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We have performed the coincidence experiments (..cap alpha..,..cap alpha..'f) and (..cap alpha..,..cap alpha..'nf) on /sup 238/U for a beam energy E/sub ..cap alpha../ = 120 MeV and for ..cap alpha..-scattering angles theta/sub ..cap alpha..'/ = 9/sup 0/, 15/sup 0/, and 17/sup 0/. The 9/sup 0/ and 17/sup 0/ data correspond to maxima in the angular distribution for the isoscalar giant quadrupole resonance, whereas the 15/sup 0/ data lie close to a minimum. Using a set of fission counters which covered roughly 80% of 4..pi.., we were able to reject neutrons associated with fission in the (..cap alpha..,..cap alpha..'n) spectrum. We present a first look at these spectra. 9 refs., 3 figs.

We have measured the coincidence cross sections /sup 238/U(e,e'f) at three values of momentum transfer (qroughly-equal0.26, 0.40, and 0.55 fm/sup -1/) over the range from 5 to 23 MeV in excitation energy; these values of q correspond approximately to the first maxima of the electric dipole, quadrupole/monopole, and octupole form factors, respectively. The angular distribution of fission fragments is peaked along the direction of q near fission threshold, indicating the dominance of K -- 0 states, but becomes isotropic above 10 MeV. We have integrated our cross sections over fission angle and compared them to recent calculations of multipole strength derived in the quasiparticle random phase approximation. Using model-dependent form factors generated from the Tassie model and the quasiparticle random phase approximation, we have extracted strength functions for the lowest electric multipoles. The deduced E1 strength agrees well with photofission results for reasonable choices of the model form factors. The E2/E0 distribution displays resonant structures at 10 and 13 MeV which agree in position with the collective E2 and E0 strength, respectively, predicted in the quasiparticle random phase approximation. If we make such an assignment for the multipolarity of these two structures, the observed E0 strength agrees with the theoreticalmore » prediction, whereas the E2 strength is low by a factor of 2-3. Higher order multipoles also contribute substantially to the cross section at our highest value of q.« less

Inclusive-electrofission cross sections for 238U have been measured by simultaneous detection of fission fragments and inelastically scattered electrons for incident-electron energies Ee=47.6, 80.3, 81.6, 118.4, and 119.1 MeV. Although our cross sections for Ee>80 MeV are significantly lower than all previously reported values, they can be accounted for by using virtual-photon spectra which include nuclear-size corrections.

The study of electrons scattered inelastically from the deuteron has been extended to 600 Mev. Data at 500 Mev were reported in an earlier paper. Results are presented for seven scattering angles between 45\ifmmode^\circ\else\textdegree\fi{} and 135\ifmmode^\circ\else\textdegree\fi{}. A comparison of the deuteron's cross section at these angles with the corresponding free proton cross sections permits a determination of the form factor associated with the magnetic moment distribution of the neutron. Two different methods of analyzing the data are described, and the rms radius of the neutron for an exponential density distribution of the magnetic cloud can be shown to lie between the limits of 0.75\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm and 0.95\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm. The rms radius of the neutron may be taken to be (0.80\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm and is very close to the value found for an exponential model of the magnetic cloud in the proton.

Data on elastic electron-deuteron scattering is obtained using a two-spectrometer coincidence-detection technique. Preliminary analysis of the data has been compared with an impulse approximation theory and has enabled the investigation of possible meson-exchange and/or relativistic effects. The measurements were made using a 1.2 cm thick liquid deuterium target and two 180 degree N=1/2, double-focusing magnetic spectrometers. Deuterons were deflected by a 72-inch, 100 MeV/c spectrometer and detected by a six-channel ladder of plastic scintillators. Electrons were deflected by a 36-inch, 550 MeV/c spectrometer and detected by a similar five-channel ladder with a liquid Cerenkov backing counter. The solid angle was defined by the 36-inch spectrometer. By demanding a coincidence between counts from each spectrometer, background events from competing inelastic processes were eliminated. De3ayed accidental coincidence rates were monitored. (Author)

