Radiation Physics Group	Peter Bradley
Education
Professional Experience
Research Interests		Contact Information Home: Ph: (858) 4510578 14303 Breezeway Place, San Diego, CA, 92128, United States. Work: Ph: (858) 6753468 Zarlink Semiconductor, Medical Business Unit Senior IC designer/Project manager 10815 Rancho Bernardo Rd, Suite 210; San Diego, CA, 92127, United States. peter.bradley@zarlink.com
PhD Summary
Publications
Conferences
Software developed
Complete Resume

Education

• BE  (Elect,1st hons, UNSW), 1987.
• ME (Biomed, UNSW), 1996.
• Grad Dip  (Biomed, UNSW),1996.
• PhD  (Physics, UW), 2000.

 

 

Masters Thesis: "The Effects of Ionizing Radiation on Implantable MOS devices"
Thesis presented the world's first evidence and analysis of cosmic radiation effects on a life supporting medical application (implantable cardioverter defibrillator).

PhD Thesis: "The Development of a Novel Silicon Microdosimeter for High LET Radiation Therapy"
Thesis presented the first comprehensive investigation of the issues confronting silicon microdosimetry and its application to radiotherapy

Research Interests

• Microdosimetry, semiconductor dosimetry,
• Radiation effects on electronics (system and device),
• Medical application of semiconductor devices and integrated circuit design.
• Medical Instrumentation

PhD Summary

The aim was to investigate and develop a silicon based microdosimeter which offers the possibility of replacing the current proportional gas counter for measurements of  radiation deposited in cellular (10um diameter) sized volumes. Four main problems were addressed

1. Inadequare requirement specifications and analysis of shape of sensitive volume
2. Diffusion of charge within the silicon obscures the charge collection volume boundary.
3. Tissue equivalence of silicon for microdosimetric measurements.
4. Poor noise performance in comparison with gas counter.

Some of the experimental and theoretical work performed is summarised below.

• Study of radiation effects on silicon and microdosimetry
• Alpha Spectroscopy, Radiation Physics Group, Department of Engineering Physics, University of Wollongong.
• Alpha and proton microbeam imaging, MicroAnalytical Research Center, Department of Physics, University of Melbourne. Figure 3 provides an example of the imaging.
• Accurate current-voltage and capacitance-voltage measurements and use of 2 MV Van Der Graff Generator, Australian Nuclear Science and Technology Organsition (ANSTO), Lucas Heights, Sydney.
• Silicon radiation damage and hardness study, exposure of devices to 24 GeV/c proton beam at CERN,  Switzerland.
• Dosimetry and charge collection experiments at the following clinical facilities
• Boron Neutron Capture Therapy (BNCT) Kyoto University Research Reactor Institute, Japan.
• Boron Neutron Capture Therapy (BNCT) Medical Department, Brookhaven National Laboratory, USA.
• Boron Neutron Capture Therapy (BNCT), Laboratory for Accelerator Beam Applications, MIT
• Fast Neutron Therapy (FNT), Superconducting Cyclotron, Gershenson Radiation Oncology Center, Harper Hospital and Wayne State University.
• 250MeV Proton beam Therapy (PT) Proton Medical Research Center, University of Tsukuba and  KEK, High Energy Accelerator Research Organization, Japan.
• 230 MeV Proton beam Therapy (PT) Northeastern Proton Therapy Center (NPTC),  Harvard University-Massachusetts General Hospital, Boston, USA.
• Modeling radiation effects on silicon and tissue
• Theoretical work performed to investigate the tissue equivalence of silicon exposed to heavy ion radiation and predict the response of a silicon microdosimeter to boron neutron capture reactions. Monte Carlo simulation program developed.
• Extensive experience using 2D and 3D semiconductor simulation tools (ISE TCAD available at Photovoltaics Special Research Center, University of New South Wales)  for modeling charge collection behavior.  Figure 2 shows a 3D simulation.
• Experimental and theoretical investigation of charge collection behavior of a prototype Silicon-On-Insulator(SOI) device is in progress. Prototype microdosimeter (see figure 1)  built at Fujitsu Research Laboratories Ltd, Japan.
• Animated simulation of a 1.75MeV alpha particle generated by thermal neutron capture in the boronated p+ region of the SOI prototype.

Figure 1: SEM Photograph of the prototype microdosimeter. The width of the photo is 24um.
The raised surfaces are Aluminium tracks electrically connecting each diode cell.
The n+ diode junction is on the right whilst the p+ contact is on the left.

Figure 2: Electron density for 2um SOI device, 100ps after 5.3MeV alpha strike at x=3.5,y=15um. (1/4 of device is shown, dimensions 15x15x2um, center of diode is nearest to viewpoint). The alpha radiation generates electron-hole pairs in the silicon. The minority carrier electrons diffuse as shown by the radial diffusion profile above. The electrons are collected at the n+ junction (red). Charge collection is efficient in this region due to the strong electric field within the depletion region. A 2D animated transient simulation is also available.

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Publications and conferences

Recent publications are listed and vieweable in PDF format from my resume. The publications contain full details of the solid-state microdosimeter and experiments performed to date.

Some useful software

• To improve the default plotting capabilities of Mathematica I have written a package which produces publication quality 2D scientific plots of functions and data lists. The package has a simple option which selects the form of output (35mm slide, overhead transparency, journal, or mathematica). Colours, image size, title and legend are all adjusted to suit the output. The function allows for easy mixing of functions and lists in the same plot. This function will soon be available here.
• A Monte-Carlo program (C based ) which calculates the energy deposited in tissue and silicon rectangular parallelipiped volumes from boron neutron capture reactions has been developed. This is available on request. The program is encapsulated in a  Mathematica input/output notebook to enable flexibility in viewing results and generating simulations.