On the Exchange Properties of the Neutron-Proton Interaction

Abstract

To determine the exchange properties of the neutron-proton interaction, the existing knowledge of the neutron-proton force in states of even parity, gained from the properties of the deuteron ground state and low energy scattering experiments, must be supplemented by information concerning the interaction in odd parity states, information which can be obtained only by observations on high energy neutron-proton scattering and deuteron photo-disintegration by energetic $\ensuremath{\gamma}$-rays. Calculations have been performed for three types of interactions with the purpose of testing the sensitivity of such experiments to variations of the exchange operator dependence of the interaction. These interactions are analogous, in isotopic spin dependence, to the potentials predicted by three forms of current mesotron theory: (I) "Symmetrical" (II) "Charged" (III) "Neutral." With the interaction in even parity states described by rectangular well potentials with constants adjusted to fit the binding energy and quadripole moment of the deuteron, and the cross section for slow neutron-proton scattering, each of these three potentials makes a definite prediction concerning the interaction in odd parity states. The scattering calculations were performed for a neutron energy of 15.3 Mev. The results for total cross sections and angular distributions in the center of mass system are as follows: ${(\mathrm{I}) \ensuremath{\sigma},=0.621\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}{\mathrm{cm}}^{2},\ensuremath{\sigma}(\ensuremath{\vartheta})\ensuremath{\sim}(1\ensuremath{-}0.080 cos\ensuremath{\vartheta}+0.077 {cos}^{2}\ensuremath{\vartheta})}{(\mathrm{II}) \ensuremath{\sigma},=0.666\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}{\mathrm{cm}}^{2},\ensuremath{\sigma}(\ensuremath{\vartheta})\ensuremath{\sim}(1+0.126 cos\ensuremath{\vartheta}+0.042 {cos}^{2}\ensuremath{\vartheta})}{(\mathrm{III}) \ensuremath{\sigma},=0.983\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}{\mathrm{cm}}^{2},\ensuremath{\sigma}(\ensuremath{\vartheta})\ensuremath{\sim}(1+0.932 cos\ensuremath{\vartheta}+0.457 {cos}^{2}\ensuremath{\vartheta}).}$The energy of the Li+H $\ensuremath{\gamma}$-rays ($\ensuremath{\hbar}\ensuremath{\omega}=17.5$ MeV) was adopted for the computations on photo-disintegration. The three theories under discussion predict the following electric dipole total cross sections and angular distributions ${(\mathrm{I}) \ensuremath{\sigma},=0.768\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}27}{\mathrm{cm}}^{2}, \ensuremath{\sigma}(\ensuremath{\vartheta})\ensuremath{\sim}({sin}^{2}\ensuremath{\vartheta}+0.015)}{(\mathrm{II}) \ensuremath{\sigma},=0.723\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}27}{\mathrm{cm}}^{2}, \ensuremath{\sigma}(\ensuremath{\vartheta})\ensuremath{\sim}({sin}^{2}\ensuremath{\vartheta}+0.077)}{(\mathrm{III}) \ensuremath{\sigma},=0.376\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}27}{\mathrm{cm}}^{2}, \ensuremath{\sigma}(\ensuremath{\vartheta})\ensuremath{\sim}({sin}^{2}\ensuremath{\vartheta}+0.36).}$ Calculations have also been performed for the small cross sections arising from magnetic dipole and electric quadripole absorption. The spherically symmetrical term in the electric dipole angular distribution is a consequence of the noncentral forces invoked to explain the deuteron quadripole moment. High energy photo-disintegration angular measurements thus constitute the most sensitive test of both the isotopic spin dependence of the neutron-proton interaction and the existence of noncentral forces.