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STUDY DESIGN An experimental study was performed using cadaveric lumbar spines to evaluate the effect of anteriorly or laterally placed interbody distraction implants on the alteration of spinal canal and neuroforaminal dimensions. OBJECTIVES To quantify changes in the spinal canal and neuroforaminal dimensions using interbody fusion devices inserted at various configurations in cadaveric lumbar spines exhibiting degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA Although several clinical studies have demonstrated successful treatment of degenerative spondylolisthesis with anterior interbody fusion, no study has shown the role of interbody distraction in improving lumbar spinal canal and foraminal stenosis. METHODS Five fresh cadaver lumbar spines exhibiting a degenerative spondylolisthesis or retrospondylolisthesis were used for the study. Computed tomography scans of each specimen and a silicon mold of the left intervertebral foramens were repeated in a consistent manner after pure compressive load (150 lb) was applied to simulate physiologic load (intact case), after two BAK (Sulzer SpineTech Inc., Minneapolis, MN) distraction plugs were anteriorly inserted into the intervertebral disc space (anterior distraction cases), and after one long BAK cage was laterally inserted from the left side (lateral distraction case). The cross-sectional area of the spinal canal was measured from computed tomography images using National Institutes of Health image software (Bethesda, MD). The spinal canal volume was calculated using the cross-sectional area and total scan thickness. Left intervertebral foraminal volumes were calculated from the weight of the silicon mold injected into the foramen. Descriptive statistics and a Student's t test were used to detect statistical differences in the spinal canal and neuroforaminal volumes before and after interbody distraction. RESULTS The cross-sectional canal area was significantly increased after anterior distraction (35.11%) and lateral distraction (33.14%). The spinal canal volume was markedly increased with anterior distraction (19.92%) and lateral distraction (21.96%). Left foraminal volume was also enhanced by 40.25% for anterior distraction and 41.03% for lateral distraction. CONCLUSIONS Interbody distraction either by anteriorly inserted plugs or laterally inserted threaded cagescan immediately improve the narrowed canal area and increase spinal canal, as well as foraminal volume for lumbar degenerative spondylolisthesis or retro- spondylolisthesis.

The angular distribution for the breakup of ${}^{8}\mathrm{B}{\ensuremath{\rightarrow}}^{7}\mathrm{Be}+p$ on a ${}^{58}\mathrm{Ni}$ target has been measured at an incident energy of 25.75 MeV. The data are inconsistent with first-order theories but are remarkably well described by calculations including higher-order effects. The comparison with theory illustrates the importance of the inclusion of the exotic proton halo structure of ${}^{8}\mathrm{B}$ in accounting for the data.

The structure of the halo nucleus ${}^{11}\mathrm{Be}$ has been studied using the reaction ${}^{9}\mathrm{Be}{(}^{11}\mathrm{Be}{,}^{10}\mathrm{Be}+\ensuremath{\gamma})X$ at 60 MeV/nucleon. The ground state structure of ${}^{11}\mathrm{Be}$ is determined by comparing the experimental cross sections to a calculation combining spectroscopic factors from the shell model with $l$-dependent single-particle cross sections obtained in an eikonal model. This experiment shows the dominant $1s$ single-particle character of the ${}^{11}\mathrm{Be}$ ground state and indicates a small contribution of $0d$ admixture in the wave function. After correction for the approximately $22%$ intensity to excited levels, a clean and precise distribution of parallel momentum for knockout from the $1s$ halo wave function is obtained for the first time.

This study evaluates the residual biomechanical stability of the spine following multilevel anterior diskectomies and anterior longitudinal ligament release using video-assisted thoracoscopic surgery (VATS). Eighteen domestic pigs were randomly divided into three groups of six pigs. Group 1 underwent thoracic anterior release from T4-T9 using a left-sided VATS approach, group 2 underwent thoracic anterior release from T4-T9 via a traditional left thoracotomy (open), and group 3 did not undergo surgery and served as a control. After surgery, the animals were euthanized, and the thoracic spinal columns were harvested for biomechanical testing. Nondestructive testing was performed on all specimens in pure compression, flexion, extension, right lateral bending, and torsion. Specimens from group 1 had significantly lower stiffness values (P

Wounds made by the Endopath nonbladed obturator, the Step trocar, and conventional pyramidal tip trocars were compared. The endopath nonbladed obturator and the Step trocar made wounds by separating tissue fibers, whereas the pyramidal tip trocar cut tissue fibers. The wounds of the Endopath nonbladed obturator and the Step trocar were similar in length but were narrower than wounds made by the pyramidal tip trocar. Further studies are needed to determine whether the wounds made by the Endopath nonbladed obturator and the Step trocar will have fewer complications than conventional pyramidal tip trocars.

