The role of spin-unsaturated subshells in calculations of optical-model spin-orbit potentials is investigated using a realistic nucleon-nucleon interaction. For projectiles of moderate bombarding energies the one-body spin-orbit potential is predicted to be quenched relative to that for nearby nuclei having only spin-saturated shells. The source of this quenching is the same as that discussed by Scheerbaum in an investigation of the quenching of spin-orbit splittings in bound states. A simple physical picture is given which permits a qualitative understanding of this quenching in terms of the components of the nucleon-nucleon interaction. An estimate of the effect on polarization-like observables is made, and a general problem with currently used tensor forces is reemphasized. The relationship of this problem to a number of other structure and scattering problems is stressed.

NUCLEAR REACTIONS, NUCLEAR STRUCTURE Calculation of contributions to the optical-model spin-orbit potential from spin-unsaturated subshells.

Surface barrier detectors at 16-18 angles measured simultaneously the differential cross sections for the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$($\alpha$,${\alpha }_0{\alpha }_1{\alpha }_2{\alpha }_3{\alpha }_4{\alpha }_5$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ in the bombarding energy range from 14.6 to 20.4 MeV and in steps of 10 keV. For $E_{\alpha }>18\mathrm{}$ MeV peak fitting techniques separated the yields of ${\alpha }_1$ ($Q=-6.05\mathrm{}$ MeV) from ${\alpha }_2$ ($Q=-6.13\mathrm{}$ MeV). The target was a differentially pumped windowless gas target of high purity ${\mathrm{O}}_2$. A total of 25 levels in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ ($16<\mathrm{}{E}_x<21\mathrm{}$ MeV) were analyzed by writing the reaction amplitude for spinless positive-parity particles as a nonresonant term which varies linearly with energy plus a sum over only resonant partial waves. Inelastic scattering angular distributions were expanded in terms of Legendre polynomials for $E_{\alpha }>18\mathrm{}$ MeV.

NUCLEAR REACTIONS ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$($\alpha$,${\alpha }_0{\alpha }_1{\alpha }_2{\alpha }_3{\alpha }_4{\alpha }_5$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, $14.6<~E_{\alpha }<~20.4$ MeV, $\Delta E_{\alpha }=10\mathrm{}$ keV; measured $\sigma (E,\theta )$ at 18 angles. Deduced ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ level parameters $J$, $\pi$, ${\Gamma }_{{\alpha }_0}$, ${\Gamma }_{{\alpha }_1}$, $\Gamma$, $E_R$. ${\mathrm{O}}_2$ gas target.

We have investigated the reaction ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$($t$,$p$)${}_{}{}^{20}{}_{}{}^{}\mathrm{O}$ using enriched (96.6%) ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ gas in a rotating gas cell and a multiangle spectrograph. Twenty-two angular distributions were measured for levels up to 10.2 MeV. Results are compared with predictions of a recent shell-model calculation.

NUCLEAR REACTIONS ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$($t$,$p$), $E_t=15.0\mathrm{}$ MeV; measured $\sigma (E_p,\theta )$. ${}_{}{}^{20}{}_{}{}^{}\mathrm{O}$ deduced levels, $L$, $\pi$, $J$. DWBA analysis. Comparison with shell and weak-coupling models. Enriched gas target.

${}_{}{}^2{}_{}{}^{}\mathrm{He}$ energy spectra were obtained for the ($d$,${}_{}{}^2{}_{}{}^{}\mathrm{He}$) reaction on targets of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at $E_d=55\mathrm{}$ MeV in a kinematically complete coincidence measurement of two protons with small relative energies. Projected proton-energy spectra show an enhancement of the cross section over phase space due to the final-state interaction between two protons in a relative ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state. ${}_{}{}^2{}_{}{}^{}\mathrm{He}$ angular distributions were found to be in reasonable agreement with predictions of microscopic distorted-wave Born-approximation calculations using spectroscopic amplitudes derived from intermediate-coupling wave functions.

NUCLEAR REACTIONS ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ($d$,${}_{}{}^2{}_{}{}^{}\mathrm{He}$), $E_d=55\mathrm{}$ MeV; measured $\sigma (E_f,\theta )$, microscopic DWBA analysis.

