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We report $^{238}\mathrm{U}(e,{e}^{\ensuremath{'}}f)$ spectra from fission threshold to 23-MeV excitation energy for three values of momentum tranfer ($q=0.26, 0.40, \mathrm{and} 0.55$ ${\mathrm{fm}}^{\ensuremath{-}1}$). The extracted strength functions for $E1$ and $\frac{E2}{E0}$ agree well with those recently calculated with the quasiparticle random-phase approximation, except that some $E2$ strength is apparently missing. $E3$ and/or higher multipoles clearly contribute a significant amount of cross section throughout the excitation region.

Measurements were made to detect differences in the velocity of propagation of $\ensuremath{\gamma}$ rays and electrons in the energy range 15-20 GeV, by using a time-of-flight technique with 1-psec sensitivity and a flight path of \ensuremath{\sim} 1 km. A relative velocity difference larger than $1\ensuremath{-}{\ensuremath{\beta}}_{e}$ (\ensuremath{\sim} 5\ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$) would imply a breakdown of special relativity. No significant difference in the velocities of light and electrons was observed to within \ensuremath{\sim} 2 parts in ${10}^{7}$.

Experimental results are presented on the scattering of 250-MeV electrons by ${\mathrm{Ca}}^{40}$, ${\mathrm{Ca}}^{42}$, ${\mathrm{Ca}}^{44}$, ${\mathrm{Ca}}^{48}$, and ${\mathrm{Ti}}^{48}$, and of 500-MeV electrons by ${\mathrm{Ca}}^{40}$ and ${\mathrm{Ca}}^{48}$. An analysis is made in terms of a phenomenological three-parameter shape, and a new, more accurate charge distribution is obtained for ${\mathrm{Ca}}^{40}$. The experiments also lead to a detailed exploration of the radial dependence of the differences in charge distributions of the various isotopes. Implications for nuclear theory are discussed. Comparison is made with the results of other electron scattering and of muonic x-ray experiments. The latter comparison permits an independent determination of an upper limit on the muon electromagnetic radius ${{〈{r}^{2}〉}_{\ensuremath{\mu}}}^{\frac{1}{2}}\ensuremath{\lesssim}0.35$ F.

The electromagnetic structure of the ${\mathrm{He}}^{3}$ nucleus has been investigated by means of high-energy electron scattering. A separation of the charge and magnetic form factors has been accomplished. The charge form-factor data extend to ${q}^{2}=20$ ${\mathrm{fm}}^{\ensuremath{-}2}$ and exhibit a diffraction minimum at ${q}^{2}=11.6$ ${\mathrm{fm}}^{\ensuremath{-}2}$; the magnetic scattering is measured to ${q}^{2}=12.5$ ${\mathrm{fm}}^{\ensuremath{-}2}$. The results are discussed in terms of models for the charge and magnetic distributions of the nucleus.

The differential scattering cross sections have been measured for electron scattering from randomly oriented and aligned Ho165 nuclei. The alignment axis was parallel to the direction of the momentum transferred to the nucleus. Incident electron energies from 160.6 MeV to 462.2 MeV were used at a fixed polar scattering angle of 36 degrees. Available theories are unable to explain the measured difference between the aligned and non-aligned cross sections. (Author)

We have measured the cross section for elastic electron scattering from ${\mathrm{He}}^{4}$ at values of ${q}^{2}$, the four-momentum transfer squared, ranging from 0.5 to 20.0 ${\mathrm{F}}^{\ensuremath{-}2}$. Previous Stanford measurements extended up to ${q}^{2}=6.2$ ${\mathrm{F}}^{\ensuremath{-}2}$ and were consistent with a Gaussian shape for the charge distribution of the ${\mathrm{He}}^{4}$ nucleus. Our results confirm the earlier data but show a deviation from the Gaussian model for ${q}^{2}g6$ ${\mathrm{F}}^{\ensuremath{-}2}$. At ${q}^{2}=10$ we observe a diffraction minimum of the scattering cross section. Among the models which have been found to fit the new data is the Fermi three-parameter charge distribution. The rms radius ${〈{r}^{2}〉}^{\frac{1}{2}}$, the half-density radius ${r}_{\frac{1}{2}}$, and the 90% to 10% skin thickness $t$ of the charge distribution have been calculated for the models which adequately fit the data. The results indicate that the surface of the ${\mathrm{He}}^{4}$ charge distribution is less diffuse than implied by the nuclear harmonic-oscillator model.

