| Popis: |
Energy levels of 139 La were populated by Coulomb excitation with 12 MeV α-particles. Alpha particles scattered at 100°, 120° and 160° from thin 139 La 2 O 3 targets were analyzed in a magnetic spectrograph. In a complementary experiment with thick La foils de-excitation γ-rays following Coulomb excitation with 4.5 MeV protons and 4–12 MeV α-particles were studied with a 2 cm 3 and a 50 cm 3 Ge(Li) detector. Levels were found at 1218.7, 1257.2, 1421.4, 1538.7, 1578.9 and 1683.8 keV (with uncertainties of ±1 keV) in addition to the wellknown 166 keV level. Assuming electric quadrupole excitation the corresponding B (E2) values for excitation are 1.65, 0.45, 0.62, 2.6, 2.4 and 0.43 single particle units. In contrast to an earlier Coulomb excitation experiment no evidence was found for levels between 166 1218 keV. The level energies determined here agree well with those found by a variety of other techniques. Our experimental results are in satisfactory accord with several recent theoretical calculations. |
