Large-space cluster model calculations for the 3He(3He,2p)4He and 3H(3H,2n)4He reactions

The ³He(³He,2p)⁴He and ³H(³H,2n)su4He reactions are studied in a microscopic cluster model. We search for resonances in the ³He+³He and ⁴He + p + p channels using methods that treat the two- and three-body resonance asymptotics correctly. Our results show that the existence of a low-energy resonance or virtual state, which could influence the ⁷Be and ⁸B solar neutrino fluxes, is rather unlikely. Our calculated ³He(³He,2p)⁴He and ³H(³H,2n)⁴He cross sections are in a good general agreement with the experimental data.     

Anisotropy of the electric susceptibility in superfluid 3He A

A technique is proposed for determining the orientation of the orbital anisotropy axis in ³He A. It relies upon the anisotropy of the dielectric tensor which is estimated to be 3×10^?7 (1?T/T_c) in ³He A.     

Statistical mechanics of dilute mixtures of 3He in superfluid 4He

A statistical mechanical theory of the dilute mixtures of ³He and ⁴He is presented. It is shown that the ground state energy is proportional to the ³He density. The chemical potential expressed in terms of the sound velocity assumes the form which has been suggested phenomenologically. From the chemical potential, the effective ³He⁴He interaction and osmotic pressure are derived. The effective mass of ³He is also calculated as a function of potential parameters.     

Scattering lengths of pionic 3He and 4He

Scattering lengths of pionic ³He and ⁴He and the charge exchange contribution to the 1s width of pionic ³He are calculated within the fixed scatterer approximation of the multiple scattering formalism. Particular attention is focussed on the nuclear physics part and on πN p-wave contributions. For the first time triple scattering and double-spin-flip contributions have been included. We find significant deviations from previous estimates and calculations. Good agreement is achieved with the experimental π^?3He scattering length, whereas in the case of ⁴He a repulsive dispersion contribution is clearly needed. We propose to use the measured 1s level shift of pionic ³He as a constraint to deduce a precise value of the isoscalar πN scattering length. Furthermore, we find that multiple scattering reduces the impulse approximation value for Γ_1s(π^?3He → π^{0 3}H) by more thsn 20 %. This result casts some doubt on impulse approximation calculations of radiative pion capture as well.     

Proton-3He elastic scattering: A phase-shift analysis by a separable potential model

All the available experimental data (cross sections, projectile and target polarizations, polarization transfer coefficients) on p-³He elastic scattering up to ~10 MeV are analyzed on a unified basis in the framework of a separable potential model. This allows a phase-shift analysis which is model dependent, but is averaged over a wide energy interval (757 experimental points are reproduced by 27 model parameters). The calculations confirm some indications, already present in the literature, of a weak S-D tensor mixing, and strong singlet-triplet mixing in the P-states. Our conclusions are that probably the leading non-central effect is given by the coupling s₁ · l between the incident proton spin s₁ and the orbital angular momentum of relative motion. Finally, the phase shifts and observables are recalculated using the p-³He potential parameters, but switching off the Coulomb interaction. The results are compared with the (few) n-³H experimental cross sections of the literature, and the agreement is good, as expected on the basis of the charge-symmetry law.     

Electromagnetic contributions to proton- and neutron-4He scattering

A proper treatment of various electromagnetic contributions toN-⁴He scattering enables one to determinen(p)-⁴He observables fromp(n)-⁴He data. Several calculations ofn-⁴He observables considering different electromagnetic effects are presented. It is shown that the contribution of thep-⁴He Coulomb corrections ton-⁴He polarizations and differential cross sections dominates over other electromagnetic effects forθ _c.m.≧30°. For smaller scattering angles, neutron magnetic scattering is important and produces a divergingn-⁴He differential cross section atθ=0° and a large peak (Mott-Schwinger effect) in the polarization. The influence of thep- andn-⁴He vacuum polarizations on then-⁴He observables is found to be small.     

Nucleon-nucleon interaction and meson exchange current effects in3He two-body breakup by polarized photons

Cross sections for the reaction³He(γ, p)d have been calculated with the Faddeev wave functions of the³He nucleus. The parametrized forms of the functions have been used for two different types ofNN interaction, viz., the separable Mongan potential (MP) and the Reid soft-core (RSC) potential. Contributions of meson exchange currents (MEC) to this process have been considered. Constraints imposed by the continuity equation for the nuclear current are discussed. The calculated results are compared with new data obtained recently at Kharkov.     

The transverse electron scattering response function of 3He

Results on the transverse response function R _T (q,ω) of ³He obtained within the Lorentz integral transform [LIT] [1] method are presented. The response is calculated using the BonnRA nucleon-nucleon potential [2], the Tucson-Melbourne [3] three-body force, and the Coulomb potential for various momentum transfers. The results are compared with available data.     

