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Department of Physics Seminars and Colloquia - Academic Year 2005-2006
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Academic Year 2005-2006
Monday, April 24,2006 in F539 at 2:30pm
Title:Photonuclear Studies at HI_{gamma}S
Speaker: Dr. Kara Keeter, Idaho State University
Abstract: The High Intensity Gamma-Ray Source is a novel light source with unprecedented photon flux, extremely small beam-related background, and a wide range of precisely tuneable gamma-ray energies. Using a Storage Ring Free-Electron-Laser (FEL), polarized gamma rays are produced by Compton backscattering FEL-photons from highly relativistic electrons. Unlike bremsstahlung photon sources where the total flux may be higher, the photon density (gamma/eV) is much higher at HI{gamma}S. Tuneability of the FEL, as well as of the electron momentum, makes it possible to set the energy to an accuracy of a few keV or better. Collimation alone makes it possible to obtain beam energy spreads better than 1%. These unique features make HI{gamma}S a very desirable venue to perform a variety of photonuclear experiments not possible elsewhere, as well as industrial based applications. Two experiments performed at HI{gamma}S will be discussed. A resonance study of the ^{13}C({gamma},n)^{12}C reaction has been conducted, and analyzing powers were measured. Relative percentages of the E1 s-wave and d-wave and the M1 p-wave neutron contributions to the cross section were used to confirm previous Jp assignments. To search for spin-flip M1 strength in^{40}Ar, the ^{40}Ar({gamma},{gamma}) photon scattering reaction was performed. Twenty-eight dipole excitations within this range were observed and their parity quantum numbers were unambiguously assigned. One M1 excitation at E_x =9.757 MeV out of all the other E1 excitations was identified. This is the first evidence for spin-flip M1 strength in ^{40}Ar.
Friday, April 21,2006
M.Sc. Thesis Defence in F539 at 10:00am
Title:Monte Carlo Simulation to Characterize Dose Enhancements Proximal to Dental Implants During Raeiotherapy
Speaker: Isaac Tavares, Laurentian University
Abstract: Monte Carlo simulations were performed using BEAMnrc and DOSXYZnrc of the EGS suite to investigate potential dose enhancements proximal to titanium dental implants in tissue. Dose enhancements in tissue proximal to implants should be taken into consideration when developing an optimal strategy for delivering radiation treatment, with particular attention to beam geometries and normal tissue tolerance doses. Exceeding these limits increases the probability of complications such as osteoradionecrosis. Using BEAMnrcMP, models of a Siemens 6 MV photon beam and a Theratron 780 Cobalt gamma-ray beam were developed and validated against available measured data including those obtained from equipment commissioning. The beams produced by these models were then applied to a variety of situations approximating those of clinical interest. Individual DOSXYZnrc models of implant geometry, based upon titanium rods of various diameters embedded in polyethylene, were used to calculated dose with and without the implant in place. The ratio of the results from these calculations yields backscatter as a function of rod diameter where the rod diameters examined ranged from 1.5mm to 16mm. Results showed that the maximum adjacent backscatter varied for different rod diameters from 1.23 to 1.32 for the 6 MV beam and 1.26 to 1.32 for the cobalt-60 beam. With this model, the maximum dose enhancements were 1.09 and 1.11 for the 6 MV and 60Co beams, respectively. When a standard head and neck geometry, parallel apposed pairs of radiation beams, was applied to models comprised of bone and titanium, calculations indicated a 6% enhancement of the dose delivered to bone at bone-titanium interfaces closest to the surface of the patient for both energies. With direct or single field arrangements, the model predicted an 18% enhancement at the same bone-titanium interface. Such dose enhancements must therefore be considered carefully in the context of beam configuration as well as tissue tolerance when developing an optimal strategy for radiation treatment of the head and neck.
