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The diffractive production of ρ0(770 @#@) mesons in muon-proton interactions is studied in the kinematic region 0.15 GeV2 < Q2 < 20 GeV2 and 20 GeV < ? < 420 GeV. The data were obtained in the Fermilab fixed-target experiment E665 with primary muons of 470 GeV energy. Results are presented on the Q2, x and ? dependence of the cross section, on the shape of the ρ+ρt - mass spectrum, on the slope of the diffraction peak and on the production and decay angular distributions of the ρ0(770). The cross section for diffractive production of ρ0 by virtual photons on protons depends mainly on Q2. At fixed Q2, no significant dependence on x or ? is observed. The extrapolation to Q2 = 0 yields a photoproduction cross section of (10.30 ± 0.33) μb. The slope of the t′ distribution has a value of (7.0 ± 0.2) GeV−2, with a tendency to decrease as Q2 increases. The production and decay angular distributions of the ρ0 depend strongly on Q2 and are consistent with s-channel helicity conservation. The ratio R = σ l /σ t deduced from the decay angular distributions rises strongly with Q2, passing the value of 1 at Q2 ≈ 2 GeV2.

Spin asymmetries for the ${}^{16}\mathrm{O}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},p{\ensuremath{\pi}}^{\ensuremath{-}})$ reaction are reported for incident photon energies of 293 $\ifmmode\pm\else\textpm\fi{}$ 20 MeV, proton angles ranging from 28$\ifmmode^\circ\else\textdegree\fi{}$ to 140$\ifmmode^\circ\else\textdegree\fi{}$ (lab), and pion angles of 35$\ifmmode^\circ\else\textdegree\fi{}$ to 115$\ifmmode^\circ\else\textdegree\fi{}$. The data are compared with calculations in a quasifree plane-wave impulse approximation model. This model is in good agreement with the data at small momentum transfer $q$, but does not follow the trend of the data at large $q$. Sensitivity to the $\ensuremath{\Delta}$-nucleus potential and to modification of the $\ensuremath{\Delta}$ lifetime from nuclear medium effects are explored using a simple modification of the $\ensuremath{\Delta}$ propagator in the calculations.

The proton and deuteron structure functions F2 p and F2 d are measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment E665 during 1991 and 1992 using liquid hydrogen and deuterium targets. The F2 measurements are reported in the range 0.0008

Inelastic neutron emission at 6.7 and 20 MeV incident energies has been measured for monoisotopic samples of 165 Ho and 181 Ta. Time-of-flight spectra were taken at several angles between 15° and 145° using a beam-swinger spectrometer. The cross sections are averaged over 1 MeV energy bins. The 20 MeV data, when compared with the quantum-mechanical statistical multistep calculations have revealed a magnitude problem in the existing theories. A gradual or “multistep” absorption in the entrance channels is proposed as a way out of the difficulty. This modification turns out to be sufficient for an adequate description of the experimental data.

We have used the relativistic impulse approximation (RIA) to study the newly measured neutron total cross section data for [sup 208]Pb, [sup 90]Zr, and [sup 40]Ca. In particular, we are interested in what we can learn from the RIA in order to build up a phenomenological optical potential. A complete set of scattering observables would be required in order to study the details of the neutron-nucleus interaction. In the absence of any such data at intermediate energy, the present study of total cross sections provides useful preliminary information on the isovector part of a generalized nucleon-nucleus interaction. We used the [ital NN] amplitude calculated by McNeil, Ray, and Wallace (MRW) and the relativistic Love-Frany [ital NN] amplitude developed by Murdock and Horowitz (MH). We found that the use of MH's amplitude in the RIA gives a good description to the neutron total cross section from 200 to 400 MeV, while the use of MRW's amplitude provides a good description from 500 MeV and above. The energy dependence of the volume integrals of the total optical potential is consistent from both calculations, but there is a large difference in the energy dependence of the volume integral of the isovector part ofmore » the potential.« less

Neutron total cross sections for $^{27}\mathrm{Al}$, $^{28}\mathrm{Si}$, and $^{40}\mathrm{Ca}$ have been measured with good statistics (\ensuremath{\sim}1%) and good energy resolution over the energy range 4\ensuremath{\le}${\mathit{E}}_{\mathit{n}}$\ensuremath{\le}20 MeV. Two techniques have been used to infer the level density of the compound nuclei. The first is the conventional procedure of deducing an average level width and relating this to the level density. An alternative method is to deduce the level density from the magnitude of the variance of the cross section. A previous study of these two techniques suggested that the two yielded results which were not completely consistent. Our examination of the discrepancies indicates that they are reduced but not eliminated with better data. It seems likely that a part of the problem is the uncertainty in input parameters.

