Pion exchange currents and nuclear charge form factors

The effect of the pion exchange current due to the Born term in the photoproduction amplitude on the charge form factors and distributions of 4He, 16O and 40Ca is calculated in the simple harmonic oscillator shell model. The exchange current contribution is most notable in the case of the α-particle while it is rather unimportant in 16O and 40Ca. The contribution to the nuclear mean square radius is small (approximately 0.03 fm2) and roughly independent of the mass number. (Auth.)