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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.

The results of different readers' interpretations of laser-digitized hand radiographs versus original radiographs were compared to determine the reproducibility of scoring of erosions (ERO), joint space narrowing (JSN), and their combination (ERO + JSN) in patients with rheumatoid arthritis (RA).Standardized radiographs of both hands were obtained at 2 visits (baseline and 6-24-month followup) from 30 patients with established RA. Conventional and laser-digitized (pixel sizes 50 microm and 100 microm) radiographs were scored independently by 3 experienced and trained radiologists who were blinded to the order of the visits. Scoring of radiographs was based on the validated Genant grading system.Intertechnique (intrareader) correlation coefficients at baseline were 0.90-0.93 for scoring of ERO, 0.90-0.94 for scoring of JSN, and 0.92-0.95 for ERO + JSN; for scoring of progression between baseline and followup, these values were 0.93-0.97, 0.87-0.95, and 0.93-0.97, respectively. Interreader (intratechnique) correlation coefficients at baseline were 0.82-0.96 for scoring of ERO, 0.69-0.91 for scoring of JSN, and 0.80-0.95 for ERO + JSN; for scoring of progression between baseline and followup, these values were 0.90-0.97, 0.80-0.92, and 0.90-0.95, respectively. Intrareader (intratechnique) correlation coefficients were 0.90-0.97 for scoring of the original radiographs and 0.90-0.98 for scoring of the digitized images at 100 microm.Using this modified grading system, scoring of RA progression directly from paired, high-resolution monitors of laser-digitized images of the hands provided highly reproducible results, comparable to those obtained from the original radiographs. Thus, this method may have useful applications in clinical trials involving RA.

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.

A two-dimensional position-sensitive ΔEE phoswich detector, 20 cm × 20 cm, was built using the fast plastic scintillator NE 102A for the thin (0.5 mm) ΔE element, and the new, slow plastic scintillator NE 115 (measured light output 35% of anthracene, decay time 225 ns) for the thick (4.5 mm) E element. Natural light loss arising from multiple reflections at an irregular surface is responsible for the position dependence of the signals. The position resolution was found to be typically 10 mm (fwhm) in each direction. The detector is able to identify protons, deuterons and alpha particles, and exhibited an energy resolution of 5–6% (fwhm) and a time resolution of 580 ps (fwhm) in a test using 60 MeV α particles scattered from a gold target.

A 4π array of plastic scintillator has been constructed and used in conjunction with high resolution solid state detectors. The array is employed principally to discriminate multinucleon transfer reactions from three-body (or more) final states. It should be useful for a broad class of experiments in which a global charged particle anticoincidence is required.

The mechanisms of transfer and breakup in heavy-ion-induced reactions have been studied for the $^{20}$Ne${+\mathrm{}}^{197}$Au system at bombarding energies of 220 and 341 MeV. A 4\ensuremath{\pi} detector was used to separate reactions leading to the production of projectilelike fragments into components having either two charged bodies in the final state (transfer) or three or more charged fragments (breakup). For both components, angular distributions, energy spectra, and production cross sections are shown for projectile fragments of Z=3--9. The ratio of transfer to inclusive yields initially drops steeply with decreasing ejectile charge, leveling off for Z\ensuremath{\le}7. The lower bounds on this ratio are \ensuremath{\simeq}60% and \ensuremath{\simeq}30% at 220 and 341 MeV, respectively. At 341 MeV, the trends in the central moments (mean, width, and skewness) of the ejectile energy spectra, as a function of Z, are similar for transfer and breakup. The primary ejectile yields are deduced from the breakup and transfer cross sections, and comparisons are made with the predictions of various models. The relatively large probabilities for primary ejectiles to be produced in charged-particle-bound states, observed for all Z and at both 220 and 341 MeV, indicate that, on average, most of the excitation energy resides in the heavy, targetlike fragment.

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 transfer reactions with heavy-ion projectiles is complicated by the frequent presence of three or more nuclei in the final state. One prolific source of three-body reactions is the production of a primary ejectile in an excited state above a particle threshold. A subset of transfer reactions, viz., those producing ejectiles in bound states, can be identified experimentally. This has been accomplished with a 4..pi.. detector constructed of one-millimeter-thick scintillator paddles of dimension 20 cm x 20 cm. The paddles are arranged in the form of a cube centered around the target with small entrance and exit apertures for the beam and the projectile-like fragments, (PLF). The detection of a light particle (e.g., a proton or an alpha particle) in coincidence with a PLF indicates a breakup reaction. The absence of any such coincidence indicates a reaction in which all the charge lost by the projectile was transferred to the target. With this technique we have studied the transfer and breakup reactions induced by 220 and 341 MeV /sup 20/Ne ions on a gold target. Ejectiles from Li to Ne have been measured at several scattering angles. The absolute cross sections, angular distributions and energy spectra for the transfer and breakup reactions are presented. Relatively large cross sections are observed for the complete transfer of up to seven units of charge (i.e., a nitrogen nucleus). The relatively large probabilities for ejectiles to be produced in particle-bound states suggest that on the average, most of the excitation energy in a collision resides in the heavy fragment when mass is transferred from the lighter to the heavier fragment. The gross features and trends in the energy spectra for transfer and breakup reactions are similar. 20 references.

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...