The cross section and angular distribution for the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$($\gamma$,$n_0$)${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ have been measured over an excitation energy range of 25-45 MeV. Neutron time-of-flight spectra were recorded at six angles (22.5°, 45°, 67.5°, 90°, 112.5°, and 135°) and at four bremsstrahlung end-point energies (30, 35, 40, and 45 MeV). Differential cross sections deduced from these spectra were fitted by a fourth-order Legendre-polynomial expansion. The cross section obtained from this expansion decreases smoothly from 3.95 mb at 25.5 MeV to 0.22 mb at 43.8 MeV. The appearance in this analysis of large first-, third-, and especially fourth-order coefficients, is strong evidence for significant $E2\mathrm{}$ cross section. An $E2\mathrm{}$ cross section extracted from the data exhausts approximately 68% of the isovector $E2\mathrm{}$ energy-weighted sum rule. The present data are compared to previous related measurements and excellent agreement is seen. In comparisons with theoretical studies on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, there is good general agreement but relatively poor detailed agreement.

NUCLEAR REACTIONS ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$($\gamma$,$n_0$)${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$, $E_x=25-45\mathrm{}$ MeV; measured $\sigma (E_x,\theta )$; deduced $E2$ strength.

Total ($p$,$n$) cross sections were measured with enriched targets of ${}_{}{}^{92,94}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{94,95,96,98}{}_{}{}^{}\mathrm{Mo}$, from each threshold energy to ∼6.7 MeV. Proton strength functions were deduced and compared with those of neighboring nuclei. The strength functions were characterized by a minimum which was interpreted as a valley between the $3s$ and $3p$ single-particle resonances. Optical-model calculations were performed to fit the deduced strength functions. Systematic variations in the depths of the absorptive potentials were found as a function of mass in the manner suggested by Johnson et al.

NUCLEAR REACTIONS ${}_{}{}^{92,94}{}_{}{}^{}\mathrm{Zr}$ ${}_{}{}^{94,95,96,98}{}_{}{}^{}\mathrm{Mo}$($p$,$n$) $E_p=1.7-6.7\mathrm{}$ MeV; measured total $\sigma \mathrm{}\left(E\right)\mathrm{}$. Deduced proton strength functions. Optical-model analysis, deduced absorptive potential well depths.

Accurate proton elastic-scattering cross sections were measured with enriched targets of ${}_{}{}^{92,94}{}_{}{}^{}\mathrm{Zr}$ from $E_p=2.0\mathrm{} \mathrm{to} 6.5$ MeV. The elastic-scattering cross sections, together with absorption cross sections, were analyzed with a Lane model which employed the optical potential of Johnson et al. The resulting parameters were compared with those obtained with a single-channel optical model and negligible differences were found. Significant differences between the ${}_{}{}^{92}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{94}{}_{}{}^{}\mathrm{Zr}$ real diffusenesses resulted from the inclusion of the ($p$,$p$) data in the analyses.

NUCLEAR REACTIONS ${}_{}{}^{92,94}{}_{}{}^{}\mathrm{Zr}$($p$,$p$)$E_p=2.0-6.5\mathrm{}$ MeV; measured $\frac{d\sigma }{d\Omega }$ at 135° and 165°. Lane-model and optical-model analyses of elastic scattering and absorption cross sections.

The polarization of 14.2 MeV neutrons elastically scattered through 20° by Cu and Pb is found to be substantially larger than calculated from standard optical model potentials, a similar effect to that reported recently for 16 MeV neutrons. It is proposed that these effects may be related to the geometry of the spin-orbit term in the optical model potential.

NUCLEAR REACTIONS Cu, Pb ($n$,$n$), $E_n=14.2\mathrm{}$ MeV; measured $\left|P\right(\theta \left)\right|$; $\theta =20\mathrm{}°, 34°$; optical model analysis

