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A study at various temperatures has been made of approximately a dozen TlBr single crystals in order to find their properties as radiation induced conduction counters. Use of alpha particle sources showed whether holes or electrons were responsible for the observed behavior. Gamma ray studies showed rudimentary spectrometric performance whereas alpha particles usually resulted in peaks of approximately 25% fwhm. Long rise times were observed in some crystals and shorter rise times in others, the variability accounting for as much as a factor of 6. The energy required to produce a free electron-hole pair was observed to be 10.3 ± 2 eV. Breakdown phenomena were observed near room temperature and are described in the text.

During a series of experiments on crystal conduction counters performed at Stanford University on thallium halide crystals, we have observed motion of both hole and electron carriers in a TlBr crystal. At a temperature near -90 /sup 0/C the hole motion produces larger pulses than electron motion. We have studied the behavior of TlBr, TlCl, and KRS-5 (40 mol % TlBr + 60 mol % TlI) crystals and examined them as possible crystal conduction detectors of ..cap alpha.. particles and ..gamma.. rays. TlBr appears to be a promising candidate for applications to nuclear physics and high-energy ..gamma..-ray physics. Modules of TlBr in ''crystal-ball'' geometry may lead to new detection possibilities. At -20 /sup 0/C space-charge accumulation in TlBr decreases to such an extent that operation at this temperature seems possible with moderate electrical gradients. In the long-neglected field of crystal conduction counters, we have potentially removed the space-charge limitation in TlBr and, allowing for both hole and electron motion, raised the possibility for spectroscopic performance of this material for ..gamma..-ray studies.

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 elastic scattering of 188-Mev electrons from gaseous targets of hydrogen and helium has been studied. Elastic profiles have been obtained at laboratory angles between 35\ifmmode^\circ\else\textdegree\fi{} and 138\ifmmode^\circ\else\textdegree\fi{}. The areas under such curves, within energy limits of \ifmmode\pm\else\textpm\fi{}1.5 Mev of the peak, have been measured and the results plotted against angle. In the case of hydrogen, a comparison has been made with the theoretical predictions of the Mott formula for elastic scattering and also with a modified Mott formula (due to Rosenbluth) taking into account both the anomalous magnetic moment of the proton and a finite size effect. The comparison shows that a finite size of the proton will account for the results and the present experiment fixes this size. The root-mean-square radii of charge and magnetic moment are each (0.74\ifmmode\pm\else\textpm\fi{}0.24)\ifmmode\times\else\texttimes\fi{}${10}^{13}$ cm. In obtaining these results it is assumed that the usual laws of electromagnetic interaction and the Coulomb law are valid at distances less than ${10}^{\ensuremath{-}13}$ cm and that the charge and moment radii are equal. In helium, large effects of the finite size of the alpha-particle are observed and the rms radius of the alpha particle is found to be (1.6\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm.

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.

Using high-resolution semiconductor detectors, a study was made of the large $K$-ionization cross sections of atoms over a wide range of atomic numbers ($Z=29\ensuremath{-}83$) and of incident electron energies ($E=150\ensuremath{-}900$ MeV). For the higher-$Z$ elements ($Zg60$), the $L$ x-ray cross sections were also measured over the incident electron energy range. Ratios of the relative intensities of various distinct lines were determined and compared to recent low-energy work. The results of the $K$-ionization experiment are compared to the recent relativistic calculations of Kolbenstvedt. The experimental $K$-ionization cross sections for each incident electron energy appear to fit a power-law dependence on the atomic number. The Kolbenstvedt theory also exhibits a power-law dependence and is in good agreement with this experiment. All differential x-ray cross sections were found to be isotropic. The $L$ x-ray cross sections measured for four high-$Z$ elements increase with atomic number and incident electron energy. The $\frac{L\ensuremath{\beta}}{L\ensuremath{\alpha}}$, $\frac{L\ensuremath{\gamma}}{L\ensuremath{\alpha}}$, and $\frac{K}{L}$ intensity ratios are also given. A search for nuclear $\ensuremath{\gamma}$ rays produced by high-energy electron scattering was also undertaken in this work. No nuclear $\ensuremath{\gamma}$-ray lines were detected. Recent theoretical calculations show that the expected cross sections are below the minimum observable levels in these experiments. However, a 511-keV $\ensuremath{\gamma}$ line was observed. This line was associated with positron annihilation and was apparently produced in the target.

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.

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)

The structure and size of the proton have been studied by means of high-energy electron scattering. The elastic scattering of electrons from protons in polyethylene has been investigated at the following energies in the laboratory system: 200, 300, 400, 500, and 550 Mev. The range of laboratory angles examined has been 30\ifmmode^\circ\else\textdegree\fi{} to 135\ifmmode^\circ\else\textdegree\fi{}. At the largest angles and the highest energy, the cross section for scattering shows a deviation below that expected from a point proton by a factor of about nine. The magnitude and variation with angle of the deviations determine a structure factor for the proton, and thereby determine the size and shape of the charge and magnetic-moment distributions within the proton. An interpretation, consistent at all energies and angles and agreeing with earlier results from this laboratory, fixes the rms radius at (0.77\ifmmode\pm\else\textpm\fi{}0.10) \ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm for each of the charge and moment distributions. The shape of the density function is not far from a Gaussian with rms radius 0.70\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm or an exponential with rms radius 0.80\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm. An equivalent interpretation of the experiments would ascribe the apparent size to a breakdown of the Coulomb law and the conventional theory of electromagnetism.

