Spin correlation coefficients for neutron-proton radiative capture

We use a theoretical model for deuteron photodisintegration below the pion production threshold, which has previously been used to calculate the observables for which experimental data is available, in order to calculate the spin correlation coefficients for radiative capture of a polarized neutron beam by a polarized proton target. We give results for the coefficients whose measurement is possible in the near future and explain how such experimental results could improve our understanding of the reaction mechanism. We also comment on exciting measurements of the neutron analyzing power at very low energies.     

Analysing power for neutron-proton scattering at 14.1 MeV

The analysing power A_γ(θ) for neutron-proton scattering has been measured at 14.1 MeV for c.m. angles between 50° and 157°. A polarized neutron beam was produced by the reaction ${}^3\text{H}\text{(}\text{d}\text{, n}\text{)}{}^4\text{He}$ at 110 keV, using polarized deuterons from an atomic beam polarized ion source. Liquid and plastic scintillators were used for proton targets and the scattered particles were detected in an array of plastic scintillators. Use of the associated alpha technique, multi-parameter recording of events and off-line computer treatment led to very low backgrounds. The results differ significantly from the predictions of the phase-shift analyses of Yale IV, Livermore X and Arndt et al. We find, however, excellent agreement with the predictions of the “Paris potential” of Lacombe et al. Existing n-p analysing power results up to 30 MeV are surveyed and found to be consistent. An attempt was made to look for an isospin splitting of the triplet P-wave phase shifts.     

Measurements of the neutron-proton analyzing power in the energy range from 17 to 50 MeV

Measurements of the analyzing power A_y for neutron-proton scattering in the energy range from 17 to 50 MeV are reported. These data improve considerably the precision of the np data base in this energy range. Preliminary phase-shift analyses indicate reduced uncertainties in the np ³P(T = 1) phases and in the ³D(T = 0) phase shifts.     

Reconciling coulomb dissociation and radiative capture measurements

We calculate the energy spectrum for 8B dissociation on a Pb target to all orders in the Coulomb and nuclear fields, and show that the slope of S17(E) obtained in previous analyses of Coulomb dissociation data is too steep, due to deficiencies in the conventional first-order analysis that was used. With a more complete theory that avoids the far-field approximation and includes E2, nuclear and dynamical projectile polarization, the disagreement between indirect and direct methods for determining the S17(E) slope and the extrapolated S17(0) values is reduced significantly.     

Discrepancy between three-nucleon calculations and neutron-deuteron elastic analyzing power data at 8.5 MeV

The analyzing power A_y(θ) in neutron-deuteron elastic scattering was measured at Eⁿ = 8.5 MeV. Comparison of the data with realistic three-nucleon calculations reveals a pronounced difference at the maximum of A_y(θ), which is most likely due to either an inadequate knowledge of the ³P components of the nucleon-nucleon interaction or to three-body effects in the three-nucleon system.     

Angular distribution effect on the integrated cross section for radiative capture of 14 MeV neutrons

In the past, many reported integrated cross sections for the 14 MeV neutron radiative capture were measured at 90° relative to the neutron beam direction and multiplied by 4π, so as to obtain a measure of the angle-integrated cross sections.In such a procedure, an isotropic angular distribution of γ-rays is assumed. We calculated this distribution using the consistent direct-semi-direct model, in which the need for the model-free parameters has been eliminated. The result is that the a₁ Legendre polynomial, averaged over the bound state transitions, is practically zero (distribution is forward-backward symmetric) and that the a₂ coefficient is a smooth function of the mass number with the values between −0.4 and −0.6, indicating anisotropy of the distribution. Reported integrated cross sections are therefore for about 20% to 30% too high relative to the properly angle integrated cross sections.     

The analyzing power for neutron scattering from 9Be at 9 to 17 MeV

Time-of-flight techniques were used to measure the analyzing power for the scattering of neutrons from ⁹Be at energies from 9 to 17 MeV. Because of the high nuclear density of beryllium, particular attention was paid to finite-geometry and multiple-scattering effects. For representing the data, an unusual method of Legendre-coefficient analysis was used to establish the smooth energy dependence of both the cross section σ(θ) and the analyzing power A_y(θ). Spherical optical-model calculations were able to describe the σ(θ) and A_y(θ) data simultaneously, but only after the introduction of an imaginary spin-orbit potential W_s.o.(r). The geometry of the W_s.o.(r) term was found to be the same as that of the surface-peaked imaginary central potential. Coupledchannels calculations using a quadrupole-deformed rotational model built on the $\text{3}\text{2}{}^{\mathrm{?}}$ ground state were able to describe inelastic scattering to the $\text{5}\text{2}{}^{\mathrm{?}}$ and $\text{7}\text{2}{}^{\mathrm{?}}$ excited states, but also required a W_s.o.r potential.     

