Search

A promising method for the production and extraction of 52Fe utilizing near-symmetric, heavy-ion fusion-evaporation reactions is presented. A 28Si beam was used to bombard a 27Al target, producing 52Fe through the reaction: 27Al (28Si, p2n)52Fe. After irradiation, the aluminum target was dissolved, and the 52Fe was separated from the aluminum matrix and other reaction products through the use of a cationic-exchange column. It was possible to recover the 52Fe (t1/2 = 8.3 h) with high specific activity, higher than can be achieved with the high energy proton spallation reactions currently used to produce this isotope, which has significance in medical research. The production yields for this reaction were measured and compared to PACE4 calculations. These results demonstrate the potential for dedicated accelerator production of 52Fe using heavy-ion beams, which will result in higher specific activities with robust radiochemical purification techniques.

Particle-induced gamma-ray emission spectroscopy is a quantitative, sensitive technique that measures light element abundance in materials using external reference standards with known beam energy and intensity. When the ion beam is used ex vacuo, gamma-ray spectroscopy on targets in air greatly increases sample throughput. However, for most targets the accuracy of these measurements is limited by the uncertainty of the collected charge. An indirect beam current measurement technique has been developed using an ion beam reaction on atmospheric argon, the only atmospheric component with sufficient abundance (~1%) that produces abundant gamma rays with low-energy proton beams. The 40Ar(p,nγ)40K reaction has been studied here, and the characteristic 770 keV gamma ray is observed to serve as a reliable monitor for proton flux. This method allows a real-time calibration of beam intensity on target to measured upstream currents for ion beam analysis at beam energies above 3.5 MeV.

Per- and polyfluoroalkyl substances (PFASs) comprise a large array of man-made fluorinated chemicals. It is an emerging chemical class of concern because many PFASs are environmentally persistent and some have known ecological and human toxicity. Consumer products treated with PFASs result in human exposure to PFASs through inhalation, ingestion, and environmental exposure to emissions from wastewater or from landfills. A rapid screening method based on total fluorine was developed and applied to quantify PFASs on consumer papers and textiles. Particle-Induced Gamma Ray Emission (PIGE) spectroscopy provides a non-destructive and quantitative measurement of total fluorine on papers and textiles. This technique is both rapid and sensitive, with a limit of detection (LOD) of 13 nmol F/cm2 for papers and 24–45 nmol F/cm2 for textiles, with reproducibility of ±12% RSD for both. PIGE is a high throughput (>20 samples/hr typically) method that was applied to 50 papers and 50 textiles in commerce to demonstrate the method.

A novel application of particle-induced X-ray emission (PIXE) has been developed to detect the presence of chlorinated and brominated flame retardant chemicals in polyurethane foams. Traditional Gas Chromatography–Mass Spectrometry (GC–MS) methods for the detection and identification of halogenated flame retardants in foams require extensive sample preparation and data acquisition time. The elemental analysis of the halogens in polyurethane foam performed by PIXE offers the opportunity to identify the presence of halogenated flame retardants in a fraction of the time and sample preparation cost. Through comparative GC–MS and PIXE analysis of 215 foam samples, excellent agreement between the two methods was obtained. These results suggest that PIXE could be an ideal rapid screening method for the presence of chlorinated and brominated flame retardants in polyurethane foams.

A liquid water target system for harvesting radioisotopes at the National Superconducting Cyclotron Laboratory (NSCL) was designed and constructed as the initial step in proof-of-principle experiments to harvest useful radioisotopes from the Facility for Rare Isotope Beams (FRIB). FRIB will be a new national user facility for nuclear science, to be completed in 2020, at which radioisotopes will be collected synergistically from the water in cooling-loops for the primary beam dump that cycle the water at flow rates in excess of hundreds of gallons per minute. As part of the development of radiochemical expertise required to harvest long-lived radioisotopes of interest in this environment, the water target system described here was constructed and successfully used to collect a test beam of relativistic 24 Na ions produced at the NSCL. Future studies will involve collecting interesting transition metal isotopes such as 67 Cu from less purified secondary projectile fragment beams.

