Search

We have directly measured, for the first time, the neutron-fission branching ratio, {Gamma}{sub {ital n}}/{Gamma}{sub {ital f}}, of an actinide nucleus ({sup 238}U) excited in inelastic scattering as a function of excitation energy. This was accomplished using a {approx}4{pi} array of fission counters to separate fission neutrons from decay neutrons in the simultaneous coincidence experiments ({alpha},{alpha}{prime}{ital f}) and ({alpha},{alpha}{prime}{ital n{bar f}}). The measured branching ratio agrees well with previous photoneutron data. In a separate experiment, we have measured the angular distribution of alpha particles scattered from {sup 238}U in coincidence with fission decay ({alpha},{alpha}{prime}{ital f}). This provides us with an estimate of the cross section (in the fission channel) for exciting the isosca- lar giant monopole and giant quadrupole resonances. This estimate, combined with the {Gamma}{sub {ital n}}/{Gamma}{sub {ital f}} measurement, allows us to place bounds on the neutron-fission branching ratio for the isoscalar giant monopole and giant quadrupole resonances themselves.

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 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.

The location of the giant monopole resonance and, therefore, the compressibility is unknown in light nuclei. The forward-backward (e, e′p) angular correlation asymmetry from 12 C has been measured and found to be very sensitive to monopole strength in the giant dipole resonance region. Similar reactions will, thus, provide a sensitive tool in the search for monopole strength in light nuclei.

The history of experiments bearing on the origin of optical activity in nature by parity non-conservation during the β-decay of radioactive isotopes is briefly reviewed. Following this, we present a more detailed description of our recent published and unpublished data and calculations regarding the generation of optical activity in DL-leucine by means of artificially produced longitudinally polarized electrons from a linear accelerator.

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

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 ${10}^{7}$.

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.

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.

Elastic electron scattering cross sections have been measured for 6Li at 500 MeV and values of q sup 2, the momentum transfer squared, up to 13 f(m sup (-2)). Calculations including nucleon-nucleon correlations predict a diffraction minimum beyond the range of previous measurements for 6Li. The results for 6Li do show a diffraction minimum at q sup 2 = 8 f(m sup (-2)); they are also compared with a phase shift calculation using an empirical charge distribution. (Author)

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)

Since April 1965, IBM and the W. W. Hansen High-Energy Physics Laboratory at Stanford University have been engaged in a joint study of use of on-line computers in high-energy physics experiments. In the High-Energy Laboratory, electrons with energies up to 1.2 BeV, produced by the Stanford Mark III 310-ft linear accelerator, are allowed to bombard various target materials. Electrons, or secondary particles produced by the electrons, are detected with several different kinds of detectors. Information from the detectors is relayed to the data-acquisition area where it is processed and stored, while control information is fed back to nuclear instrumentation by the computer. This paper not only contains a description of the computer and instrument interfaces, but also the application-oriented programming approaches used to operate these devices in various experiments. Several different experiments using the data-acquisition computer system are described, and plans for future modifications and improvements are discussed.

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 spectra of electrons scattered inelastically from 4 He have been measured at incident energies from 150 MeV to 400 MeV for scattering angles from 38° to 90°. Through the use of a liquid 4 He target, a high momentum resolution (≈0.25%) was obtained, and the 20 MeV 0 + state of the α-particle was observed for the first time in electron scattering. The excitation energy and the total width of this state were determined and are in good agreement with the results from other experimental methods. It was found that the total disintegration cross section appears be smaller than 2(σ p +σ n ) by more than an order of magnitude at the lowest q 2 (≈ 0.33 fm −2 ). In earlier work the assumption of a total cross section of 2(σ p +σ n ) was found to be quite accurate for higher q 2 . As a new result, the partial radiative width for the 0 + state is determined to be Γ rad = 1.1±0.3 meV.

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)

A system is described which allows as many as five different low temperature targets to be positioned vertically inside a vacuum system. The targets normally contain liquid hydrogen or deuterium. The vertical travel is obtained by using a bellows system in such a way that the over‐all external height of the system is constant. A maximum travel of 4 in. can be obtained.

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 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.

