A new form of Siegert’s theorem has been obtained, exploiting the vanishing of the contribution of the nuclear center-of-mass convective current ${\mathrm{j}}^{\mathrm{c}.\mathrm{m}.\mathrm{}}$ to the photoabsorption amplitude in the frames of physical interest. Unlike the traditional version of the theorem, the new one is independent of ${\mathrm{j}}^{\mathrm{c}.\mathrm{m}.\mathrm{}}$. This version can be further simplified if the irrotational part of the electric multipole potential satisfies the Helmholtz equation. Some previous results on the deuteron photodisintegration are critically reviewed. The total cross section of this reaction is also studied numerically.

In this work we calculate the inelastic electron scattering charge form factor of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ using several N-N interactions. We employ the hyperspherical harmonics expansion method and include the contribution of harmonics above the minimal subset ($L_{\min )}$. We find that the inelastic electron scattering form factor obtained by us is in excellent agreement with the experimental observations of Walcher. However, the inelastic form factor is insensitive to the N-N interaction. Further, we find that the minimal subset approximation is inadequate for form factor calculations when the momentum transfer is large. We also calculate the elastic electron scattering form factor and find the usual disagreement between theory and experiment. A possible explanation for this discrepancy is given.

Measurements of neutron differential scattering cross sections at 4.55 MeV, and of neutron total cross sections at low energies have been made with an isotopically enriched sample of ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$. These results are combined with earlier neutron scattering data measured at 2.5 MeV in a consistent set of coupled channels analyses based on the low-lying collective excitations of ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$. The results of these measurements and analyses extend the tests of the collective character of ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$, and show the strong relationship between scattering and the dynamics of nuclear excitations. We are able to discriminate amongst different models which have been offered to interpret the low-lying structure of this nucleus. Some information from an associated 8 MeV neutron scattering experiment is also included; the entire neutron data set allows us to determine that the strength of the real scattering potential has a nonlinear neutron energy dependence, and further that its geometry must be energy dependent.

The interaction of positrons emitted by a ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ga}$ radioactive source with a thorium target was studied. Positron and electron energy spectra were measured in coincidence by using mini-orange spectrometers and high-resolution Si(Li) detectors. Peak structure which could be related to a new phenomenon has not been found in the spectra. All of the lines observed are explained in terms of well-known nuclear or atomic mechanisms.

The effect of geometrical considerations in the detection of flying spectator particles in projectile fragmentation processes is discussed. It is shown that different Fermi momenta have different probabilities of being detected in a detector of finite opening. A comparison of experimental inclusive deuteron spectra from the ${(\mathrm{}}^3$He,d) reaction on ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ with the spectator particle mechanism, including the corrections for the probabilities of detection of various Fermi momenta, shows that very good agreement can be found for the centroid position, width, and angular dependence of the peak due to the projectile fragmentation.

For the reaction ${}_{}{}^{20}{}_{}{}^{}$Ne${+\mathrm{}}^{197}$Au at the bombarding energy of 290 MeV the number of neutrons emitted in coincidence with quasielastic projectile-like fragments is counted eventwise with high efficiency and is used to discriminate between the two most frequent processes leading to a given ejectile, (i) the transfer of n nucleons from the projectile to the target, and (ii) the transfer of (n-4) nucleons together with the (subsequent) emission of an α particle. The two processes differ in the excitation energy given to the target-like residue and hence in the number of neutrons evaporated, and this difference appears also in the neutron-number ejectile-energy correlations. In the average, for each (9.3±1.0) MeV of excitation energy, one neutron is emitted. For process (i) (all missing projectile nucleons transferred to the target) the ejectiles’ mean kinetic energies follow conventional momentum matching conditions up to the transfer of five nucleons. A marked deviation from the same momentum matching conditions is observed for the pure pickup channels and is attributed to an interesting correlation of excitation energy distribution with the direction of nucleon transfer.

The n+α scattering problem is examined for the purpose of learning whether or not a correct consideration of the motion of the total center of mass is essential in a resonating-group calculation. The result indicates that, in the low-energy region where a sharp p-wave resonance level exists, it is important to properly take this motion into account. At high energies, our finding is that, in this system where the nucleon-number ratio of the interacting nuclei is not very different from 1, the differential cross sections calculated with and without a proper consideration of the center-of-mass degree of freedom are rather similar at forward angles, but greatly differ in the backward angular region.

