Measurements of the ($p,n$) continuum spectra for targets of ${}_{}{}^{103}{}_{}{}^{}\mathrm{Rh}$, ${}_{}{}^{104,105,106,108,110}{}_{}{}^{}\mathrm{Pd}$, and ${}_{}{}^{107,109}{}_{}{}^{}\mathrm{Ag}$ at proton energies of 18, 22, and 25 MeV are compared with the predictions of the hybrid model for pre-equilibrium reactions. The systematics of the odd-even differences in spectral shape are found to be much clearer than in a previous measurement at lower energy with targets near a closed shell. Most of the variation in spectral shape between even- and odd-$A$ targets is attributed to energy shifts produced by pairing effects. Comparisons between the various even-$A$ or odd-$A$ targets show little change in shape and magnitude of the highest energy portion of the measured ($p,n$) spectra over this range in $A$; this is consistent with the predictions of the model. The density of one-proton one-neutron-hole states at low excitations is calculated from a single-particle basis; the calculated values show more structure than is implied by the data, but do have the correct energy dependence when averaged over a wide enough interval.

NUCLEAR REACTIONS ${}_{}{}^{103}{}_{}{}^{}\mathrm{Rh}$, ${}_{}{}^{104,105,106,108,110}{}_{}{}^{}\mathrm{Pd}$, ${}_{}{}^{107, 109}{}_{}{}^{}\mathrm{Ag}\mathrm{}(p,n)\mathrm{}$, $E_p=18, 22, 25$ MeV; measured $\sigma (E_n,\theta )$; deduced $\sigma \left(E_n\right)$; natural (Rh) and enriched (Pd and Ag) targets.

The levels of ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ have been investigated via the ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}(\alpha ,n\gamma ){}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ reaction up to 3.4 MeV excitation. The level scheme which has been obtained includes most of the previously reported levels. The lifetimes of 18 levels in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ have been measured by the Doppler shift attenuation method at bombardment energies between 6.4 and 8.0 MeV.

NUCLEAR REACTIONS ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}(\alpha ,n\gamma )$, $E_{\alpha }=6.4\mathrm{}-8.0$ MeV, enriched targets, measured $E_{\gamma }$, $I_{\gamma }$, $\Delta E_{\gamma }\left(\tau \right)$ confirmed ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$ levels, deduced $\tau$.

The giant resonance regions in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ have been investigated by inelastic scattering of 61-MeV protons with an energy resolution of about 100 KeV. Cross sections for the giant quadrupole resonance at $E_x\approx 63A^{-\frac{1}{3}}$ MeV exhaust 90±15% of the energy-weighted sum-rule strength for an isoscalar $E2\mathrm{}$ excitation in both nuclei. The angular distribution for the giant quadrupole plus giant dipole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ is compared with microscopic-model distroted-wave Born approximation calculations. A pronounced fine-structure resonance is observed in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at $E_x\approx 56A^{-\frac{1}{3}}$ MeV (9.4 MeV). The angular distribution for this resonance is well described by distroted-wave Born approximation calculations for an $E2\mathrm{}$ or $E3\mathrm{}$ excitation, but not for an $E0\mathrm{}$ excitation. No prominent fine-structure resonances are observed in ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. The spectra in the bound-state region for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ show a pronounced structure centered at $E_x\approx 4$ MeV, for which the angular distribution is best described by distorted-wave Born approximation calculations for $E3\mathrm{}$ or $E4\mathrm{}$ excitations.

NUCLEAR REACTIONS ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}(p,p^{\prime })$, $E_p=61\mathrm{}$ MeV, $E_x=0\mathrm{}-31$ MeV; measured $\sigma (E_x,\theta )$; discuss giant resonances, deduced $L$, ${\beta }_L$.