Reaction mechanism studies have been performed on the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ + ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ system at energies of 7-35 MeV/nucleon and on the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ + ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ system at 12-35 MeV/nucleon. Measurements included (1) forward-angle elastic scattering, (2) angular distributions and total cross sections for fission, (3) fission-fragment angular correlations, and (4) fragment charge, mass, and energy distributions for ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$($\alpha$,$f$) at 140 MeV. Total inelastic cross sections and interaction radii were derived from the elastic scattering data. These values were found to be in good agreement with the total cross section for fission for the ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ + ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ system, confirming the assumption that ${\sigma }_R\simeq {\sigma }_f$. Fission-fragment angular-correlation measurements were performed in order to deduce the distribution of linear momenta which characterize the residual heavy nuclei formed in these collisions. Complete linear momentum transfer probabilities (complete fusion) were also derived for both target-projectile systems as a function of energy. The data are compared with predictions of the proximity potential with one-body energy dissipation and with the intranuclear cascade code. The results of these comparisons are consistent with a picture in which complete fusion dominates the reaction mechanism below 10 MeV/nucleon, but pre-equilibrium processes assume increasing importance above this energy at the expense of fusion. In addition, evidence for a possible reduction in the interaction radius above 20 MeV/nucleon is reported.

NUCLEAR REACTIONS ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$($\alpha$,$\alpha$), ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$($\alpha$,$\alpha$), $E=69.2, 140$ MeV, ${\sigma }_R\mathrm{}\left(E\right)\mathrm{}$; ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$($\alpha$,$f$), $E=69.2, 140$ MeV, ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$($\alpha$,$f$), $E=28-140\mathrm{}$ MeV, $\sigma \left(\theta \right)$, $\sigma \mathrm{}\left(E\right)\mathrm{}$, fission-fragment angular correlations, $Z$ and $A$ distributions at 140 MeV; linear momentum transfer to residual nucleus deduced; results compared with ion-ion potential models and intranuclear cascade code.

For the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, experimental data are available for cross sections for complete fusion and all reactions from 80-102 MeV and for elastic scattering from 80 to 313 MeV. Most of these data can be adequately described by an energy-independent spherical optical potential with the proximity formulation for the real part and a Woods-Saxon form for the imaginary part. Three parameters have been varied, radius and surface width in the proximity potential and radius in the imaginary potential. The sum of the equivalent sharp radii of the interacting nuclei must be enlarged significantly in order to fit the fusion and scattering data. As a consequence, the sum of the "best fit central radii" for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ is ≈ 0.8 fm larger than the sum of the independently measured radii. If the proximity formulation is correct this implies dynamical shape or density adjustments during the collision.

NUCLEAR REACTIONS Optical model analysis for the reaction system ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$: fusion and reaction cross sections (80-102 MeV) and elastic scattering cross sections (80-313 MeV).

Spins, parities, and ${\alpha }_0$-decay branching ratios have been determined for a number of states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ using the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$*(${\alpha }_0$)${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$*(${\alpha }_0$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ reactions. The ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ nuclei were detected at 0°, and the alpha particles from the decay of the excited states formed in the (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$) reactions were detected over the range $40°\le {\theta }_{\mathrm{lab}}\le 97°$, typically corresponding to a range in the heavy-recoil center-of-mass system of $50°\le {\theta }_{\mathrm{RCM}}\le 120°$. Structure observed at an excitation energy of 22.5±0.5 MeV in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ appears to correspond to an $8^{+}$ state which is then a candidate for identification as the $8^{+}$ member of the $K^{\pi }=0^{+}, 4\mathrm{p}-4\mathrm{}\mathrm{h}$ rotational band. In ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ we have confirmed a number of spin assignments for states below 16 MeV in excitation, and in addition we have made the following assignments: 16.63 MeV ($7^{-}$), 17.3 MeV ($8^{+}$), 21.08 MeV ($9^{-}$), and 22.87 MeV ($9^{-}$). All of the ${\alpha }_0$ branching ratios for the strongly populated states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ are found to be roughly 100%, with the exception of those for the 17.3 MeV ($8^{+}$) and 21.08 MeV ($9^{-}$) levels which are found to be 40% and 65%, respectively.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$*(${\alpha }_0$)${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$) ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$*(${\alpha }_0$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, particle-particle angular correlations; $E_{\mathrm{lab}}=78\mathrm{}$ MeV, ${\theta }_{{}_{}{}^8{}_{}{}^{}\mathrm{Be}}\approx 0°$. Deduce $J^{\pi }$, $\frac{{\Gamma }_{{\alpha }_0}}{{\Gamma }_{\mathrm{total}}}$.

