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Over 120 million vehicles enter the United States each year. Many are capable of transporting hidden nuclear weapons or nuclear material. Currently deployed X-ray radiography systems are limited because they cannot be used on occupied vehicles and the energy and dose are too low to penetrate many cargos. We present a new technique that overcomes these limitations by obtaining tomographic images using the multiple scattering of cosmic radiation as it transits each vehicle. When coupled with passive radiation detection, muon interrogation could contribute to safe and robust border protection against nuclear devices or material in occupied vehicles and containers.

Highly penetrating cosmic ray muons constantly shower the earth at a rate of about 1 muon per cm2 per minute. We have developed a technique which exploits the multiple Coulomb scattering of these particles to perform nondestructive inspection without the use of artificial radiation. In prior work [1]-[3], we have described heuristic methods for processing muon data to create reconstructed images. In this paper, we present a maximum likelihood/expectation maximization tomographic reconstruction algorithm designed for the technique. This algorithm borrows much from techniques used in medical imaging, particularly emission tomography, but the statistics of muon scattering dictates differences. We describe the statistical model for multiple scattering, derive the reconstruction algorithm, and present simulated examples. We also propose methods to improve the robustness of the algorithm to experimental errors and events departing from the statistical model.

New high-precision measurements of p( γ , π) and p( γ , γ) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photo-pion amplitude. The E2/M1 mixing ratio for the N → Δ transition extracted from this analysis is EMR = -3.0% ± 0.3 (stat + sys) ± 0.2 (model).

We present new break-up and coherent data for $\ensuremath{\eta}$ meson photoproduction on the deuteron, using a deuterium target and tagged bremsstrahlung photons up to 1 GeV. The differential cross sections for the coherent process were measured from threshold to 800 MeV. They are much smaller than those previously reported. The break-up channel provides a direct measurement of the neutron to proton differential cross section ratios. At the ${S}_{11}(1535)$ resonance peak, ${\ensuremath{\sigma}}_{n}/{\ensuremath{\sigma}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.68\ifmmode\pm\else\textpm\fi{}0.06$ leading to an isoscalar to isovector amplitude ratio of ${A}_{s}{/A}_{\ensuremath{\upsilon}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.096\ifmmode\pm\else\textpm\fi{}0.02$.

Total cross sections, differential cross sections and asymmetries for the reaction p( p ,π 0 )pp from threshold to 1 GeV have been measured. The outgoing π0 was detected by a 4π neutral meson spectrometer. Our data are compared with the corresponding np→NNπ± reactions. The isoscalar partial cross sections are extracted from the relevant total cross sections. They are significant throughout the whole energy range. Below the Δ-region, energy-integrated differential cross sections show a large anisotropy difference between the neutral and charged pion channels, respectively. A partial-wave fit shows that the initial T = 0 state is dominated by the 3D1 wave in this energy region. Finally, predictions of phenomenological models give reasonable good account of the measured observables but cannot reproduce the sign of the asymmetries.

Differential cross sections for the elastic scattering of 20 and 40 MeV [pi][sup [minus]] by nuclei ranging from [sup 12]C to [sup 208]Pb are reported. Comparisons are made with the predictions of the Michigan State University (MSU) optical potential.

Absolute total and differential cross sections for the reaction [pi][sup +]+[ital d][r arrow][ital p]+[ital p] have been measured for pion energies from 3.7 to 20.5 MeV. A crossed-field velocity separator was used to enhance the purity of the pion beam, and a deuterated scintillator was used both as the target and to count the incident flux. The total cross sections are 4.0[plus minus]0.5, 4.4[plus minus]0.2, 4.2[plus minus]0.2, 4.2[plus minus]0.2, and 4.8[plus minus]0.3 mb for incident pion energies of 3.7, 5.0, 9.6, 15.2, and 20.5 MeV, respectively. The measured differential cross sections indicate the presence of [ital p]-wave strength at all energies studied and are in good agreement with recent measurements for the reaction [ital n]+[ital p][r arrow][ital d]+[pi][sup 0] near threshold and a recent parametrization of the total and differential cross sections for the process.

Results from three independent measurements of the {ital p}({rvec {gamma}},{pi}{sup 0}) reaction are presented for incident photon energies between 243 and 314 MeV, and for c.m. angles of 105{degree}, 122{degree}, and 150{degree}. The ratio of cross sections measured with orthogonal states of linear polarization is sensitive to the {ital E}2 excitation of the {Delta} resonace. Comparisons are made to the predictions of various models, all of which fail to reproduce these data.

Total cross sections for the reaction p+p→p+p+π0 have been measured for proton incident energies ranging from 480 to 560 MeV in 20 MeV steps, by detecting the decay γ-rays of the π0 emitted at forward angles. Isoscalar partial cross sections (σ01) are extracted by comparison to the known total cross sections of the n+p→n+n+π+ measured at the same incident energies. No signal in the energy dependence of the π0 production excitation function due to possible narrow, isovector dibaryon resonance is noticeable in the data.

