T. F. Wang

Bio: T. F. Wang is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Nuclear reaction & Fission. The author has an hindex of 15, co-authored 37 publications receiving 925 citations. Previous affiliations of T. F. Wang include Yale University & University of Manchester.

Fabrication of nanopillars by nanosphere lithography

Abstract: A low cost nanosphere lithography method for patterning and generation of semiconductor nanostructures provides a potential alternative to the conventional top-down fabrication techniques. Forests of silicon pillars of sub-500 nm diameter and with an aspect ratio up to 10 were fabricated using a combination of the nanosphere lithography and deep reactive ion etching techniques. The nanosphere etch mask coated silicon substrates were etched using oxygen plasma and a time-multiplexed 'Bosch' process to produce nanopillars of different length, diameter and separation. Scanning electron microscopy data indicate that the silicon etch rates with the nanoscale etch masks decrease linearly with increasing aspect ratio of the resulting etch structures.

Binary decay of 56Ni formed in the 32S

Abstract: Fully energy-damped yields from the {sup 32}S+{sup 24}Mg reaction have been measured at center-of-mass energies of {ital E}{sub c.m.}=51.6 and 60.5 MeV with the use of an experimental arrangement where both of the resulting heavy fragments could be detected in coincidence. Energy, velocity, and angular distributions of the reaction fragments have been determined. The cross sections prior to secondary light-particle emission have been deduced for the breakup of the compound system into different mass channels. These data are discussed in terms of two possible reaction mechanisms: fusion followed by fission and deep-inelastic orbiting.

Study of porous glass doped with quantum dots or laser dyes under alpha irradiation

Abstract: We demonstrate that nanocomposite materials based on semiconductor quantum dots have potential for radiation detection via scintillation. While quantum dots and laser dyes both emit in the visible range at room temperature, the Stokes shift of the dyes is significantly larger. The scintillation output of both systems was studied under alpha irradiation and interpreted using a combination of energy loss and photon transport Monte Carlo simulation models. The comparison of the two systems, which allows the quantification of the role played by the Stokes shift in the scintillation output, opens up exciting possibilities for a new class of scintillators that would take advantage of the limitless assembly of nanocrystals in large, transparent, and sturdy matrices.

Entrance-channel effects in quasifission reactions.

Abstract: The entrance-channel dependence of the distribution of reaction strength has been studied for three systems, namely $^{32}\mathrm{S}$${+}^{182}$W, $^{48}\mathrm{Ti}$${+}^{166}$Er, and $^{60}\mathrm{Ni}$${+}^{154}$Sm, which all lead to the compound system $^{214}\mathrm{Th}$ in complete fusion reactions. The cross sections for elastic/quasielastic scattering, deeply inelastic, and fissionlike processes were measured at beam energies of ${\mathit{E}}_{\mathrm{lab}}$ =166, 177, 222, 260 MeV for $^{32}\mathrm{S}$${+}^{182}$W, ${\mathit{E}}_{\mathrm{lab}}$=220, 240, 270, 298 MeV for $^{48}\mathrm{Ti}$${+}^{166}$Er, and ${\mathit{E}}_{\mathrm{lab}}$=339, 390, 421 MeV for $^{60}\mathrm{Ni}$${+}^{154}$Sm, respectively. The maximum contribution of complete-fusion fission processes to the fissionlike cross section is estimated on the basis of expected angle-mass correlations for such reactions. The results show a strong entrance-channel dependence as predicted by the extra-push model. \textcopyright{} 1996 The American Physical Society.

Search for X-Ray Induced Acceleration of the Decay of the 31-Yr Isomer of 178Hf Using Synchrotron Radiation

Abstract: Releasing the energy stored in an isomeric nuclear state in a controlled way with an atomic or electromagnetic trigger is an attractive speculation: the energy gain may be on the order of the ratio of nuclear/atomic energies - MeV/keV. (Nuclear isomers are loosely defined as excited nuclear states with lifetimes longer than 10{sup -9} s.) Nuclear isomers, therefore, represent an opportunity for a stand-alone energy source if suitable schemes for trigger and control of the energy release can be found. Potential applications include space drive, as well as very bright {gamma}-ray sources. The nucleus {sup 178}Hf has a nuclear isomer with excitation energy E{sub x} = 2.447 MeV. The 2.447-MeV isomeric state decays slowly (t{sub 1/2} = 31 y) to the nearby state at 2.433 MeV. The J{sup {pi}} = 13{sup -} state loses energy in a rapid (t {approx} 10{sup -12} s) {gamma}-ray cascade ending at the 8{sup -} rotational band head which in turn decays via the ground-state rotational band cascade. The {gamma}-ray cascade is delayed at the 8{sup -} state at 1.147 MeV, since the 8{sup -} state is also isomeric, with t{sub 1/2} = 4 s. Very scarce quantities of the 16{sup +}, 31-yr isomer aremore » available for research ({approx} 10{sup 15} atoms). Reports of triggered decay of the {sup 178}Hf isomer induced by x-rays delivered by a dental x-ray machine have been made [2,3]. Enhancements of {approx} 1 - 2% in the isomer decay rate (dN/dt = - (1 + {var_epsilon})N/{tau}) had been reported for various {gamma}-rays in the cascade (distinguished by red and vertical lines in Figure 1). The reported integrated cross section for triggering the decay is cm{sup 2} keV, so large as to demand new physics. We have sought to verify these reports taking advantage of the intense photon flux available at the Advanced Photon Source.« less

Colloidal self-assembly meets nanofabrication: from two-dimensional colloidal crystals to nanostructure arrays

Abstract: Self-assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self-assembly with nanofabrication techniques, two-dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as "colloidal lithography", which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self-assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal-crystal-assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.