We detected 1-10 MeV neutrons at laboratory angles from 80° to 140° in coincidence with 470 GeV muons deep inelastically scattered from H, D, C, Ca, and Pb targets. The neutron energy spectrum for Pb can be fitted with two components with temperature parameters of 0.7 and 5.0 MeV. The average neutron multiplicity for 40

The (γ↘,π−p) reaction was measured for 16O at photon energies of 200 to 320 MeV, and angles ranging from about 20° to 160° for the proton and 32° to 135° for the pion. The photon asymmetry data are compared with calculations in a DWIA framework. The agreement between the present data and calculations is reasonable at quasifree kinematics, but disagree as the momentum transfer to the residual nucleus becomes large.

Pulsed-beam time-of-flight techniques are used in a transmission measurement with a continuous spectrum of neutrons to determine neutron total cross sections with good precision up to 600 MeV. Neutrons are produced by spallation of the 800 MeV proton beam from the Los Alamos Meson Physics Facility accelerator incident on a thick, heavily shielded tungsten target at the Weapons Neutron Research facility at Los Alamos National Laboratory. Transmission measurements were completed for fifteen elements with 9\ensuremath{\le}A\ensuremath{\le}209 and three isotopically enriched samples of $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, and $^{208}\mathrm{Pb}$. Principal features of the experiment are the intensity and time structure of the neutron source, tight collimation of the neutron beam line, good geometry, rapid cycling of the samples, stable electronics, and a small, fast neutron detector. Errors due to counting statistics were generally less than 1% for each of several hundred energy bins for each target. The measurements represent steps in the development of a neutron-nucleus optical potential at intermediate energy and important input for the clarification of isovector effects in the nucleon-nucleus interaction. The data also provide insight into the long-standing discussion of mean free paths of the nucleon in the nucleus.

New measurements of differential elastic neutron scattering for {sup 209}Bi at energies between 7.5 and 24.0 MeV are presented along with new measurements of {sigma}{sub {ital T}} up to 60 MeV. These data, taken together with earlier measurements at lower energy, provide a very large data set for testing and extending the dispersive optical-model analysis. The dispersion correction to the optical model has been obtained from the scattering and total cross-section data. The potential is extrapolated to negative energy for comparison with bound-state properties. A very good description of all of the data is obtained from {minus}20 to +60 MeV. The present analysis suggests somewhat less depletion of the Fermi sea in this mass region than has been obtained from electron-scattering data and from other recent treatments of the dispersion correction to the optical model.

The 96Mo(p, n) and 96Mo(p, nγ) reactions have been studied for proton energies between 3.8 and 5.5 MeV. Energy levels in 96Tc up to 632 keV excitation energy have been determined. Possible spin and parity assignments are given for several levels based on the neutron enhancement and angular distributions observed on and off resonance of the 5 2 >+ isobaric analog state in 97Tc, as well as the observed γ-yields. The first excited state reported at 34 keV was found to be a close doublet only 0.8 keV apart. The observation of this doublet in the (p, n) reaction was used to determine the ground state Q-value Q = − 3.760±0.010 MeV.

Cross sections for the /sup 12/C( p,p')/sup 12/C and /sup 14/N( p,p')/sup 14/N reactions have been measured at E/sub p/=122 MeV. Scattered protons were momentum analyzed in a dispersion-matched magnetic spectrograph and detected in a helical-cathode position-sensitive proportional counter. Transitions to states in /sup 12/C at 4.44 MeV (2/sup +/,T=0), 12.71 MeV (1/sup +/,0), 15.11 MeV (1/sup +/,1), 16.11 MeV (2/sup +/,1), and in /sup 14/N at 2.31 MeV (0/sup +/,1) and 3.95 MeV (1/sup +/,0), are very useful for studying the spin-isospin dependence of the effective two-nucleon interaction. Cross sections for these states from the present experiment and from earlier measurements at 185 MeV have been analyzed in the distorted-wave impulse approximation. Simultaneous consideration of (e,e') data for the same transitions helped to disentangle some nuclear-structure and reaction-mechanism effects. The distorted-wave impulse approximation provides a good description of those transitions in /sup 12/C mediated predominantly by the S=T=1 part of the effective interaction and also gives a reasonable description of the S=T=0 transitions in both nuclei. The mechanisms for excitation of the 12.71-MeV state in /sup 12/C (S=1, T=0) and the 2.31-MeV state in /sup 14/N (S=1, T=1) remain a puzzle.

The Ohio University time-of-flight spectrometer has been completely redesigned to make use of a beam swinger magnet. Flight paths of 4–30 m are available over the angular range from −4° to +160°. Improved shielding, collimation and detector design provide substantial improvements in neutron scattering experiments for neutron energies up to 26 MeV.

Low-lying states in 98Tc have been studied via the 98Mo(p, n)98Tc and 98Mo(p, nγ)98Tc reactions for proton energies between 2.4 and 4.2 MeV. The γ-ray decay schemes are reported. Additional information was obtained from the study of the 97Mo(3He, d)98Tc reaction at E 3 He = 19 and 23 MeV . Proton transfer l-values and spin assignments are discussed.