Thursday, April 20,2006 in F539 at 2:30pm
Title:Micro-Raman Imaging of Normal and Malignant Human Skin Cells
Speaker: Dr. Michel Short, Simon Fraser University
Abstract: Several methods are available that allow researchers to construct images of living cells. Both temporal and spatial changes can be observed and time resolutions of a few seconds and spatial resolutions of around a micron are achievable. These images are a powerful tool for gaining insights into molecular processes and may help in understanding the pathology of certain diseases. Raman spectroscopy is one such method, and although it is not a new technique, it has enjoyed something of a resurgence mainly due to better and cheaper optics, lasers and CCD manufacturing. The advantage of Raman spectroscopy over other techniques is that nearly all molecules are Raman active. Therefore, samples do not have to be labeled with fluorescent markers that may cause molecular changes and can be potentially toxic to living cells. In this talk I will give an introduction to Raman spectroscopy and present some Raman images of both normal and malignant human skin melanocytes and keratinocytes. The cells were either cultivated on glass microscope slides or were located within thin sections of skin biopsies. Differences were observed between the Raman images of normal and malignant cells. Spectra from purified DNA, RNA, lipids, proteins and melanin were obtained and these spectra were compared with the skin cell spectra with the aim of understanding how they are distributed over a cell and how the distribution changes between different cells.
Tuesday, April 18,2006 in F539 at 2:30pm
Title:Life With Monte Carlo Dosimetry
Speaker: Dr. Iulian Badragan, Tom Baker Cancer Centre
Abstract: The talk provides an insight into the inner mechanisms and subtleties of the Monte Carlo techniques and reveals the way they are connected to radiation dosimetry. Various applications, as well as advantages and disadvantages of the method are briefly discussed. The work and results obtained by the speaker over a period of four years are also briefly presented. These have to do mainly with - but not being limited to - prostate seed implants, electron dosimetry, linear accelerator beam modeling and HDR quality assurance.
Thursday, April 13,2006 in F539 at 3:00pm
Title:Status and Perspective of the COBRA Double Beta Decay Experiment
Speaker: Dr. Kai Zuber, University of Oxford, UK
Abstract: COBRA is a new double beta decay experiment using CdZnTe semiconductors for the search. In total nine interesting isotopes are part of the detector with Cd106, Cd116 and Te130 as the most promising ones. The current status of the experiment at Gran Sasso Laboratory is presented as well as first results. An outlook on the option of using pixelated detectors for signal identification and background reduction is given.
Tuesday, April 11,2006 in F539 at 1:00pm
Title:SalSA: A Teraton UHE Neutrino Detector
Speaker: Dr. Kevin Reil, Stanford Linear Accelerator Center
Abstract: The observed spectrum of ultra-high energy cosmic rays virtually guarantees the presence of ultra-high energy neutrinos due to their interaction with the cosmic microwave background. Unlike cosmic rays, each of these neutrinos will point back directly to its source and will arrive at the Earth unattenuated, from sources perhaps as distant as z=20. The neutrino telescopes currently under construction, should discover a handful of these events, probably too few for detailed study. In this talk I will describe how an array of VHF and UHF antennas embedded in a large salt dome, SalSA (Saltdome Shower Array) promises to yield a teraton detector (>500 km3-sr) for contained neutrino events with energies above 1017 eV. Our simulations show that such a detector may observe several hundreds of these neutrinos over its lifetime. Our simulations also show how such interactions will provide high energy physicists with an energy frontier for weak interactions an order-of-magnitude larger than that of the LHC. The flavor ID capalities of SALSA, combined with the extreme L/E (distance over energy) of these neutrinos, will provide a window on neutrino oscillations and decay times eight orders of magnitude higher than laboratory experiments. In addition to the latest simulation results, I will show progress on detectors and site selection.