A search for the neutron-unbound nucleus $^{21}$C was performed via the single proton removal reaction from a beam of 22 N at 68 MeV/u. Neutrons were detected with the Modular Neutron Array (MoNA) in coincidence with $^{20}$C fragments. No evidence for a low-lying state was found, and the reconstructed $^{20}$C+n decay energy spectrum could be described with an s-wave line shape with a scattering length limit of |as| < 2.8 fm, consistent with shell model predictions. A comparison with a renormalized zero-range three-body model suggests that $^{22}$C is bound by less than 70 keV., Accepted for publication in Nuclear Physics A

The elemental concentrations of five trace elements in tempered sheet glass fragments were determined using particle-induced X-ray emission (PIXE) spectrometry. The trace element concentrations for calcium, iron, manganese, strontium, and titanium are compared to those obtained by inductively-coupled plasma-atomic emission spectrometry (ICP-AES) following complete digestion by hydrofluoric acid. For these five elements, the absolute concentrations obtained by both methods are shown to agree well over a wide range of concentrations. The limits of detection for trace elements are typically lower for the ICP-AES method. However, we show that the concentrations of these five elements can be accurately measured by the PIXE method. Since PIXE is an entirely non-destructive method, there exists a niche for this technique to be used as a complement to the more sensitive ICP-AES technique in the forensic analysis of sheet glass.

An absolute measurement of the heavy element concentrations in a dried sample of aqueous protein solution has been combined with the absolute measurement of protein molecular concentration in the same sample. The ratio of these two measurements yields the metal-to-protein compositional stoichiometry of the metalloprotein. This combination of two Ion Beam Analysis techniques (Particle-Induced X-ray Emission and Proton Elastic Scattering Analysis) allows quantitative assessment of the metal atom to protein ratio in metalloproteins without direct measurement of sulfur atoms within the protein for the first time. While these results only demonstrate success with a single well-known metalloprotein, this combination of measurement ratios holds promise for future Ion Beam Analysis studies of metalloproteins.

The adverse effects of metal contamination in sediments require methods that can quickly and accurately assess the extent of environmental pollution. Particle induced X-ray emission spectrometry (PIXE) is demonstrated to be a viable alternative to an established method, which consists of acid digestion and Inductively coupled plasma-optical emission spectrometry (ICP-OES) to measure trace metals in sediment. The analysis of trace metal composition by both techniques on a NIST Standard Reference Material mud gives results that are consistent with the certified values for fourteen measured metals, seven of which are common to both methods. A comparison study conducted on a sediment core from a freshwater lake with a known chromium contamination in Muskegon County, MI also shows a good correlation between the methods for transition metals of environmental interest over a wide range of metal concentrations. Total sample preparation and analysis time for the PIXE measurements is roughly one third that of acid digestion and ICP-OES. Also, the acid digestion step does not elute all the metal, while the nondestructive PIXE approach is a total metals analysis method. However the PIXE method generally has higher limits of detection for many environmental metal contaminants. By combining the two techniques, the acid digestion elution factor can be quantified by running PIXE on an original sample and on the residue resulting from acid digestion.

The method of sequential neutron decay spectroscopy beginning with a primary beam of 60 MeV/nucleon 48Ca was investigated as a potential tool to measure unbound resonances in neutron-rich nuclei. Neutrons were measured in coincidence with fragments, and unbound resonances were observed for 10Li, 12,13Be, and 23O. The method is currently limited to resonances with small decay energies ( E decay ≲ 100 keV ) in lighter ( Z ⩽ 10 ) nuclei, and the possibility of extending it to heavier, more neutron-rich nuclei will be discussed.

A large, segmented neutron detector array, the “neutron wall”, has been constructed for use with the TwinSol radioactive nuclear beam facility at the University of Notre Dame. At present, the array consists of 16 position-sensitive plastic scintillator bars. The position and energy resolution of the array, and its neutron-detection efficiency are described.

Spectroscopy of neutron rich exotic isotopes via their isobaric analog states (IAS) in less exotic nuclei is discussed. Several different experimental techniques, which can be applied to search for IAS of exotic isotopes, are described. Successful application of these techniques to the studies of heavy helium isotopes 7 He and 9 He led to the observation of unknown IAS in 7 Li and 9 Li. Spectroscopic information for these states were obtained, and implication of these findings to the structure of 7,9 He is considered.

