Nuclear fission of neutron-deficient protactinium nuclides

Abstract

Fragment velocity, kinetic energy, mass yield, and element yield distributions in the fission of neutrondeficient Pa isotopes produced in the reactions of 16 O and 18 O on 209 Bi have been measured at incident beam energies near and above the Coulomb barriers by the time-of-flight and radiochemical methods. An asymmetric mass-division component has been observed. Measured fission cross sections were compared with the results of statistical model calculations which take into account two fission barrier heights for symmetric and asymmetric yields. The fission barrier height deduced for the asymmetric fission is found slightly lower than that for the symmetric one. The difference between the two barrier heights in the fission of the present protactinium nuclides (Nϳ135) is considerably smaller than that in the neutron-rich nuclide of 233 Pa (Nϳ142), indicating that the difference sensitively depends on the neutron number of the fissioning nuclide.

Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission

“…In the peculiar case of low-energy fission, measuring the Z of the light fragment allows to extract the nuclear charge of the heavy partner since light-charged particle evaporation of the latter is unlikely. Radiochemical and γspectroscopy [198,199,200,201] methods have been employed to determine Z of the heavy reaction product. Unfortunately, these techniques do not allow systematic investigations and the information is restricted to the isotopes of a few elements.…”

“…Two values for the initial CN excitation energy are given for fusion experiments: E * and E * (l) are, respectively, the intrinsic excitation energy without and with taking the rotational energy into account [60]. [60,61] and references therein, except a from [205], b from [198] and c from [199]. Fifth column: estimate of the Zwidth based on the UCD assumption and on the measured mass width of the fourth column, see the text.…”

Isotopic yield distributions of transfer- and fusion-induced fission from238U+12C reactions in inverse kinematics

“…Unfortunately, information on full isotopic-fragment distributions is scarce; it mainly consists of thermal neutron-induced fission of a limited number of actinides [4,5,29,34,[38][39][40][41][42], and is restricted to the light fragments, due to the low kinetic energy of fission fragments that induces important straggling and ionic charge-states fluctuations in the ionization detectors, preventing for the atomic-number identification of the heavy fragments. The isotopic distribution of the heaviest fragments can be determined with radio-chemical techniques [43,44] or β-delayed γ spectroscopy [3], but with poor precision or in a reduced range of the total production. The limitation in the investigation of the isotopic distributions of heavy fission fragments is critical for the interpretation of the role that nuclear shell structure plays in the process.…”

Complex fission phenomena

“…In binary fission, it is now better understood due to a longstanding effort of systematic analysis [17,18,19,20]. One knows three types of shape elongations: LDM (liquid drop model) governed mass symmetrical elongated shape (deformation β ≃ 1.65); mass asymmetrical deformation (β ≃ 1.53), and shell-influenced mass symmetrical deformation (β ≃ 1.43).…”