⁴He has been measured for c.m. angles between 51.8° and 158.9° and deuteron energies in the range 11.5 to 17 MeV. The results show that d-α scattering is a convenient analyzer for deuteron vector polarization in the energy range investigated, since the angular dependence of iT₁₁ is fairly insensitive to energy and the magnitude of iT₁₁ is quite large at some angles.     

Odd-even absorption in 3He + 3He scattering and level structure of 6Be

Differential cross sections for ³He + ³He elastic scattering are calculated at c.m. energies from 2.95 to 37.44 MeV using the one-channel resonating-group method. A phenomenological imaginary potential, whose strength depends on whether the relative orbital angular momentum is even or odd, is included in order to account approximately for open reaction channels. The introduction of such an odd-even feature leads to a significantly improved agreement with experiment, especially at the larger scattering angles. In addition, an analysis of the calculated resonant phase shifts confirms recent experimental observations of highly excited levels in ⁶Be.     

The polarization of 3He elastically scattered from 27Al and 28Si at 21 MeV

The polarization of 21 MeV ³He elastically scattered from ²⁷Al and ²⁸Si has been measured in an angular range of θ_lab = 25°–55°. Differential cross-section data have been obtained out to angles of approximately 100°. The small values observed in the polarization distributions differ somewhat from optical-model predictions based on fits to the differential cross-section data and cannot be used to obtain significant information about the optical-model spin-orbit potential. It is concluded that statistically significant, non-zero ³He polarization measurements will not be possible using traditional double scattering techniques for ³He energies ≦ 27 MeV and targets of $\text{Z ≧ 13}$.     

Two-body photodisintegration of 3He and 4He in the Δ(1236) region

Differential cross sections for the reactions ³He(γ, p)d and ⁴He(γ, p)t were measured at proton c.m. angles of 60° and 90° for photon energies ranging from 150–450 MeV with an average resolution of 8 MeV. Bremsstrahlung was used as the photon source; deuterons/tritons were analyzed in a magnetic spectrometer whereas coincident protons were detected in a plastic scintillator telescope. The experimental method includes a calibration by means of ¹H(γ, π⁰)p differential cross section measurement at 90° c.m. in the same photon energy range. The ³He and ⁴He two-body photodisintegration differential cross sections show a monotonically decreasing variation with photon energy. In addition, partial data on the differential cross section of the reaction ⁴He(γ, n)τ at 90° and 120° neutron c.m. angle are given.     

A study of the 90Zr(6Li, 6He)90Nb reaction at E6Li = 93 MeV

The energy spectra of ⁶He nuclei from the ⁹⁰Zr(⁶Li, ⁶He) reaction at E_{⁶Li = 93 MeV} have been measured over the angular range of 7 ° ? θ_lab ? 20 °. The theoretical DWBA analysis of these spectra and angular distributions was performed employing transition densities of bound and resonance states obtained on the basis of the theory of finite Fermi systems. It is shown that up to excitation energies of E_x ≈ 10 MeV in ⁹⁰Nb a direct charge-exchange mechanism dominates in this reaction, while at higher E_x the contribution made by multistep processes increases significantly. It is also shown that the quasi-elastic cross section is determined by a sum of partial contributions of spin-isospin-flip transitions with multipolarities L=0 through L=6.     

Elastic π± + 3He scattering

Differential cross sections have been measured at θ≈20–120° at 50, 100 and 200 MeV. Salient features of the angular distributions are Coulomb interference effects at 50 MeV and clear spin-flip contributions to π^? compared to π⁺ scattering in the angular region of θ≈80° dominated by the πN p-wave minimum. Comparison with optical model calculations account for the data up to 200 MeV while this first-order scattering theory misses conspicuous features of data at 295 MeV.     

Investigation of the 6Li(d, α)4He reaction between 1.5 and 11.5 MeV

The differential cross section σ₀(θ) and the analysing powers T₁₁(θ), T₂₀(θ), T₂₁(θ) and T₂₂(θ) of the reaction ⁶Li(d, α)⁴He have been measured for twelve energies between 1.5 and 11.5 MeV at c.m. angles between 3.5° and 90°. The results were fitted with Legendre polynomials. The energy dependence of the resulting coefficients indicates resonance-like behaviour at several energies corresponding to excitation between 22 and 32 MeV in ⁸Be. The reaction ⁶Li(d, α)⁴He shows excellent features as an analyser for deuteron vector and tensor polarization over the whole energy range investigated.     

The 4He(p,d)3He reaction at 770 MeV

The differential cross section of the ⁴He(p, d)³He pick-up reaction has been measured at E_p = 770 MeV. The data are analysed in the framework of the DWBA; both one-nucleon and one-N¹ transfers are considered.     

The heavy-ion reaction channels of the system 16O + 16O

The reaction channels of the system ¹⁶O + ¹⁶O with outgoing heavy particles from lithium to magnesium have been measured using a ΔE-E telescope. Excitation functions from 49 to 65 MeV at θ_Lab = 30° and angular distributions from θ_Lab = 10° (20°) to 50° at E_Lab = 51.5 MeV are presented for the strong transitions. The excitation function of the ¹²C-²⁰Ne (4.25 MeV) channel shows a pronounced regular cross structure with peaks at 52 and 60 MeV. A selective excitation of certain states in the inelastic scattering and the ¹²C-²⁰Ne channel is observed; the yields of the other heavy-ion channels being weaker by at least one order of magnitude. An explanation of this phenomenon is given by considering the angular momentum matching between entrance and exit channels. Furthermore it is shown that no strong dependence of the cross sections on the transferred angular momentum or on the nuclear structure of the final states is observed. Possible implications of these results on the reaction mechanism are discussed.     

