J.D.T. Arruda-Neto

Electrofission of 234U, 236U and 238U: Angular distributions and E2 strength functions

Abstract The electrofission angular distributions for 234 U in the energy range 5.5 to 25 MeV were measured and are analyzed together with those obtained previously for 236 U and 238 U. The competition between the K = 0 and K = 1 fission channels following E2 excitation is established, showing a dominance of the K = 0 channel for near-barrier fission. The E2 fission strength functions for 234 U, 236 U and 238 U are deduced as well, and the E2 fission probabilities (at energies below the pairing gap) are estimated. A substantial concentration of E2 strength near the fission barrier is found, in good agreement with earlier photofission angular-distribution studies.

Study of the 232Th fission barrier by electron-induced fission

Abstract Fission fragment angular distributions and the electrofission cross section of 232 Th were measured in the electron energy region 4.5–7.9 MeV. Below 5.20 MeV two distinct shelves were observed in the isotropic component of the total electrofission cross section, indicating the presence of resonances in the photofission cross section at 4.55 [(2 + , 0) channel] and at 4.95 MeV [(1 − , 0) channel]. These resonances are interpreted as associated to vibrational levels in the second well of the 232 Th fission barrier. Moreover, a resonance observed at 5.65 MeV in both channels is interpreted as a signature for a vibrational level in the third well of the triple-humped fission barrier deduced for this nucleus.

Evidence for isomeric electron induced fission of 232Th

Abstract Fragment angular distributions and yields were measured for the electrofission of 232 Th in the electron energy E e range 4.54–6.64 MeV. The behaviour of the angular distribution with changing E e and the observation of an isotropic angular distribution for E e =4.54 MeV together with a shelf in the electrofission yield for E e V ∥

Study of 7Li(p, pn) and 7Li(p, 2p) reactions at 70 MeV

Abstract Differential cross sections for the reactions 7 Li( p , pn ) and 7 Li( p , 2 p ) were simultaneously measured at an incident proton energy of 70 MeV. The measured spectra were decomposed into contributions from 1 p and 1 s shells. The obtained cross sections were analyzed in the framework of the DWTA approach.

Electrofission of 237Np in the energy range 6-60 MeV

The electrofission cross section of 237Np has been measured in the energy interval from 6 to 60 MeV. By using both the virtual photon formalism and a previously measured photofission cross section, the electrofission cross section corresponding to non-electric-dipole transitions has been deduced. The analysis of this latter quantity has indicated the presence of a substantial E2 and M1 strength in the photofission of 237Np.

Observation of M1 strength in the photofission of actinide nuclei

Electrofission-fragment angular distributions for 234U, 236U and 238U in the energy range 5-7 MeV are analysed in the framework of the virtual-photon formalism, which allows the separation of the multipolar components in the fission channel. Evidence for a substantial concentration of M1 strength in the fission decay of these nuclei is found.

Non-electric-dipole photofission of 235U

The electrofission cross section for 235U has been measured from 5.8 to 22 meV. From a combined analysis of this and the photofission cross section measured previously, using the virtual-photon formalism, the photofission cross section for excitations other than E1 has been determined.

Electrofission of 233U

The electrofission cross section of 233U has been measured in the energy interval from 5.75 to 31 MeV. Making use of the photofission cross section and the virtual photon formalism, the electrofission cross section corresponding to non-electric-dipole transitions has been obtained. Assuming as well that the fission decay of 233U is statistical, the E2 photofission cross section has been calculated, from which in turn the M1 strength has been deduced.