A class of functions having the same analytic properties as the Jost function is introduced. In momentum space these functions can be calculated through solutions of some auxiliary integral equations. The present approach is applicable for both local and nonlocal potentials and suggests an unified calculational scheme for bound states and scattering problems.

We have extended our past measurements of the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(t,α)n reaction near the low-energy ${\mathrm{}(3/2)\mathrm{}}^{+}$ resonance by measuring eight more data points over the lab deuteron energy range 80–116 keV. This was accomplished by bombarding a tritium gas target with deuterons, in contrast to the previous measurements in which a deuterium gas target was bombarded with tritons. The present data are accurate to 1.6%. The results of including the present data in a simple two-channel, two-level, R-matrix analysis and also in a large three-channel, multilevel, R-matrix analysis are presented. The resonance is characterized by giving the S-matrix poles from the R-matrix analyses. Of interest is the discovery that both analyses give two resonance poles on different (unphysical) Riemann sheets, one of them being a so-called ‘‘shadow pole.’’ This is the first experimental observation of a shadow pole in nuclear and particle physics. Maxwellian reactivities up to a plasma temperature of 20 keV are presented.

Differential cross sections for elastic scattering of tagged, monochromatic photons have been measured on a water target for incident photon energies between 21.7 and 27.5 MeV and at scattering angles of 135° and 45°. These data are interpreted in terms of the total photoabsorption cross section in the region of the giant dipole resonance. We find that the data are reasonably consistent with previous direct measurements of the total photoabsorption cross section and inconsistent with more recent determinations of the total cross section by summing the various partial cross sections.

The excitation-energy distribution of transition strength to $1^{+}$ states excited via the ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$(p,n${)}^{26}$Al reaction at 134.4 MeV was measured for excitation energies up to 25 MeV. The structures observed in the neutron spectra with ΔL=0 angular distributions were identified as $1^{+}$ states, except for the isobaric analog transition. The total $1^{+}$ strength in this reaction was extracted by normalizing the intensity of the four lowest $1^{+}$ states to the strength measured for the analogous beta decays to these states. A detailed comparison of the experimental results with known analogous transitions and with a large-basis shell-model calculation leads to the conclusion that strengths to states of isospin T=0, 1, and 2 were observed in this reaction. The apportionment of the observed strength among the three isospin values is compared with the shell-model prediction. The total strength observed to all states below an excitation energy of 15 MeV is 57 percent of the total strength predicted by the shell-model calculation with the assumption of the ‘‘free-nucleon’’ normalization of the Gamow-Teller beta decay operator.

High-accuracy angular distribution measurements relative to that at 90° were performed for the ${}_{}{}^2{}_{}{}^{}(\gamma$,n)H reaction throughout the energy range of 4–18 MeV and for reaction angles of 45°, 135°, and 155°. The results indicate a significant departure from existing theoretical calculations below a photon energy of 10 MeV.

Elastic and inelastic scattering cross sections and analyzing powers have been determined for 16 MeV polarized protons incident on ${}_{}{}^{116}{}_{}{}^{}$,120,124Sn. Data extracted for these isotopes include scattering from the lowest $2^{+}$ and $3^{\mathrm{-}}$ collective states and two other less collective states ${(5\mathrm{}}^{\mathrm{-}}$,$4^{+}$) below 3 MeV in excitation. Our analysis of the data uses a coupled-channel formalism based on the harmonic vibrational model with a ($0^{+}$,$2^{+}$,$3^{-}$,$5^{-}$$4^{+}$) coupling scheme. Nuclear deformation parameters of the central and spin-orbit potentials for the excited states have been extracted and compared with similar quantities deduced from (n→,n) scattering from the same isotopes.

The ${}_{}{}^{78}{}_{}{}^{}$,80,82Kr${(}^3$He,d) reactions have been used to measure proton spectroscopic factors for many low-lying levels in ${}_{}{}^{79}{}_{}{}^{}$,81,83Rb. Summed spectroscopic strengths and the distributions of strength among states are compared to recent theoretical predictions. The spreading of strength is found to be less than predicted, especially for the 2$p_{1/2}$ and 1$g_{9/2}$ orbitals.