The (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$,$d$) reaction has been used to study high spin states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ at excitation energies of 16.6 and 17.4 MeV. Spectra of deuterons at 0° which are coincident with alpha decays to the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ground state show that the reaction excites a multitude of high spin states in this energy region. An attempt to parametrize the observed coincidence spectra in terms of two overlapping Breit-Wigner resonances was unsuccessful. The group at 17.4 MeV is probably two levels with $J=8\mathrm{}$ and $J=7\mathrm{}$. The $J=8\mathrm{}$ assignment is in agreement with a recent study with the (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$) reaction of a state at 17.3 MeV.

NUCLEAR REACTIONS ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${}_{}{}^6{}_{}{}^{}\mathrm{Li}$,$d$)${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$($\alpha$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ g.s. measured $d-{\alpha }_0$ angular correlation, deduced $J^{\pi }$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ high spin states.

The ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=180\mathrm{}°$ elastic and inelastic excitation functions have been measured for the systems ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ($27.8\le E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 31.5$ MeV) and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ($30.0\le E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 32.7$ MeV) in small steps ($\delta E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<100\mathrm{}$ keV). In both systems it is observed that the gross structures previously found ($\Gamma \approx 1-2$ MeV) are strongly split into finer structure. A statistical analysis of the data has been made to determine the average width, strength, and cross correlation of these narrow structures. The results are compared to the predictions of Hauser-Feshbach calculations. It is concluded that it is impossible within the standard statistical model to simultaneously reproduce both the observed widths and the average fluctuating cross sections.

NUCLEAR REACTIONS Measured elastic and inelastic excitation functions at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=180\mathrm{}°$ for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, $27.8<~E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~31.5$ MeV, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, $30.0<~E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~32.7$ MeV. Deduced average width, strength, and cross correlation of observed structures. Compared with Hauser-Feshbach predictions.

High-spin states in ${}_{}{}^{210}{}_{}{}^{}\mathrm{Rn}$ were observed with the aid of the ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}$(${}_{}{}^9{}_{}{}^{}\mathrm{Be}$,$3n$)${}_{}{}^{210}{}_{}{}^{}\mathrm{Rn}$ reaction. $\gamma -\gamma$ coincidence, excitation function, $\gamma$-ray angular distribution, and pulsed beam lifetime measurements were used to construct a decay scheme. Mean lives of four levels were deduced and multipolarities of $\gamma$-ray transitions and level spins were inferred.

NUCLEAR REACTIONS ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}$(${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, $3n\gamma$)${}_{}{}^{210}{}_{}{}^{}\mathrm{Rn}$, $E=40-55\mathrm{}$ MeV; measured $\gamma -\gamma$ coincidences, excitation function, $\gamma$-ray angular distributions, pulsed beam lifetimes, deduced level energies $T_{\frac{1}{2}}$, inferred multipolarities of $\gamma$-ray transitions, level spins.

The application of the maximal entropy approach as a dynamical procedure to collisions when there is incomplete resolution of the final states is discussed. The major objective is to provide a collision theoretic foundation for the phenomenological procedure of surprisal analysis which is applied to heavy-ion induced reactions in a companion paper. A reduced description where during the entire time evolution the degree of detail is commensurate with that available for the analysis of the final state is introduced. An exact equation of motion, in the form of a continuity equation, is derived for the reduced description. The most notable feature of the equation is the inherent presence of a dissipative term. Because of the finite duration of the collision, the final reduced distribution need not, however, be fully relaxed. It is shown it is possible to characterize the deviance from the statistical limit in terms of time-dependent constants of the motion. The post-collision measure of this deviance is the surprisal. The significance of the (time-independent) constraints, identified by surprisal analysis of experimental results, is discussed and the use of sum rules as a practical route to the identification of such constraints is noted. The formulation of the approach as a sophisticated statistical theory capable of representing direct reactions is discussed in the appendix. The variational character of the procedure of maximal entropy is also noted therein as a route to approximate descriptions.

NUCLEAR REACTIONS Statistical theories of heavy-ion reactions, surprisal analysis of the deviation of the observed distribution from the statistical limit, dynamical derivation of functional form of the surprisal, identification of constraints using sum rules, procedure of maximal entropy, equation of motion for reduced description.