Previous measurements of the transition probabilities for low-energy excitations in 12 C, using high-energy electron scattering techniques, required considerable extrapolation of the data to obtain the desired results. The present paper reports the results of new data obtained at lower values of momentum transferred to the nucleus. Transition widths for the three lowest-energy excited states in 12 C are determined using the new data. The results of the experiment allow a much greater confidence in the method employed in this study for determining transition widths.

Measurements of average separation energies and of Fermi momenta for40Ca and48Ca are reported. Evidence for the possible existence of “bump” structure in the quasi-elastic scattering of electrons from48Ca is also presented.

A picosencond time measurement method is described based on the microwave properties of beams from electron linear accelerators or from possible remodulated external proton beams at proton synchrotrons. A conventional RF separator (RFS) is used operating at the same frequency as the microwave structure of beams and driven by the same master oscillator which modulates the beam. For example, the 2856 MHz microwave at SLAC corresponds to 350 psec between beam RF buckets; accelerated electrons with an RF phase bite of about 5 degrees are time structured and correspondingly have about 5 psec time spread in every 350 psec interval. Charged particles produced in interactions or decays originate with this time structure. An RFS is placed at the last stage of a double focussing spectrometer, providing a lever arm between it and the final (few mm) small spot size focus. Reference calibration charged particles are timed by setting the RFS relative phase to null deflections. Other observed particles arriving at different times than this standardare deflected a few tenths ofa anm per psec of delay. A multi-wire proportional chamber (IMPC) having a 0.05 mm space resolution can provide time measurements with sub-picosecond resolution. The technique is used in an experiment to search for changes in the velocity of light with high energy photons at SLAC. The devised timing method is presented and the properties of a new, fine space resolution MWPC is demonstrated.

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.)

We have searched for virtual excited states of 3 He by inelastic electron scattering at E = 200 MeV and θ = 60°. No evidence for narrow states excited with cross section greater than 3 × 10 −33 cm 2 /sr has been found for excitation energies up to 17 MeV.

High momentum transfer elastic electron scattering data (q = 0.8 – 3.7 fm−1) from 24Mg, 28Si and S are presented and analysed with phenomenological charge distributions ϱ(r); and oscillation in ϱ(r) due to shell-model structure is obtained. An analysis in terms of a Woods-Saxon potential is described and the 2s-1d occupation numbers are deduced.

FOLLOWING Wu's experimental demonstration1 of Lee and Yang's predicted violation of the parity principle during β decay2 and following Goldhaber's demonstration3 of the circular polarisation of the bremsstrahlung produced by β-decay electrons, Vester and coworkers (ref. 4 and F. Vester, unpublished) proposed the following unique mechanism for the abiotic origin of optically active organic molecules Attempts to demonstrate this mechanism experimentally4,5 were unsuccessful, however, until Garay's report in 1968 that D-tyrosine in dilute aqueous alkali was more decomposed (as evidenced by greater eradication of its ultraviolet absorption bands) than was L-tyrosine after 18 months exposure to 0.36 mCi of 90SrCl2 in solution6. One of us has attempted7 to repeat Garay's experiment using DL-tyrosine in alkaline solution, looking for optical rotation after exposing the sample to a dose of 4.1 × 108 rad of β-ray bremsstrahlung in a 61,7000-Ci 90Sr–90Y source at Oak Ridge National Laboratory for 1.34 yr. No optical activity was noted, using optical rotary dispersion (ORD) measurements in the region 250–630 nm. At the same time7 Garay's experiments were extended to include other racemic amino acids, both in the solid state and in neutral, acidic or alkaline solution. In no case, after the same 1.34-yr exposure, did we notice the development of optical activity either by ORD measurements or (in the case of DL-leucine) by the gas-chromatographic determination of the enantiomeric composition of the irradiated samples. Our explanation7 for these negative results has been that most of the bremsstrahlung causing radiolysis of the samples was of low energy8 and therefore of very slight circular polarisation3,9. In the hope of overcoming this difficulty, we have now undertaken similar experiments using longitudinally polarised electrons (and their bremsstrahlung) from a linear accelerator.

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.