Friday April 7, 2006 in room F539 at 10:00 - noon
4th Year Thesis Final Reports
Speaker: David Braid
Title: Ultralow Level Gamma Ray Spectroscopy - Measurements and Analysis
Speaker: Jeff Frimeth
Title: Calculations and Utilization of Dose Volume Histograms for Tumour Radiotherapy
Speaker: Kristie Herranen
Title: Theory and Measurements of Acoustic Properties of the Outer Ear
Friday April 7, 2006 in room F539 at 3:00-5:00pm
4th Year Thesis Final Reports
Speaker: Emerik Mehes
Title: Phantom Gamma Ray Images using Single Photon Emission CT
Speaker:Matt Rodrigues
Title: Extrinsic Efficiency and Sensitivity Measurements for the Gamma Camera
Speaker: Stefan Kaluzienski
Title: The feasibility of real time transmission gamma radiography: A phantom study
Speaker: Marianne Schwendener
Title: Radon Detection at the Sensitivity Limit with ESCs
Speaker: Matt Cousineau
Title: Evaluation of a New Technique for Induced Polarization Mineral Exploration
Undergraduate Students, Laurentian University
Thursday, April 6,2006 in F539 at 2:30pm
Title:What's the Matter in the Universe? Looking for WIMPs with the Cryogenic Dark Matter Search
Speaker: Dr. Richard Schnee, Case Western Reserve University
Abstract: The stuff that makes up us (and everything else on the Earth) appears to be quite unusual in the universe. Astrophysical observations indicate that at least 90% of the mass of any galaxy -- and as much as 98% of the mass of the universe -- is in the form of matter that cannot be seen. Furthermore, most of this matter isn't even made from protons and neutrons -- or any other known particles. What could this matter be and how can we find out? Perhaps the best motivated possibility is weakly interacting massive particles (WIMPs) left over from the Big Bang; these particles naturally arise, for example, under supersymmetry. Detection of these particles requires sophisticated detectors such as the CDMS experiment's crystals of silicon or germanium cryogenically cooled to 20 milliKelvin. Operation of these novel detectors and the prospects for discovering what's the matter in the universe will be discussed.
Wednesday, April 5,2006 in F539 at 2:30pm
Title:Mutual Growth Inhibition Between Metastases
Speaker: Dr. Dianne Cameron, Laurentian University
Abstract: Metastasis is the primary underlying cause of treatment failure and death in cancer patients. Innovations in surgical techniques, chemotherapeutics and radiation therapies have made substantial advances in the treatment of primary neoplasms, but there has been relatively dismal progress in the treatment of metastatic cancer. Whether cells shed from a primary tumor survive their transit to secondary locations to form metastases depends on their successful evasion of destruction by biomechanical forces or immune responses during transit, as well as the properties of both the cancer cells and the host tissues in which they arrive. The hypothesis that characteristics of both the malignant cell and the destination tissue determine whether metastases will be established was proposed by Fuchs in 1882, and elaborated by Paget in 1889, becoming widely known as the "seed and soil hypothesis". Since then, researchers have explored relationships between tumor cells and organ specificity, and between tumor cells and their environments, including interactions between existing primary tumors and metastases which has led to promising new antiangiogenic therapies. My previous work to establish details of the time course and location of development of metastases of murine melanoma B16F1 and B16F10 cells in liver and lungs revealed intriguing suggestions of additional interactions between metastatic foci. This talk presents new data from subsequent experiments on interactions between individual metastases, and highlights transient but highly significant mutual growth suppression between adjacent lesions in mouse lung.
Tuesday, April 4,2006 in F539 at 2:30pm
Title:Biospeckle Application For Skin Assessment
Speaker: Dr. Lioudmila Tchvialeva, BC Cancer Agency
Abstract: Medical physics is seeking the new approaches, which might provide objective biomedical information. One of these new techniques is biospeckle that can be applied to skin cancer diagnostics. In my presentation I briefly describe the origin of speckle which is a stochastic interference pattern formed by coherent radiation transmitted through (reflected from) scattering objects. Initially speckle was considered as a noise, however, it was discovered that it carries important information about the probed media. Specific features characteristic of biospeckle are discussed. The variation coefficient of speckle intensity - contrast - is widely used as a metrological quantity. The theoretical part of my research relates to the proper analysis of numerous factors affecting the contrast to prevent from misinterpretation of contrast measurements. In particular, we have applied the Fresnel approach of diffraction theory for the free-space geometry and have figured out that the contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source but also on optical geometry. Theoretical results were used to design an experimental setup, which provides information about skin lesions. Being illuminated by low coherent light, skin surface creates a speckle pattern, which is captured by a CCD camera and analyzed. The contrast of the speckle pattern is used to derive the skin roughness parameters. Roughness is one of the main physical characteristics of the surface, so it is reasonable to use this parameter as an objective quantification criterion for diagnosing skin diseases such as cutaneous malignant melanomas and seborrheic keratoses. The system was tested using reference objects (metal surface standards, abrasive papers, and human skin replicas) and the results were consistent with the independent precise profilometry data. The system shows potential to be a reliable, rapid, noninvasive, and simple method for skin lesions differentiating. Advantages, problems of proposed techniques, and future research are discussed. Our next goal is to move towards an assessment of utility in separating seborrheic keratoses from melanocytic proliferations in vivo, and assessing the system for other medical uses.