Heavy-ion transfer reactions to highly excited states are examined in terms of surprisal analysis-a constrained statistical approach motivated by information-theoretic considerations. The practical use of the procedure is discussed and illustrated by application to the available data from a variety of reactions. The experimentally measured energy spectra for multinucleon transfer are found to be well described by a distribution of maximal entropy subject to constraints. These constraints are shown to imply that the distribution of single nucleon occupation numbers in the heavy residual nucleus is fully relaxed but that the two-particle (and higher) correlation functions are not. For few-nucleon transfers the energy spectra contain a second, smaller, component which is more strongly damped. The dynamical origin of the constraints is discussed in terms of sum rules derived from models for the transfer process. A simple model for grazing collisions which includes the effects of tangential friction (with the same damping constant for all exit channels) provides a qualitative and a quantitative account of the variation of the optimal $Q$ value with the number of transferred nucleons.

NUCLEAR REACTIONS Heavy ions, ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$X$), $X={}_{}{}^{17,16,15}{}_{}{}^{}\mathrm{N}, {}_{}{}^{15,14,13,12}{}_{}{}^{}\mathrm{C}, {}_{}{}^{13,12,11}{}_{}{}^{}\mathrm{B}, {}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$, $E=105\mathrm{}$ MeV. ${}_{}{}^{96}{}_{}{}^{}\mathrm{Mo}$(${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$,$X$), $X={}_{}{}^{15}{}_{}{}^{}\mathrm{O}, {}_{}{}^{13}{}_{}{}^{}\mathrm{C}, {}_{}{}^{10}{}_{}{}^{}\mathrm{B}, {}_{}{}^9{}_{}{}^{}\mathrm{Be}, {}_{}{}^7{}_{}{}^{}\mathrm{Li}$, $E=97\mathrm{}$ MeV. ${}_{}{}^A{}_{}{}^{}\mathrm{Mo}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},X)$, $X={}_{}{}^{13}{}_{}{}^{}\mathrm{C}, {}_{}{}^{12}{}_{}{}^{}\mathrm{B}$, $A=100, 98,97,96,95,94,92$, $E=97\mathrm{}$ MeV. ${}_{}{}^{53}{}_{}{}^{}\mathrm{Cr}$(${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$,$X$), $X={}_{}{}^{13}{}_{}{}^{}\mathrm{C}, {}_{}{}^{11}{}_{}{}^{}\mathrm{B}, {}_{}{}^9{}_{}{}^{}\mathrm{Be}$, $E=90\mathrm{}$ MeV. ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$(${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$,$X$), $X={}_{}{}^{14,12}{}_{}{}^{}\mathrm{C}, {}_{}{}^{13,11}{}_{}{}^{}\mathrm{B}, {}_{}{}^{10}{}_{}{}^{}\mathrm{Be}, {}_{}{}^9{}_{}{}^{}\mathrm{Li}$, $E=145\mathrm{}$ MeV. ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$(${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$,$X$), $X={}_{}{}^{26}{}_{}{}^{}\mathrm{Na}, {}_{}{}^{19,18}{}_{}{}^{}\mathrm{O}, {}_{}{}^{17}{}_{}{}^{}\mathrm{N}, {}_{}{}^{16,15}{}_{}{}^{}\mathrm{C}$, $E=174\mathrm{}$ MeV. ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$X$), $X={}_{}{}^{15}{}_{}{}^{}\mathrm{N}, {}_{}{}^{11}{}_{}{}^{}\mathrm{B}, {}_{}{}^9{}_{}{}^{}\mathrm{Be}$, $E=218\mathrm{} \mathrm{and} 250$ MeV. Ni(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$)Zn, $E=96\mathrm{}$ MeV Energy and nucleon occupation numbers in the ejectiles. Models for optimal Q values. Tangential friction.

Multiple Coulomb excitation and Doppler-broadened lineshape analyses have been applied to the nucleus ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$, allowing ground-band energies through the ${18}^{+}$, lifetimes through the ${14}^{+}$, and reduced transition probabilities through the ${18}^{+}$ state to be determined. Energy levels show smooth departure from the rotational model with no backbending, while the $B\left(E2\mathrm{}\right)\mathrm{}$ values are consistent with the rotational model through spin 18. Comparison is made to similar results for high spins in other good rotors. The results strengthen our conclusions reached in previous papers: The compression of energy levels observed at high spins in good rotors is largely due to pairing changes, which have only a small effect on transition probabilities.