A new device (TwinSol) installed at the Nuclear Structure Laboratory at the University of Notre Dame implements a pair of large-bore 6 T superconducting solenoids for producing relatively pure, high-intensity beams of exotic light nuclei at low-energies (10–80 MeV). Typical beams include 8 Li and 6 He (T 1/2

We propose a method to produce usable amounts (1–100/s) of low-energy, very neutron-, proton-rich or highly-polarized radioactive nuclear beams (RNBs) via a two-stop production method which utilizes a high-intensity secondary RNB with a second production target. For example: 7 Li+ 9 Be→ 8 Li+ 9 Be→ 9 Li. The latter ( 9 Li) is very difficult to produce at low energies (a few MeV/u) as it is several nucleons away from the line of stability and no efficient one-step mechanism exists. In contrast, high-cross-section transfer reactions such as 9 Be( 7 Li, 8 Li) combined with a high-efficiency ion-optical collection devices can produce 8 Li and other near-stability RNBs ( 8 B, 7 Be, 6 He,…) at very good intensities, viz. 10 4 –10 8 /s. Thus, it appears feasible to use a second, high cross-section reaction – perhaps now with a radioactive or polarized second production target, to produce and exotic, low-energy tertiary RNBs, including polarized RNBs. These and other aspects are described together with some initial tests using the new UM-UND TwinSol RNB apparatus (see M. Lee, this Proceedings).

The use of a high-efficiency BaF spectrometer for in-beam γ-tagged γ-ray spectroscopy of low-energy radioactive nuclear beams (RNBs) is examined in this study. Our results demonstrate that although BaF detectors have poor energy resolution, they still can (with proper tagging to eliminate background) be a highly efficient tool for in-beam γ-ray spectroscopy of RNBs.

The fusion of ${}^{6}\mathrm{He}$ with a ${}^{209}\mathrm{Bi}$ target has been studied at energies near to and below the Coulomb barrier. Despite the weak binding of the valence neutrons in ${}^{6}\mathrm{He}$, little evidence is found for suppression of fusion due to projectile breakup. Instead, a large enhancement of sub-barrier fusion is observed. It is suggested that this enhancement may arise from coupling to positive $Q$ value neutron transfer channels, resulting in ``neutron flow'' between the projectile and the target.

Total reaction cross sections, σ R , on Si were measured near 40 A MeV for the proton-halo candidate 12 N and the two-proton-halo candidate 17 Ne, and were compared with σ R for other light proton-rich nuclei. The A -dependence shows enhanced σ R 's for 12 N and 17 Ne, relative to their neighbors, but the effect is smaller than for 8 B which has been argued to have a proton halo. In general, nuclei with loosely bound last protons ( S p ⩽ 1.5 MeV) have significantly larger σ R 's than their neighbors. Cross sections for charge-removal from 12 N and 17 Ne also were obtained.

We have made the first attempt at determining the ${}^{8}$Li$(n,\ensuremath{\gamma})$${}^{9}$Li cross section at astrophysical energies. This reaction competes with the ${}^{8}$Li$(\ensuremath{\alpha}{,n)}^{11}$B reaction in the inhomogeneous big bang model and with ${}^{8}$Li $\ensuremath{\beta}$ decay in the $r$ process. It may affect the primordial abundance and the stellar production of Ag12 nuclei. Using a radioactive beam of ${}^{9}$Li and the Coulomb dissociation method we attempted to measure the cross section of the inverse reaction ${}^{9}$Li$(\ensuremath{\gamma}{,n)}^{8}$Li. We report only an upper limit because we were unable to determine and subtract the nuclear dissociation. Through the detailed balance theorem, this lead to an upper limit for the cross section of interest, ${}^{8}$Li$(n,\ensuremath{\gamma})$${}^{9}$Li. The limit is 19$\ifmmode\pm\else\textpm\fi{}$8 b for ${E}_{n}$ = 0--500 keV or, when expressed as a reaction rate, 7200 cm${}^{3}$ s${}^{\ensuremath{-}1}$ mole${}^{\ensuremath{-}1}$.