The decay schemes of ${}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ were studied by $\gamma$-ray spectroscopy with the ${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}(\alpha ,2\mathrm{}n){}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},p2\mathrm{}n){}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ reactions. $\gamma$-singles spectra and $\gamma$-angular distributions were taken. A $\gamma -\gamma$-coincidence measurement was carried out with the ($\alpha ,2\mathrm{}n$) reaction. Twenty four new energy levels were established. A stretched spin band built on the isomeric ${9/2}^{+}$ level at 86 keV and a ${3/2}^{-}$ ground-state quasirotational band were found.

NUCLEAR REACTIONS ${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}(\alpha ,2\mathrm{}n)$, $E_{\alpha }=22.5\mathrm{}$ MeV, measured $E_{\gamma }$, $I_{\gamma }$, $\gamma -\gamma$-coin, $\gamma \left(\theta \right)$, ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},p2\mathrm{}n)$, $E_{{}_{}{}^{16}{}_{}{}^{}\mathrm{O}}=52\mathrm{}$ MeV, measured $E_{\gamma }$, $I_{\gamma }$, $\gamma \left(\theta \right)$, ${}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ deduced levels, $J$, $\pi$ Enriched targets.

The ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}(\gamma ,n){}_{}{}^{139}{}_{}{}^{}\mathrm{Ce}$ reaction has been studied near threshold with high energy resolution. The angular distribution of photoneutrons was measured at 90° and 135°, and the $M1\mathrm{}$ and $E1\mathrm{}$ strength functions at an excitation of approximately 9.1 MeV were determined. The measured integrated $M1\mathrm{}$ strength was found to be consistent with the existence of a giant $M1\mathrm{}$ resonance centered at 8.7 MeV as suggested both by calculation and previous electron scattering data. The integrated $E1\mathrm{}$ strength was also found to be consistent with what is known of the $E1\mathrm{}$ strength function in the threshold region.

NUCLEAR REACTIONS ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}(\gamma ,n)$, $E=9.1\mathrm{}$ MeV, measured $\sigma (E_n,\theta )$, deduced $\Sigma {\Gamma }_{\gamma 0}\mathrm{}\left(M1\mathrm{}\right)\mathrm{}$ and $\Sigma {\Gamma }_{\gamma 0}\mathrm{}\left(E1\mathrm{}\right)\mathrm{}$.

Particle-$\gamma$ angular correlations have been measured for transitions from the 373, 593, 990, 2877, 3027, and 3270 keV states in ${}_{}{}^{43}{}_{}{}^{}\mathrm{Ca}$. In addition, information about the decay schemes of states at 2695 and 2943 keV was obtained. These levels were populated with known initial alignment by detection of $\alpha$ particles from the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}{({}_{}{}^3{}_{}{}^{}\mathrm{He}, \alpha )}^{43}$ reaction at 0° relative to the beam. The measured value of the $\frac{M2\mathrm{}}{E1\mathrm{}}$ mixing ratio of the 990→ 373 keV transition is $\delta =0.012\mathrm{}\pm 0.017$. This small value of $\delta$ implies an upper limit on the $M2\mathrm{}$ strength for this transition which is consistent with the systematics of other $M2\mathrm{}$ rates in this mass region. The measured angular correlations, in conjunction with previous work, suggest spin-parity values of ${\frac{3}{2}}^{+}$ for the 2877 keV state, ${\frac{3}{2}}^{+}$ for the 3027 keV state, and ${\frac{5}{2}}^{+}$ or ${\frac{5}{2}}^{-}$ for the 3270 keV state.

NUCLEAR REACTIONS ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha )$, $E=15\mathrm{}$; measured coincidence $\gamma$ spectra, $I_{\gamma }\left({\theta }_{\gamma }\right)$. ${}_{}{}^{43}{}_{}{}^{}\mathrm{Ca}$ deduced $\delta$, $B\left(\Lambda \right)$, $J$.