Thursday, March 30,2006 in F539 at 2:30pm
Title:Calibration of the SNO detector
Speaker: Dr. Christine Kraus, Queen's University
Abstract: The Sudbury Neutrino Observatory (SNO) is a 1000 ton heavy water Cerenkov detector, that is currently taking data with an array of 36 3He counters. In this configuration it can detect neutrons produced by the neutral current interaction of solar neutrinos by neutron capture in these counters (Neutral-Current Detection Array - NCDs). The Cerenkov detector (Array of ~9600 Photo mulitplier (PMTs)) is used to detect electrons produced by solar neutrino charged current (CC) or electron elastic scattering interactions. The calibration of the optical properties of the SNO experiment is essential for the measurement of the charged current flux. The addition of the NCDs complicates the spacial and energy reconstruction of Cerenkov events. A manipulator system which allows to position a source in two perpendicular planes is used to deploy light, gamma or neutron sources. A dye laser with 6 different wavelengths between 337 and 620nm and a diffusing sphere is used for optical calibration. The energy calibration is performed with a 16N source which emits 6.13MeV gammas and is used to determine the energy response. The neutron sensitivity of each string in the array is repeatedly calibrated with an 241Am-Be source. This enables us to monitor the efficiency and the stability of the counters and the electronics. In addition a 24Na source was mixed into the heavy water to measure the neutron response to an uniformly distributed source. An increased frequency of calibrations and the improvements in the calibration methods are an essential part of the forthcoming analysis of the solar 8B neutrino flux with the NCDs.
Tuesday, March 28,2006 in F539 at 1:30pm
Title:Finding Dark Matter
Speaker: Dr. Ubi Wichoski, Université de Montréal
Abstract: The nature of dark matter is presently one of the most important challenges for physics and astronomy. Observations indicate that most of the matter in the Universe is dark: Its presence is only revealed by its gravitational effects as it does not emit or absorb electromagnetic radiation. There is a strong belief that dark matter is made of a new kind of particle. The detection of this particle will certainly have a profound impact in many fundamental aspects of physics and astronomy. Although extremely exciting and motivating, the search for dark matter is not an easy one. In this talk I will introduce the evidence for the existence of dark matter, discuss the status, strategies and techniques that have been used for the dark matter search, in particular the PICASSO dark matter search experiment. I will also discuss some of the implications of the dark matter detection for new physics
Monday March 27, 2006 in room F539 at 2:00pm
PHYS 3116 Advanced Laboratory
Speaker: Dina Saleh Hammoud
Title: X-ray generation and its detection using a cadmium zinc telluride detector.
Speaker: Brandon Ramakko
Title: Measuring the wavelength of a beam of electrons using diffraction.
Speaker: Calvin Colard
Title: Measurement of axial and radial induced magnetic fields from current carrying coils.
Speaker: Matthew Cousineau
Title: Vacuum techniques
Speaker: Johnathan Woods
Title: Transfer of spatial frequencies in a digital imaging system: A Fourier Analysis
Wednesday March 29, 2006 in room F539 at 2:30pm
PHYS 3116 Advanced Laboratory
Speaker: Marc-André Brais
Title: Measurement of the ionization potentials of N2 and Ar and identification of an unknown substance using a mass spectrometer.
Speaker:Patrick Nadeau
Title: Measurement of the linear attenuation coefficient of Al using x rays and a cadmium zinc telluride detector.
Speaker: Joshua Maule
Title: Detection of radon and radon daughters in a basement storage room.
Speaker: Jesse Leeson
Title: Measurement of the characteristic hysteresis curve of a sample of iron
Speaker: Rui Cao
Title: Magnetic fields from circular coils and a solenoid: theory and Experiment.
