Giant multipole resonances in the deformed fissionable nucleus 238U: breakdown of the hydrodynamical models?

The deformed, fissionable nucleus 238u was studied with inelastic scattering of 87.5 MeV electrons between 5 and 40 MeV excitation energy with inelastic momentum transfers ranging from 0.32 fm -1 to 0.58 fm -1 for an excitation energy of 15 MeV. Resonance cross sections extracted were compared with DWBA calculations using the Goldhaber-Teller, Steinwedel-Jensen, and Myers-Swiatecki models of the giant resonance. It is demonstrated that up to the first minimum of the form-factor the cross section is nearly completely determined by one parameter, the transition radius Rtr. Using the known systematics of various multipole resonances in other, non-fissionable, nuclei as a guide, it was found that the assumed ground state radius of 238u had to be enlarged by about 10% for all multipolarities, to bring the strength found in agreement with the systematics and with other experiments in 238u. In particular, while the model-independent values for position and width of the GDR agree well with photon experiments, a scaled version of the Myers-Swiatecki model had to be used to produce agreement in strength. Similarly a scaled Goldhaber-Teller model was used for the isoscalar E2 resonance at 9.9 MeV. The situation for the isovector states above the GDR, E2 and E3 (or EO) is even more complicated. It is argued that with proper caution and consideration of other available data the use of the collective models mentioned above may give valuable insight into the charge distribution of 238u at higher excitation energies

Resonant octupole strength at 13 MeVin (58)Ni and (60)Ni and the character of the 53A(-1/3) state in heavy nuclei

Inelastic electron scattering reveals a concentration of resonant E3 strength at (13.3 ± 0.2) MeV in 51Ni and (12.8 ± 0.2) MeV in 60Ni. The energy agrees closely with the 52 A- 1/ ' MeV predicted by Hamamoto for the isovector (1 hwl E3 mode on the basis of the Bohr-Mottelson self-consistent shell model, but the strength, (13 ± 1)% and (8 ± 2)% of the energy weighted sum rule, respectively, is a factor of 5 too large. This result weakens recent arguments in favor of a monopole assignment for the 53 A-i/ 3 MeV resonance found by (e,e'l in heavy nuclei.National Science FoundationNaval Postgraduate School Foundatio

The braid groups of the projective plane and the Fadell-Neuwirth short exact sequence

International audienceWe study the pure braid groups $P_n(RP^2)$ of the real projective plane $RP^2$, and in particular the possible splitting of the Fadell-Neuwirth short exact sequence $1 \to P_m(RP^2 \ {x_1,...,x_n} \to P_{n+m}(RP^2) \stackrel{p_{\ast}}{\to} P_n(RP^2) \to 1$, where $n\geq 2$ and $m\geq 1$, and $p_{\ast}$ is the homomorphism which corresponds geometrically to forgetting the last $m$ strings. This problem is equivalent to that of the existence of a section for the associated fibration $p: F_{n+m}(RP^2) \to F_n(RP^2)$ of configuration spaces. Van Buskirk proved in 1966 that $p$ and $p_{\ast}$ admit a section if $n=2$ and $m=1$. Our main result in this paper is to prove that there is no section if $n\geq 3$. As a corollary, it follows that $n=2$ and $m=1$ are the only values for which a section exists. As part of the proof, we derive a presentation of $P_n(RP^2)$: this appears to be the first time that such a presentation has been given in the literature

Isospin of the fine structure between 8 and 12 MeV in (208)Pb and its implication for the multipole assignment of the 8.9-MeV resonance

The giant-resonance region between 8 and 12 MeV measured by (e, e') in (208)Pb is disentangled into narrow lines (I,& 4 keV) and broad resonances (I,& 1800 keV). The narrow lines at 10.07, 10,60, and 11.37 MeV have an E2 angular distribution, and assumption of b, T = 1 for them explains controversial experimental results of electromagnetic and hadronic experiments. The new analysis makes an assignment for the 8.9-MeV resonance other than monopole difficult to understand.Supported in part by the National Science Foundation and the Naval Postgraduate School Research FoundationApproved for public release; distribution is unlimited