$\alpha$ particles from the ${}_{}{}^{60, 62, 64}{}_{}{}^{}\mathrm{Ni}(p,\alpha )$ reactions were analyzed with the Notre Dame modified 100 cm broad-range magnetic spectrograph. Data were taken at bombarding energies of 13 to 16 MeV and at observation angles of 16 to 140°. Approximately 125 new levels were observed and uncertainties in excitation energies average 1.3 keV. Systematics of the ($p,\alpha$) reaction on the cobalt isotopes have been used to discuss spin assignments to several states in ${}_{}{}^{61}{}_{}{}^{}\mathrm{Co}$. Level densities and energy spacings are calculated for all the cobalt isotopes from $A=55\mathrm{}$ to $A=61\mathrm{}$.

NUCLEAR REACTIONS ${}_{}{}^{60,62,64}{}_{}{}^{}\mathrm{Ni}(p,\alpha )$, $E=13\mathrm{}-16$ MeV $\theta =16\mathrm{}-140°$, enriched targets. ${}_{}{}^{57,59,61}{}_{}{}^{}\mathrm{Co}$ levels deduced. High-spin state postulated using ($p,\alpha$) reaction systematics. Level densities deduced ${}_{}{}^{55-61}{}_{}{}^{}\mathrm{Co}$.

The ($p,t$) reaction at $E_p=19.0\mathrm{}$ MeV has been used to study five isotopes of Os ($A=190, 188, 184, 187, 185$) which lie in a transition region between the deformed rare earths and spherical nuclei. Cross sections and angular distributions have been measured to states up to about 2 MeV of excitation in all cases except ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}$ and ${}_{}{}^{190}{}_{}{}^{}\mathrm{Os}$ in which states were seen up to 4 MeV. The energies of the $J^{\pi }=0^{+}$ states which we see and their summed cross sections in percent of the ground state (in parenthesis) are: 913 (4.7), 1551 (1.8), and 1734 keV (6.3) in ${}_{}{}^{190}{}_{}{}^{}\mathrm{Os}$, 1087 (5.7), 1480 (3.7), 1705 (1.2), and 1765 keV (<1) in ${}_{}{}^{188}{}_{}{}^{}\mathrm{Os}$, and 1042 (8.4) and tentatively 1982 (1.2) and 2268 keV (1.3) in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Os}$. The $L=0\mathrm{}$ transitions seen in the odd isotopes are at 9.8, 77, 730, and 1657 keV in ${}_{}{}^{187}{}_{}{}^{}\mathrm{Os}$ and 1070 and 1213 keV in ${}_{}{}^{185}{}_{}{}^{}\mathrm{Os}$. The results show no positive evidence for the existence of strongly populated shape isomeric $0^{+}$ states similar to those seen in the transition region around $N=88\mathrm{}$. In ${}_{}{}^{188,190}{}_{}{}^{}\mathrm{Os}$ and possibly ${}_{}{}^{192}{}_{}{}^{}\mathrm{Os}$ the lowest exicted $K=0\mathrm{}$ and $K=4\mathrm{}$ bands have the properties expected for two phonon $\gamma$ vibrations. In addition to the rotational excitations in the odd isotopes, two strong transitions have been seen to states at 599 and 802 keV in ${}_{}{}^{185}{}_{}{}^{}\mathrm{Os}$ which we have postulated to be the $|K_0\pm 2|\gamma$ vibrations based on the ${1/2}^{-}$ [510] state with admixed one quasiparticle components. Similar states have been seen in ${}_{}{}^{187}{}_{}{}^{}\mathrm{Os}$. The lowest $L=0\mathrm{}$ transfers to states in ${}_{}{}^{185,187}{}_{}{}^{}\mathrm{Os}$ were found to have significantly lower intensity than the ground states in the adjacent even-$N$ nuclei. In the case of ${}_{}{}^{187}{}_{}{}^{}\mathrm{Os}$ the low lying $L=0\mathrm{}$ strength is split between two states. Calculations have been made to understand these phenomena in terms of blocking effects and Coriolis mixing.

