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The recoil spectrometer Lohengrin of the Institute Laue-Langevin in Grenoble was used to measure the yields of light fission fragments separated according to their mass and nuclear charge for the mass-number range 76 ⩽ A L ⩽ 93 in the cold fission regime. Neutron emission being forbidden energetically, the correlated heavy fission fragments including their kinetic energies, as well as the total excitation energy TXE of both fragments were determined by conservation laws. Close to TXE = 0, the yields seem to be strongly influenced by the level density of the fragments. In order to obtain yields for the fission into the ground-states of the two fragments, the measured yields per excitation energy interval were divided by calculated level densities for the two fragment system and extrapolated to TXE = 0. These deduced ground-state yields are influenced by the Q values and by the potential energy of the fragments at the scission configuration. The observed trends in the ground-state yields as a function of nuclear charge and mass may qualitatively be reproduced by calculated penetrabilities through the scission barrier. In these calculations, no correspondence between the calculated penetrabilities and the ground-state yields is found if calculated fragment ground-state deformations are used. There is no difference in the influence of neutron and proton pairing on the ground-state yields.

At the recoil spectrometer “Lohengrin” of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of 239 Pu were measured as a function of A , Z , the kinetic energy E and the ionic charge states q . The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even- Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd- Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data 1 ) for thermal-neutron-induced fission of 235 U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for 235 U and 239 Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances σ z 2 . for thermal-neutron fission of 235 U and 239 Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of σ z 2 is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed.

The actual situation of the research on ternary fission, mainly α-particle accompanied fission, is reviewed, with the accentuation on recent experimental and theoretical investigations. The results of multiparameter experiments are discussed in more detail, and the role of fragment deformation for a correct description of the ternary fission process is outlined.

Cross sections for elastic scattering of 40 Ar on 40 Ca have been measured at energies E lab = 191, 236 and 272 MeV employing position-sensitive detectors and the method of kinematical coincidences. The experimental data are first compared with the ordinary and the generalized Fresnel models. Only the generalized Fresnel model describes the experimental data well. An optical model analysis with a Woods-Saxon potential yields an energy independent set of parameters ( V R = −21.76 MeV, r OR = 1.37 fm, a R = 0.45 fm; W 1 = −13.69 MeV, r 01 = 1.40 fm, a 1 = 0.36 fm) very similar to the one found in 40 Ca- 40 Ca scattering at corresponding energies. Values deduced for the total reaction cross sections for the three energies are in good agreement with those predicted by the generalized Fresnel model. The data are also compared with optical model calculations with the real part of the potential replaced by various microscopically determined potentials. The proximity, Fleckner-Mosel and the Krappe-Nix-Sierk potentials like the phenomenological optical model potential reproduce the measured data fairly well over several orders of magnitude.

The yields of light fission products from thermal-neutron induced fission of 233U are measured as a function of their mass A, their nuclear charge Z, their kinetic energy E and their ionic charge state q at the recoil spectrometer Lohengrin of the Institut Laue-Langevin in Grenoble. The mass yields are determined by intercepting the fragments with an ionization chamber of high energy resolution positioned at the focal plane of the spectrometer. The nuclear charges and their yields are determined with the same ionization chamber by measuring the residual energy of fission products, selected monoenergetically by Lohengrin, behind a passive absorber made of parylene-C. The nuclear charge resolution enabled by this detector device is considerably improved to Z/dZ = 58. The nuclear charge and mass distributions summed over all ionic charge states are listed within the mass range 79 ⩽ A ⩽ 106 at 6 energies: E = 85.34, 90.41, 95.46, 100.50, 105.55 and 110.55 MeV. The energy-integrated nuclear charge and mass yields are also given. The isotonic and isotopic yields are shown. An odd-even effect in the yields is found for the protons as well as for the neutrons at all kinetic energies. The yield weighted total odd-even effect for the protons is found to be (22.1 ± 2.1)%, for the neutrons (5.4 ± 1.7)%. An odd-even effect for the protons in the mean kinetic energy is also observed. The displacement of the mean isobaric nuclear charges from the unchanged charge-density values and the variances of the isobaric nuclear-charge distributions reveal fine structures in their mass dependences.

Cross sections for strongly damped collisions of 40Ar on 40Ca have been measured at energies Elab = 191, 236 and 272 MeV. The angular distribution and energy loss of the reaction fragments as well as the charge spread of the element distribution are reported. Furthermore, the measured data are compared to the already existing 40Ca-40Ca data at similar bombarding energies. An attempt to explain the energy and angular distribution of the reaction fragments is made by applying a trajectory calculation which employs the one-body window friction as the dissipative mechanism.