The mirror nuclei of tritium and helium-3 have been studied by the method of elastic electron scattering. Absolute cross sections have been measured for incident electron energies in the range 110-680 MeV at scattering angles lying between 40 and 135\ifmmode^\circ\else\textdegree\fi{} in this energy range. The data have been interpreted in a straightforward manner and form factors are given for the distributions of charge and magnetic moment in the two nuclei over a range of four-momentum transfer squared 1.0-8.0 ${\mathrm{F}}^{\ensuremath{-}2}$. Model-independent radii of the charge and magnetic-moment distributions are given and an attempt is made to deduce form factors describing the spatial distribution of the protons in tritium and helium-3.

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.

New information is reported on differences between the charge distributions of Ca40 and of Ca44, obtained by means of elastic scattering of 250 MeV electrons. Attention is focused, experimentally and theoretically, on the difference in scattering between the two isotopes.

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)

The absolute elastic electron-scattering cross sections of Ca/sup 40/, V/ sup 51/, Co/sup 59/ In/sup 115/ Sb/sup 121//sup / ,>s/sup 123/,and Bi/sup 209/ were measured at a number of angles at a primary electron energy of 183 Mev. The cross sections were obtained by comparison with scattering from the proton. The data were compared with the previous relative angular distributions of Hahn, Ravenhall, and Hofstadter. The present data are in closer agreement with the charge distributions found from fitting a Fermi two-parameter model to the older data than with those found from a fit of the Ford and Hill charge distributions. The absolute cross sections for Bi/sup 209/ show the least agreement: they are 35% larger than the predictions of the Fermi model and about 70% larger than the Ford and Hill model. (auth)

We have observed inelastic scattering of 183-Mev electrons through angles of 40\ifmmode^\circ\else\textdegree\fi{}-90\ifmmode^\circ\else\textdegree\fi{} in the laboratory, leading to excitation of discrete nuclear excited states in ${\mathrm{Ni}}^{58}$, ${\mathrm{Co}}^{59}$, ${\mathrm{Pb}}^{208}$, and ${\mathrm{Bi}}^{209}$. The excitation energies were below 8 Mev. Born-approximation analysis of the measured inelastic form factors was used to deduce the multipolarities $\ensuremath{\lambda}$ (when not previously known), and, by extrapolation, the transition rates for 15 corresponding gamma transitions. A number of groups of electric transitions for $\ensuremath{\lambda}=2, 3, \mathrm{and} 4$ were observed, each group having strikingly similar form factors. In all but one of these groups the ratios $G$ of the observed gamma transition rates to the single-particle predictions were greater than 15, and for some transitions from 30 to over 100. One of the groups, in cobalt and the nickels, contains the 1.33-Mev $E2$ transition to the first excited state of ${\mathrm{Ni}}^{60}$. Another group consists of fast $E3$ transitions, seen in all five nuclei, from states known as the "anomalous levels." They included the transition to the first excited state in ${\mathrm{Pb}}^{208}$ ($G=31$) and a transition in ${\mathrm{Bi}}^{209}$ identical in energy and form factor. Among three slow $E4$ transitions in cobalt and the nickels was the 2.50-Mev ${4}^{+}$\ensuremath{\rightarrow}${0}^{+}$ transition in ${\mathrm{Ni}}^{60}$. The $E4$, $E3$, and an $E2$ transition in ${\mathrm{Co}}^{59}$ identify states analogous to the ${4}^{+}$, ${3}^{\ensuremath{-}}$, and ${2}^{+}$ seen in the neighboring even-even nuclei. The last two transitions are strongly enhanced. A pair of fast 4.30-Mev $E4$ transitions was observed in ${\mathrm{Pb}}^{208}$ and ${\mathrm{Bi}}^{209}$; their speed ($G=37$) indicates they may constitute the lowest-energy configuration of 16-pole mode of excitation of the nuclear surface. Values of the collective vibrational parameters ${C}_{\ensuremath{\lambda}}$ and ${B}_{\ensuremath{\lambda}}$ and the degree to which some of the transitions exhaust ordinary sum rules support the conclusion that the inelastic scattering process is strongly exciting nuclear collective excitations. Some of the observed results are expected on the basis of the theory of collective vibrational excited states; some are the consequence of unidentified configurations.

