NeutronProton Scattering Cross Section at a Few Electron Volts and Charge Independence
Abstract
We have measured the neutronproton total cross section in hydrogen gas at 0°C between 0.3 and 400eV lab energy to help improve the data for computing the np singlet effective range r_{s}. To obtain the free np scattering cross section at "zero" energy, we subtract the capturecrosssection, effectiverange, and molecularbinding 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 +/ 0.023 b for the free np scattering cross section. Using this number, the coherentscatteringlength measurements by Koester, a model due to Lomon and Feshbach for the triplet and singlet shape parameters, and the np cross section in the MeV range due to Engelke et al., we obtain r_{s}=2.56+/0.05 F, 0.09 F higher than the former value. Adopting an energy scale due to Davis and Barschall for the higherenergy data raises r_{s} to 2.74 F, which is in close agreement with the value 2.70 F predicted by the chargeindependence hypothesis. A measurement of the neutroncarbon cross section, formerly related to this problem, is also discussed.
 Publication:

Physical Review C
 Pub Date:
 May 1971
 DOI:
 10.1103/PhysRevC.3.1886
 Bibcode:
 1971PhRvC...3.1886H