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

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

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

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

Fighting fit: thermal plasticity of metabolic function and fighting success in the crayfish Cherax destructor

1. We examined the effect of thermal acclimation on fighting success and underlying performance traits in the crayfish Cherax destructor. We tested the hypothesis that animals will be more successful when fighting at their acclimation temperature than at a colder or warmer temperature, and that changes in metabolic capacity underlie differences in behavioural performance. 2. Thermal acclimation (to 20 degrees C and to 30 degrees C) had a significant effect on behavioural contests, and the likelihood of winning was significantly greater when individuals fought at their acclimation temperature against an individual from an alternate acclimation temperature. 3. The ratio of ADP stimulated respiration to proton leak (respiratory control ratio) of isolated mitochondria increased significantly in chelae muscle of the cold-acclimated group, and differences in respiratory control ratio between winners and losers were significantly correlated with the outcome of agonistic encounters. However, acclimation did not affect tall muscle mitochondria or the activity of pyruvate kinase in either chelae or tail muscle. 4. The force produced by closing chelae was thermally insensitive within acclimation groups, and there were no significant differences between acclimation treatments. None the less, differences in chelae width between contestants were significantly correlated with the outcome of agonistic encounters, but this perceived resource holding power did not reflect the actual power of force production. 5. Thermal acclimation in C destructor has beneficial consequences for dominance and competitive ability, and the success of cold acclimated animals at the cold temperatures can be at least partly explained by concomitant up-regulation of oxidative ATP production capacity