Near-Threshold Charged Pion Photoproduction from BORON-10 and BORON-11.

Differential cross sections for charged pion photoproduction from ('10)B and ('11)B have been measured at 90(DEGREES) in the lab. Measurements were made in the near threshold region (pion energies less than 50 MeV). Pions were observed with a quadrupole-dipole double focusing magnetic spectrometer at the M.I.T.-Bates linear accelerator. Measurements were made of positive pion photoproduction from ('10)B leading to the ground state of ('10)Be at pion energies of 17, 29, and 42 MeV. Measurements were also made of the same reaction leading to the first excited state of ('10)Be at pion energies of 29 and 42 MeV. Negative pion photoproduction from ('10)B leading to the ground state of ('10)C was studied at 29 MeV. Measurements of negative pion photoproduction from ('11)B leading to the ground and first excited states of ('11)C were made at 17 and 29 MeV. The ('10)B results are compared with several theoretical calculations. These calculations all use the impulse approximation with pion distortions. The various calculations use different pion production operators, pion-nucleus optical potentials, and nuclear structure inputs. There are marked discrepancies between the data and most of the calculations. Further work is necessary to determine the source of these discrepancies.