Measurements are reported of the inelastic scattering of electrons from the mirror nuclei of tritium and helium - 3. The ratio of the quasi-elastic electron-tritium and electron-helium -3 cross sections was measured to a precision of about 3% for values of the square of the four-momentum transfer, equal to 2.5 and 4.6/F sq. Detailed measurements of the shape of the entire inelastic spectra and estimates of the total inelastic cross sections were made. While these data are primarily intended to furnish additional experimental information which will be of use in determining the structure of the three-body nuclei, it is also pointed out that such data are a possible source of information on the structure of the neutron. (Author)

High-energy electron scattering measurements have demonstrated clearly the existence of deviations from point-nucleon scattering laws. The results obtained in the proton and neutron investigations have been interpreted as evidence of the finite sizes of the nucleons. The results already established as well as some of the most recent findings of the electron-scattering method are summarized. A brief account of the significance of the observed deviations from point-nucleon scattering is presented. (W.D.M.)

Electron scattering from the bound neutron and proton in the deuteron has been studied at various scattering angles between 75\ifmmode^\circ\else\textdegree\fi{} and 135\ifmmode^\circ\else\textdegree\fi{} for 500-Mev and 600-Mev electrons. A comparison of these scattering cross sections with those of the free proton permits a determination of the density distribution of the magnetic cloud around the neutron. By using theories developed by Jankus and Blankenbecler, the root-mean-square radius of the neutron is shown to lie between the limits 0.80\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm and 0.90\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm. The choice between these radii depends on whether the deuteron total cross sections or differential (peak) cross sections are compared with the protonic scattering cross section. Since presently available theory has not yet developed sufficiently to decide definitely between these possibilities, the root-mean-square size may be taken to be (0.85\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm with small error. The neutron's magnetic cloud clearly does not have the small size obtained by measurement of its charge cloud from experiments on the neutron-electron interaction, and this anomaly challenges the present concepts of nucleon size.

The long-standing discrepancies between theory and experiment in the magnetic elastic and inelastic scattering of electrons from the deuteron at high momentum transfer are reexamined. It is concluded that the predictions using most deuteron models agree with the elastic scattering data if one employs the presently accepted dipole fit (with scaling) for the proton and neutron form factors. A second conclusion is that the inelastic scattering to the $^{1}S_{0}$ state is not affected by small changes in the nucleon form factors, but is completely dominated by dynamic effects such as those due to meson-exchange diagrams.

The electromagnetic form factors of the neutron have been measured in the ${q}^{2}$ range from 1.0 to 30.0 ${\mathrm{F}}^{\ensuremath{-}2}$. It is found that for values of ${q}^{2}$ greater than about 6.0 ${\mathrm{F}}^{\ensuremath{-}2}$ the square of the neutron's charge form factor ${({G}_{\mathrm{En}})}^{2}$ is consistent with zero to within an error of the order of 5% in the existing theoretical cross section. For values of ${q}^{2}$ less than 6.0 ${\mathrm{F}}^{\ensuremath{-}2}$ it is concluded that meaningful values of the neutron form factors cannot be given until the necessary corrections to the theory are better understood. The present results on the neutron form factors are combined with recent measurements of the proton form factors to provide experimental determinations of the isotopic nucleon form factors. It is found that the $\ensuremath{\omega}$ and $\ensuremath{\phi}$ mesons provide a good approximation to the observed isoscalar form factors but that it is difficult to understand the behavior of the isovector form factors in terms of the $\ensuremath{\rho}$ meson alone.

The authors propose to measure the inclusive deep inelastic electron-nucleon scattering cross sections on hydrogen and deuterium. Cross sections will be measured in the range of momentum transfers Q{sub min}{sup 2} = 0.160 (GeV/c){sup 2} and Q{sub max}{sup 2} = 160.0 (GeV/c){sup 2}, in the range of recoil hadronic mass squared of W{sub min}{sup 2} = 2 GeV{sup 2} and W{sub max}{sup 2} = 450 GeV{sup 2}. The electromagnetic structure functions, {nu}W{sub 2}(Q{sup 2},{nu}) and W{sub 1}(Q{sup 2},{nu}), of both protons and neutrons will be measured and separated by well-known methods, in the highest possible unexplored FERMILAB kinematical regions. The high intensity Proton-West superconducting beam will be used to yield an electron beam of high purity, based on a synchrotron radiation compensated tuning technique. The electron beam will be used at 150 GeV (5 x 10{sup 8} e{sup {+-}}/pulse), at 175 GeV (3.6 x 10{sup 8} e{sup {+-}}/pulse) and at 250 GeV (1 x 10{sup 8} e{sup {+-}}/pulse). The scattered electron will be detected with good acceptance, good resolution and excellent identification. The detector will be the E-192 apparatus with small additions. A simple self-calibration procedure is available, both in experiment and apparatus, removing beam-associated and target-associated background in themore » entire (Q{sup 2}, W{sup 2}) kinematical regions. Usually, interesting physics occurs where counting rates are small. This experiment will be completely trust-worthy in such regions because their apparatus provides excellent information on the tracking and identification of scattered electrons.« less