Analyzing-power and cross-section measurements for 3He(d,d)3He scattering

Complete angular distributions of the differential cross section and all four deuteron-analyzing powers for ³He(d, d)³He scattering have been measured at 14 energies between 1.5 and 11.5 MeV. For all components the major changes in the observables occur below 7 MeV deuteron energy.     

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.     

Differential cross section,analyzing power and phase shifts for p-3He elastic scattering below 1.0 MeV

Differential cross sections and analyzing powers for the elastic scattering of polarized protons by unpolarized ³He nuclei have been measured at eight energies between 0.3 MeV and 1.0 MeV for scattering angles θ_c.m. = 52.4°–173.3°. The cross-section values were normalized to the Rutherford cross section for proton-krypton scattering. The analyzing powers have been measured with a statistical accuracy of about 0.001. The phase-shift analysis based on these data included all phases for orbital angular momenta l ≦ 1 and the channel-spin mixing parameter for the P waves. An energy parametrization of the phase shifts by an effective-range approximation allowed a simultaneous utilization of all data.     

The reaction 14C(3He,n)16O and the coexistence model of 16O

The reaction ¹⁴C(³He, n)¹⁶O has been measured at a ³He bombarding energy of 25.4 MeV. The zero-degree differential cross section for the excitation of the three low lying 0⁺T = 0 states, at energies 0.0, 6.05 and 12.05 MeV are, respectively, 1.33 ± 0.10, 0.49 ± 0.10, and 0.50 ± 0.10 mb/sr These measured cross sections are in rough agreement with single-step zero-range DWBA calculations using an empirically determined ¹⁴C ground state wave function and in which the Brown and Green coexistence-model wave functions are used to describe the ¹⁶O 0⁺ states. The angular distribution of the transition to the ground state is measured between 0° and 32°.     

Elastic scattering of 56 MeV polarized deuterons on 4He

The differential cross section and the vector and tensor analyzing powers A_y, A_xx, A_yy and A_xz were measured for the d-⁴He elastic scattering at 56 MeV. The measurement of A_xz was performed using a deuteron beam polarized in the horizontal plane. An optical-model analysis of the experimental data was carried out. The magnitude of the tensor analyzing powers could not be reproduced without the tensor potential. By including the T_R type tensor potential, the optical-model calculations give a reasonable reproduction of the experimental data at θ_c.m. < 120°. The obtained T_R tensor potential was much stronger than that predicted by the folding model. The strength of the real T_R potential was roughly in accordance with that obtained from the optical-model analysis of d-⁴He elastic scattering at 20.2 MeV.     

Inclusive π4He scattering and the πN interaction in the nuclear medium

Double differential cross sections for the inclusive reaction ⁴He(π, π′)X have been measured for six pion energies between 90 and 320 MeV and an angular range from 30° to 135°. The data are interpreted in terms of the Δ-hole formalism. Medium corrections to the free π-nucleon scattering operator are important for a quantitative understanding of our results. Total inelastic cross sections are obtained and estimates for the absorption cross section are given.     

Absolute cross sections for the 6Li(p, 3He)4He reaction at energies below 1 MeV

Total cross sections and angular distributions in the ⁶Li(p,³He)⁴He reaction have been measured over the energy range E_p = 100?700 keV. The extrapolation of the cross section to the energy region which is of interest in controlled thermonuclear reactors is given. The values of the “astrophysical S-function” are deduced from the cross sections.     

Elastic proton-3He scattering at large angles and intermediate energies

Large-angle p-³He elastic scattering differential cross section have been measured at E_p = 415 and 600 MeV where they look very similar, and at 800 MeV where the cross section is 10% of the value at 600 MeV. A one-meson-plus-2N exchange mechanism could explain this feature.     

Effects of exchange and final-state interactions in the reactions 2H(3He, 3H p)p and 2H(3He, 3He p)n

Absolute coincidence cross sections for the ²H(³He, ³He p)n and ²H(³He,³H p)p reactions were measured at E_He = 35.9 MeV. Spectra dominated by the nucleon-nucleon final-state interaction (FSI) are fitted by a fully antisymmetrized PWBA theory which includes the effects of FSI in all its matrix elements. Previously reported 26.8 MeV data showing both FSI and quasi-elastic scattering (both with and without charge exchange) are also fitted by the theory, which qualitatively describes the shapes of all these spectra and the ratios of the cross sections for the various processes. Predictions of Watson-Migdal theory are fitted to the FSI spectra and differences between the two theories are analyzed.     

Angular distributions of neutron polarization from the 14C(p,n)14N and 11B(α, n)14N reactions and R-matrix analysis oF 15N in the excitation-energy range between 11.5 and 12.5 MeV

Angular distributions of neutron polarization from the ¹⁴C(p, n)¹⁴N and ¹¹B(α, n)¹⁴N reactions have been studied for the particle energies E_p = 1.788, 2.025, 2.272 and 2.450 MeV, and E_α = 2.049 MeV. The polarization was derived from the left-right asymmetry induced by elastic scattering from ⁴He. Together with existing measurements of angular distributions and total cross sections for several reaction channels leading to ¹⁵N with an excitation energy between 11.5 and 12.5 MeV, these data were used to deduce from R-matrix analysis a set of resonance parameters for the ¹⁵N levels in this energy range.