Small nuclear physics laboratories of all kinds traditionally have processed the signals from radiation detectors with a variety of discrete NIM- or CAMAC-based electronic modules. The logic signals associated with signal processing are often passed through gate generators, coincidence modules, fan-in/fan-out modules, delay units, counters, and other assorted logic modules. These multi-component systems generate gates for acquisition systems, gates for specific linear electronics modules (ADCs and TDCs), or measure count rates and dead times. This can involve a significant number of individual modules each of which can be quite costly and each of which provides only limited functions. We describe here an upgrade to our acquisition system where all the needed logic functions are performed in just a single unit: a Universal Logic Module based on a Field Programmable Gate Array (FPGA) from JTEC Corporation. This module also contains flash memory that holds three separate configurations allowing for rapid changes from one electronics configuration to a different one. Both CAMAC and VME versions of the unit are available. The system described here is just one example of the huge variety of functionality that can be programmed into this single module. It can accommodate very complicated circuits and is easily reprogrammed. In the small nuclear physics laboratory the Universal Logic Module can save cost when upgrading systems and reduce the number of instances where one has an insufficient number of channels of a particular function.

A collaboration of ten institutions, including a large number of undergraduate schools, proposed and constructed a highly efficient large-area neutron detector. The modular neutron array (MoNA) is designed to detect high-energy neutrons in experiments with fast rare isotopes at the National Superconducting Cyclotron Laboratory. It consists of 144 individual detector modules of plastic scintillator, is position sensitive, and features multi-hit capability. The MoNA project involves undergraduate students from the collaborating colleges and universities and gives them the possibility to take part in research at the forefront of nuclear physics.

The heavy helium isotopes 7,9 He were studied via their isobaric analog states (IAS) in 7,9 Li. The IAS were populated via resonance reactions of protons with radioactive beams of 6,8 He. The isospin-conserving neutron decay of T=3/2 resonances in 7 Li and proton decay of T=5/2 resonances in 9 Li were measured. New spectroscopic information on these states were obtained, and compared with the properties of levels in 7,9 He.

Excitation of the Isovector Giant Quadrupole Resonance in 208Pb by Coulomb Inelastic Scattering R. L. Varner, J. R. Beene, M. Chartier, ∗ J. F. Liang, D. Shapira, D. Bazin, B. Blank, ∗ B. Sherrill, M. Thoennessen, P. A. DeYoung, and G. F. Peaslee Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6368 National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824

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

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.

Two-particle azimuthal correlations have been used to extract reaction plane dispersion free triple-differential cross sections for d, t, and alpha particles for the midcentral collisions of Kr-84+Au-197 at E/A = 35, 55, and 70 MeV. Both experimental measurements and extrapolations from lower incident energies suggest that rotational flow disappears at E/A approximate to 100 MeV for light charged particles and that reaction plane dispersions introduce large uncertainties in extracting the disappearance of rotational flow.

The impact parameter dependence of light charged particle $(p,d,t,\ensuremath{\alpha})$ emission has been studied using an impact parameter selection based on coincident detection of residues or fission fragments. The energy spectra at twelve angles between $20\ifmmode^\circ\else\textdegree\fi{}$ and $150\ifmmode^\circ\else\textdegree\fi{}$ have been fit by a multiple moving source parametrization. The angle and energy integrated preequilibrium proton multiplicities decrease with increasing impact parameter in qualitative agreement with a Fermi jet calculation. The preequilibrium $d/p$ and $t/p$ multiplicities increase slowly with increasing impact parameter and are nearly identical at the two bombarding energies. The preequilibrium $\ensuremath{\alpha}/p$ ratio shows a less consistent dependency on impact parameter but decreases significantly with increasing bombardment energy. A calculation of the $d/p$ and $t/p$ multiplicity ratios with a transport model incorporating complex particle emission is quite successful in reproducing the absolute magnitude, impact parameter dependence, and bombarding energy dependence of the experimental total multiplicities.

Measurements are reported for fragment masses and velocities from the reactions $(17--115)A\mathrm{MeV}$ ${}^{40}\mathrm{A}\mathrm{r}+\mathrm{C}\mathrm{u},$ Ag, and Au. Charged particle multiplicities were used to select the most violent reactions, and systematics are reported for the momentum and energy deposition. These reactions are fusionlike for $\ensuremath{\lesssim}44A\mathrm{MeV}$ ${}^{40}\mathrm{Ar}$ with a large fraction of momentum and energy deposition in the heavy nuclear system. However, for $\ensuremath{\gtrsim}44A\mathrm{MeV}$ ${}^{40}\mathrm{Ar},$ a majority of the projectile energy and momentum is carried away by a multibody spray of light ejectiles and only a minority is deposited in the heavy nucleus. Nevertheless heavy composite systems are formed with up to 9--12 MeV per source nucleon for $115A\mathrm{MeV}$ ${}^{40}\mathrm{Ar}.$

