A supersonic gas jet target built for studying heavyion induced nuclear reactions with high energy resolution is described. The present gas target has already been used in an Enge split-pole magnetic spectrograph and a standard 48 cm ORTEC scattering chamber, and could also be used with the Elbek magnetic spectrograph and the time-of-flight spectrometer. The gas jet is formed with a convergent-divergent Laval nozzle which allows for rapid supersonic expansion of gas at high pressures into the target region. The crucial ingredient of any gas jet target is the vacuum pumping system. The energy loss measurements and Rutherford scattering show good agreement with the calculated target density. There seems to be a wide variety of experiments including studies of continuum and high resolution spectra of products from heavy ion induced reactions for which a gas jet target is very useful.

The back-angle yields of the oxygen and carbon particles from the P-31 + O-16 reaction have been measured at E(lab)(P-31) = 135.6 MeV by using reverse kinematics. Comparison with similar data for the Cl-35 + C-12 reaction forming the same compound nucleus at the same excitation energy and with a very similar spin distribution shows very small entrance-channel dependence of back-angle yields. These results are in contrast to a similar study of the reactions Si-28 + C-12 and Mg-24 + O-16. It is evident that the oxygen and carbon yields from the P-31 + O-16 and Cl-35 + C-12 reactions have a predominantly compound nucleus origin in contrast to those from the Si-28 + C-12 and Mg-24 + O-16 reactions. Possible connection of this nonequilibrium entrance channel dependence with the presence of nuclear molecular resonances is discussed.

Gamma-ray angular correlations have been measured for the strongly damped reactions C-12(Si-28, C-12)Si-28 between theta-cm = (120-degrees - 160-degrees) for E(cm) = 43.5 and 48 MeV. We find that the density matrices for the C-12(2(1)+) and Si-28 states are almost diagonal with respect to the direction of motion of the outgoing particle. The measured density matrices and spin alignments are consistent with the picture of formation of a long-lived dinuclear complex undergoing orbiting, bending and wriggling motions, but not with those obtained from statistical compound nucleus or sticking model calculations.

We describe herein a set of tracking detectors used in the identification of particles produced in relativistic nucleus-nucleus collisions.

Gamma-ray angular correlations have been measured for the damped reactions C-12(Si-28, C-12)Si-28 between theta-c.m. = 120-degrees and 160-degrees for E(c.m.) = 43.5 and 48 MeV. The spin alignments and density matrices have been deduced from the observed angular distribution of the gamma rays for Si-28 states in -10 < Q < 0 and -16 < Q < 0 MeV for E(c.m.) = 43.5 and 48 MeV, respectively, and for C-12(2(1)+) state in strongly damped region Q < -10 MeV. We find that the spin angular momenta of the nuclei are poorly aligned with respect to the normal to the reaction plane and the density matrices for the C-12(2(1)+) and Si-28 states are almost diagonal with respect to the direction of motion of the outgoing particle. We also find qualitatively similar behavior of the spin alignments for Si-28 states in strongly damped region. The measured density matrices and spin alignments are consistent with the picture of formation of a long-lived dinuclear complex undergoing orbiting, bending, and wriggling motions, but not with those obtained from statistical compound nucleus or sticking-model calculations.

Investigations of interpolating cathode pad readout have been carried out for high-multiplicity, two-dimensional position-sensitive detection of minimum ionizing particles and heavy ions. A detector configuration representing only 0.6% of a radiation length and covering an area of 26 cm by 16 cm, with over 1000 readout channels, has been developed. In a prototype chamber using this technique, a re...

The design and performance of a detector system for tracking charged particles in an environment of high track density and rates up to 1 MHz are described. The system operates in the forward spectrometer of the Brookhaven National Laboratory heavy ion experiment E814 and uses principles of general interest in high-rate, high-multiplicity applications such as at the Relativistic Heavy Ion Collider ...

Two types of MWPC with interpolating cathode pad'' readout for two dimensional position sensitive detection have been studied. One type uses rectangular pads and resistive charge division. A detector with an active area of 26 cm {times} 16 cm, over 1000 readout channels has been built. With readout spacing of 1 cm, a position resolution of {approximately}70{mu}m (rms) for 5.4 keV x-rays and a differential non-linearity of {plus minus}6% have been achieved. Another type of detector uses chevron'' shaped pads for geometrical charge division. Position resolution {approximately}50{mu}m (rms) for 5.4 keV x-rays has been observed in a test detector and results of an investigation to reduce differential non-linearity are reported. 11 refs., 6 figs.