NUCLEAR REACTIONS ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$(${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$, ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$′), $E_{\mathrm{lab}}=547, 612$ MeV, measured $\tau$, $E_{\gamma }$; deduced $B\left(E2\mathrm{}\right)\mathrm{}$.

Total fission kinetic energies $E_K$ have been measured as a function of excitation energy in the ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ nucleus excited in the ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$\alpha$) reaction. A small negative slope of $\frac{d{E}_K}{d{E}^{*}}\simeq -0.05\mathrm{}$ is observed in the excitation energy region $E^{*}=5-9\mathrm{}$ MeV. This is substantially smaller than the slope of $\frac{d{E}_K}{d{E}^{*}}=-1.1\mathrm{}$ observed in the ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$($\alpha$,${\alpha }^{\prime }f$) reaction and slightly smaller than the slope of $\frac{d{E}_K}{d{E}^{*}}\simeq -0.35\mathrm{}$ obtained from ($d$,$\mathrm{pf}$) and neutron capture reactions. It is concluded that the primary reaction mechanism plays a decisive role for the total kinetic energy release at near barrier energies but that the angular momentum transfer is not the important parameter. The data are discussed in terms of a simple scission-point model, and in particular the effect of the $Z=50\mathrm{}$, $N=82\mathrm{}$ spherical doubly magic shell in the nascent fragments.

NUCLEAR REACTIONS, FISSION ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$; measured mass and total kinetic energy distributions as function of excitation energy.

We have measured the mass-yield distribution from fission of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ induced by 14.8-MeV neutrons. Yields were measured for 57 fission products from ${}_{}{}^{86}{}_{}{}^{}\mathrm{Rb}$ to ${}_{}{}^{161}{}_{}{}^{}\mathrm{Tb}$. Data for 38 total chain yields were used to construct the mass-yield curve. Absolute fission yields were obtained with an accuracy of about 4% by the requirement of unit total yield in each half of the mass-yield distribution. Absolute yields were also obtained by means of the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$($n$,$f$) monitor reaction, but the results from the two methods are not in agreement. The disagreement may be due to uncertainty in the ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ fission cross section; from our data we infer a cross section of 2.32±0.09 b at 14.8 MeV. The peak-to-valley ratio in the mass-yield distribution is about 3.4. Several independent and cumulative fractional chain yields were measured, and $Z_p$ values inferred from these measurements are in good agreement with those estimated from independent-yield systematics. Several partial isomer yields and isomer ratios were measured.

NUCLEAR REACTIONS, FISSION ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$($n$,$f$), $E=14.8\mathrm{}$ MeV; measured fission yields, deduced fission mass distribution and ${\sigma }_{\mathrm{}(n,f)\mathrm{}}$. Measured independent and cumulative fractional chain yields and partial isomeric yields; deduced isomer ratios from fission.

We have measured seven and compiled from the literature seventeen excitation functions for spallation residues from the interaction of 10-100 MeV protons on ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$. Calculations of these excitation functions have been made using the theoretical framework of the pre-equilibrium exciton model of nuclear reactions to which has been added a fission option. The fit of the theory to the experimental data is excellent, lending confidence to our treatment of the competition between fission and particle emission. After showing and discussing the comparison of the calculated and experimental results, we present representative graphs of the variations in fissionability with $\frac{Z^2}{A}$ and with the excitation energy.

NUCLEAR REACTIONS ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$($p$,$\mathrm{xn}$), $x=1, 3, 5-7$; ($p$,$\mathrm{pxn}$), $x=1, 4-6$; ($p$,$2pxn$), $x=3-7\mathrm{}$; ($p$,$3pxn$), $x=5-7\mathrm{}$. $E=10-100\mathrm{}$ MeV; measured $\sigma \mathrm{}\left(E\right)\mathrm{}$, calculated $\sigma \mathrm{}\left(E\right)\mathrm{}$, ${\Gamma }_f$, ${\Gamma }_n$, ${\Gamma }_p$, ${\Gamma }_{\alpha }$.