Neutron-proton Total Cross Section Research Articles

Measurements of energy behaviour of spin-dependentnp—observables over 1.2–3.7 GeV energy region Dubna “Delta-Sigma” Experiment

New accurate data on the neutron-proton spin-dependent total cross section difference ΔσL(np) at the neutron beam kinetic energies 1.4, 1.7, 1.9 and 2.0 GeV are presented. A number of physical and methodical results on investigation of an elasticnp→pn charge exchange process over a few GeV region are also presented. Measurements were carried out at the Synchrophasotron and Nuclotron of the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research.

Double polarized neutron-proton scattering and nucleon-nucleon tensor force: An alternative analysis

Previous neutron-proton total cross-section difference measurements $\ensuremath{\Delta}{\ensuremath{\sigma}}_{L}$ and $\ensuremath{\Delta}{\ensuremath{\sigma}}_{T}$ between ${E}_{n}=7.43$ and 17.1 MeV have been analyzed in a new way that reduces experimental systematic uncertainties. The results obtained for the ${}^{3}{S}_{1}{\ensuremath{-}}^{3}{D}_{1}$ mixing parameter ${\ensuremath{\epsilon}}_{1}$ are very similar to the published values, substantiating the previous conclusion that the nucleon-nucleon tensor force at low energies is stronger than predicted by the Nijmegen partial-wave analysis and, therefore, by all the recent high-precision nucleon-nucleon potential models as well.

Low-energyNNtensor force fromn→−p→scattering: Results of an accurate experimental approach

The spin-dependent neutron-proton total cross-section differences $\ensuremath{\Delta}{\ensuremath{\sigma}}_{L}$ and $\ensuremath{\Delta}{\ensuremath{\sigma}}_{T}$ have been measured between ${E}_{n}=5$ and 20 MeV in longitudinal and transverse nucleon spin orientations. From these data the ${}^{3}{S}_{1}{\ensuremath{-}}^{3}{D}_{1}$ mixing parameter ${\ensuremath{\varepsilon}}_{1},$ which characterizes the nucleon-nucleon tensor force at low and intermediate energies, was determined in a model-insensitive way. In combination with measurements at higher energies, our values for ${\ensuremath{\varepsilon}}_{1}$ support a nucleon-nucleon tensor interaction that is stronger than predicted by all modern high-precision nucleon-nucleon potential models and phase-shift analyses.

Measurements of the np total cross section difference $\Delta \sigma_L$ at 1.59, 1.79 and 2.20 GeV

New results of the neutron-proton spin-dependent total cross section difference $\Delta\sigma_L(np)$ at the neutron beam kinetic energies 1.59, 1.79 and 2.20 GeV are presented. Measurements were performed at the Synchrophasotron of the Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna. A quasi-monochromatic neutron beam was produced by break-up of extracted polarized deuterons. Neutrons were transmitted through a large polarized proton target. Measurements were performed either with a parallel or an antiparallel beam and target polarizations, both oriented along the beam momentum. The results at the two higher energies were measured with two opposite beam and target polarization directions. Only one target polarization direction was available at 1.59 GeV. The present measurements agree well with existing data. A fast decrease of the $-\Delta\sigma_L(np)$ values with increasing energy above 1.1 GeV was confirmed. The new results are also compared with model predictions and with phase shift analysis fits. The $\Delta\sigma_L$ quantities for isosinglet state I=0, deduced from the measured $\Delta\sigma_L(np)$ values and known $\Delta\sigma_L(pp)$ data, are given.

Measurements of the neutron-proton total cross section difference Δσ p (np) at 1.59, 1.79 and 2.20 GeVat 1.59, 1.79 and 2.20 GeV

New results for the np spin-dependent total cross section difference Δσp(np) at neutron beam kinetic energies of 1.59, 1.79 and 2.20 GeV are presented. Measurements of the Δσp(np) energy dependence were carried out at the Synchrophasotron of the Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna. The values of ΔσL were measured as a difference between the np total cross sections for parallel and antiparallel beam and target polarizations, both oriented along the beam momentum. A fast decrease of Δσp(np) with increasing energy above 1.1 GeV, as it was first seen from our previous data, was confirmed. The new results are also compared with model predictions and with the phase shift analysis fits. The ΔσL quantities for isosinglet state I=0, deduced from the measured values of Δσp(np) and known Δσp(pp) data, are given.

Double Polarized Neutron-Proton Scattering and Meson-Exchange Nucleon-Nucleon Potential Models

We report on polarized beam--polarized target measurements of the spin-dependent neutron-proton total cross-section differences in longitudinal and transverse geometries ( $\ensuremath{\Delta}{\ensuremath{\sigma}}_{L}$ and $\ensuremath{\Delta}{\ensuremath{\sigma}}_{T}$, respectively) between ${E}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5$ and 20 MeV. Single-parameter phase-shift analyses were performed to extract the phase-shift mixing parameter ${\ensuremath{\varepsilon}}_{1}$, which characterizes the strength of the nucleon-nucleon tensor interaction at low energies. Consistent with the trend of previous determinations at ${E}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}25$ and 50 MeV, our values for ${\ensuremath{\varepsilon}}_{1}$ imply a stronger tensor force than predicted by meson-exchange nucleon-nucleon potential models and nucleon-nucleon phase-shift analyses.