This investigation deals with a semiclassical expansion of the microscopic nucleon-nucleus optical potential utilizing the Green’s function approach. By expanding the relevant system of equations for the single-particle propagator, the nucleon self-energy, and the effective interaction in the mixed position-momentum representation, a quasi-ħ expansion is obtainable which is treated, in more detail, theoretically and numerically up to the second order. The resulting corrections to the standard local-density folding approach change the optical potential in the surface region and are important, it seems, in the energy region below 100 MeV.

We have irradiated natural chromium with protons and deuterons to produce ${}_{}{}^{52}{}_{}{}^{}\mathrm{Mn}_{}^{\mathrm{g}}{}_{}{}^{}$,m, primarily from the ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$(p,n) and ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$(d,2n) reactions. The excitation functions up to 27 MeV were measured by the foil activation method and were compared with results from a statistical model calculation based on the Hauser-Feshbach formalism with preequilibrium emission. For ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$(p,n${)}^{52}$${\mathrm{Mn}}^{\mathrm{g}}$,m, both the total cross section, σ(g+m), and the isomer ratio, σ(m)/σ(g), are reproduced to within 10% by the calculations. By contrast, for the ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$(d,2n${)}^{52}$${\mathrm{Mn}}^{\mathrm{g}}$,m reaction, we find that calculations overestimate σ(g+m) by ∼50% and underestimate σ(m)/σ(g) by nearly one-half. We find that arbitrary adjustments of level density or preequilibrium parameters can yield approximate agreement for σ(g+m) but do not improve the agreement for σ(m)/σ(g). A part of this discrepancy may be due to the fact that the preequilibrium calculations do not include angular momentum. However, to fully understand this discrepancy, deuteron breakup effects in the entrance channel must be taken into account. A companion paper explores this idea.

Recent experimental cross sections for the reaction ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$(d,2n${)}^{52}$${\mathrm{Mn}}^{\mathrm{g}}$,m are in marked disagreement with the standard statistical-model analysis. We have, therefore, analyzed the data with an approach that emphasizes direct-reaction contribution to the cross section. This is done in two steps. In the first step, the compound-nucleus formation cross section is defined such that only the internal part of the target nucleus is allowed to absorb the deuteron, thus leading to the formation of ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}_{}^{\mathrm{*}}{}_{}{}^{}$. The contribution of the external part is interpreted as going to direct reaction. The calculation of the internal part then proceeds by statistical evaporation of two neutrons to produce ${}_{}{}^{52}{}_{}{}^{}\mathrm{Mn}$. In the second step, the dominant part of the direct reaction, i.e., the deuteron breakup, followed by the capture of the proton, is considered. This quantum mechanical, breakup fusion process forms ${}_{}{}^{53}{}_{}{}^{}\mathrm{Mn}_{}^{\mathrm{*}}{}_{}{}^{}$, which then evaporates one neutron to produce ${}_{}{}^{52}{}_{}{}^{}\mathrm{Mn}$. The sum of the cross sections from these two processes fits the data quite well. The consistency of this twofold treatment is confirmed by our finding that the total reaction cross section for the deuteron is accounted for by summing the above two fusion cross sections with the additional direct-reaction cross sections that do not contribute to the production of ${}_{}{}^{52}{}_{}{}^{}\mathrm{Mn}$.

Transport coefficients for nucleon and momentum transport induced by the direct two-body collisions are calculated using a Fermi gas model for the colliding nuclei. It is found that at temperatures around T=5–6 MeV, the two-body transport coefficients are larger than the one-body transport coefficients by a factor of 2–3, resulting in much broader fragment distributions in nuclear collisions.

Higher-order couplings to inelastic excitations of surface vibrations can strongly affect the enhancement of heavy-ion fusion cross sections at sub-barrier energies. Detailed second-order calculations are presented for reactions between different nickel isotopes. The agreement with measured fusion cross sections is considerably improved with respect to conventional coupled channels calculations based on linear couplings.

The total capture cross section for the system ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$${+}^{238}$U has been measured at energies from 0.93 to 1.08 times the s-wave interaction barrier by detecting coincident fission fragments following full momentum transfer reactions. The subbarrier cross section cannot be reproduced by a one-dimensional barrier penetration model. Using a quantum mechanical coupled channels model, good agreement is obtained. The measured angular distributions of fission fragments were compared to the predictions of saddle and scission point transition state theory. Saddle point transition state model calculations fail to reproduce the data, while scission point transition state calculations are in agreement with their qualitative trend. Evidence for nonequilibrium processes is presented.