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.)

The doubly-magic nucleus of Ca(40) has been investigated by the electron scattering technique at an incident energy of 250 MeV. The elastic scattering behavior has been resolved from the inelastic scattering and absolute data on cross sections have been obtained for both types of events. In the case of the elastic scattering the first and second diffraction features have been observed and measured. It has been possible to make a comparison of the elastic data with theoretical calculations based on a phase shift analysis for certain assumed models of the nuclear charge density distribution. The combination of such an analysis with the present data, and also with earlier data on the same nucleus, permits the determination of the radius and skin thickness of the Ca(40) nucleus with a precision greater than has been attainable heretofore. An investigation of the dependence of the density distribution on a third parameter indicates that a Fermi distribution, or models close to this type, are required to fit the experimental data. A Fermi radial charge density distribution with radius c =3.60 F, and skin thickness t = 2.50 F fits the data extremely well. (Author)

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 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.

We have studied elastic electron scattering from 4He at values of q2, the momentum transfers squared. ranging from 0.5 fm−2 to 10.0 fm−2. Among the models which have been found to fit the new data is modified Gaussian distribution with a half density radius of 1.19 fm and a skin thickness of 1.61 fm.

Distributions of electrons elastically scattered by He/sup 3/ and T are compared in order to analyze the three-body forces acting in these mirror nuclei. The charge and magnetic form factors for the nuclei are calculated. Three of these form factors are nearly equal to one another but the charge form factor of He/sup 3/ is different from the other three. (T.F.H.)

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.

Elastic electron scattering studies from isotopes of calcium are briefly summarized. A study of the inelastic level structure of Ca40 and Ca48, as well as the quasi-elastic scattering from both isotopes was initiated. Preliminary results show the probable existence of excited levels or groups of levels previously unreported from electron scattering experiments. Especially interesting is the appearence of an 'edge' in the Ca40 spectrum beginning at an excitation energy of 15.7 MeV corresponding to the threshold of the state (Ca39 + n).

The magnetic form factors of the $1p$-shell nuclei ${\mathrm{Li}}^{6}$, ${\mathrm{Li}}^{7}$, ${\mathrm{Be}}^{9}$, ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, ${\mathrm{N}}^{14}$, have been measured by high-energy electron scattering at an angle of 180\ifmmode^\circ\else\textdegree\fi{}. Incident electron energies up to 230 MeV (${q}^{2}\ensuremath{\simeq}5.2$ ${\mathrm{F}}^{\ensuremath{-}2}$) were used. The incident- and scattered-electron paths were separated by use of a uniform magnetic field. Back-ground due to charge scattering was subtracted by varying the scattering angle around 180\ifmmode^\circ\else\textdegree\fi{}. At the higher momentum transfers the scattering from those nuclei having spin $\ensuremath{\ge}\frac{3}{2}$, was dominated by the octupole moment distributions. Results are interpreted in terms of harmonic-oscillator and finite-square-well shell models. Parameters dependent only on the coupling of the angular momenta in the $1p$ shell may be obtained from the data. They show a general trend from $L\ensuremath{-}S$ coupling to $j\ensuremath{-}j$ coupling as the mass number increases, in agreement with calculations of magnetic dipole moments and energy-level schemes. The outstanding exception is ${\mathrm{Li}}^{7}$, whose form factor is accurately described by the extreme independent-particle model. ($L\ensuremath{-}S$ coupling is quite incompatible with the data.) The ${\mathrm{Li}}^{6}$ results may also be interpreted in terms of an "alpha plus deuteron" model. Numerical results for the harmonic-well strengths are obtained and compare favorably with electron-charge-scattering values. It is also possible to estimate magnetic octupole moments, where applicable, with fair accuracy, although these estimations are to a certain extent model-dependent.