Showing papers by "Hyun-Chul Kim published in 1991"

Populations of excited states and reaction mechanisms in the emission of complex fragments for collisions of 58Ni+58Ni at 11 MeV/nucleon.

Abstract: Cross sections for emission of complex fragments ({ital Z}{gt}2) in their ground and excited states are presented for the reaction {sup 58}Ni+{sup 58}Ni at a bombarding energy of 630 MeV. Measurements of energy spectra, angular distributions, and angle-integrated cross sections were made for fragments of {ital Z}=4 to 20. {gamma} rays emitted in coincidence with the fragments were measured in a 4{pi} geometry using 62 NaI detectors and 8 Compton-suppressed germanium detectors. Data presented are mostly for the cross sections extracted by {gamma}-ray techniques. A simple statistical approach to associate the ratio of cross sections for excited states and ground states to the temperature of the emitter fails to give the expected temperatures. However, it is shown that this is mostly due to the fact that the fragments that {gamma} decay are secondary fragments produced by particle decay of the primary fragments. A Hauser-Feshbach analysis accounts well for the fragment cross sections, energy spectra, and extracted temperatures, provided that evaporation from the primary fragments is included.

Semiconductor memory device having netlike power supply lines

Abstract: A semiconductor memory device for minimizing the resistance attendant on reaching as far as each sense amplifier connected to a memory cell. A first plurality of power supply lines are alternatively disposed between column select lines which is formed over a plurality of lines of semiconductor memory device in a column direction. The first plurality of power supply lines the first plurality of ground lines are connected to a second plurality of power supply lines and a second plurality of ground lines which are disposed under the column select lines in a row direction, to thereby provide a netlike power supply structure. Consequently, the operating speed of a chip is improved by minimizing the resistance attendant on reaching as far as the sense amplifiers connected to each memory cell and the efficiency of the semiconductor memory device is greatly promoted by suppressing a coupling phenomenon caused between the column select lines.

Compound nucleus origin of back-angle yields in the 31P+16O and 35Cl+12C reactions.

Abstract: The back-angle yields of the oxygen and carbon particles from the {sup 31}P+{sup 16}O reaction have been measured at {ital E}{sub lab}({sup 31}P)=135.6 MeV by using reverse kinematics. Comparison with similar data for the {sup 35}Cl+{sup 12}C 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 {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O. It is evident that the oxygen and carbon yields from the {sup 31}P+{sup 16}O and {sup 35}Cl+{sup 12}C reactions have a predominantly compound nucleus origin in contrast to those from the {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O reactions. Possible connection of this nonequilibrium entrance channel dependence with the presence of nuclear molecular resonances is discussed.

The HILI - a multidetector system for light ions and heavy ions

Abstract: A detector system with a large acceptance, high granularity and a logarithmic response, has been built. It is well suited to detect simultaneously, heavy and light fragments from nucleus-nucleus collisions at energies higher than 10 MeV/nucleon. The angular range spanned by this detector system is ± 20° in-plane and ± 16° out-of-plane with the exclusion of a 2.5° cone around the beam axis. Coverage with a large dynamic range is provided with four large gas filled ionization chambers and behind them a 192-element hodoscope made of individual fast + slow plastic scintillation telescopes in a “phoswich” arrangement.

Spin alignment and density matrix measurement in 28Si+12C orbiting reaction.

Abstract: Gamma-ray angular correlations have been measured for the strongly damped reactions {sup 12}C({sup 28}Si,{sup 12}C){sup 28}Si between {theta}{sub cm} = (120{degree} {minus} 160{degree}) for E{sub cm} = 43.5 and 48 MeV. We find that the density matrices for the {sup 12}C(2{sub 1}{sup +}) and {sup 28}Si 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. 17 refs., 2 figs., 1 tab.

Exclusive p-p correlations from the 58Ni+58Ni reaction at

Abstract: Exclusive {ital p}-{ital p} correlations from the {sup 58}Ni+{sup 58}Ni reaction at 850 MeV incident energy have been measured. The enhancement in the {ital p}-{ital p} correlation function observed for small values of {Delta}{ital p} with a gate on {ital v}{sub rel} is satisfactorily explained by stochastic proton emission followed by the {ital p}-{ital p} final-state interaction. A strong dependence of the {ital p}-{ital p} correlation function on the relative angle between the two-proton c.m. and the fragment velocities has been found. Also a dependence of the {ital p}-{ital p} correlation function on the {Delta}{bold p} orientation with respect to the plane defined by the two-proton c.m. and the fragment velocities has been observed. This latter behavior has been attributed to angular momentum effects.

Multinucleon-transfer reactions for the 50Ti+93Nb system at sub- and near-barrier energies.

Abstract: Target and target-like ejectiles emitted forward from {sup 93}Nb-beam bombardment of thin {sup 50}Ti targets were investigated at sub- and near-barrier energies using a magnetic spectrograph. Reaction products from three single-nucleon-transfer and seven multinucleon-transfer channels were observed. Multinucleon-transfer products were observed with a sharp onset only for those collisions with apsidal distances smaller than about 12.6 fm, while single-nucleon-transfer products were observed throughout the apsidal distance range studied. Average {ital Q} values of the multinucleon-transfer-reaction products are much more negative than the respective optimum values. These results suggest the formation of a neck at subbarrier energies.

Microprobe photoluminescence measurement on heteroepitaxial gaas on si grown by metalorganic chemical vapor deposition

Abstract: Microprobe photoluminescence (PL) measurements at 77 K were used to study the effect of the GaAs layer thickness on optical quality and variations in strain in GaAs/Si containing microcracks. PL peak intensities increase with the increase in thickness of GaAs layers and the peak intensity for the 5.5 μm GaAs layer was a factor of 20 higher than those for the 1–2 μm GaAs layers. Spatial nonuniformities in strain in the vicinity of two microcracks reveal that stress was almost released at the intersection of two microcracks and is maximum half way between two microcracks.