On the determination of isospin-0 nucleon-nucleon elastic-scattering amplitudes

At angles and energies where the isospin-1 ($\mathrm{pp}$) nucleon-nucleon elastic-scattering amplitudes are known, a considerable amount of information on the isospin-1 nucleon-nucleon amplitudes can be obtained from $\mathrm{np}$ spin-parameter measurements with polarized neutron beam and polarized proton targets. Data at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}$ and $\pi -{\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}$ can be combined to give pure isospin-0 spin parameters and quantities which are expressible as products of isospin-0 and isospin-1 amplitudes. This information is summarized in preparation for the analysis of such data from LAMPF and for the planning of similar experiments at other accelerators. The special case of the isospin-0 amplitudes at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=90\mathrm{}$° is also considered, and a number of consistency checks for such data are derived.