Fission following the fusion of {sup 6}He with a {sup 209}Bi target has been studied near the Coulomb barrier, at excitation energies of 32 and 34 MeV in the compound system. These new experimental data are in disagreement with previous work which reported an anomalously large fusion-fission yield, when compared with {sup 4}He-induced fission of {sup 209}Bi at similar excitation energies. In fact, the {sup 6}He-induced fusion-fission yield appears to be smaller than that for {sup 4}He, in qualitative agreement with conventional statistical model calculations. {copyright} {ital 1998} {ital The American Physical Society}

STUDY DESIGN Two surgical techniques for anterior discectomy were compared biomechanically. The surgical procedures were performed in live, anesthetized, skeletally immature pigs. Spine flexibility was measured in vitro. OBJECTIVE To determine whether endoscopic techniques for discectomy are as effective as open procedures in increasing spine flexibility. SUMMARY OF BACKGROUND DATA Although studies have verified that discectomy increases spine flexibility, no study has confirmed whether endoscopic techniques increase flexibility as effectively as standard thoracotomy, which is a substantially different procedure. METHODS The intervertebral disc between vertebrae T8 and T9 was resected from 30 live, anesthetized, adolescent pigs. In 15 pigs, the chest was opened via thoracotomy of the eighth rib, and the disc was excised. In the other 15 pigs, the disc was removed endoscopically. These motion segments and six intact controls were tested mechanically in side bending, flexion-extension, and axial rotation. RESULTS No statistically significant differences in flexibility were found between open and endoscopic groups in any loading direction. The statistical power to detect a 20% difference between surgical groups was > or = 95%. CONCLUSIONS Endoscopic and open techniques were equally effective in increasing spine flexibility. Because endoscopy may reduce surgical morbidity compared with open discectomy, these results support the use of endoscopy for the surgical correction of scoliosis before instrumentation.

We present new calculations and experimental measurements of the quasielastic cross section angular distribution for ${}^{8}$He scattering from ${}^{12}$C at 60 MeV/nucleon. ${}^{8}$He is treated as a five-body $\ensuremath{\alpha}+4n$ system and the six-body ${}^{8}$He+target scattering calculations make use of the eikonal few-body method and the cluster orbital shell model approximation for the ${}^{8}$He wave function. The qualitative features of the new data are successfully described without parameter variation. The sensitivity of the calculations to correlations in the ${}^{8}$He wave function is assessed.

The neutron spectroscopy of the $\ensuremath{\beta}$-delayed neutron decay of ${}^{14}$Be has been investigated. A strong neutron group, which accounts for much of the $\ensuremath{\beta}$-decay yield and could explain the discrepancy in total neutron branching ratio found in a previous experiment, was observed. We found that the total width of the final state for this transition is $60\ifmmode\pm\else\textpm\fi{}5\ifmmode\pm\else\textpm\fi{}6$ keV, and the measured half-life of the ${}^{14}$Be $\ensuremath{\beta}$ decay was $4.29\ifmmode\pm\else\textpm\fi{}0.18$ ms. The limits on the branching ratio and log$\mathrm{ft}$ value determined for this group are compared with the earlier work and the results of a shell-model calculation.

A radioactive beam of 26 MeV 8 B has been utilized to measure the Coulomb dissociation of 8 B on 58 Ni. At these subcoulomb barrier energies, the method provides an accurate means to understand the role of E2 photons in the breakup reaction. The results are critical for the determination of the S 17 factor of the inverse reaction — the astrophysically relevant radiative proton capture of 7 Be - using the method of Coulomb excitation.

Subcoulomb breakup of 8 B on a 58 Ni target has been studied, at an incident energy of 26 MeV. These data provide a measure of the E2 component of the breakup cross section as a function of the astrophysical factor S 17 for radiative capture of protons on 7 Be . Implications for the solar neutrino problem are discussed.

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus Be-11 has been examined through the 10Be(d,p) reaction in inverse kinematics at equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of Be-10 on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of Be-10 on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in Be-11 were analyzed using the Finite Range ADiabatic Wave Approximation (FR-ADWA). Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4) respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor., 16 Pages, 10 figures

The fusion cross sections of radioactive ${}^{134}$Te + ${}^{40}$Ca were measured at energies above and below the Coulomb barrier. The evaporation residues produced in the reaction were detected in a zero-degree ionization chamber providing high efficiency for inverse kinematics. Both coupled-channel calculations and comparison with similar Sn + Ca systems indicate an increased sub-barrier fusion probability that is correlated with the presence of positive $Q$-value neutron transfer channels. In comparison, the measured fusion excitation functions of ${}^{130}$Te + ${}^{58,64}$Ni, which have positive $Q$-value neutron transfer channels, were accurately reproduced by coupled-channel calculations including only inelastic excitations. The results demonstrate that the coupling of transfer channels can lead to enhanced sub-barrier fusion but this is not directly correlated with positive $Q$-value neutron transfer channels in all cases.