Measurement of the Neutron-Proton Differential Cross Section at 14.1 MeV

A new measurement of the differential cross section for neutron-proton scattering was performed at a neutron energy of 14.1 MeV. The neutrons were scattered from a polyethylene foil and the associated recoil protons were observed. Data were taken at 6 angles between 89.7° and 155.7° in the centre-of-mass system. Extensive Monte-Carlo simulations were performed in order to optimize the experimental setup and to reduce the influence of systematical errors. The data were normalized to the well-known neutron-proton total cross section. The overall uncertainty is about ±2%. The data are in excellent agreement with the prediction of the multi-energy phase shift analysis SM94 of Arndt and coworkers.

Total cross sections, elastic scattering observables and direct reconstruction of scattering matrix in np Interactions between 0.8 and 1.1 GeV at SATURNE II

Neutron-proton total cross section differences with the beam and target polarizations orientated either transversally or longitudinally with respect to the beam direction, as well as 11 spin dependent elastic scattering observables measured at SATURNE II as a function of energy and angle are presented. A major part of results was measured using the quasimonoenergetic polarized neutron beam and/or the polarized proton target. A small part of data was obtained using a polarized deuteron beam considered as a beam of quasifree neutrons and protons. The present paper represents a review of measured observables. Several sets of present data are compared with results obtained in other laboratories below 0.8 GeV. Imaginary parts of spin dependent forward amplitudes for np scattering and for the isospin stateI=0 were determined. First direct reconstruction of the np scattering matrix at 0.84 GeV is shown.

Measurement of the longitudinal spin-dependent neutron-proton total cross-section difference Delta sigma L(np) between 500 and 800 MeV.

A measurement of \ensuremath{\Delta}${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}$(np), the difference between neutron-proton total cross sections for pure longitudinal spin states, is described. Data were taken at LAMPF for five neutron beam kinetic energies: 484, 568, 634, 720, and 788 MeV. The statistical errors are in the range of 0.64--1.35 mb. Various sources of systematic effects were investigated and are described. Overall systematic errors are estimated to be on the order of 0.5 mb and include an estimate for the uncertainty in the neutron beam polarization. The \ensuremath{\Delta}${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}$ results are consistent with previous results from PSI and Saclay. These data, when combined with other results and fitted to a Breit-Wigner curve, are consistent with an elastic I=0 resonance with mass 2214\ifmmode\pm\else\textpm\fi{}15 (stat) \ifmmode\pm\else\textpm\fi{}6 (syst) MeV and width 75\ifmmode\pm\else\textpm\fi{}21\ifmmode\pm\else\textpm\fi{}12 MeV. Because of a lack of \ensuremath{\Delta}${\mathrm{\ensuremath{\sigma}}}_{\mathit{T}}$(np) data between 500 and 800 MeV, it is not possible to differentiate between a singlet or coupled-triplet partial wave being responsible.

Spin-dependent neutron-proton total cross section differences ΔσL and ΔσT from 140 to 590 MeV

A polarized neutron beam at PSI has been used to measure the spin-dependent neutron-proton total cross sections Δσ L and Δσ T from 140 to 590 MeV. The results are compared with recent phase-shift calculations.

Energy dependence of the neutron-proton total cross section differences Δσ T and Δσ L between 0.31 and 1.1 GeV

Final results for total cross section differences Δσ T and Δσ L measured with a polarized neutron beam transmitted through a polarized proton target are presented. Measurements were carried out at SATURNE II, at 11 energies between 0.63 and 1.1 GeV for Δσ T and at 9 energies between 0.312 and 1.1 GeV for Δσ L. The results are compared with measurements at PSI and LAMPF as well as with Δσ L data points deduced from p-d and p-p transmission experiments at the ANL-ZGS. The present results together with the corresponding pp data allow to determine two of the three imaginary parts of forward scattering amplitudes for isospin I = 0.

Measurements of ΔσL (np) between 500 and 800 MeV

A measurement of Δσ L (np), the difference between neutron-proton total cross sections in pure longitudinal spin states, is described. Data were taken for five energies between 500 and 800 MeV, with statistical errors of ≈ 1.5 mb and an estimated normalization error of 6%. The data, combined with other results, show some evidence for an elastic I=0 spin-singlet resonance with mass ∼ 2213 MeV and width ∼ 74 MeV, or a coupled-triplet resonance with similar mass and width.

Measurements of the total cross section differences ΔσL(np) and ΔσT(np) in the energy range from 140 to 590 MeV

At PSI a polarized neutron beam facility has been set up and was used to measure neutron-proton total cross section differences Δσ L and Δσ T in the energy range from 140 to 590 MeV.