Inelastic ${\mathrm{\ensuremath{\pi}}}^{\ifmmode\pm\else\textpm\fi{}}$ cross-section measurements at pion incident energies of 150 and 180 MeV were made on ${6}^{\mathrm{\ensuremath{-}}}$ states in $^{24,26}\mathrm{Mg}$. In particular, we have determined the (${\mathit{f}}_{7/2}$${\mathit{d}}_{5/2}^{\mathrm{\ensuremath{-}}1}$${)}_{6}^{\mathrm{\ensuremath{-}}}$ isoscalar ${\mathit{Z}}_{0}$=0.21\ifmmode\pm\else\textpm\fi{}0.02 strength for the strongest T=0, ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${6}^{\mathrm{\ensuremath{-}}}$ state located at 12.11\ifmmode\pm\else\textpm\fi{}0.05 MeV in $^{24}\mathrm{Mg}$, and the isoscalar ${\mathit{Z}}_{0}$=0.17\ifmmode\pm\else\textpm\fi{}0.04 and isovector ${\mathit{Z}}_{1}$=0.21\ifmmode\pm\else\textpm\fi{}0.02 strength for the strongest T=1, ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${6}^{\mathrm{\ensuremath{-}}}$ state located at 9.18 MeV in $^{26}\mathrm{Mg}$. The distorted-wave impulse-approximation pion cross-section calculations required a multiplicative normalization factor of 1.2\ifmmode\pm\else\textpm\fi{}0.1 in order to reproduce the pure isovector strength deduced from electron scattering for the well-known T=1, $^{\mathrm{\ensuremath{\pi}}}$=${6}^{\mathrm{\ensuremath{-}}}$ state at 15.15 MeV in $^{24}\mathrm{Mg}$ and the T=2, ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${6}^{\mathrm{\ensuremath{-}}}$ state at 18.05 MeV in $^{26}\mathrm{Mg}$.

New precision angular distribution data for the D({gamma},{ital p}){ital n} reaction are presented for incident photon energies of 191 and 222 MeV. The difference of cross sections measured with orthogonal states of linear polarization is sensitive to the short-range behavior of the tensor interaction in models of the nuclear force. Comparisons with the Bonn and Paris potentials illustrate the sensitivity.

Absolute total and differential cross sections for the reaction {pi}{sup +}+{ital d}{r arrow}{ital p}+{ital p} have been measured for pion energies from 3.7 to 20.5 MeV. Evidence for {ital p}-wave strength was observed for all energies. Using detailed balance and corrections for Coulomb effects, the measured differential and total cross sections were found to be consistent with recent measurements for the reaction {ital n}+{ital p}{r arrow}{ital d}+{pi}{sup 0}, offering no evidence for charge-independence breaking. The measured total cross sections for energies below 30 MeV are in disagreement with predictions by Blankleider and by Vogelzang, Bakker, and Boersma.

We present measured angular distributions for ${\ensuremath{\pi}}^{+}$-elastic scattering at 30 and 50 MeV from selected targets with $A=12 \mathrm{to} 208$. These angular distributions were analyzed using a phenomenological optical potential of first-order form. The mass dependence of the potential strength parameters displays the isospin dependence expected from the free $\ensuremath{\pi}N$ interaction.NUCLEAR REACTIONS Elastic scattering of 30 and 50 MeV ${\ensuremath{\pi}}^{+}$ from $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, $^{208}\mathrm{Pb}$. Angular distributions: $25\ifmmode^\circ\else\textdegree\fi{}l{\ensuremath{\theta}}_{\mathrm{LAB}}l160\ifmmode^\circ\else\textdegree\fi{}$. Optical model analysis of cross-section data.

The reaction {sup 58}Ni({pi}{sup +},{ital pp}) was studied with good energy resolution for an incident pion energy of 160 MeV. The angular correlation of the outgoing protons was measured for {theta}{sub lab}=30{degree}, 75{degree}, and 130{degree}. From these angular correlations the contribution from direct two-nucleon absorption was extracted. A Monte Carlo calculation modeling the absorption process in terms of initial-state scattering of the pion before absorption, two-nucleon absorption, and final-state scattering of the outgoing nucleons is compared to the data. We conclude that within this framework the two-nucleon mechanism can account for less than half of the total absorption cross section in {sup 58}Ni. We report results for the low-energy coincidence proton spectra (down to 5 MeV) which suggest that most of these protons come from evaporation. Angular correlation data for the reaction {sup 58}Ni({pi}{sup {minus}},{ital pp}) are also presented.