Proton pair correlations relevant for the neutrinoless double-$\ensuremath{\beta}$ decay of ${}^{76}$Ge have been probed via the ${}^{74,76}$Ge(${}^{3}$He,$n$) reactions at 16 MeV. No evidence for pairing vibrations in either nucleus is observed at sensitivity limits of $\ensuremath{\sim}$6$%$ and $\ensuremath{\sim}$19$%$ of the ground-state strength in ${}^{76}$Se and ${}^{78}$Se, respectively. These results are relevant for the understanding of matrix elements for neutrinoless double-$\ensuremath{\beta}$ decay. The lack of pairing vibrations is consistent with a simple BCS structure for the ground states of ${}^{76}$Ge and ${}^{76}$Se, assumed in quasiparticle random phase approximation (QRPA) models of the process.

The structure of ${}^{10}$Be was studied via resonant $\ensuremath{\alpha}$-particle scattering of a neutron-rich ${}^{6}$He beam. A time projection chamber, PAT-TPC, was operated in an active-target mode to provide a gaseous ${}^{4}$He target and trace the beam and reaction products traversing its active tracking volume. This significantly lowered the detection threshold of reaction products at low energies. Elastic scattering, inelastic scattering to the ${}^{6}$He 2${}^{+}$ state, and the ${}^{6}$He($\ensuremath{\alpha}$, 2$n$)${}^{8}$Be reaction were measured below an energy of 6 MeV in the center-of-mass frame. Continuous spectra of excitation functions and angular distributions were obtained from unambiguously-identified recoiling $\ensuremath{\alpha}$ particles for the elastic and inelastic channels. While a resonance of the 4${}^{+}$ state at 10.15 MeV in ${}^{10}$Be previously reported was confirmed, no other resonances were identified in the elastic channel over the measured energy region. The results are in line with antisymmetric molecular dynamics calculations that predict the limits of $\ensuremath{\alpha}$ clustering in high-spin states due to a spin-orbit force.

Evaporation protons from the fusion of the ${}^{3}\mathrm{He}{+}^{58}$Ni system were measured at three energies near but above the Coulomb barrier. The respective elastic scattering angular distribution was also determined for one of these energies. The fusion data, after being properly reduced to eliminate size and charge effects, are compared to the recently measured fusion excitation function for the proton-halo system ${}^{8}\mathrm{B}{+}^{58}$Ni. As a reference, fusion data for the ${}^{16}\mathrm{O}{+}^{58}$Ni system are also presented. With respect to this reference, the fusion cross sections for the proton-rich systems show an enhancement likely related to static effects. An excitation function for the respective total-reaction cross section was extracted from the measured elastic data along with additional data from the literature. Surprisingly, this excitation function follows the trend expected for weakly bound systems.

The scintillation and ionization yields produced by 33.5 MeV/u {sup 18}O and 31.9 MeV/u {sup 36}Ar ions in neat liquid argon and in liquid argon with 10 ppm allene have been measured. Application of an external electric field of about 3 kV/cm leads to an initial enhancement of the scintillation by 17{percent} in the neat liquid and as much as 22{percent} in allene solutions. Scintillation and ionization yields generally are strongly dependent on field strength, they are similar for both ions, and they are usually very different from that found with {alpha} particles. Ionization yields are found to increase by more than an order of magnitude with the addition of 10 ppm allene. This increase occurs mainly because of the photoionization of allene by the liquid-argon scintillation. A considerable amount of quenching is observed in these systems and even with the huge increase in ionization allene is not very efficient in converting scintillation to ionic pairs. The potential energy resolution of allene-doped liquid-argon detectors is discussed. {copyright} {ital 1996 The American Physical Society.}

Total reaction cross sections, ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$, of 20--60A MeV $^{4,6,8}\mathrm{He}$, $^{6--9,11}\mathrm{Li}$, and $^{10}\mathrm{Be}$ were measured by injecting magnetically separated, focused, monoenergetic, identified secondary beams of those projectiles into a Si detector telescope and measuring their energy-deposition spectra. These ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$'s, accurate to about 3%, were compared with predictions of optical, strong absorption, and microscopic models. The latter gave the best overall fit to the data, providing long-tailed matter densities were assumed. The best available optical potentials generally overpredicted the data by about 10%. Strong absorption calculations, in which the isospin-dependent term is quite important, were often unsuccessful, especially for projectiles with large neutron excess. Two-neutron removal cross sections were measured for $^{6}\mathrm{He}$ and $^{11}\mathrm{Li}$; the $^{11}\mathrm{Li}$ data were slightly overpredicted by a microscopic model which includes correlation effects for the $^{11}\mathrm{Li}$ valence neutrons. Both 2n and 4n removal from $^{8}\mathrm{He}$ were observed, in about a 2:1 ratio. Subtraction analysis of the data indicates that $^{4}\mathrm{He}$ is a good core within $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$, as is $^{9}\mathrm{Li}$ within $^{11}\mathrm{Li}$. \textcopyright{} 1996 The American Physical Society.