Differential cross sections for elastic scattering of neutrons from /sup 54,56/Fe have been measured at several energies in the 20--26 MeV region. The data have been analyzed both in terms of the standard phenomenological optical model, and in the framework of two different microscopic models based upon nuclear matter calculations using realistic nucleon-nucleon interactions and a local density approximation. Isospin consistency of the microscopic-model calculations was also tested by analyzing proton elastic differential cross section data in the same energy region, as well as both proton and neutron elastic analyzing power data. The microscopic calculations yield quite reasonable agreement with the data, even though they contain no free geometrical parameters. The quality of the results for the analyzing power data is particularly impressive, indicating that the very simple, density- and energy-independent spin-orbit force used in the calculations is sufficient. The differences between the various models are clarified by examining the momentum-space representations of the potentials.

Differential cross sections for inelastic scattering of neutrons to numerous levels in $^{54}$,56Fe have been measured at incident neutron energies of 11 and 26 MeV. The data have been analyzed in terms of a collective model using a distorted-wave Born approximation as well as a full coupled-channels treatment. Analysis has also been performed with a microscopic folding model using an energy- and density-dependent effective interaction. Both collective and microscopic analyses have also been applied to inelastic proton scattering in the same energy region in order to extract information on the isospin nature of the measured excitations.

The differential cross section and polarization of 2.63 MeV neutrons scattered from 12C have been measured at eight angles between 17° and 118° in the laboratory system. By simultaneously fitting the cross section and polarization data, a set of scattering phase shifts was obtained. The values of the resulting d-wave phase shifts were larger than those of other existing sets of phase shifts in the energy region. A subsequent R-function analysis, reflecting these larger d-wave phase shifts, gave excellent fits to other experimental data below 3 MeV neutron energy region. The influence of narrow states at 7.50 and 7.55 MeV excitation energy in 13C is discussed.

Differential cross section data for inelastic proton and neutron scattering to the first 2/sup +/ states in /sup 54/Fe and /sup 56/Fe at several energies in the 11--26 MeV range have been analyzed using a microscopic distorted wave Born approximation model. The entrance- and exit-channel optical potentials and the transition form factors were calculated consistently in a folding model using a density-dependent interaction obtained from nuclear matter calculations based upon a free nucleon-nucleon interaction. These microscopic calculations yield reasonable agreement with the data. The model was used to determine the ratio of neutron and proton transition matrix elements M/sub n//M/sub p/ for these excitations.

New experimental data for the elastic scattering of 7--24-MeV neutrons from /sup 208/Pb are presented, and a microscopic folding-model study of neutron and proton elastic scattering data for /sup 208/Pb at energies below 60 MeV is made to examine the isospin dependence of an effective interaction derived from nuclear-matter calculations. The theoretically derived interaction yields reasonable agreement with the data if the Coulomb potential is treated properly.

Inelastic scattering of 5\char21{}11 MeV neutrons to the ${3}_{1}^{\mathrm{\ensuremath{-}}}$ state in $^{208}\mathrm{Pb}$ is reanalyzed in the distorted wave Born approximation using phenomenological potentials and form factors that explicitly reflect the ``threshold anomaly'' effects observed in the elastic scattering channel. A previously reported energy dependence of the deformation length ${\ensuremath{\delta}}_{3}$ is largely removed by this analysis. We conclude that dispersion corrections to the one-channel optical potentials are important in the off-diagonal elements of the potential matrix.

Recent measurements of differential elastic and inelastic neutron scattering from oxygen, nitrogen and calcium at 18 less than En less than 26 MeV are presented and analysed in terms of the optical model. These data, together with earlier measurements of scattering and total cross sections, are used to construct model potentials that may be used to calculate various quantities of interest in neutron dosimetry in an energy region (20-60 MeV) where very few cross section data are available. The heavy-ion-recoil contribution to kerma is obtained directly from the data at each energy. The value of proton inelastic scattering data for validating potential models at high energy is discussed.

New measurements of differential elastic and inelastic neutron scattering from 12C at En = 20.8, 22, 24 and 26 MeV are presented and analysed in terms of both spherical and deformed optical model potentials. Results of these analyses are compared with other recent differential and total cross-section measurements in order to obtain a consistent representation of the energy dependence of neutron scattering over a broad energy range. Heavy ion recoil kerma factors are calculated and compared with earlier measurements and estimates of these quantities.

Differential cross sections for neutron elastic scattering from /sup 12/C, /sup 14/N, /sup 16/O, and /sup 27/Al have been measured in the energy range 18--26 MeV. These data, together with previously published neutron and proton data for these nuclei and for /sup 12/C in the energy region 20 to 65 MeV, have been analyzed in terms of two microscopic optical potentials. The spherical potential derived from the work of Jeukenne, Lejeune, and Mahaux provides a consistent representation of the differential data, provided the imaginary central potential is renormalized. Predictions from the interaction of Brieva and Rook give less satisfactory agreement. In particular, there is a significant overprediction of the forward angle data below approx.25 MeV and an underprediction above approx.35 MeV.

Elastic and inelastic neutron scattering data from /sup 208/Pb and /sup 209/Bi are analyzed.