Reported are measurements of angular distributions of resonance-energy positive and negative pions exciting approximately 40 states in {sup 24}Mg and {sup 26}Mg. These include the (ground state, 0{sup +}), (1.36 MeV, 2{sup +}), (4.14, 2{sup +}), (5.93, 4{sup +}), (6.44, 0{sup +}), (7.34), (7.55, 3{sup {minus}}), (8.33, 3{sup {minus}}), (9.32, 4{sup +}), (9.97, 5{sup {minus}}), (11.08, 3{sup {minus}}), (12.06), (13.26), (13.96, 3{sup {minus}}), (15.1, {ital T}=1, 6{sup {minus}}), and (15.4) states in {sup 24}Mg and the (ground state, 0{sup +}), (1.81, 2{sup +}), (2.92, 2{sup +}), (3.59, 0{sup +}), (4.31, 2{sup +}+4{sup +}), (4.90, 4{sup +}), (5.31, 2{sup +}), (5.44, 4{sup +}), (5.69, 4{sup +}), (6.86, 3{sup {minus}}), (7.33, 3{sup {minus}}), (7.79, 3{sup {minus}}), (8.17, 3{sup {minus}}), (9.2, possible 6{sup {minus}}), (10.30, 4{sup +}), and (18.1, {ital T}=2, 6{sup {minus}}) states in {sup 26}Mg. The distorted-wave impulse approximation with a Kisslinger form for the optical potential using a {pi}-nucleon {ital t} matrix at a shifted energy of {minus}25 MeV was found to explain the elastic scattering data from {sup 24,26}Mg in the energy range 116--292 MeV that is spanned by these data. Inelastic distorted-wave impulse approximation calculations employing collective-model deformation parameters were simultaneously fitted to the {pi}{sup +} and {pi}{supmore » {minus}} data for each state.« less

Differential cross sections were measured for 50 MeV {pi}{sup +} and {pi}{sup {minus}} elastic scattering from {sup 12}C and for 50 MeV {pi}{sup +} inelastic scattering to the (4.44 MeV, 2{sup +}), (7.65 MeV, 0{sub 2}{sup +}), (9.64 MeV, 3{sup {minus}}), (12.71 MeV, 1{sup +}), and (15.11 MeV, 1{sup +}) levels in {sup 12}C. Comparisons of the data obtained in this study to data taken previously for these states resolve discrepancies between the earlier data sets. Using a recently discussed procedure, one-step and coupled-channels calculations using a modified MSU potential were performed. The results of both one-step and coupled-channels calculations describe the data for the ground, first, and third excited states, indicative of the collective isoscalar structure of those states. The one-step analysis fails to describe the excitation of the 0{sub 2}{sup +} state. The coupled-channels calculations are more successful in describing those data, indicating that the failure of the one-step calculations may be attributed to coupled-channels effects.