The quasielastic scattering of {sup 9}Li on a {sup 12}C target has been measured at an incident energy of 540 MeV. The new experimental data are used to extract an effective interaction for {sup 9}Li + {sup 12}C scattering. The uncertainty in this interaction was previously a major obstacle to extracting information on the structure of {sup 11}Li from existing {sup 11}Li + {sup 12}C quasielastic-scattering data.

The sub-Coulomb breakup of {sup 8}B on a {sup 58}Ni target is studied at an incident energy of 26 MeV. These data provide a measure of the {ital E}2 component of the breakup cross section as a function of the astrophysical factor S{sub 17} for radiative capture of protons on {sup 7}Be. Implications for the solar neutrino problem are discussed. {copyright} {ital 1996 The American Physical Society.}

Projectiles of 11 Li were photodisintegrated into 9 Li + n + n by absorption of a virtual photon in a Pb target. The momenta of the three particles in the final state were measured, and the dipole strength function was determined up to about 1 MeV above the disintegration threshold. On the average, the 9 Li residue had a greater velocity than the neutrons. Interpreted as a post-breakup acceleration of 9 Li in the coulomb field of the Pb nucleus, the lifetime of the excited 11 Li was found to be too short for the disintegration process to have gone through a resonant state such as the soft dipole resonance. Because the complete kinematics was measured, we could view the events in the rest frame of 11 Li. In that frame the distribution of angle between the two neutrons, when the response of the neutron detection system was taken account of, was isotropic. Hence, we have no evidence for a dineutron in 11 Li. Two recently-constucted neutron walls will be used in future experiments.

The {beta}-delayed neutron decay of {sup 17}B was studied using a radioactive ion beam. The neutron energies, measured via time of flight, give information on states in {sup 17}C above the {sup 16}C+neutron threshold. States in {sup 17}C were found at excitation energies of 2.25(2), 2.64(2), and 3.82(5) MeV, and possibly at 1.18(1) MeV. These low-lying states are of possible interest for nuclear physics as well as for astrophysics. {copyright} {ital 1996 The American Physical Society.}

Small angle correlations between two neutrons emitted at a laboratory angle near 45° from the 16 O+ 27 Al reaction at 220 MeV have been measured. The results show a positive correlation peak centered near a relative momentum of 7.5 MeV/ c . However, when restrictions are placed on the total momentum of the two-neutron system, the strength of the correlation function is found to be dependent on the total momentum of the two-neutron system. A possible anti-correlation is observed at low relative momentum for low total momentum pairs.

Fusion excitation functions were obtained for $^{16}\mathrm{O}$ + $^{70,72,73,74,76}\mathrm{Ge}$ at energies from about 4 MeV below to 15 MeV or more above the Coulomb barrier. The barrier parameters extracted from the data agree within 2% with those obtained from the systematics for fusion above the barrier. Low-energy enhancements are observed whose behavior is explained within the context of simple model calculations by assigning appropriate degrees of freedom to the respective reaction partners. These degrees of freedom are consistent with those used in similar analysis of different data sets where either the same projectile or the same targets were used. An analysis of the barrier distributions is made which supports the previous conclusions.

The β-delayed neutron emission of 19 C has been studied with the hope of observing states in 19 N close enough to the 18 N+n threshold to be of astrophysical significance. Although transitions to three-neutron unbound states in 19 N have been observed, no states in the energy region of astrophysical relevance were found. The 19 C β-decay branching ratios to the observed states have been measured. All states show log( ft ) values typical of allowed transitions. The results are compared with shell-model predictions carried out in the psd model space.

Many astrophysical events, such as novae and X-ray bursts, are powered by reactions with radioactive nuclei. Studying the properties of these nuclei in the laboratory can therefore further our understanding of these astrophysical explosions. The TwinSol separator at the University of Notre Dame has recently been used to produce intense (~106 pps) beams of 17F. In this article, some of the first measurements with these beams are discussed.