Small-angle $p$-$p$, $p$-$d$, $d$-$\ensuremath{\alpha}$, and $\ensuremath{\alpha}$-$\ensuremath{\alpha}$ correlation functions were measured following the reaction ${}^{16}$O+${}^{27}$Al at 40 MeV/nucleon ${}^{16}$O. These light charged particles (LCP's) were measured with a closely packed hexagonal array of CsI detectors, located at $35\ifmmode^\circ\else\textdegree\fi{}$, with a center to center opening angle of 2.35$\ifmmode^\circ\else\textdegree\fi{}$ for adjacent detectors. Coincident particles were simultaneously detected in the NSCL $4\ensuremath{\pi}$ detector. This measurement was intended to be a complement to earlier results from the same system. Based on studies of this system at lower energies and other published correlation measurements, it was expected that at 40 MeV/nucleon there would be significant positive correlations from the nuclear force and deep anticorrelations from Coulomb repulsion. However, correlation functions from this higher energy are remarkably similar to those previously measured at $\ensuremath{\approx}$15 MeV/nucleon. Correlation functions formed from events with a high multiplicity or high total detected energy (central collisions) are not significantly different from the inclusive measurements. As a possible explanation we suggest that significant correlations are most readily seen in experiments sensitive to LCP's from fast preequilibrium processes and that measurements at more backward angles are primarily sensitive to LCP's from a longer-lived source formed after preequilibrium processes are done. This idea is supported by trends of $p$-$p$ correlation functions from a wide range of systems. A schematic calculation based on a Boltzmann-Ueling-Uhlenbeck (BUU) model and statistical emission qualitatively reproduces the results from this work.

Charge and transverse energy distributions for intermediate mass fragments have been extracted for central Kr1Au collisions at E/A5352400 MeV. The slopes of the measured fragment charge distributions decrease monotonically with incident energy, consistent with the expectations for highly charged systems, but not with recent critical exponent analyses. Statistical model calculations, which reproduce the experimental trends, suggest that post-breakup fragment secondary decays alter significantly the observed charge distributions. Radial expansion velocities extracted from these calculations follow the systematics of Au1Au collisions. @S0556-2813~97!50205-6#

In an effort to investigate the production of ${}^{74}$Se in $p$-process nucleosynthesis, the ${}^{74}$Ge($p$,$\ensuremath{\gamma}$)${}^{75}$As reaction cross section was measured in the relevant energy range of ${E}_{p}=1.6$--4.2 MeV. The measurements were carried out using the NSCL SuN detector at the University of Notre Dame. The results are in good agreement with previous work, extending the measurements to both lower and higher energies. The measurements are compared to theoretical predictions using the non-smoker and talys nuclear reaction codes. New and improved reaction rates are offered, and these reaction rates are used in a 25M${}_{\ensuremath{\bigodot}}$ Type II Supernova model to study their impact on the production of ${}^{74}$Se.

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.

Differential cross sections for evaporation residues and fission fragments for 35A, 100A, 130A and 155A MeV $^{14}\mathrm{N}$ on targets ranging from $^{154}\mathrm{Sm}$ to $^{197}\mathrm{Au}$ have been measured. The angle-integrated cross sections are larger than what might be expected. The fission fragment-fission fragment folding angle correlations for 35A, 100A MeV $^{14}\mathrm{N}$ and 25A MeV $^{16}\mathrm{O}$ on similar targets were also measured. The average linear momentum transfer has been deduced from both the fission angle correlation and from the fore-aft asymmetry of the fission angular distributions in the laboratory system. The data are all consistent with a picture where pre-equilibrium particle emission removes an increasing fraction of the orbital angular momentum as the bombarding energy increases. This allows a large range of partial waves to contribute to formation of a composite nucleus with a finite fission barrier. \textcopyright{} 1996 The American Physical Society.

