Photospallation yields /Bremsstrahlung (100 Me V, 200 Me V) / 13 3 Cs and 13 * La targets /Isotopic and charge dispersions /Rudstam formula /Isomeric yield ratios Abstract Spallation yields relative to the 1 " Au yield from 1 " Au (γ, n) of 26 to 46 nuclides of Sb, Te, I, Xe, Cs and/or Ba and La from 133 Cs and ,3 'La targets irradiated with bremsstrahlungs of end energies of 100 MeV and 200 MeV were radiochemical^ determined. The isomeric yield ratios for 13 2 La and 131 Ba from the ( 13 'La + 100MeV-y), '"La, 131 Ba, ,21 Te and "'Tefrom the C 3 ' La + 200 MeV-τ), and 120 I, 121 Te and "'Tefrom the( 133 Cs + 200 MeV-7) were also determined. The isotopic yields from the (y,yn) reactions decrease exponentially with increase ofy up to 5, and show no dependence on energy and targets studied, indicating that the reactions of a few neutron emissions occur at energies lower than 100 MeV. When the product yields from the (γ, xpyn) reactions were plotted against (x+y) for each χ (isotopic distribution), a regular variation of the Gaussian distributions, typical of nuclear spallation, was observed. Isobaric mass distributions and charge dispersions were deduced to extract characteristic features of these reactions. The isobaric distributions due only to photons of 100 MeV ~ 200 MeV, which were obtained by subtracting the 100 MeV-yields from the 200 MeV-yields, are very close to a symmetric one peaking at about 8 amu from the target masses. Nuclear charges are also dispersed symmetrically, with most probable N/Z p of about 1.3 replaced by about 1 amu to the neutron-deficient side from the beta stability valley in all the cases studied. Parameters included in RUDSTAM's semiempirical formula were examined by comparing with the observed yield curves. The Ρ values of 0.45 and 0.65, chosen for a better fit to the 200 MeV data on 133 Cs and 13 ' La, respectively, were larger than the predictions reported in the literature. The magic number effects of 1 " La may explain the target-differences in mass distributions.
