Landon Prisbrey

Modeling the Electrostatic Signature of Single Enzyme Activity

Charge sensors based on nanoscale field-effect transistors are a promising new tool to probe the dynamics of individual enzymes. However, it is currently unknown whether the electrostatic signals associated with biological activity exceed detection limits. We report calculations of electrostatic signatures of two representative enzymes, deoxyribonuclease I and T4 lysozyme. Our simulations reveal that substrate binding to deoxyribonuclease and internal dynamics of lysozyme are detectable at the single-molecule level using existing point-functionalized carbon nanotube sensors.

Controlling the function of carbon nanotube devices with re-writable charge patterns

We use atomic force microscopy lithography to write charge patterns in close proximity to carbon nanotube field-effect transistor devices. The silicon dioxide substrate retains the charge for days, allowing various charge configurations to be tested. We show that the written charge can move the Fermi level in the nanotube by 1 eV and we use this charge lithography to reconfigure a field-effect transistor into a pn junction. The substrate charge can be erased and rewritten, offering a new tool for prototyping nanodevices and optimizing electrostatic doping profiles.

Fusion of {sup 9}Li with {sup 208}Pb

We have measured the fusion excitation function for the {sup 9}Li+{sup 208}Pb reaction for near-barrier projectile center-of-mass energies of 23.9 to 43.0 MeV using the ISAC2 facility at TRIUMF. The {alpha}-emitting evaporation residues ({sup 211-214}At) were stopped in the {sup 208}Pb target, and their decay was measured. The isotopic yields at each energy were in good agreement with the predictions of a statistical model code (HIVAP). The measured fusion excitation function shows evidence for substantial sub-barrier fusion enhancement not predicted by current theoretical models. There is a suppression of the above barrier cross sections relative to these model predictions. The implications of this measurement for studying the fusion of {sup 11}Li with {sup 208}Pb are discussed.

Evaporation residue yields in reactions of heavy neutron‐rich radioactive ion beams with 64Ni and 96Zr targets

As hindrance sets in for the fusion of heavier systems, the effect of large neutron excess in the colliding nuclei on their probability to fuse is still an open question. The detection of evaporation residues (ERs), however, provides indisputable evidence for the fusion (complete and incomplete) in the reaction. We therefore devised a system with which we could measure ERs using low intensity neutron‐rich radioactive ion beams with an efficiency close to 100%. We report on measurements of the production of ERs in collisions of 132,134Sn, 134Te and 134Sb ion beams with medium mass, neutron‐rich targets. The data taken with 132,134Sn bombarding a 64Ni target are compared to available data (ERs and fusion) taken with stable Sn isotopes. Preliminary data on the fusion of 132Sn with 96Zr target are also presented.

{sup 132}Sn+{sup 96}Zr reaction: A study of fusion enhancement/hindrance

Capture-fission cross sections were measured for the collision of the massive nucleus {sup 132}Sn with {sup 96}Zr at center-of-mass energies ranging from 192.8 to 249.6 MeV in an attempt to study fusion enhancement and hindrance in this reaction involving very neutron-rich nuclei. Coincident fission fragments were detected using silicon detectors. Using angle and energy conditions, deep inelastic scattering events were separated from fission events. Coupled-channels calculations can describe the data if the surface diffuseness parameter, a, is allowed to be 1.10 fm instead of the customary 0.6 fm. The measured capture-fission cross sections agree moderately well with model calculations using the dinuclear system model. If we use this model to predict fusion barrier heights for these reactions, we find the predicted fusion hindrance, as represented by the extra push energy, is greater for the more neutron-rich system, lessening the advantage of the lower interaction barriers with neutron-rich projectiles.