The neutron spectroscopy of the {beta}-delayed neutron decay of {sup 14}Be has been investigated. Two neutron groups were observed, and energy limits are given for a third (unobserved) group that receives most of the {beta}-decay strength. Branching ratios and log{ital ft} values deduced for all three groups are compared with the results of a shell-model calculation.

We have measured angular distributions of the 2 H( 8 Li, 7 Li) 3 H and 2 H( 8 Li, 9 Be)n reactions at E c.m. = 1.5 to 2.8 MeV using an 8 Li- radioactive-beam technique. Astrophysical S -factors and reaction rates were calculated form the measured cross sections. Although the 2 H( 8 Li, 9 Be)n cross section is small, it can contribute to 9 Be synthesis. The 2 H( 8 Li, 7 Li) 3 H reaction has a sufficiently large cross section to destroy 8 Li, which may decrease the synthesis of heavier elements. No products from the 2 H( 8 Li, 9 Li)p reaction were detected. We also present the results of calculations using the inhomogeneous model of primordial nucleosynthesis in several regions of parameter space.

A radioactive nuclear beam of 10.2 MeV $^{6}\mathrm{He}$, with typical intensity 5\ifmmode\times\else\texttimes\fi{}${10}^{4}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, was produced via the $^{9}\mathrm{Be}$${(}^{7}$Li${,}^{6}$He${)}^{10}$B reaction and elastically scattered from targets of $^{12}\mathrm{C}$, $^{\mathrm{nat}}\mathrm{Ni}$, and $^{197}\mathrm{Au}$. Scattering from C and Ni was observed through sufficiently large angles (up to 60\ifmmode^\circ\else\textdegree\fi{} c.m. and 85\ifmmode^\circ\else\textdegree\fi{} c.m., respectively) to show large deviations from Rutherford scattering. The Au target gave, as expected, pure Rutherford scattering. Optical potential previously used for low-energy $^{6}\mathrm{Li}$ and $^{8}\mathrm{Li}$ ions generally accounted for the shapes of the angular distributions but, for $^{12}\mathrm{C}$, predict oscillations not present in the $^{6}\mathrm{He}$ data. $^{4}\mathrm{He}$ optical potentials predict much smaller deviations from Rutherford scattering than those observed.

Liquid scintillation detectors have shown promise as neutron detectors for characterizing special nuclear materials in various arms-control applications. Deuterated liquids, such as EJ315, are attractive for spectroscopy applications because the backward-peaked n-d scattering results in enhanced coupling between incident neutron energy and resulting pulse height. In the context of discrete neutronenergy spectra, this produces peaks in detector pulse-height spectra which correspond to the neutron energy groups present. With continuous spectra, increased coupling may yield better spectrum unfolding. In this work, we present a neutron response matrix for a three-by-two-inch cylindrical EJ315 detector, and compare to the hydrogen-based liquid EJ309 in the same active geometry. A 'white' neutron source, obtained with the bombardment of liB with 5.5-MeV deuterons at the tandem Van de Graaff accelerator at University of Notre Dame, was used for the measurement. Detected neutrons were sorted by time of flight and pulse height into 100-keV energy bins and 50-keVee light-output bins, over the energy-range from 0.5 to 15 MeV. The resulting response matrix represents a full characterization of pulse-height response to neutrons over that energy range.

Fusion excitation functions for the reactions of ${}^{124,132}$Sn with ${}^{40,48}$Ca were measured at energies near and below the Coulomb barrier. Weak sub-barrier fusion enhancement accounted for by coupling to the first 2${}^{+}$ and 3${}^{\ensuremath{-}}$ states in the target and projectile was observed for ${}^{124,132}\text{Sn}+{}^{48}\text{Ca}$. However, the ${}^{124,132}\text{Sn}+{}^{40}\text{Ca}$ fusion cross sections are very strongly enhanced below the barrier and this difference survives even after correcting for trivial size effects. Although the enhancement appears to be related to the existence of large positive $Q$ values for neutron transfer reactions, it is not proportional to the magnitudes of those $Q$ values, which are much larger for ${}^{132}\mathrm{Sn}+{}^{40}\mathrm{Ca}$ than for ${}^{124}\mathrm{Sn}+{}^{40}\mathrm{Ca}$.

