H.J. Boersma

Angular and energy dependence of the polarization of D-D neutrons

Abstract The polarization of D-D neutrons has been measured for a deuteron energy of 375 keV at 10 different reaction angles between 0° and 80° (lab) and for deuteron energies of 275 keV and 450 keV at 50° (lab). The thickness of the targets was 50 keV. The experimental setup used He 4 as analyser and included α-n coincidence measurement and γ-n discrimination. Attention has been paid to the elimination of false coincidences that reduce the polarization. The maximum polarization for 375 keV is found to be −13.5% the absolute value being larger than the value of Pasma (−9%). The differential polarization contains a small sin 4ϑ contribution; Π (mb) = −(0.627 ± 0.016) sin 2 Π + (0.0.7 ± 0.014) sin 4 Π .

Rescattering effects in coherent pion production on the deuteron

We present a calculation for coherent pion production on the deuteron in which rescattering corrections are included to all orders. These rescattering contributions are computed by solving the Faddeev equations for the πNN system. The corrections turn out to be fairly unimportant in the numerical description of the cross section in the resonance region. However, the inclusion of rescattering in the multipoles for pion production on a single nucleon has a large effect on the cross section for pion production on the deuteron. We also study the effect of the neutron contribution on the observables for pion production on the deuteron.

The d-d reactions below 500 keV

Abstract The d(d, n) 3 He and d(d, p)T reactions are studied for deuteron energies below 500 keV. The semi-phenomenological model of Konopinski and Teller is criticized and shown to be applicable to at most a few hundred keV. A new, simpler and in principle quantitative description is given for these energies. The low-energy data are analysed qualitatively in the first part of the paper. The energy dependence of the cross sections and the ratio of the cross sections for both reactions can very well be described in this way. It has been rediscovered that the ratio A 2 / A 0 of anisotropy coefficients ought not to be zero at zero deuteron energy, thus the cross section not isotropic, and the data of Eliot and Theus agree now very well. Moreover the polarization of the outgoing nucleons must not necessarily vanish in the limit of zero deuteron energy. With regard to the experiments with a polarized deuteron beam it is not necessary to assume a narrow resonance at about 100 keV. A simplified quantitative calculation with Hamada and Johnston potentials gives a l = 1 contribution in the cross sections that is too small. This supports the assumption of large effects of the negative parity states of the α-particle at 21.4 (0 − ) and 22.4 (2 − ) MeV.

Coherent pion production on the deuteron spin observables

Abstract Spin observables for electro- and photoproduction of neutral pions on the deuteron are derived. The number of independent amplitudes and observables is discussed and the expression of the observables in terms of ratios of cross-section combinations is given. Besides these model-independent results, approximate symmetries in the observables are discussed. These symmetries become apparent when some simplifying assumptions are made. The latter are relevant, as the full model gives results that are in many cases close to the results for the simplified model.

Pion absorption on the deuteron

Abstract The total and differential cross sections for the absorption of positive pions on deuterons have been calculated for pion kinetic energies between 3 and 220 MeV. The model is based on perturbation theory and includes the backward-moving pion. We varied several parts of the dynamical input, like the πN T -matrix and the absorption formfactor, and studied the effect of relativistic definitions of the relative momentum and of the choice of subsystem energies. Because of positive interference, the contribution of the backward-moving pion doubles the cross sections. The definition of the relativistic relative momentum according to Aaron, Amado and Young is to be preferred over that of Wightman and Garding. Also the off-shell behaviour of the πN interactions and the choice of subsystem energies influence the cross sections significantly. We need rather low values for the cutoff at the absorption vertex (0.4–0.5 GeV/ c ) in order to fit the experimental data.

Model dependence of the Coulomb-corrected p-p scattering length

Abstract It is shown that the requirement of a fixed intermediate-range 1 S 0 proton-proton interaction considerably reduces the model dependence of the Coulomb-corrected p-p scattering length. A possible relation with the off-shell effective range parameter is discussed.

A calculation of π-3He elastic scattering at low energies employing microscopic 3He-wave functions

Abstract We have calculated the differential cross sections and analyzing power for the elastic scattering of pions from 3 He at incident pion energies of 20, 25, 30, 35, 45 and 65 MeV. For this purpose we have used a first-order optical potential, constructed from a microscopic (theoretical) 3 He wave function. We took the Fermi motion into account in an exact way by calculating the complete Fermi integral. We have used different forms for the pion-nucleon interaction. We took the effect of true absorption into account via a nuclear density-squared potential, and we add the Coulomb potential to the nuclear optical potential according to the method of Vincent and Phatak. We made a detailed comparison with the model of Landau and Thomas. Our main conclusions are: (i) the factorization method is inadequate, (ii) the results are sensitive with respect to the off-shell pion-nucleon T -matrix, (iii) the density-squared absorption model, though giving good agreement with measurements, does not allow a meaningful physical interpretation of the parameter values.

Some approximate symmetries of spin observables in elastic scattering of pions off deuterium

Abstract A number of approximate relations between polarization observables in elastic pion—deuteron scattering below 300 MeV is derived. They shed some light on the degree to which experimental data can be used obtain information on the dynamics of the process.

Realistic non-local potentials from inverse scattering theory for the3S1−3D1nucleon-nucleon interaction

Abstract Rank-three and -four separable 3 S 1 − 3 D 1 potentials have been constructed which reproduce the experimental phase shifts and a realistic deuteron wave function. The off-shell behaviour has been investigated and triton binding energies were calculated.

Pion absorption in the deuteron

Pion absorption in the deuteron is mainly sensitive to the absorption form factor, the propagator of the rescattered pion and the off-shell behaviour of the pion-nucleon interaction. Current ideas about them are difficult to reconcile with existing experimental data.