The fragmentation of E/A=40 MeV $^{20}\mathrm{Ne}$ projectiles into exit channels containing only p, d, t, $^{3}\mathrm{He}$, \ensuremath{\alpha}, $^{6}\mathrm{He}$, $^{6}\mathrm{Li}$, and $^{7}\mathrm{Li}$ fragments has been investigated. Relative shifts between the average longitudinal velocity of each fragment type were measured with $^{120}\mathrm{Sn}$ and $^{197}\mathrm{Au}$ targets. A post-breakup Coulomb acceleration component of these shifts was isolated. Its magnitude indicates that the projectile broke up while in near contact with the target. On the other hand, correlations between projectile fragments indicate that a significant fraction of these fragments are produced by the sequential decay of long- and short-lived unstable intermediates. A fully sequential decay process, although consistent with the experimental relative angle distributions, fails to reproduce the correlation function. Thus, a picture emerges of a prompt breakup step producing stable and unstable particles with the subsequent decay of the latter extending over a long time period.

Previous work has examined light particle correlations from O+Al reactions over a range of energies within a framework of statistical emission from a composite source. The source of these light particles was assumed to be an excited composite nucleus because the excitation energy of the source was not so high that exotic processes such as fragmentation or preequilibrium emission were significant. In this Brief Report we examine correlation functions between light charged particles emitted from reactions of S+Al at 105 MeV and 215 MeV. As in previous work, the proton-proton and proton-deuteron correlations are well described by the results of Monte Carlo simulations based on statistical emission. In this Brief Report we will also compare the results of alpha-alpha and deuteron-alpha correlations to the predictions of models which include the emission of heavier unstable particles (such as {sup 8}Be and {sup 6}Li{sup *}) from the excited source. The results presented here can serve as additional validation of the correlation technique and also as tests of the statistical model.

Coincidence measurements have been made between 4 He 1 H and a second particle ( 4 He 1 H ) produced in the reactions 905 and 1030 MeV 121 Sb + 27 Al and 550 and 750 MeV 86 Kr + 63 Cu . All four of the reactions lead to composite systems of 149Tb∗ or 148Gd∗ which facilitates comparisons of matched reactions. In the two 121 Sb + 27 Al reactions and the 550 MeV 86 Kr + 63 Cu reaction, the particle-particle coincidences are dominated by processes that lead to evaporation residues. In the 750 MeV 86 Kr + 63 Cu reaction, about half of the 1H and 4He are associated with evaporation residue production. These particle-particle coincidences arise from cross sections that are subsets of the total evaporation residue cross sections. The derived individual particle chain lengths are ∼ 2 for both protons and alphas in each of the four reactions. The particle multiplicities and subset cross sections associated with the evaporation residues are quite similar for the matched reactions, in contrast to fission-like processes where spin-dependent entrance channel effects were observed.

Intermediate-mass-fragment emission has been studied in central {ital E}/{ital A}=30 MeV {sup 129}Xe+{sup nat}Cu reactions. The measured fragment multiplicities, reduced-velocity correlation functions, and emission velocities have been compared with schematic three-body trajectory calculations and with three statistical models with input based upon a dynamical BNV code. The statistical models which include expansion either explicitly or implicitly are able to generate a sufficient number of fragments. The three-body trajectory calculations indicate a mean emission time of {approx}200 fm/{ital c}, consistent with sequential decay. Dynamical expanding-emitting source calculations predict a similar time scale for fragment emission and give satisfactory agreement with the experimental correlation functions if the experimental angular distributions are incorporated into the model. The Berlin multifragmentation model gives good agreement with the experimental charge distributions, and, depending upon the choice of radius parameter, can provide agreement with either the correlation functions or the fragment emission velocities, but not with both simultaneously. Although an overall good agreement is obtained in the statistical model comparisons, even in the most violent collisions the angular distributions and fragment emission velocities are incompatible with completely equilibrated decay from a single source.

Multifragment decays of heavy nuclei have been studied at the ALADIN spectrometer system at beam energies between 100 and 1000 MeV per nucleon. The observed fragment distributions signal a universality of spectator decays at bombarding energies E A ≥ 400 MeV . The role of the radial flow for the fragmentation process is explored by comparing fragment distributions measured for Au+Au collisions at E A = 100 MeV in central collisions and at E A = 1000 MeV in more peripheral reactions. At both energies the maximum multiplicity of intermediate mass fragments (IMFs) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at E A = 100 MeV may be related to a reduction of the density in momentum space which is caused by a large collective expansion velocity component.

We have developed an analysis package for event-mode data based on Interactive Data Language (IDL) from Research Systems Inc. This high-level language is high speed, array oriented, object oriented, and has extensive visual (multi-dimensional plotting) and mathematical functions. We have developed a general framework, written in IDL, for the analysis of a variety of experimental data that does not require significant customization for each analysis. Unlike many traditional analysis package, spectra and gates are applied after data are read and are easily changed as analysis proceeds without rereading the data. The events are not sequentially processed into predetermined arrays subject to predetermined gates.

