S.B. Herdade

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.

Formalism and applications of electrofission and photofission fragment angular distributions

Abstract A formalism for the joint analysis of angular distributions of electro- and photofission fragments is presented, utilizing the vitual-photon spectrum technique in DWBA. This formalism is applied to the study of angular distributions for the electrofission of 238 U, measured near the fission barrier, to obtain information about the low-lying levels ( J π , K ) of the transition nucleus. The (2 + , 0), (1 − , 0), and (1 − , 1) levels, previously detected in photofission experiments, were confirmed. Evidences of a significant contributions of (1 + , 1), (2 + , 1)and (2 + , 2) levels are also presented.

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.