The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightly-bound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus Be-11, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the Be-10(d,p) reaction has been used in inverse kinematics at four beam energies to study the structure of Be-11. The spectroscopic factors extracted using the adiabatic model, were found to be consistent across the four measurements, and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in a nlj = 2s1/2 state coupled to the ground state of Be-10 is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p1/2 state., 5 pages, 4 figures

Recent experimental results for the fusion of the proton-halo system ${}^{8}\text{B}\phantom{\rule{-0.16em}{0ex}}+\phantom{\rule{-0.16em}{0ex}}{}^{58}\text{Ni}$ are discussed. A strong enhancement is observed both below and above the barrier. This is qualitatively different from the usual sub-barrier enhancement observed for many heavy-ion systems. Arguments are given that relate the enhancement to a static halo effect directly associated to the extended size of the proton-halo state. A simple single-barrier model is proposed which describes the fusion cross sections in terms of a maximum angular momentum for fusion, ${L}_{f}$. It is shown that a linear energy dependence for ${L}_{f}$ gives a surprisingly good description of the experimental fusion excitation function not only for ${}^{8}\text{B}\phantom{\rule{-0.16em}{0ex}}+\phantom{\rule{-0.16em}{0ex}}{}^{58}\text{Ni}$ but also for the neutron-halo systems ${}^{6}\text{He}\phantom{\rule{-0.16em}{0ex}}+\phantom{\rule{-0.16em}{0ex}}{(}^{209}\text{Bi},{}^{64}\text{Zn})$. The model is also applied to several weakly bound systems.

The ionization yields produced by 33.5 MeV/amu 18 O, 31.9 MeV/amu 36 Ar, and 23.1 MeV/amu 129 Xe in liquid argon with 80 ppm allene have been measured. Energy resolutions for these particles were found to be 0.37, 0.57, and 1.74% FWHM, respectively, at an electric field strength of 1.67 kV/cm. Charge collection with all of the particles is strongly dependent on the applied electric field.

The quasielastic scattering of the exotic neutron-drip-line nucleus $^{14}\mathrm{Be}$ on a $^{12}\mathrm{C}$ target has been studied at an incident energy of 796 MeV, and compared with that of the $^{12}\mathrm{Be}$ ``core'' at the same energy per nucleon. Evidence is presented that the phenomenological optical-model potential for the former system requires an attractive real surface term, as well as the ``expected'' surface imaginary term, in order to reproduce the experimental angular distribution.

A program of study of the reaction mechanisms of exotic “halo” nuclei at energies near the Coulomb barrier is described. The unique opportunities presented by the ReA3 reaccelerated beam facility at the NSCL, coupled with an active-target time projection chamber (AT-TPC), will be fully exploited in this program. An approximately half-scale “prototype” AT-TPC has been constructed and is currently undergoing tests. This device has recently been installed on the TwinSol [1] beam line at the University of Notre Dame, and preliminary results of reaction studies using a low-energy 6 He beam are reported.

Fusion cross sections were measured for the exotic proton-halo nucleus {sup 8}B incident on a {sup 58}Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a proton-halo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.

Angular distributions for the elastic scattering of $^{8}\mathrm{B}$, $^{7}\mathrm{Be}$, and $^{6}\mathrm{Li}$ on a $^{12}\mathrm{C}$ target have been measured at ${E}_{\mathrm{lab}}=25.8$, 18.8, and 12.3 MeV, respectively. The analyses of these angular distributions have been performed in terms of the optical model using Woods-Saxon and double-folding type potentials. The effect of breakup in the elastic scattering of ${}^{8}\mathrm{B}+{}^{12}\mathrm{C}$ is investigated by performing coupled-channels calculations with the continuum discretized coupled-channel method and cluster-model folding potentials. Total reaction cross sections were deduced from the elastic-scattering analysis and compared with published data on elastic scattering of other weakly and tightly bound projectiles on $^{12}\mathrm{C}$, as a function of energy. With the exception of $^{4}\mathrm{He}$ and $^{16}\mathrm{O}$, the data can be described using a universal function for the reduced cross sections.

Fusion cross sections were measured for the exotic proton-halo nucleus ⁸B incident on a ⁵⁸Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a proton-halo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.

The response of large (4×6) deuterated liquid scintillators (up to 10 cm diameter by 15 cm) to neutrons in the energy range from 0.5 MeV to 20 MeV has been studied using several nuclear reactions, including d(d,n), and 12C(d,n)13N, at the University of Notre Dame FN tandem accelerator. The latter two reactions utilized 9 MeV and 16 MeV deuteron beams, including a pulsed beam that also permitted time‐of‐flight (ToF) measurements. Combining pulse‐shape discrimination and (ToF) allows gating on specific neutron energy groups to determine the detector response to specific neutron energies. Newly‐obtained and optimized pulse shape discrimination using digitized pulse analysis from these detectors will be presented in this paper. These measurements confirmed the ability of these detectors to provide useful neutron spectra without ToF.