Analyzing power measurements for n-p scattering between 13.5 and 16.9 MeV

The analyzing power A_γ(θ) for neutron-proton scattering has been measured for θ = 90°(c.m.) from 13.5 to 16.9 MeV and from θ = 50° to 145°(c.m.) at 16.9 MeV. Extensive Monte Carlo calculations have been made to correct for multiple scattering effects. Overall uncertainties are about ± 0.002. All the A_γ(θ) data, but primarily those at 16.9 MeV, disagree with predictons based on the phase-shift sets which have been derived previously by way of global analyses of nucleon-nucleon scattering data. Data for the product σ(θ)A_γ(θ) have been fitted with an expansion of the form (sin θ)($\text{a}{}_0\text{+ a}{}_1\text{cos}\text{θ + a}{}_2\text{cos}{}^2\text{θ)}$. For the first time the need for a non-zero a₂ has been illustrated for energies below 20 MeV. This parameter is shown to be related to the nucleon-nucleon F-state spin-orbit phase parameter. In addition, the P, D, and F spin-orbit phase parameter values derived from the present data differ significantly from the ones based on the Yale-IV and Liver-more-X global analyses. The derived D and F spin-orbit phase parameters also differ from those obtained in the recent analysis of nucleon-nucleon scattering data by Arndt et al.     

Exclusive measurements of light fragment production at forward angles in Ne-Pb and Ne-NaF collisions at E/A=400 MeV and 800 MeV

Emission of light fragments at small angles is studied in relativistic heavy ion collisions using the Diogene plastic wall for both symmetrical and non-symmetrical target-projectile systems with 400 MeV per nucleon and 800 MeV per nucleon incident neon nuclei. Efficiency of multiplicity measurements in the small angle range for the selection of central or peripheral collisions is confirmed for asymmetric systems. Differential production cross sections of Z = 1 fragments show evidence for the existence of two emitting sources. The apparent temperature of each source is obtained from comparison with a thermodynamical model.     

Analyzing power for elasticn-d scattering at 13 MeV

The analyzing power for elasticn-d scattering was measured atE _n=13 MeV. The result is in good agreement with experimental data atE _n =12 MeV andE _n =14.1 MeV. At backward angles the data are well above the predictions of a rigorous Faddeev calculation using the Paris potential.     

Exciton model comparison of the activation and the integrated 14 MeV neutron radiative capture cross sections

The exciton model for the γ-emission was tested in its abilities to describe the radiative capture of 14 MeV neutrons over a wide scale of atomic numbers (Al-27, Sc-45, V-51, Mn-55, I-127, Pr-141, Pb-208, and Bi-209). Special attention was paid to the difference between the activation cross section and the cross section integrated over the prompt capture γ-ray spectra. Relatively good agreement of theoretical and experimental data was obtained in this case, while the spectra agree in their gross structure only for medium weight and (possibly) heavy nuclei.     

Vector and tensor analyzing powers in deuteron-proton elastic scattering atE d=70 MeV

Angular distributions of analyzing powersA _yandA _yyhave been measured ind-p elastic scattering at 70 MeV. The data are compared with Faddeev calcuiations using various tensor nucleon-nucleon interactions.     

Spin radiative corrections to the radiation probability and power in classical and quantum electrodynamics

Spin radiative effects in a one-particle sector of QED have a dual nature and can be understood with the Frenkel classical rotating-electron model. In the region of parameters under study γ_⊥² ? 1 (γ_⊥² = 1 + p_⊥²/m²) and χ ? 1 (χ = \({{\sqrt {{{\left( {e{F_{\mu v}}{p_v}} \right)}^2}} } \mathord{\left/ {\vphantom {{\sqrt {{{\left( {e{F_{\mu v}}{p_v}} \right)}^2}} } {{m^3}}}} \right. \kern-\nulldelimiterspace} {{m^3}}}\)), the imaginary part of the mass shift and radiation power contain two types of spin contributions. The contributions of the first type are related to the intrinsic magnetic moment of a fermion representing an additional source of electromagnetic radiation. The contributions of the second type have the opposite sign and are caused by a small change in the electron acceleration appearing due to the Frenkel addition to the particle mass. Contributions of the second type dominate, which explains the “wrong” sign of total spin corrections. We show that not only the sign but also the values of coefficients can be explained with specified accuracy using classical electrodynamics if corrections to the mass shift (action) and radiation power are calculated in canonical variables, i.e., for fixed velocity and momentum values, respectively. The results can be treated as a demonstration of the correspondence principle in the field of radiative spin effects, in addition to correspondence between classical and quantum theories at the tree (in the external filed) level. For a_e ≡ (g–2)/2 ? χ ? 1, equations of the Frenkel model lead to generalization of the system of Lorentz–BMT (Bargmann–Michel–Telegdi) equations taking into account the Frenkel addition to mass. Some features of experimental observations of the spin light are discussed.