Friday March 24, 2006 in F539 at 2:00pm
Title:Spectrometric, radiographic, metallurgical, and dosimetric studies of a new 125I brachytherapy source
Speaker: Dr. Eduardo Galiano, Laurentian University
Abstract: A new 125I source known as BraquibacTM has been developed in Argentina for applications in interstitial brachytherapy. The aim of this work is to study the new seed design and to calculate its dosimetric parameters. Radiographic and metallurgical studies were carried out on inactive seeds to determine the physical characteristics of the source. Values of the radial dose function g(r), the dose rate constant ?, the anisotropy function F(r, ?), and the anisotropy factor and constant, were obtained in water by simulation using the MCNP5 Monte Carlo code according to the methodology recommended by the American Association of Physicists in Medicine in Task Group 43. The dose rate constant was determined to be 0.880 ± 0.080 cGy h-1 U-1, which is lower than the Amersham model 6711 source. Sk per unity activity was calculated to be 1.036 cGy cm2 h-1 mCi-1 by simulation of the seed in dry air. Spectroscopic studies were done using a HPGe planar detector. Photon spectra showed 125I characteristic x-rays with energies of 27.20 keV, 27.47 keV, 31 keV and 31.70 keV, gamma photons of 35.5 keV, and fluorescent x-rays from the silver rod of 22.10 keV, 24.94 keV and 25.45 keV. The angular dependence of the photon intensity in air around the seed was analyzed by using the HPGe detector in two planes, one parallel and the other transverse to the seed longitudinal axis passing through its center.
Thursday, March 23, 2006 in F539 at 3:00pm
Annual Canadian Association of Physicists' Lecture
Title:Understanding Protein Folding from Statistical Physics
Speaker: Jeff Z.Y. Chen, Department of Physics, University of Waterloo
Abstract: The current understanding of the characteristics of protein folding is widely based on statistical-physics models of polymers that capture the essential interactions in real protein systems. The reduction of the degree of freedoms of the involved coordinates in such a model, in comparison with the all-atom modelling approach, allows for accumulation of adequate statistics in computer simulations. This type of models has been successfully used to explore the underlying physical mechanism of structural formation, folding dynamics and protein-protein interaction.
Friday, February 10, 2006 in F539 at 3:00pm
Title:The Design and Construction of an Aluminum Bar Phantom for Determining Resolution and Pseudo Uniformity of a Scintillation Gamma Camera.
Speaker: Ali Saleh, Laurentian University
Abstract: The Anger type scintillation nuclear camera is the most commonly used device in clinical radionuclide imaging. The objective of this investigation was the introduction of a new type of phantom for the purpose of evaluating certain performance parameters of the department's Elscint SP-4 gamma camera. A novel aluminum bar phantom was designed, built, and tested. The device was shown to be effective in measuring camera resolution, and uniformity. Phantoms have traditionally been constructed out of lead due to its high attenuation coefficient, but our results demonstrate the feasibility of using aluminum for the same purposes. Aluminum has the advantages of being non-toxic, relatively inexpensive, easy to machine, and copiously available in very high industrial standards. Using the phantom, the extrinsic spatial resolution of the instrument was shown to be between 3 and 6 mm. The uniformity was shown to be within the National Electrical Manufacturer's Association (NEMA) standards. Our work has established the feasibility of constructing a nuclear medicine phantom with aluminum for routine clinical use, and of measuring both uniformity and resolution simultaneously with this phantom.