Measurement of the spin dependent neutron-proton total cross section differences ΔσT and ΔσL between 0.63 and 1.08 GeV

We present first measurements of total cross section differences Δσ T and Δσ L for a polarized neutron beam transmitted through a polarized proton target. Measurements were carried out at SATURNE II, at 0.63, 0.88, 0.98 and 1.08 GeV. The results are compared with Δσ L data points deduced from p-d and p-p transmission experiments, and with phase shift analyses predictions. The present results together with the corresponding pp data yield two of the three spin dependent forward scattering amplitudes for isospin I=0.

Neutron-proton total cross sections between 120 and 580 MeV

Neutron-proton total cross sections have been measured in the energy range from 120 MeV to 580 MeV in steps of 20 MeV. The transmission technique was applied in “good geometry”. Cyclohexane (C 6H 12) was used as the absorber target together with a graphite absorber of corresponding thickness. The results agree extremely well with a recent measurement from LAMPF and disagree with older measurements above 200 MeV by up to 6%.

Measurement of the neutron-proton total cross section in the 25-75-MeV range.

The neutron-proton total cross section has been measured at 27.1, 39, 52.6, 62.7, and 72.7 MeV, with an error less than 1%. Our high precision data are in good agreement with some of the previous measurements.

Measurement of the neutron-proton total cross section at 132 eV

The neutron-proton scattering cross section at zero (${\ensuremath{\sigma}}_{0}$), which is an important experimental parameter in the analysis of low energy $np$ data, has been accurately redetermined by transmission measurements at 132 eV neutron energy on ${\mathrm{H}}_{2}$O, ${\mathrm{C}}_{6}$${\mathrm{H}}_{6}$, C${\mathrm{H}}_{3}$OH, and ${\mathrm{C}}_{7}$${\mathrm{H}}_{8}$. We obtain the total cross sections per molecule (132 eV) 44.731 \ifmmode\pm\else\textpm\fi{} 0.027, 151.40 \ifmmode\pm\else\textpm\fi{} 0.10, 90.37 \ifmmode\pm\else\textpm\fi{} 0.08, and 197.20 \ifmmode\pm\else\textpm\fi{} 0.34 b, respectively. To evaluate ${\ensuremath{\sigma}}_{0}$ we subtract the well-known cross sections of carbon and oxygen, and correct for the small contributions (0.1%) of capture, molecular binding, effective range, and deuterium. Combining all known errors from the experimental and evaluation procedure, we find ${\ensuremath{\sigma}}_{0}=20.491\ifmmode\pm\else\textpm\fi{}0.014$ b. This is 0.27%, or 2.4 standard errors, above the best previous measurement by Houk, and \ensuremath{\sim}0.6% above the mean of former data. Our result of ${\ensuremath{\sigma}}_{0}$ implies changes in the $np$ effective-range parameters towards higher values, by about twice the present standard errors in ${a}_{s}$, ${a}_{t}$, and ${r}_{0t}$ and 1 standard error in ${r}_{0s}$.NUCLEAR REACTIONS $^{1}\mathrm{H}(n, n)$, $E=132$ eV; measured ${\ensuremath{\sigma}}_{T}$. Cobalt-resonance neutron beam, targets ${\mathrm{H}}_{2}$O, ${\mathrm{C}}_{6}$${\mathrm{H}}_{6}$, C${\mathrm{H}}_{3}$OH, ${\mathrm{C}}_{7}$${\mathrm{H}}_{8}$.

Neutron-Proton Total Cross Sections from 30 to 280 GeV/c

Neutron-Proton Total Cross Sections from 30 to 280 GeV/<i>c</i>

Neutron-Proton Scattering Cross Section at a Few Electron Volts and Charge Independence

We have measured the neutron-proton total cross section in hydrogen gas at 0\ifmmode^\circ\else\textdegree\fi{}C between 0.3- and 400-eV lab energy to help improve the data for computing the $n\ensuremath{-}p$ singlet effective range ${r}_{s}$. To obtain the free $n\ensuremath{-}p$ scattering cross section at "zero" energy, we subtract the capture-cross-section, effective-range, and molecular-binding contributions from the total cross section. We used the asymptotic "MTV" theory of molecular binding due to Messiah, which limits our final analysis to the range 6.02 to 329 eV. From these data we obtain 20.436 \ifmmode\pm\else\textpm\fi{} 0.023 b for the free $n\ensuremath{-}p$ scattering cross section. Using this number, the coherent-scattering-length measurements by Koester, a model due to Lomon and Feshbach for the triplet and singlet shape parameters, and the $n\ensuremath{-}p$ cross section in the MeV range due to Engelke et al., we obtain ${r}_{s}=2.56\ifmmode\pm\else\textpm\fi{}0.05$ F, 0.09 F higher than the former value. Adopting an energy scale due to Davis and Barschall for the higher-energy data raises ${r}_{s}$ to 2.74 F, which is in close agreement with the value 2.70 F predicted by the charge-independence hypothesis. A measurement of the neutron-carbon cross section, formerly related to this problem, is also discussed.

Precise Measurement of Neutron-Proton Total Cross Section from 25 to 60 MeV

Precise Measurement of Neutron-Proton Total Cross Section from 25 to 60 MeV