The Modular Neutron Array (MoNA), a highly efficient time-of-flight neutron detector, is being constructed for use at the National Superconducting Cyclotron Laboratory. The modular design of the detector provides significant flexibility and allows the bulk of the assembly and testing to be done by undergraduates at nine of the schools participating in the project.

In the preceding Comment, Fortune argues that, in our original paper [Peters et al., Phys. Rev. C 83, 057304 (2011)], we did not or could not separate the two neutron-unbound states in ${}^{11}\mathrm{Be}$ near 4 MeV. However, including the suggested contribution of the 3.887-MeV state decaying via 18 keV to the ${2}^{+}$ state in ${}^{10}\mathrm{Be}$ does not fit the data; neither do any other attempts incorporating any contribution of this decay channel. The best fit was achieved with a single resonance of decay energy 80(2) keV.

Impact-parameter filtered longitudinal and transverse two-proton correlation functions measured for 36Ar+ 45Sc collisions at [ital E]/[ital A]=80 MeV are compared to predictions of the BUU transport model. For a cut on large transverse energies, the overall trends of the measured correlated functions are rather well reproduced by calculations for central collisions. Systematic discrepancies become visible, however, for calculations with larger impact parameters.

The relationship between observed intermediate mass fragment and total charged particle multiplicities has been measured for [sup 84]Kr + [sup 197]Au collisions at energies between [ital E]/[ital A]=35 and 400 MeV. Fragment multiplicities are greatest for central or near-central collisions. For these collisions, fragment production increases up to [ital E]/[ital A][approx]100 MeV, and then decreases at higher energies.

Highly fragmented exit channels produced by the decay of excited 24Mg projectiles were detected. The longitudinal velocity spectra of protons and alpha particles from such channels are offset. This offset is consistent with post-breakup Coulomb accelerations from the 197Au target nuclei implying that the protons were emitted within 3 X 10−22 s after the target-projectile separation.

Neutron-unbound resonant states of $^{11}\mathrm{Be}$ were populated in neutron knockout reactions from $^{12}\mathrm{Be}$ and identified by $^{10}\mathrm{Be}$--$n$ coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in $^{11}\mathrm{Be}$ at 3.949(2) MeV decaying to the ${2}^{+}$ excited state in $^{10}\mathrm{Be}$. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state, suggesting a spectroscopic factor near unity for this $0p3/{2}^{\ensuremath{-}}$ level, consistent with the detailed shell model calculations.

Azimuthal correlations of particles emitted in collisions between 197Au target nuclei and projectiles 36Ar (at E A = 35, 50, 80 and 110 MeV ) and 129Xe (at E A = 50 MeV ) have been measured with the MSU Miniball, a 4π phoswich array with a low detection threshold. Various impact parameter filters, based on the charge-particle multiplicity, transverse energy and midrapidity charge are tested by their ability to suppress collective motion as measured by the azimuthal correlations. The usefulness of a directivity cut in selecting central collisions for these systems is evaluated.

Multifragment disintegrations observed in 36 Ar+ 197 Au and 129 Xe+ 197 Au collisions are compared with theoretical predictions.

Transverse kinetic energy spectra of fragments in the reaction 36 Ar + 197 Au are used to probe the multifragmentation mechanism at intermediate energies. The mass dependence of the average transverse kinetic energy is examined in the context of the statistical decay of an expanding, emitting source. The role of source expansion during emission is explored. Results suggest the onset of volume emission at the highest incident energy.

The spatial and temporal extent of a system decaying by multifragment emission is deduced. Two-particle intermediate mass fragment correlation functions measured for central $^{36}\mathrm{Ar}$${+}^{197}$Au collisions at E/A=50--110 MeV indicate a rapid decay, 75 fm/c, of the highly excited system. Furthermore, the behavior of the correlation function at large relative velocities suggests that considerable charge loss occurs prior to fragment emission.