NUCLEAR REACTIONS ${}_{}{}^{192,190,186,187,189}{}_{}{}^{}\mathrm{Os}\mathrm{}(p,t)\mathrm{}$, $E_p=19\mathrm{}$ MeV; measured $\sigma \left(\theta \right)$; deduced ${}_{}{}^{190,188,184,185,187}{}_{}{}^{}\mathrm{Os}$ levels, $J^{\pi }$; pairing plus DWBA calculations, comparison with expt. for lowest $L=0\mathrm{}$ states.

Differential cross sections for the elastic scattering of 2.754-MeV photons by lead have been measured for angles ranging from 15° to 150°. A comparison with theoretical data obtained from the Rayleigh scattering amplitudes of Cornille and Chapdelaine and the Delbrück scattering amplitudes of Papatzacos and Mork shows good agreement at 15°, 120°, and 150° and a discrepancy of up to a factor 1.7 at intermediate angles. Definite evidence for the real part of the Delbrück scattering amplitude has been obtained.

NUCLEAR REACTIONS $\mathrm{Pb}(\gamma ,\gamma )$ $E=2.754\mathrm{}$ MeV; measured Delbrück scattering, $\sigma \left(\theta \right)$, $\theta =15\mathrm{}°-150°$.

Discrepancies among experiments and theory on electron scattering from oriented holmium are partially resolved. An estimate is presented which suggests that the distorted-wave Born-approximation orientation effect calculated by Wright is too large by about a factor of 2. Distorted-wave Born-approximation calculations (made with a coupled-channel program) are presented which confirm this suggestion. They agree well with the Stanford data for orientation perpendicular to the scattering plane. The previous discrepancy for orientation along the recoil-momentum direction is reduced, but is not removed. The sensitivity of these results to the charge shape is examined although a fit to the data is not made. Results are given of a complete coupled-channel calculation for the first three nuclear states. Suggestions are made for future work, and cross sections and orientation effects for energyresolved scattering from holmium at 200 MeV are given.

NUCLEAR REACTIONS ${}_{67}{}^{165}{}_{}{}^{}\mathrm{Ho}(e,e^{\prime })$ oriented deformed nuclei, calculations; estimate for energy-unresolved scattering, based on elastic scattering alone; DWBA results; coupled-channel corrections; results for energy-resolved scattering, and for other orientations.

The finite-range full-recoil distorted-wave Born-approximation calculations have been done for the reaction ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$)${}_{}{}^{62}{}_{}{}^{}\mathrm{Ni}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$ employing the surface transparent "Brookhaven" potentials. It is found that for this reaction the recoil effects considerably affect the shape of angular distribution at angles greater than 30°. The no-recoil treatment is shown to overestimate the distorted-wave Born-approximation cross section by a factor of about 4.

NUCLEAR REACTIONS ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$), $E=65\mathrm{}$ MeV; calculated differential cross sections; ground state; finite-range, full-recoil, DWBA.

The reaction of 288 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ions with thick ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ targets has been studied experimentally with nuclear chemistry techniques. The formation cross sections of 130 radioactive nuclides were measured. The data have been used to delineate charge and mass distributions. The mass distribution is interpreted as a superposition of several components: transfer products (quasielastic component, 400±120 mb), multinucleon transfer products (deep inelastic component, 100±50 mb) and products from complete fusion-fission (620±150 mb). In addition, there is evidence for sequential fission of heavy products formed in quasielastic and deep inelastic transfer reactions. In the first case a double-humped mass distribution (150±30 mb) with the characteristics of low-energy fission is observed. Apparently, the sequential fission after deep inelastic processes occurs at higher excitation energies. For the quasielastic component the mass to charge ratio is close to that of the projectile or target, whereas for the deep inelastic component and for the fusion-fission component the mass to charge ratios appear to be full equilibrated. Proton pickup reactions in the deep inelastic reactions of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ lead to a buildup of products up to at least $Z=26\mathrm{}$, indicating a continuous development from deep inelastic transfer to fusion-fission.