An experimental determination has been made of the radial and longitudinal distribution of energy produced in showers initiated by electrons of 118 Mev and 157 Mev in copper. A small crystal CsBr(Tl) coupled to a thin light pipe and photomultiplier was used as a probe. Graphs of the radial distributions are given from which, by numerical integration, transition curves are determined. Calculations are made for an approximately optimum design of scintillation crystal [e.g., NaI(Tl)] to capture a large fraction of the energy within a shower.

The ${\mathrm{Li}}^{6}$ nucleus has been studied at 426 Mev by electron scattering methods between laboratory angles of 33\ifmmode^\circ\else\textdegree\fi{} and 57.5\ifmmode^\circ\else\textdegree\fi{}. Absolute values of the ${\mathrm{Li}}^{6}$ cross sections have been obtained by comparison with scattering measurements made on the proton at 426 Mev and 40\ifmmode^\circ\else\textdegree\fi{}. Unique values of the experimental form factors are given in tabular form. The results are analyzed in terms of various possible charge distributions. Several examples of models showing a good fit are presented and appropriate radius and skin thickness values are given. Several unsuccessful models are also discussed.

Elastic scattering of 192-Mev electrons from deuterium has been studied using both solid (C${\mathrm{D}}_{2}$) and high-pressure gas targets. The results obtained by these two methods are in agreement and yield the following conclusions: (1) The range of the neutron-proton potential is between 1 and 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm if a square potential well is assumed and if the deuteron wave functions predicted by the binding energy of the deuteron are used. (2) It is, however, impossible with the present data to eliminate the possibility of other charge distributions for deuterium such as uniform or Gaussian.Inelastic electron scattering from deuterium was also investigated, and promises to give independent information of the deuteron structure.

Separate proton form factors were obtained from electron scattering studies by choosing a pair of experimentally measured cross sections at the same value for the square of the momentum transfer but at different values of electron energy and scattering angle. The proton form factors obtained were plotted against the square of the momentum transfer. The new F/sub 2/ indicated that the Pauli magnetic moment cloud is a spread-out distribution. The constancy of F, however, suggested that the Dirac electric/magnetic cloud has a small, perhaps point-like, core. (M.C.G.)

A total absorption Nal(TI) detector can be used to define the energy of an incident electron, or γ-ray, to a precision of I to 2 per cent in the range of 4 to 14 GeV.

Mechanical, or sound, vibrations were observed in ceramic piezoelectric disks of lead-zirconate-titanate (PZT) struck by high energy electrons. Four 1/2 inch thick disks of PZT were used. A wide band, low impedence, common base configuration amplifier was used to examine the induced vibrations. Since the most prominent resonant frequencies of the disks were near 40 kHz (radial mode) and 158 kHz (compressional mode) most of the studies were concentrated on these modes. Electrons of energy 1.00 BeV and 0.20 BeV were used in pulses, each lasting about 1.0 microsecond and contained 10,000 to 1,000,000 to electrons. The cross section of the incident 1.00 BeV beam was about 3 mm x 3 mm. (Author)

With apparatus previously described1,2 we have studied the elastic scattering of electrons of energies 100, 188, and 236 MeV from protons initially at rest. At 100 MeV and 188 MeV, the angular distributions of scattered electrons have been examined in the ranges 60°-138° and 35°-138°, respectively, in the laboratory frame. At 236 MeV, because of an inability of the analyzing magnet to bend electrons of energies larger than 192 MeV, we have studied the angular distribution between 90° and 138° in the laboratory frame. In all cases a gaseous hydrogen target was used.

In concluding this discussion it may be appropriate to return to the theme introduced earlier and raise the question once again of the deeper, and possibly philosophical, meaning of the term "elementary" particle. As we have seen, the proton and neutron, which were once thought to be elementary particles, are now seen to be highly complex bodies. It is almost certain that physicists will subsequently investigate the constituent parts of the proton and neutron—the mesons of one sort or another. What will happen from that point on? One can only guess at future problems and future progress, but my personal conviction is that the search for ever-smaller and ever-more-fundamental particles will go on as long as man retains the curiosity he has always demonstrated ( 29 ).

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 original elastic electron scattering experiments on nuclei produced charge distributions that were characterized by two basic parameters; the half-density radius r0.5 and the skin thickness t . It was possible using a phenomenological charge distribution, containing only these two parameters, to fit the experimental data from a wide range of nuclei. This situation has changed considerably in recent years. The amount of experimental cross sections in existence has increased and the data has been extended to higher values of the recoil momentum q . The ability to measure cross sections at larger values of q together with the better accuracy of the experimental data allows details of the charge distribution to be seen that were previously unobservable.

With apparatus previously described1,2 we have studied the elastic scattering of electrons of energies 100, 188, and 236 MeV from protons initially at rest. At 100 MeV and 188 MeV, the angular distributions of scattered electrons have been examined in the ranges 60°-138° and 35°-138°, respectively, in the laboratory frame. At 236 MeV, because of an inability of the analyzing magnet to bend electrons of energies larger than 192 MeV, we have studied the angular distribution between 90° and 138° in the laboratory frame. In all cases a gaseous hydrogen target was used.

A method using an accelerator and thin targets is suggested for investigating very small energy losses in highenergy electron or proton scattering events. (C.E.S.)