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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.

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.

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...

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.