We have initiated a search for strange quark matter in the products of 14.6 GeV/c per nucleon 28Si collisions with nuclei, utilizing the apparatus of E-814 at Brookhaven National Laboratory's AGS. We report the first results of this search, which is sensitive to particles with charge-to-mass ratios between 0.1 and 0.3 (GeV/c2)−1 that are produced within approximately ±0.5 units of the center of mass rapidity.

Cross sections for the fusion of $^{28}\mathrm{Si}$ + $^{12}\mathrm{C}$ and $^{30}\mathrm{Si}$ + $^{12}\mathrm{C}$ have been measured at energies between 6.4 and 9.4 MeV/nucleon and 5.2 and 8.3 MeV/nucleon, respectively. Comparison with existing data for compound systems with $A=40 \mathrm{and} 42$ shows that the extracted critical angular momentum at saturation (${l}_{\mathrm{cr}}^{max}$) depends strongly on the entrance channel mass asymmetry. This effect is not accounted for by the standard entrance channel or compound nucleus models. A calculation of the conditional saddle-point shapes for touching spheroidal nuclei indicates that this mass asymmetry effect is a consequence of the dynamical fusion thresholds at high angular momentum. Quantitative agreement is obtained with the experimentally measured ${l}_{\mathrm{cr}}^{max}$ using the finite range model of Sierk for diffuse-surface nuclei.

The charge and mass distribution of orbiting yields from the $^{28}$Si${+\mathrm{}}^{14}$N interaction have been studied at center of mass energies between 30 and 56.7 MeV. The data indicate that the orbiting system lives sufficiently long for the exit channel yields to be determined by phase space considerations. The data are compared with compound nucleus and orbiting calculations, and clearly favor the latter. Further comparisons between the data and the orbiting calculations indicate that full phase space equilibration of the orbiting yields is hindered at low excitation energies by the inaccessibility of single nucleon transfer channels. Also evident in the data is a correlation in the behaviors of the charge width, mass width, and final product kinetic energies, which is interpretable as arising from a maximum angular momentum that the $^{28}$Si${+\mathrm{}}^{14}$N orbiting composite can sustain.

We present a model that provides a unified description of fusion and the full momentum transfer component of dissipative collisions (orbiting), in light-heavy-ion-induced reactions. The model is applied successfully to describe measured cross sections for fusion and orbiting over a wide range of bombarding energies for the $^{28}$Si${+}^{12}$C system.

Forward-angle yields of targetlike products in reactions between a $^{28}\mathrm{Si}$ beam and a $^{14}\mathrm{N}$ target have been measured at laboratory energies between 100 and 170 MeV. The $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ yields are found to be higher than those of $^{14}\mathrm{N}$ over the measured range of energies. This is interpreted as evidence for the equilibration of charge and mass in orbiting reactions.

An extension of the diffusion model is proposed for describing the intermediate processes and the compound nucleus formation in heavy ion collisions. The model describes the intermediate processes and fusion in terms of the formation and the evolution of long-lived dinuclear molecular complex (DMC) and its subsequent decay by fragmentation. The colliding ions can be trapped into the pocket of the entrance channel nucleus-nucleus potential and a DMC is formed. This DMC acts as a doorway state towards formation of a completedly equilibrated compound nucleus. It evolves through the exchange of nucleons to different dinuclear configurations. At each stage of its evolution, there is a finite probability to emit fragments into outgoing channels by thermal penetration over the barrier. The doorway states that do not fragment relax into a compound nucleus configuration and are identified as the fusion yield. The model is applied to the analysis of Si + C collisions for which the fusion cross section and the orbiting data are available for a wide range of bombarding energies. 7 refs., 2 figs. (LEW)

The question of compound nucleus or entrance channel-type limitation to the fusion cross section has been approached effectively in experiments where the same compound nucleus is populated by different projectile-target combinations. Fusion data are available for several systems leading to the compound nuclei /sup 40/Ca and /sup 42/Ca. In this study we report on measurements of fusion cross sections done on /sup 28/Si + /sup 12/C and /sup 30/Si + /sup 2/C over a wide range of bombarding energies. These data are combined with available data to show the presence of a strong entrance channel limit for fusion these two systems.