0000000000007910
AUTHOR
U. Kneissl
Total photofission cross section for 238U as a substitute for the photon absorption cross section in the energy range of the first baryon resonances
Abstract The total photofission cross section σγ, F for 238U has been measured as a substitute for the total photon absorption cross section σtot in the energy range of the first baryon resonances (50⩽Eγ⩽800 MeV). The experiments were performed at the tagging facility of the new 855 MeV Mainz Microton MAMI B using monochromatic photons and a sophisticated 4π-arrangement of position sensitive fragment detectors. The measured cross section agrees in the Δ-resonance region with previous results and the so-called universal curve αtot/A. In the energy region of the D13-resonance near 710 MeV resonancelike structure could be observed as is seen for the free proton.
Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions
The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors,…
(e,e'f) Coincidence experiments on 235U and 238U
Abstract Coincidence experiments for (e, e'f) on the actinide nuclei 235 U and 238 U have been performed at the Mainz Microtron (MAMI A) concentrating on three subjects: multipole strength distributions and form factors for the lowest multipolarities, the mass split in the fission decay of various giant multipole resonances, and the separation of near barrier fission channels. Data were taken at four values of momentum transfer ( q eff ≈ 0.20, 0.28, 0.53, and 0.71 fm −1 for 238 U, q eff ≈ 0.20, 0.44, 0.57, and 0.71 fm −1 for 235 U) for excitation energies ω = 4–22 MeV. The fission fragments have been detected using the Giessen PPAC-Ball. A model-independent multipole analysis yields both fo…
Multipole strength distributions and form factors forE1,E2/E0, andE3 fromU238(e,e’f) coincidence experiments
A model-independent multipole analysis of $^{238}\mathrm{U}$(e,e'f) coincidence data, taken at four momentum transfers (0.2\ensuremath{\le}${q}_{\mathrm{eff}\mathrm{\ensuremath{\le}}0.7}$ ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$; \ensuremath{\omega}=4--22 MeV) yields both E1, E2/E0, and E3 form factors and strength distributions. The E2/E0 strength distribution in the fission channel shows two distinct bumps centered at \ensuremath{\omega}\ensuremath{\simeq}10 and 14 MeV, exhausting up to 12 MeV (19\ifmmode\pm\else\textpm\fi{}2)% of the isoscalar E2 sum rule. The extracted form factors can be described within a hydrodynamical model by use of parameters ${c}_{\mathrm{tr}/{c}_{0}=1.2}$ and …
(e,e′f)-Coincidence Experiments on Uranium Isotopes
(e,e′f)-coincidence experiments represent the most powerful tool to investigate the decay properties of giant multipole resonances, especially of the isoscalar giant quadrupole resonance (GQR), in heavy nuclei. Besides the advantages of the inelastic electron scattering, the coincidence between the fission fragments and the scattered electron causes a complete suppression of the huge radiation tail. The study of the fission decay of giant resonances in heavy nuclei provides interesting information about the coupling of the collective phenomena of fission and giant resonances. In particular the fission decay of the GQR has been subject of controversial experimental studies, using hadrons [1]…