NUCLEAR REACTIONS ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ + ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, $E\le 288$ MeV; measured $\sigma \mathrm{}(Z,A)\mathrm{}$; deduced charge and mass distributions, $\sigma$ for quasielastic transfer, deep inelastic transfer, fusion-fission, ${\sigma }_r$, $l$.

Different descriptions of the reaction ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ (${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$) ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ at 36 MeV leading to the ground and first excited states of ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ are examined. Sensitivity of the reaction cross section to various families of optical parameters is investigated and the so-called "surface transparent potential" is used as an alternate treatment. Exact finite-range distorted-wave Born approximation and coupled-channels Born approximation analyses of the reaction are performed, showing that the coupled-channels Born approximation analysis, even in its presently restricted form, leads to an improvement over the distorted-wave Born approximation predictions.

NUCLEAR REACTIONS ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ (${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$) calculated cross sections using exact finiterange CCBA with "surface transparent potential."

The fission probability was measured for a series of actinide nuclei as a function of the excitation enery using (${}_{}{}^3{}_{}{}^{}\mathrm{He},df$) and (${}_{}{}^3{}_{}{}^{}\mathrm{He},tf$) reactions. From these data, $\frac{{\Gamma }_n}{{\Gamma }_f}$ was determined from threshold up to ∼ 12 MeV of excitation energy, and fitted by evaporation calculations which do not contain any arbitrary normalization factors. For heavier actinides, these fits are possible only if one assumes the fission process to proceed through a first saddle point which is not axially symmetric. These results and calculations also reproduce previously known empirical trends of average values of $\frac{{\Gamma }_n}{{\Gamma }_f}$, as a function of $A$ and $Z$.

NUCLEAR REACTIONS, FISSION Measured fission probability in ${}_{}{}^{230-233}{}_{}{}^{}\mathrm{Pa}$, ${}_{}{}^{231-232}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{233-239}{}_{}{}^{}\mathrm{Np}$, ${}_{}{}^{237-238}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{239-243}{}_{}{}^{}\mathrm{Am}$, ${}_{}{}^{241-244}{}_{}{}^{}\mathrm{Cm}$. Determined barrier heights.

We study the effect of ordinary viscosity on nuclear fission by solving clasical equations of motion for the time evolution of fissioning nuclei. The collective potential energy is calculated both by means of the usual liquid-drop model and by means of a modified liquid-drop model that takes into account the lowering in the nuclear macroscopic energy due to the finite range of the nuclear force. The collective kinetic energy is calculated for incompressible, nearly irrotational hydrodynamical flow by use of the Werner-Wheeler method. The Rayleigh dissipation function, which describes the transfer of energy of collective motion into internal excitation energy, is calculated under the assumption that nuclear dissipation arises from individual two-body collisions. Prior to scission the nuclear shape is specified in terms of smoothly joined portions of three quadratic surfaces of revolution. After scission the fission fragments are represented by two spheroids with collinear symmetry axes. In addition to slowing the system down and converting some of the collective energy into internal energy, two-body viscosity hinders the formation of a neck. This leads to a more elongated scission configuration and consequently to a smaller final fission-fragment kinetic energy. From a comparison of calculated and experimental most probable fission-fragment kinetic energies for nuclei throughout the periodic table, we determine that at high excitation energies the average value of the viscosity coefficient $\mu$ is $\mu =0.015\mathrm{}\pm 0.005 \mathrm{TP}=9\mathrm{}\pm 3\times {10}^{-24\mathrm{}}$ MeV s/${\mathrm{fm}}^3$, provided that nuclear dissipation arises from two-body collisions. This is about 30% of the value that is required to critically damp the quadrupole oscillations of idealized heavy actinide nuclei.