We report new high-precision measurements of $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},\ensuremath{\gamma}),$ $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{0})$ and $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{+})$ cross section and beam asymmetry angular distributions for photon beam energies in the range from 213 MeV to 333 MeV. The cross sections for all three channels are locked together with a small common systematic scale uncertainty of 2%. A large overdetermination of kinematic parameters was used to achieve the first complete separation of the Compton scattering and ${\ensuremath{\pi}}^{0}$-production channels. This has also allowed all detector efficiencies for the $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},\ensuremath{\gamma})$ and $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{0})$ channels to be measured directly from the data itself without resorting to simulations. The new Compton results are approximately 30% higher than previous Bonn data near the peak of the $\ensuremath{\Delta}$ resonance, resolving a long-standing unitarity puzzle. However, our $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{0})$ and $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{+})$ cross sections are also about 10% higher than both earlier Bonn data and recent Mainz measurements, while our $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{+})$ cross sections are in good agreement with results from Tokyo. Our polarization asymmetry data are of the highest precision yet available and have considerable impact upon multipole analyses. These new data have been combined with other polarization ratios in a simultaneous analysis of both Compton scattering and $\ensuremath{\pi}$ production, with Compton scattering providing two new constraints on the photopion amplitude. This analysis has improved the accuracy in the $E2/M1$ mixing ratio for the $\stackrel{\ensuremath{\rightarrow}}{N}\ensuremath{\Delta}$ transition, $EMR=\ensuremath{-}[3.07\ifmmode\pm\else\textpm\fi{}0.26(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\ifmmode\pm\else\textpm\fi{}0.24(\mathrm{model})](%),$ and the corresponding $\stackrel{\ensuremath{\rightarrow}}{N}\ensuremath{\Delta}$ transverse helicity amplitudes, ${A}_{1/2}=\ensuremath{-}[135.7\ifmmode\pm\else\textpm\fi{}1.3(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\ifmmode\pm\else\textpm\fi{}3.7(\mathrm{model})]{(10}^{\ensuremath{-}3}{\mathrm{GeV}}^{\ensuremath{-}1/2})$ and ${A}_{3/2}=\ensuremath{-}[266.9\ifmmode\pm\else\textpm\fi{}1.6(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\ifmmode\pm\else\textpm\fi{}7.8(\mathrm{model})]{(10}^{\ensuremath{-}3}{\mathrm{GeV}}^{\ensuremath{-}1/2}).$ From these we deduce an oblate spectroscopic deformation for the ${\ensuremath{\Delta}}^{+}.$ The same simultaneous analysis has been used to extract the proton dipole polarizabilities, $\overline{\ensuremath{\alpha}}\ensuremath{-}\overline{\ensuremath{\beta}}=+[10.39\ifmmode\pm\else\textpm\fi{}1.77(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}{)}_{\ensuremath{-}1.87}^{+1.02}(\mathrm{model})]{(10}^{\ensuremath{-}4}{\mathrm{fm}}^{3})$ in agreement with previous low energy measurements, and $\overline{\ensuremath{\alpha}}+\overline{\ensuremath{\beta}}=+[13.25\ifmmode\pm\else\textpm\fi{}0.86(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}{)}_{\ensuremath{-}0.58}^{+0.23}(\mathrm{model})]{(10}^{\ensuremath{-}4}{\mathrm{fm}}^{3})$ in agreement with recent evaluations of the Baldin sum rule. Our simultaneous analysis has also provided the first determination of the proton spin polarizabilities, ${\ensuremath{\gamma}}_{\ensuremath{\pi}}=\ensuremath{-}[27.23\ifmmode\pm\else\textpm\fi{}2.27(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}{)}_{\ensuremath{-}2.10}^{+2.24}(\mathrm{model})]{(10}^{\ensuremath{-}4}{\mathrm{fm}}^{4}),$ ${\ensuremath{\gamma}}_{0}=\ensuremath{-}[1.55$$\ifmmode\pm\else\textpm\fi{}0.15(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}{)}_{\ensuremath{-}0.03}^{+0.03}(\mathrm{model})]{(10}^{\ensuremath{-}4}{\mathrm{fm}}^{4}),$ ${\ensuremath{\gamma}}_{13}=+[3.94\ifmmode\pm\else\textpm\fi{}0.53(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}{)}_{\ensuremath{-}0.18}^{+0.20}(\mathrm{model})]{(10}^{\ensuremath{-}4}{\mathrm{fm}}^{4}),$ and ${\ensuremath{\gamma}}_{14}=\ensuremath{-}[2.20\ifmmode\pm\else\textpm\fi{}0.27(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}+\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}{)}_{\ensuremath{-}0.09}^{+0.05}(\mathrm{model})]{(10}^{\ensuremath{-}4}{\mathrm{fm}}^{4}).$ The extracted value of the backward spin polarizability, ${\ensuremath{\gamma}}_{\ensuremath{\pi}},$ is considerably different from other analyses and this has been instrumental in bringing the value of $\overline{\ensuremath{\alpha}}\ensuremath{-}\overline{\ensuremath{\beta}}$ extracted from high energy data into agreement with low energy experiments.

The photodisintegration of deuterium with linearly polarized light has been measured in the energy range of 110-315 MeV. The results of five independent measurements using three detector systems, two liquid target geometries, and two photon energy distribution end points are presented. These data are combined into one average data set with a systematic uncertainty of {+-}5%. The statistical precision of this combined data set, coupled with the sensitivity to the strength of the short range tensor interaction observed in the parallel-perpendicular cross section difference, makes this an attractive reaction for investigating aspects of the NN interaction. To do this reliably requires a complete, systematic description of the reaction through the {delta} region. Recent NN-N{delta} coupled-channel calculations which include fully retarded pion potentials are compared with multipole fits to the data. These calculations cannot reproduce the energy and angle dependence of the data. The character of the disagreement suggests that the remaining problems may lie with the treatment of the {delta}. (c) 1999 The American Physical Society.

Measurements of the total and differential cross sections for η-meson photoproduction on 1H, 2D, and 14N liquid targets from threshold to 1.2 GeV, have been taken using the tagged Bremsstrahlung photon beam produced by the electrons extracted from the ELSA storage ring at Bonn. The reaction was identified by detecting the η decay products in the neutral meson spectrometer SPES0-2π, while the recoil baryons (proton, neutron or deuteron) were detected by a variety of large angle scintillator detectors. We present here our experimental results on the Deuterium target, both the comparison of the quasi-free proton and neutron as well as results on the coherent production. Our preliminary results for the counting rates integrated on the S11 excitation show significantly smaller figures for the neutrons than for the protons. This is consistent with an Isoscalar part of the Amplitude roughly ten times smaller than the Isovector one and also explains the very low rate of coherent deuterons observed.