Element distributions and fragment multiplicity distributions have been measured for E/A=50 MeV $^{129}\mathrm{Xe}$${+}^{12}$C, $^{27}\mathrm{Al}$, $^{51}\mathrm{V}$, $^{\mathrm{nat}}\mathrm{Cu}$, $^{89}\mathrm{Y}$, and $^{197}\mathrm{Au}$ reactions using a low threshold 4\ensuremath{\pi} detector. Both distributions show a strong correlation with the detected charged particle multiplicity and a large degree of target independence. The measured distributions are compared with hybrid model calculations which incorporate important dynamical aspects in both the preequilibrium and statistical emission phases. Results of these calculations are in reasonable agreement with the data. However, uncertainties with regard to the compressibility of nuclear matter remain due to uncertainties in the coupling of the two models.

Collisions between 36Ar projectiles and 197Au target nuclei at E A = 50, 80 and 110 MeV have been studied with the MSU Miniball, a 4π phoswich array with a low detection threshold. Various impact-parameter filters, based upon total charged-particle multiplicity, transverse energy, midrapidity charge and multiplicity of emitted hydrogen nuclei, are compared and cross-correlated. The relative selectivity of each prescription for small impact-parameter collisions is evaluated by assessing the suppression of fast-particle emission at forward angles.

An analysis of charged particle distributions is performed to search for large fluctuations and signals of intermittency in 36 Ar + 197 Au reactions at E/A=35–110 MeV. When the effects of impact-parameter averaging are reduced by appropriate cuts on the total transverse energy, charged particle multiplicity distributions narrower than Poisson distributions are observed. Such distributions are inconsistent with intermittency signals of non-trivial origin.

Relative abundances of intermediate mass fragments and light particles measured for 36 Ar+ 197 Au collisions at E A = 50, 80 and 110 MeV lie within the range of percolation model predictions, but for 129 Xe+ 197 Au collisions at E A = 50 MeV , the percolation model predicts too small admixtures of intermediate mass fragments among the emitted charged particles.

A segmented silicon-silicon-plastic array was constructed for studying complex fragment production in heavy-ion reactions with incident energies of 35–100 MeV/u. The array was designed: (1) to measure the energy, position and charge of fragments with 1≤Z≤Zproj; (2) to have high efficiency for detecting fragments produced in reverse-kinematics reactions; (3) to detect events with two or more fragments; and (4) to have a flexible configuration. Each array telescope consists of a 300 μm Si detector, a 5 mm Si(Li) detector and a 7.6 cm plastic scintillator. The elements of the telescope are held by interconnecting modular packages which allow the telescopes to be close packed about the beam direction. This modular array has been used in several different experimental configurations and examples of its performance are presented.

The $^{211,212}\mathrm{At}$ yields resulting from the interaction of the radioactive projectile $^{8}\mathrm{Li}$ with a $^{208}\mathrm{Pb}$ target have been measured at energies between $3$ and $8.5$ MeV above the Coulomb barrier. They are signatures for fusion of the whole charge but not necessarily the whole mass of the projectile, so they are included in a corresponding operational definition of complete fusion. Within this definition, a fusion suppression factor of $0.70\ifmmode\pm\else\textpm\fi{}0.02$ (stat.) $\ifmmode\pm\else\textpm\fi{}0.04$ (syst.) is deduced from a comparison to a one-dimensional barrier-penetration-model calculation using parameters extrapolated from values for $^{6,7}\mathrm{Li}+^{209}\mathrm{Bi}$ and $^{9}\mathrm{Be}+^{208}\mathrm{Pb}$ taken from the literature. Possible incomplete fusion processes are discussed and the results are fitted with a phenomenological model assuming breakup prior to fusion followed by capture of a $^{7}\mathrm{Li}$ fragment.

An excited state of $^{22}\mathrm{N}$ unbound with respect to neutron emission was observed in a stripping reaction from a 85 MeV/nucleon $^{26}\mathrm{F}$ beam. The observed decay energy of 650(50) keV places the level, which is interpreted to be the first ${3}^{\ensuremath{-}}$ state, at an excitation energy of 1.93(22) MeV. Together with the previously measured bound states of $^{22}\mathrm{N}$, reduction of the $N=14$ shell gap compared to less neutron-rich nitrogen isotopes at the neutron dripline is observed. Based on the magnitude of the reduction of the shell gap for $^{22}\mathrm{N}$, a disappearance of the gap and even a level inversion of the $\ensuremath{\nu}1{s}_{1/2}$ and the $\ensuremath{\nu}0{d}_{5/2}$ levels in the neutron-unbound nucleus $^{21}\mathrm{C}$ seems likely.