The inherent power of inelastic scattering to probe the nuclear response function in the nuclear continuum is completely exploited only in the coincident detection of decay products. The coincidence requirement effectively eliminates the strong elastic radiative tail which hitherto plagued the analysis of single arm (e,e’) experiments. Large physical backgrounds (e.g. due to multistep processes as encountered in inelastic hadron scattering) are negligible due to the dominance of single photon exchange. Thus, coincidence electron scattering is a unique tool for quantitatively testing modern calculations of the nuclear response function. We have measured 238U(e,e’f) cross sections at three values of the momentum transfer (q≊0.26, 0.40, and 0.55 fm−1, which correspond closely to the first maxima of the E1, E2/E0, and E3 form factors respectively) from below fission threshold to 23 MeV excitation energy. The angular correlations were measured at six or seven angles in each run. The data permit a clear multipo...

The purpose of the paper is to present a summary of recent developments in high energy electron physics at Stanford. The material is divided into the following topics: nucleon form factors; deuteron form factors; (coincidence studies of elastic scattering, inelastic continuum studies); nuclear physics; (Ca40, Ca44 Investigations, study of the inelastic continuum in He3, magnetic octupole moments in light nuclei); shower studies at 900 MeV.

The electron-and bremsstrahlung-induced fission cross sections of the isotopes $_{92}^{238}\mathrm{U}$, $_{83}^{209}\mathrm{Bi}$, $_{82}^{208}\mathrm{Pb}$, $_{70}^{174}\mathrm{Yb}$, and $_{62}^{154}\mathrm{Sm}$ have been measured over the energy range 60-1000 MeV. The consistency of the theoretical expressions for the bremsstrahlung spectrum and the virtual-photon spectrum associated with the electron has been tested using the experimental data. Good agreement was obtained on the assumption of $E1$ or $M1$ transitions. The photofission cross sections obtained on the basis of this procedure were analyzed in terms of the photon-interaction cross section and the fission probability. It was found that the rapid increase in the photofission cross section with increasing energy for $^{209}\mathrm{Bi}$ and the lighter isotopes is due to the normal increase in fission probability with energy, and not to the onset of $\ensuremath{\pi}$-meson photoproduction as was previously suggested. The photon-interaction cross section predicted by the quasideuteron model seems to account for all of the interaction leading to fission in these elements, even at energies above the threshold for $\ensuremath{\pi}$-meson production. In the case of $^{238}\mathrm{U}$, however, since the fission probability is approximately constant as a function of energy, the fission cross-section behavior reflects the characteristics of the total photon-interaction cross section. In the latter case it was found that the $\ensuremath{\pi}$-meson photoproduction and the quasideuteron interaction are both involved in producing excitation leading to fission. The difference between the behavior of $^{238}\mathrm{U}$ and the lighter isotopes is understood in terms of differences in fission barriers and differences in energy deposition associated with the two interaction mechanisms. The asymmetric fission of $^{238}\mathrm{U}$ at high electron or bremsstrahlung energies is also explained on this basis.

Over the past several years the Stanford superconducting linac has been evolving from an experimental accelerator towards an operational facility capable of providing a high duty cycle electron beam for users. The linac has recently been fitted with bending magnets and other transport elements to allow its beam to be accelerated several times by the same linac sections (recirculated1). At present, with one orbit of recirculation, an 84 MeV beam has been extracted. By the end of this year we expect to have a 170 MeV beam and by the end of 1978, with the completion of four orbits, the beam energy will be 280 MeV. The beam duty cycle will be between 20% and 100%, and the maximum beam current will be between 20 ?A and 100 ?A.