Cross sections and beam asymmetries for the reaction p(pπ0)pp have been measured for incident polarized proton energies from the threshold to 1 GeV, and compared with those for the charged pion channels in p(n,π±)NN reactions. The observed anisotropy difference around 540 MeV has been ascribed to the 3D1 partial wave contribution to the np initial state. (AIP)

Measurements of the total and differential cross sections for η-meson photoproduction on 1H, 2D, and 14N liquid targets from threshold to 1.2 GeV have been taken using the tagged Bremsstrahlung photon beam produced by the electrons extracted from the ELSA storage ring at Bonn. The reaction was identified by detecting the η decay products in the neutral meson spectrometer SPESO-2π, while the recoil baryons (proton, neutron, or deuteron) were detected by a variety of large angle scintillator detectors. We present here our experimental results on the deuterium target, both the comparison of the quasi-free proton and neutron as well as results on the coherent production. Our preliminary results for the counting rates integrated on the S11 excitation show significantly smaller figures for the neutrons than for the protons. This is consistent with an isoscalar part of the amplitude roughly ten times smaller than the isovector one and also explains the very low rate of coherent deuterons observed.

We have measured total and differential cross sections for η‐meson photo‐production on 7 cm thick 1H, 2D, and 14N liquid targets from threshold to 1.2 GeV, using the tagged Bremsstrahlung photon beam produced by the electrons extracted from the ELSA storage ring at Bonn. The photoreaction was identified by detecting the η decay products in the neutral meson spectrometer SPES0‐2π, while the recoil baryons (proton, neutron, or deuteron) were detected by a variety of large angle scintillator detectors. Some of our recent preliminary results, both theoretical and experimental, will be discussed.

The associated strangeness production in pp collisions was studied at bombarding energies of 2.3 and 2.7 GeV by detecting the outgoing K + particles with a high resolution magnetic spectrometer at forward angles up to 23.5° laboratory angle. The kaons were separated from an immense background of protons and pions by a highly resolving TOF electronics addition to vetoes from Cerenkov detectors utilizing either β differing Cerenkov light cones in lucite or different thresholds for light production in aerogel. The hyperon-nucleon missing mass spectra obtained show strong deviations from pure phase space which is ascribed to final state interactions of the pΛ and the Nσ systems. The structures found are discussed and compared with results from K − d → π − YN experiments, with theoretical calculations in the frame of OBE models, and with the prediction of sharp strange dibaryon resonances from several quark-bag models.

In constituent quark models, a tensor interaction, mixing quark spins with their relative motion, is introduced to reproduce the observed baryon spectrum. This has a consequence completely analogous to the nuclear tensor force between the n and p in deuterium. A D state component is mixed into what would otherwise be a purely S-wave object. The D-wave component breaks spherical symmetry, resulting in a non-vanishing matrix element for the nucleon and a static quadrupole moment and deformation for its first excited state, the Δ resonance, at ∽325 MeV. The magnitude and sign of this D-state component are quite sensitive to the internal structure of the proton and have been of great interest in recent years [1].

The Laser Electron Gamma Source (LEGS)[1] has recently begun operations at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory. At LEGS, laser light is Compton backscattered from the 2.5 GeV electrons circulating in the X-Ray storage ring of the NSLS. The backscattered photons have gamma ray energies, k < 320 MeV. The corresponding scattered electrons are detected in a tagging spectrometer which is incorporated into the storage ring. This tag provides a determination of the photon energy to ~ 5 MeV [2]. Since the laser light is polarized, and since the spin-flip amplitude in Compton backscattering is very small, the resulting polarization of the gamma-ray beam is very high.

Angular distributions for the elastic and inelastic scattering of 0.8 GeV protons from /sup 12/C, /sup 13/C, and /sup 208/Pb have been measured. Reported are data for the ground, 4.4 MeV 2/sup +/, 7.6 MeV 0/sup +/, 9.6 MeV 3/sup -/, and 14.1 MeV 4/sup +/ states of /sup 12/C; the ground, 3.1 MeV 1/2/sup +/, 3.7 MeV 3/2/sup -/, 6.9 MeV 5/2/sup +/, 7.6 MeV 5/2/sup -/, and 11.9 MeV () states of /sup 13/C; and the ground, 2.6 MeV 3/sup -/, and 3.2 MeV 5/sup -/ states of /sup 208/Pb. Analyses of the elastic angular distributions are made using the partial wave formalism and the Kerman-McManus-Thaler approach to the nucleon-nucleus optical potential; a realistic spin-orbit term is included. The inelastic transitions are analyzed within the framework of the distorted-wave Born-approximation, using transition strengths consistent with previous low-energy studies of inelastic scattering. A simple single-particle-plus-excited-core model is used for /sup 13/C. In terms of this analysis, an assignment of J/sup ..pi../ = (5/2,7/2)/sup +/ is made for the 11.9 MeV state in /sup 13/C.