Cross sections for the $^{8}\mathrm{Li}$(d,n${)}^{9}$Be (ground state) and $^{8}\mathrm{Li}$(d,t${)}^{7}$Li reactions, both important to primordial nucleosynthesis in the inhomogeneous models, have been measured using a radioactive beam technique. The cross section for the former reaction is found to be small, so it is important only for synthesis of $^{9}\mathrm{Be}$. The cross section for the latter reaction, however, is found to be large enough to destroy significant quantities of $^{8}\mathrm{Li}$, and thus could affect predictions of primordial nucleosynthesis yields.

We have performed a kinematically complete measurement of the Coulomb dissociation of 28 MeV/nucleon $^{11}\mathrm{Li}$ into $^{9}\mathrm{Li}$ and two neutrons by a Pb target. From the energies and angles of the emitted neutrons and of $^{9}\mathrm{Li}$, the excitation energy E of $^{11}\mathrm{Li}$ was determined on an event-by-event basis, and the Coulomb dissociation cross section as a function of excitation energy was constructed. The photonuclear cross section ${\mathrm{\ensuremath{\sigma}}}_{\mathit{E}1}$(E) and the dipole strength function dB(E1)/dE were determined from the Coulomb dissociation cross section. ${\mathrm{\ensuremath{\sigma}}}_{\mathit{E}1}$(E) has a peak at E=1.0 MeV and a width \ensuremath{\Gamma}=0.8 MeV. These parameters are consistent with the picture of a soft dipole mode. However, a significant post-breakup Coulomb acceleration of $^{9}\mathrm{Li}$ suggests instead a direct breakup. The complete kinematical measurement also allowed neutron and $^{9}\mathrm{Li}$ momentum distributions to be constructed in the rest frame of the $^{11}\mathrm{Li}$. The momentum distributions were fitted with Gaussian functions, yielding width parameters ${\mathrm{\ensuremath{\sigma}}}_{9}$=18\ifmmode\pm\else\textpm\fi{}4 MeV/c and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{n}}$=13\ifmmode\pm\else\textpm\fi{}3 MeV/c. A more general feature of the breakup mechanism of $^{11}\mathrm{Li}$ could be deduced from these measurements. It was found that the $^{9}\mathrm{Li}$ and neutron momentum distributions and the neutron-neutron relative momentum distribution could be reproduced if the $^{11}\mathrm{Li}$ excitation energy was partitioned between the $^{9}\mathrm{Li}$ and the neutrons by a three-body phase space distribution. This indicates there is no directional correlation between the halo neutrons, and shows that the halo neutrons do not exist as a dineutron bound to a $^{9}\mathrm{Li}$ core.

Elastic and inelastic scattering, one-nucleon transfers [mostly ${(}^{8}$Li, $^{7}\mathrm{Li}$)] and the ${(}^{8}$Li,\ensuremath{\alpha}) fusion-evaporation reaction have been studied on a variety of targets (A=1--58) at E${(}^{8}$Li)\ensuremath{\approxeq}13--20 MeV using the University of Michigan--University of Notre Dame radioactive nuclear beam (RNB) facility. The latter, which produces an energy-resolved (\ensuremath{\sim}500 keV FWHM), focused beam with intensity \ensuremath{\gtrsim}${10}^{6}$ $^{8}\mathrm{Li}$/s, permitted measurements to selected nuclear levels with cross sections down to approximately 1 mb/sr. Based on the systematics of the measured $^{8}\mathrm{Li}$ elastic scattering an appropriate $^{8}\mathrm{Li}$ optical potential was deduced. Large inelastic scattering cross sections (and B[E2\ensuremath{\uparrow}]) are observed for $^{8}\ensuremath{\rightarrow}^{8}$${\mathrm{Li}}_{0.98}^{\mathrm{*}}$. Large cross sections are also observed for the ${(}^{8}$Li${,}^{7}$Li) transfer reaction corresponding to quasielastic (viz., Q\ensuremath{\approxeq}0) neutron transfer to selected high spin excited levels in the residual nucleus. The ${(}^{8}$Li,\ensuremath{\alpha}) fusion-evaporation reaction also appears to be significant and can produce very-high-energy \ensuremath{\alpha} particles, viz., ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$\ensuremath{\gg}${\mathit{E}}_{\mathrm{beam}}$. Although observed using $^{8}\mathrm{Li}$, these features appear to be important for many RNB-induced reactions and they must be considered, for example, in nucleosyntheis calculations involving $^{8}\mathrm{Li}$ and other short-lived radioactive nuclei.