Thursday, February2, 2006 in room F539 at 9:40am
4th Year Thesis Progress Reports
Speaker: Stefan Kaluzienski
Title: The feasibility of real time transmission gamma radiography: A phantom study
Undergraduate Student, Laurentian University
Thursday, January 26, 2006 in F539 at 2:30pm
Title: Overview of the Majorana Experiment
Speaker: Dr. Jason Detwiler, University of Washington
Abstract:
Now that the oscillation of massive neutrinos has been conclusively established as the solution to the solar neutrino problem, the question of the absolute neutrino mass and whether the neutrino mass hierarchy is normal, inverted, or degenerate, is generating more and more interest in the community. In addition, excitement over the very real possibility that the neutrino may also be the only known massive fermion that is its own antiparticle is reaching a crescendo.The Majorana Experiment proposes to address both of these issues by searching for the neutrinoless double beta decay of 76Ge to 76Se, a second-order weak process which requires the neutrino to be a massive majorana particle. This talk will present the reference design of the experiment, a modular design in which 120 kg of 76Ge will likely be deployed initially, follwoed by additional modules, ultimately moving toward a 1000 kg experiment in collaboration with the European Gerda effot. Technological and analytical improvements over previous generation 76Ge 0nbb searches will be stressed. The chief backgrounds in the region-of-interest for the rare decay search will be discussed, along with the purity requirements necessary to attain our goal of 1 background event per ton-year. At these backgrounds, Majorana will achieve after 5 years of running a sensitivity of T_1/2 = 6.1 x 10^26 years (90% CL), corresponding to a majorana neutrino mass sensitivity of ~120 meV (using the latest RQRPA nuclear matrix element calculations). Recent progress and future plans for the experiment will also be presented.
Thursday, January 12, 2006 in room F539 at 1:30pm
4th Year Thesis Progress Reports
Speaker: David Braid
Title: Ultralow Level Gamma Ray Spectroscopy - Measurements and Analysis
Speaker: Jeff Frimeth
Title: Calculations and Utilization of Dose Volume Histograms for Tumour Radiotherapy
Speaker: Kristie Herranen
Title: Theory and Measurements of Acoustic Properties of the Outer Ear
Speaker: Emerik Mehes
Title: Phantom Gamma Ray Images using Single Photon Emission CT
Speaker:Matt Rodrigues
Title: Extrinsic Efficiency and Sensitivity Measurements for the Gamma Camera
Speaker: Stefan Kaluzienski
Title: The feasibility of real time transmission gamma radiography: A phantom study
Speaker: Marianne Schwendener
Title: Radon Detection at the Sensitivity Limit with ESCs
Speaker: Matt Cousineau
Title: Evaluation of a New Technique for Induced Polarization Mineral Exploration
Undergraduate Students, Laurentian University
Thursday, December 8, 2005 in F539 at 2:30pm
Title: Energy Dispersion in High Temperature Superconductors using the Rotating Antiferromagnetism Theory
Speaker: Mr. Pete Watson, University of Waterloo
Abstract: Advances in spectroscopic techniques, such as Angle Resolved Photoemission Spectroscopy (ARPES), have allowed for the experimental determination of the electronic structure and Fermi surface in high temperature superconductors (HTSCs). In this talk, the energy spectra calculated using the rotating antiferromagnetism theory will be compared to ARPES data and other theoretical models. The electron occupation number will also be discussed.
Wednesday, December 7, 2005 in room F539 at 1:30pm
4th Year Thesis Progress Reports
Speaker: David Braid
Title: Ultralow Level Gamma Ray Spectroscopy - Measurements and Analysis
Speaker: Jeff Frimeth
Title: Calculations and Utilization of Dose Volume Histograms for Tumour Radiotherapy
Speaker: Kristie Herranen
Title: Theory and Measurements of Acoustic Properties of the Outer Ear
Speaker: Emerik Mehes
Title: Phantom Gamma Ray Images using Single Photon Emission CT
Speaker:Matt Rodrigues
Title: Extrinsic Efficiency and Sensitivity Measurements for the Gamma Camera
Speaker: Stefan Kaluzienski
Title: The feasibility of real time transmission gamma radiography: A phantom study
Speaker: Marianne Schwendener
Title: Radon Detection at the Sensitivity Limit with ESCs
Speaker: Matt Cousineau
Title: Evaluation of a New Technique for Induced Polarization Mineral Exploration
Undergraduate Students, Laurentian University
Thursday, December 1, 2005 in F539 at 2:30pm
Title: The challenges of high temperature superconductivity.