J. FONG 1, T.S. BAUER, G.J. IGO, G. PAULETTA, R. RIDGE i, R. ROLFE l, j. SOUKUP 2, C.A. WHITTEN, Jr. Department of Physics, University of California, Los Angeles, CA 90024, USA G.W. HOFFMANN University of Texas, Austin, Texas 78712, and Los Alamos Scientific Laboratory, Los Alamos, NM87545, USA N. HINTZ, M. OOTHOUDT Department of Physics, University of Minnesota, Minneapolis, MN 55455, USA G. BLANPIED, R.L. LILJESTRAND Department of Physics, University of Texas at Austin, Austin, TX 78712, USA and T. KOZLOWSKI Brookhaven National Laboratory, Upton, NY 11973, USA Received 20 June 1978 The p-4He elastic cross section at 788 MeV has been measured for laboratory angles between 13.3 ° and 165.5 ° corre- sponding to a range of four-momentum-transfer, -t, from 0.11 to 4.19 GeV2/c 2 . Evidence is presented for a backward diffraction-like structure not previously observed (3.4 < -t < 4.22 GeV2/c2). In the region 1.6 < -t < -3.4 GeV2/c 2 a smooth fall off from the shoulder due to triple scattering is observed with no evidence for quadruple scattering. In the present letter we present the measurement of essentially the entire angular distribution for p-4He elastic scattering at 788 MeV. For the first time da/dt has been systematically studied in the intermediate range of angles as well as for the far backward angles, thus allowing a connection to be made between the direct amplitude and exchange amplitudes which may be important at back angles. In recent years there has been considerable exper- imental and theoretical work on the elastic scattering of protons on 4He at intermediate energies (order of 1 GeV). From an experimental point of view, this 1 Present address: Formal Computers Inc., 925 Westwood Boulevard, Los Angeles, Calif 90024. 2 Present address: Department of Physics, University of Al- berta, Edmonton T6G2J 1, Canada. elastic scattering process is relatively easy to study since the ground state of 4He is separated from a mul- tibody continuum by at least 20 MeV. With regard to theoretical interpretation of the data, the nuclear structure of 4He is reasonably well known so that proton:He elastic scattering is a good test for theo- ries of nucleon-nucleus elastic scattering at interme- diate energies. The experimental data can be used to study various effects on the reaction mechanism such as two body correlations in the nuclear wave func- tion [1], effects due to the spin dependence of the nucleon-nucleon amplitudes [2], the effects of iso- bar intermediate states [3], non-eikonal effects in the reaction mechanism [4-6], and exchange effects at backward angles [7]. Most of the past experimen- tal data, which include both cross section [8] and polarization measurements [9], have been taken for 205

The pion double-charge exchange reaction (${\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}}$) has been used to measure the ground-state masses of $^{12}\mathrm{O}$, $^{16}\mathrm{Ne}$, $^{24}\mathrm{Si}$, and $^{32}\mathrm{Ar}$. The mass excesses were found to be 32.059(48), 24.051(45), 10.682(52), and - 2.181(50) MeV, respectively. These are the first reported measurements of the masses of $^{24}\mathrm{Si}$ and $^{32}\mathrm{Ar}$ and the values for $^{12}\mathrm{O}$ and $^{16}\mathrm{Ne}$ are improved over previous results. Good agreement with the isobaric multiplet mass equation $M=a+b{T}_{z}+c{{T}_{z}}^{2}$ is obtained for the known members of all four quintets.NUCLEAR REACTIONS Pion double-charge exchange, $^{9}\mathrm{Be}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{9}\mathrm{C}$, $^{12}\mathrm{C}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{12}\mathrm{O}$, $^{13}\mathrm{C}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{13}\mathrm{O}$, $^{16}\mathrm{O}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{16}\mathrm{Ne}$, $^{24}\mathrm{Mg}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{24}\mathrm{Si}$, $^{32}\mathrm{S}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})^{32}\mathrm{Ar}$, $E=180$ MeV, measured $Q$ and $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$ (5\ifmmode^\circ\else\textdegree\fi{}).

Elastic cross sections for the scattering of positive and negative pions from /sup 58,60,64/Ni were measured at 30 MeV incident pion energy. A clear isotope effect was observed in the ..pi../sup -/ cross sections while no effect was observed in the ..pi../sup +/ cross sections. The cross sections were compared to predictions made by various optical model calculations. In general, both ..pi../sup +/ and ..pi../sup -/ cross sections were poorly described and the ..pi../sup -/ isotope effects were not well reproduced. Anomalous effects first observed in pionic atoms may also appear in the present data.

A method to accurately and quickly measure target thickness and uniformity for large area targets is described. The technique takes advantage of the fact that typical transmission curves for continuous beta-ray spectra are exponential up to very small transmission (⪡1%) under suitable conditions. Depending upon the particular beta source used, the technique can be optimized for any region of target thickness between 0–800 mg/cm 2 . A system to measure target thicknesses between 1–30 mg/cm 2 using a 147 Pm beta source was constructed and its performance is evaluated.

Elastic cross sections for the scattering of negative pions from /sup 12/C were measured at 19.5 and 30 MeV incident pion energy. At both energies the new cross sections show fair agreement with optical model predictions. At 30 MeV the new cross sections disagree at forward angles with previously measured values, while at 19.5 MeV the data represent the first report of /sup 12/C ..pi../sup -/ scattering at this energy.