Threshold 3He and 3H Transverse Electron Scattering Response Functions

The threshold transverse response functions R _T (q, ω) for ³He and ³H are calculated using the AV18 nucleon–nucleon potential, the UrbanaIX three-body force, and the Coulomb potential. Final states are completely taken into account via the Lorentz integral transform technique. Consistent two-body π- and ρ-meson exchange currents as deduced using the Arenhövel-Schwamb technique are included. The convergence of the method is shown and a comparison of the corresponding MEC contribution is made to that of a consistent MEC for the meson theoretical r-space BonnA potential. The response R _T is calculated in the threshold region at q = 174, 324, and 487 MeV/c and compared with available data. The strong MEC contributions in the threshold region are nicely confirmed by the data at q = 324 and 487 MeV/c although some differences between theoretical and experimental results remain. A comparison is also made with other calculations, where the same theoretical input is used. The agreement is generally rather good, but leaves also some space for further improvement.     

T-violation neutron experiment and polarized3He

An experimental scheme of the spin detailed balance in polarized neutron transmission through a polarized nuclear target is discussed for the T-violation test. The value of the spin detailed balance is estimated by using the data of the scattering amplitudes. The nuclear polarizations of proton,³He and¹³⁹La are discussed for the T-violation experiment.     

Time reversal violation in the nuclear interaction and p-3He scattering

Using T-violating boson-exchange interactions T-violating effects in low energy p-³ He scattering are calculated. The results are below 10^?3 even for full strong (not millistrong) T-violation in the nucleon-nucleon system. It is argued, that the smallness of the effects is not a particularity of the p-³He system but a general property of low energy processes.     

Investigation of (3He,3He)- and (3He,t)-reactions on10B,11B and13C

The³He-elastic scattering and the (³He,t)-reactions on¹⁰B,¹¹B and¹³C were studied. Excitation functions for the reactions¹⁰B(³He,t)¹⁰C and¹¹B(³He,t)¹¹C were measured at incident energies between 11 and 17 MeV. All angular distributions were taken at 14 MeV³He-energy. From an optical model analysis of the³He-elastic scattering data the parameters of the optical potentials were determined. Best fits were obtained using surface peaked potentials. The (³He,t)-reactions were interpreted in terms of a microscopic model, which, in general, gave a good account of the data. Corrections due to nonlocality effects were included in the calculations. A satisfactory agreement of the predicted and the measured cross sections required an effective nucleon-nucleon interaction of the Yukawa form (α^?1=1.2 fm). Using a Serber exchange mixture the isospindependent- and the spin-isopin-dependent strength parameters of the potential were deduced to beVτ=21.4±2.3 MeV andV _{σ τ}=19.5 ± 2.7 MeV, respectively.     

Effective Field Theory of 3He

We examine the effects of the long range Coulomb force on the three-body contact interaction in a pionless effective theory of ³He. The corresponding interaction in ³H exhibits limit-cycle behavior and we show that this is not altered by the 1/r singularity of the potential.     

The superfluidd transition temperature of a Fermi liquid: 3He and 3He4He mixtures

The superfluid transitions temperature is calculated from the microscopic theory of a Fermi liquid in terms of the Landau parameters and one unknown scale factor. Determining the latter from the observed transition in ³He leads to an estimate that the superfluid transition in ³He⁴He mixtures may be presently observable.     

Determination ofn-4He observables fromp-4He scattering data between 20 and 55 MeV

We usep-⁴He data to determinen-⁴He observables, i.e. differential cross sections and polarizations, in the energy range between 20 and 55 MeV. Comparison of our calculations with experimental values at 23 MeV shows good agreement. In addition we also present examples of polarizationsT _z,z andT _z,x .     

Interaction potentials of Hg* + He at moderate interatomic separations and the radiative decay of the Hg(63 P 2) metastable state in collisions with He atoms

By using the modified method of the Fermi pseudopotential and the effective Hamiltonian method, a multiconfiguration calculation of the potential curves is performed for the Hg(6^{1, 3} P _J ) + He and Hg(7^{1, 3} S _J ) + He interactions in the region of interatomic separations R≥5a ₀. In this calculation, the interactions of different excited configurations and the spin-orbit coupling of singlet and triplet states were taken into account. The Hg⁺ + He ion-atom interaction potential was obtained by the nonempirical configuration interaction method MRD-CI with the use of the relativistic effective core potential (RECP) for the Hg atom. Based on the calculated potential curves and the transition dipole moments, the process of radiative decay of the Hg(6³ P ₂) metastable state in collisions with He atoms is considered and the temperature dependence of the rate constant is calculated.     

Experimental Study of Photon Induced Reactions on 3He and 4He at Low Energies

Data are reported for the photodisintegration cross section of the reaction ³He(??, p)²H at ten energies between 7.0 and 16.0?MeV. Very preliminary data are presented for the reaction ⁴He(??, p)³H between 22.0 and 29.5?MeV in 0.5?MeV energy steps, and for the reaction ⁴He(??, n)³He at three energies around 28.0?MeV. High-pressure He/Xe gas scintillators served as target and detector. Our data are in better agreement with recent theoretical calculations than the majority of the existing data for all three reactions, but differ significantly from recent data taken with a mono-energetic photon beam and a time-projection chamber.     

A calculation for p-3H and n-3HeS-matrix elements

Starting from nucleon-nucleon forces containing spin-orbit and tensor parts p-³H and n-³HeS-matrix elements are calculated; all possible couplings of p-³H and n-³He channels are considered. The results are discussed and compared to a preliminary experimental phase shift analysis.