Speaker: Prof. Andre-Marie Tremblay, Université de Sherbrooke
Abstract: High temperature superconductors have been discovered almost twenty years ago, yet they still challenge us. New experimental techniques and new theoretical methods and concepts had to be refined or invented. In this talk I will outline why the problem is so difficult for theorists and explain some of the recent discoveries that suggest that there is light at the end of the tunnel.
Thursday, November 24, 2005 in F539 at 2:30pm
Title: Energy dispersive x-ray diffraction system for breast tissue characterization
Speaker: Michel Boileau, Laurentian University
Abstract: The detection and diagnosis of breast disease is an important part of health care delivery. In our research group we are investigating whether we can successfully characterize a breast tissue biopsy sample by measuring its x-ray diffraction signature. In this talk I will describe our methodology in detail. A custom built energy dispersive x-ray diffraction system in conjunction with a semi-analytic model is used to extract the differential linear scattering coefficients s(x) of breast tissue on an absolute scale. These coefficients describe the probability of scatter events occurring per unit length of material per unit solid angle of detection. They are a function of the momentum transfer argument, x = sin( /2)/ where is the scattering angle and is the incident wavelength. A 5 mm diameter 5 mm thick sample of water is used to validate our technique. Values of s are obtained by interrogating the water with a 3 mm diameter 50 kV polychromatic x-ray beam. The scattered beam is measured at various angles with a 3 mm x 3 mm x 2 mm thick cadmium zinc telluride detector. Our results compare well with data in the literature. We obtain a 7.68% difference for which most of the discrepancy can be attributed to the background noise at low angles. Preliminary measurements of breast tissue are encouraging.
Thursday, November 17, 2005 in F539 at 2:30pm
Title: Nonlinear dynamics and game theory of vaccination
Speaker: Chris Bauch, Department of Mathematics & Statistics, University of Guelph
Abstract: The decision by parents whether or not to vaccinate their children depends upon a number of factors. Although perception of vaccine risks is important at the individual level, there is also an important role for the "strategic interaction" between parents at the population level: when vaccine coverage is high (and disease prevalence is therefore low), there is a temptation to stop vaccinating since children are unlikely to get infected. Hence, voluntary vaccination policies can be victims of their own success. This population perspective on vaccination policy has received relatively little attention in the literature. In this talk, I show how game theory can be used to construct nonlinear differential equations that can capture this strategic interaction, as well as the time evolution of vaccine coverage in a population with a voluntary vaccination policy. The model is compared with real-world data from a whooping cough vaccine scare in England & Wales in the 1970s.
Friday, November 4, 2005 in F539 at 3:00pm
Title: Accelerated partial breast irradiation
Speaker: Julie Gratton-Liimatainen, Laurentian University
Abstract: An overview of the current status of accelerated partial breast irradiation techniques (APBI) including the rationale for APBI, patient selection criteria and technical and dosimetric aspects of the various APBI techniques will be given. Standard APBI prescriptions and Biologically Effective Doses (BED) for each APBI technique will be compared to those for standard whole breast irradiation. Reported cosmetic results, toxicities and recurrence rates for early phase selective trial studies will be presented. The talk concludes with a discussion of the radiobiological issues of various radiotherapy schedules.
Julie Gratton-Liimatainen is a third-year Radiation Therapy student at Laurentian who also holds a prior MSc in Physics. Julie spent her summer on a research project with Dr. Tai K. Yeung, Ph.D., FCCPM, a Senior Medical Physicist in the Radiation Treatment Program of the Sudbury Regional Cancer Program.
Thursday, October 20, 2005 in F539 at 1:30pm
Canadian Undergraduate Physics Conference Talks
Title: Preliminary Results from a New Ultra-Low Level Gamma Ray Spectrometer
Speaker: David Braid, Laurentian University
Title: O-ring Emanation in SNO's Heavy Water System
Speaker: Emerik Mehes, Laurentian University
Title: A Comparison Of Different Analytical Methods Of Determining The Solid Angle Of A Circular Coaxial Source - Detector System
Speaker: Matthew Rodrigues , Laurentian University
Wednesday, September 7, 2005 in F539 at 2:00pm
Title: Fourth Year Thesis Defense
Study of the antiferromagnetic Heisenberg bilayer at finite temperature
Speaker: Aleksy Jones, Laurentian University
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