The inelastic scattering of 162-MeV pions was studied over the angular range 35/sup 0/ to 100/sup 0/ in the laboratory system and the data were analyzed with a model that incorporates shell-model wave functions into a distorted-wave impulse approximation formalism. Reduced transition probabilities were obtained for low-lying levels and compared with information previously reported. In addition, evidence is obtained for theoretically predicted levels with high spin that have not been observed previously.

Angular distributions are reported for 0.8 GeV proton elastic and inelastic scattering from /sup 14/N. The data are analyzed with the optical model using a spherical Woods-Saxon potential and the distorted wave Born approximation with collective form factors.

Angular distributions for the elastic and inelastic scattering of 0.8 GeV protons from /sup 24/Mg and /sup 26/Mg are presented. Cross sections for protons exciting states of energy up to about 10 MeV are measured using a high resolution spectrometer. Coupled channels analyses of scattering data to the 0/sup +/, 2/sup +/, 4/sup +/, and 6/sup +/ states in the ground state rotational band, the 2/sup +/, 3/sup +/, 4/sup +/, and 6/sup +/ states in the ..gamma..-vibrational band, the 0/sup +/, 2/sup +/, and 4/sup +/ states in the ..beta..-vibrational band, and the 3/sup -/ and 5/sup -/ members of the K/sup ..pi../ = 0/sup -/ and 3/sup -/ vibrational bands in /sup 24/Mg are presented. Also reported are coupled channels analyses of the experimental angular distributions in /sup 26/Mg for the 0/sup +/, 2/sup +/, and 4/sup +/ states in the ground state band, the possible 2/sup +/, 3/sup +/, and 4/sup +/, ..gamma..-band members, and several 3/sup -/ members of K/sup ..pi../ = 0/sup -/ and 3/sup -/ bands. The data for the 3/sup -/ states in both /sup 24/Mg and /sup 26/Mg differ both in shape and angular positions of the maxima and minima. Coupled channelsmore » analyses are able to account for these differences in the 3/sup -/ experimental cross sections by selecting K/sup ..pi../ = 0/sup -/ or 3/sup -/. This is believed to be the first observation of ''K dependence'' for l = 3 excitations in inelastic scattering by s-d shell nuclei. Distorted wave Born approximation analyses of the other states in /sup 26/Mg excited by l transfers from 2 to 4 are also described. Several new assignments of J/sup ..pi../ for excited states in /sup 26/Mg are proposed based upon the distinctive l transfer dependence found in the positions of the first maximum and in the general shapes of the angular distributions. Multipole moments extracted from the deformed optical potentials are related to those of the matter distributions by Satchler's theorem. These are compared to multipole moments obtained from analyses of hadronic scattering data, as well as with the moments of the charge distributions determined by electromagnetic measurements.« less

Elastic scattering analyzing powers and differential cross sections for 800 MeV → p + 54Fe, 58,64Ni are reported. An approximately mode-independent technique is used to extract information concerning the neutron density distributions of these nuclei.

DWIA predictions and comparison with experiment are made for 650 and 800 MeV proton scattering to low lying states in 24 Mg, 26 Mg, 28 Si, 30 Si, 34 S, 40 Ca and 42 Ca. Electromagnetic constraints on proton and neutron ground-state and transition densities are used to minimize nuclear structure uncertainties. Generally good agreement with the data is seen.

Results are presented of coupled-channels analyses of proton inelastic scattering data for the nucleus /sup 24/Mg, in which the 2/sup +//sub 2/, 4.24 MeV, 3/sup +/, 5.2 MeV, 4/sup +//sub 2/, 6.01 MeV, and 5/sup +/(.), 7.8 MeV states of the ..gamma..-vibrational band are excited, at incident proton energies of 20.3, 40, and 800 MeV. Previous coupled-channels analyses of proton and ..cap alpha.. particle inelastic scattering data for these states in /sup 24/Mg have completely failed to account for the shapes and magnitudes of the 3/sup +/, 4/sup +//sub 2/, and 5/sup +/ inelastic cross sections. In the present analysis, the inclusion of an additional nuclear vibrational multipole which permits a direct transition from the ground state to the 4/sup +//sub 2/, 6.01 MeV state is shown to provide a tremendous improvement in the theoretical description of the inelastic cross sections of all the members of the ..gamma..-vibrational band, at each of the three incident proton energies considered. The same nuclear structure parameters are used at all three incident energies, along with phenomenological optical potentials specific to each energy. The new results for the 3/sup +/, 5.2 MeV state also shed light on the energy dependence of the direct spin-flipmore » mechanism in proton inelastic scattering.« less

New differential cross section and analyzing-power data for 800-MeV p/sub pol/ + /sup 12/C, /sup 116,124/Sn inelastic scattering to the first 2/sup +/ states are presented. A distorted-wave Born-approximation analysis which utilizes collective form factors and includes deformation of the spin-orbit potential is shown to provide a reasonable description of the analyzing-power data.