NUCLEAR REACTIONS, FISSION Calculated dependence of most probable fission-fragment kinetic energies on viscosity and compared with experimental values. Liquid-drop model, hydrodynamical model, nuclear potential energy of deformation, nuclear inertia, nuclear dissipation, numerical solution of classical equations of motion for fissioning nuclei.

The development of the mass asymmetry vibrations in the final stages of the fission process is studied with an approximate treatment of the coupling to relative motion. A parametrized friction is introduced and its effects are studied. Numerical results are presented for ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$, together with estimates for the kinetic energy of the fragments.

RADIOACTIVITY, FISSION ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$; calculated mass distribution, kinetic energy distribution. Collective dynamics, shell correction method, cranking model.

Fission probabilities and mass distribution have been measured as a function of excitation energy for ${}_{}{}^{228}{}_{}{}^{}\mathrm{Ra}$ excited in the ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}\mathrm{}(t,pf)\mathrm{}$ reaction. Triple peaked mass distributions are observed for which the symmetric component has an apparent higher threshold by over 1 MeV. Results are analyzed in a statistical model which suggests the presence of a resonance in the fission probability for the asymmetric mass component and the need for level density enhancements (possibly due to axial asymmetry at the barrier) in the analysis of the fission probability for the symmetric component.

NUCLEAR REACTIONS, FISSION ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}\mathrm{}(t,pf)\mathrm{}$; measured fission probabilities for symmetric and asymmetric components; deduced fission barrier parameters, fission mass distributions.

Coherent photoproduction of ${\pi }^0$ on ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ is studied in the energy region $E_{\gamma }=200\mathrm{}-400$ MeV, with particular emphasis on the questions: where is rescattering important, what structure does it have, and what approximate scheme can be applied for calculating it? For this purpose, the second-order scattering term has been calculated in a model which incorporates the Fresnel correction to the Glauber theory, and takes into account the spin and the charge exchange effects. It is noted that near the threshold the correction would be very small. However, where rescattering is important, the spin and charge exchange effects and also Fresnel corrections are found to be important. This means that only in specific cases will a distorted-wave approach or a Glauber expansion provide the correct higher-order contributions for these reactions.

NUCLEAR REACTIONS ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(\gamma ,{\pi }^0)$; $E=200\mathrm{}-400$ MeV; rescattering terms are calculated to lowest order.

We have calculated differential cross sections for elastic ${\pi }^{+}$ and ${\pi }^{-}$ scattering from ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at several incident pion energies from 24 to 110 MeV. A full multiple-scattering treatment incorporating all orders of scattering was used. A separable form for the pion-nucleon $t$ matrix having off-shell cutoff form factors was assumed. Inclusion of an effective angle transformation, which takes into account the motion of the struck nucleon, along with binding and recoil factors in the pion-nucleon amplitude, leads to good over-all agreement with the experimental data.

NUCLEAR REACTIONS ${}_{}{}^4{}_{}{}^{}\mathrm{He}({\pi }^{\pm },{\pi }^{\pm })$ elastic scattering, $E=24\mathrm{}-110$ MeV; multiple-scattering theory; separable pion-nucleon $t$ matrices, angle transformation; $\sigma \left(\theta \right)$.

The emission of protons of energy 20-120 MeV in the interactions of 9 GeV/c negative pions with xenon nuclei was studied using the xenon bubble chamber. The tracks of 8009 protons in 2290 interactions have been measured. A tendency of the sideward collimation of protons is observed at an angle of about 60° to the beam. A possible interpretation of the effect as a manifestation of the shock wave propagating through the xenon nucleus is discussed.

NUCLEAR REACTIONS $\mathrm{Xe}\left({\pi }^{-}p\cdots \right)$; $E=9\mathrm{}$ GeV; measured ranges and angles; possibility of shock wave propagation in nuclei.