Form-Factor Ratio GE(n)/GE(p) at Low Momentum Transfers

Measurements of the ratio of the deuteron to proton electric form factors, GE(d)/GE(p), were made from elastic electron-deuteron scattering to a precision of approximately 1% for the range of momentum transfers ...Work supported by the U.S. Office of Naval Research Contract No. Nonr 225-67 (Stanford) and the Research Foundation Program of the Office of Naval Research (Monterey)

Elastic Electron Scattering from Li6 and Li7 at Low Momentum Transfer

Elastic electron scattering experiments were performed on 6Li and YLi at momentum transfers less than 1 F ~. Charge form factors are reported, and model-independent as well as model-dependent rms radii are calculated. The model-independent radii for 6Li and 7Li are 2.51 +or - 0.10 and 2.35 +or - 0.10 F, respectively

Giant multipole resonances in the deformed fissionable nucleus 238U

The deformed, fissionable nucleus 238U was studied with inelastic scattering of 87.5 MeV electrons between 5 and 40 MeV excitation energy with inelastic momentum transfers ranging from 0.32 fm ' to 0.58 fm ' for an excitation energy of 15 MeV. Resonance cross sections extracted were compared with distorted-wave Born-approximation calculations using the Goldhaber-Teller, Steinwedel-Jensen, and Myers-Swiatecki models of the giant resonance. It is demonstrated that up to the first minimum of the form factor the cross section is nearly completely determined by one parameter, the transition radius Rt„. Using the known systematics of various multipole resonances in other, nonfissionable nuclei as a guide, it was found that the assumed ground state radius of ' U had to be enlarged by about 10% for all multipolarities, to bring the strength found into agreement with the systematics and with other experiments in 238U. In particular, while the model-independent values for position and width of the giant dipole resonance agree well with photon experiments, a scaled version of the Myers-Swiatecki model had to be used to produce agreement in strength. Similarly a scaled Goldhaber-Teller model was used for the isoscalar E2 resonance at 9.9 MeV. The situation for the isovector states above the giant dipole resonance, E2, and E3 (or EO) is even more complicated. It is argued that with proper caution and consideration of other available data the use of the collective models mentioned above may give valuable insight into the charge distribution of 238U at higher excitation energies.This work was supported in part by the Naval Postgraduate School Research Foundation and the National Science FoundationApproved for public release; distribution is unlimited

Evidence for an isovector octupole resonance at 28.4 MeV and other Giant Resonances in 238U

The deformed, fissionable nucleus 238U was studied with inelastic scattering of 87.5 MeV electrons between 5 and 40 MeV excitation energy, at scattering angles of 45°, 60° 75° and 90°. Resonance cross sections extracted from the spectra were compared with DWBA calculations using the Tassie (Goldhaber-Teller) model. The results agree with the known positions, widths and cross sections of the two branches of the giant dipole resonance at Ex = 10.9 MeV and 14.0 MeV, thus confirming the validity of the evaluation method. In addition, isoscalar and isovector E2 resonances and an isovector EJ resonance were found at 9.9 MeV (r = 2.9), 21.5 MeV (r = 4.9) and 28.4 MeV (r = 8.1), exhausting 40%, 50% and 90% of the respective EWSR. Although isospin cannot be determined from (e,e'), ∆T assignments were based on microscopic and macroscopic considerations.National Science FoundationNaval Postgraduate School Research Foundatio

Cavity-coupling investigation for the PHERMEX 50 MHz rf accelerator

The PHERMEX accelerator is a three-cavity rf linac that operates at 50 MHz. Each cavity has a radius of 2.3 m and a length of 2.6 m. The accelerator produces an electron beam with a peak current of 500 A and energy of 30 MeV. The rf power is supplied by multiple 2.5-MW tetrodes feeding coaxial lines with loops in the cavity wall. To increase the fields, multiple tetrodes and coupling loops must be used in each cavity; the problems associated with multiple-loop coupling are investigated. 3 refs., 4 figs