80 MeV positive and negative pions inelastically scattered from targets of /sup 12/C and /sup 40/Ca have been studied at laboratory angles between 50/sup 0/ and 120/sup 0/. Angular distributions are presented for scattering from the 4.44 MeV (2/sup +/) state in /sup 12/C, the 3.7 MeV (3/sup -/), 13.4 MeV, and 17.5 MeV states in /sup 40/Ca. The cross sections are compared with distorted wave calculations using potentials obtained from elastic scattering.

Differential cross sections for the reaction ..pi../sup +/+d..-->..p+p were measured for pion laboratory energies of 65, 72.5, 80, 95, 110, 125, and 140 MeV. The integrated cross sections for these energies were found to be 7.51 +- 0.19, 7.91 +- 0.16, 8.64 +- 0.15, 9.61 +- 0.15, 11.3 +- 0.2, 11.7 +- 0.3, and 11.3 +- 0.3 mb, respectively. These values indicate that the centroid and width of the energy dependence for the resonance in this reaction is lower and greater, respectively, than predicted by most theoretical models of the process. Comparisons made with predictions by Blankleider and Afnan show a qualitative difference between experimental measurements and calculations of the P/sub 4/(costheta) term in the polynomial expansion of the differential cross section. This may indicate a more important role for rho-like exchange in the reaction mechanism than that included by the calculations.

Analyses of 0.8 and 1 GeV $p$+$^{208}\mathrm{Pb}$ elastic angular distribution data have obtained neutron-proton root-mean-square radius differences ($\ensuremath{\Delta}{r}_{\mathrm{np}}$) which are not consistent. Therefore, the 0.8 GeV experiment was repeated using a high resolution spectrometer. The new higher precision data are consistent with the older data, apart from a 15% overall normalization difference. A second order Kerman-McManus-Thaler optical model analysis of the new data, using a model-independent neutron density, yields $\ensuremath{\Delta}{r}_{\mathrm{np}}=0.14\ifmmode\pm\else\textpm\fi{}0.04$ fm, in good agreement with the most recent result obtained (0.16\ifmmode\pm\else\textpm\fi{}0.05 fm) from a similar analysis of the older 0.8 GeV data. In addition, the elastic angular distribution was extended to 42.5\ifmmode^\circ\else\textdegree\fi{} center of mass in order to explore the momentum transfer region from 3.5 to 5.3 ${\mathrm{fm}}^{\ensuremath{-}1}$. Although the familiar diffraction pattern persists to 42.5\ifmmode^\circ\else\textdegree\fi{}, it was not possible within the framework of our application of the Kerman-McManus-Thaler optical model to fit the data even qualitatively at the larger momentum transfers.NUCLEAR REACTIONS $^{208}\mathrm{Pb}$($p$,$p$), $E=0.8$ GeV, measured $\ensuremath{\sigma}(\ensuremath{\theta})$; enriched target; resolution \ensuremath{\simeq} 100 keV, ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=2.5\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 42.5\ifmmode^\circ\else\textdegree\fi{}$. Microscopic optical model analysis using KMT potential; deduced $\ensuremath{\Delta}{\mathcal{r}}_{\mathrm{np}}$; error analysis and comparison with other results.

The first elastic-scattering analyzing-power (${A}_{y}$) data at 0.8 GeV are presented and discussed. Angular distributions of ${A}_{y}$ over the range 2\ifmmode^\circ\else\textdegree\fi{} to 20\ifmmode^\circ\else\textdegree\fi{} (30\ifmmode^\circ\else\textdegree\fi{} for $^{12}\mathrm{C}$) have been obtained for $^{12}\mathrm{C}$, $^{58}\mathrm{Ni}$, $^{90}\mathrm{Zr}$, and $^{208}\mathrm{Pb}$ using the high-resolution spectrometer at the Clinton P. Anderson Meson Physics Facility. The analyzing powers oscillate sharply over positive values in qualitiative agreement with expectations.

New differential cross sections for 0.8 GeV proton inelastic excitation of the first 2+ and 4+ states in 58Ni are compared with distorted wave Born approximation and coupled-channels predictions. Multistep processes and multi-phonon mixing are both shown to be important in describing the excitation of the 4+ state.

The initial results of a systematic investigation into pion-double-charge-exchange reactions are reported. Data consisting of angular distributions and excitation functions have been measured in an effort to determine the reaction mechanism and understand its implications for nuclear physics. Cross sections are presented for (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{\ensuremath{-}}$) reactions on $^{9}\mathrm{Be}$ $^{12,13}\mathrm{C}$, $^{16,18}\mathrm{O}$, $^{24,26}\mathrm{Mg}$, $^{32}\mathrm{S}$, and $^{209}\mathrm{Bi}$. Surprising systematics of the reaction as functions of pion scattering angle and energy, as well as target mass and isospin, are revealed. The data are discussed in terms of two reaction models, one involving a higher-order optical potential and the other involving multiple reaction amplitudes.