A Small Van De Graaff Accelerator

Brian Winey, Prof. M. Yuly, Houghton College,

A small, low-cost Van de Graaff electrostatic accelerator capable of accelerating electrons and producing bremsstrahlung x-rays has been constructed using components commonly found in most undergraduate physics laboratories. The electrons originate within the negative high-voltage terminal and are accelerated by a uniform electric field through an evacuated glass tube. Electron currents of up to 6 m A were collected in a Faraday cup. The end-point of the bremsstrahlung x-ray energy spectrum has been measured to be between 200 and 300 keV.
 

Detection of W ®m n Decays in Proton-Antiproton Collisions

Andrew Kowalik, Prof. Paul Tipton, University of Rochester

In 1995, the top quark was discovered at Fermi National Laboratory. Since the top quark nearly always decay to W’s, understanding the detection of one of the W’s decay modes in single W events, is potentially useful for later top studies. Additionally, this type of decay has not been investigated since the collider detector was upgraded for its second data collection run. Using off-line physics data and related processing tools we developed a filter module to separate probable W ® m n events from a data sample of muon candidates. Though our work was still in progress at the time of my departure, there is evidence that these decays may be identified successfully by setting simple limits on muon and detector variables, including momentum, calorimetry, and isolation measurements.
 

A Table-Top Apparatus to Measure the Magnetic Moment of the Muon

D. Ely, D. Kroening, Prof. M. Yuly. Houghton College

An apparatus was constructed to measure the magnetic moment of cosmic ray muons using their precession in a uniform magnetic field. A 102.0 ´ 20.6 ´ 5.4 cm plastic scintillator was sandwiched between two 102.0 ´ 20.6 ´ 1.6 cm scintillators inside a uniform, 44 G magnetic field. A small veto scintillator eliminated events occurring in the non-uniform region of the field, which was produced by a large solenoid. A logic circuit identified muons stopping in the center scintillator and, and the subsequent decay of these muons. The time difference between the muon stopping and its decay was recorded for about 67,000 events, allowing the decay constant and the magnetic moment to be determined.
 

A Measurement of the Muon Magnetic Moment Using Cosmic Rays

D. Kroening, D. Ely and M. Yuly. Houghton College

The muon magnetic moment was measured via the decay of polarized cosmic-ray muons in a constant magnetic field with a three-scintillator detector system. Cosmic-ray muons stop in the central detector, precess in the magnetic field, and then decay by emitting a positron along the muon spin axis. A quantum-mechanical calculation allows the g-factor to be extracted from a measurement of the number of positrons emitted into one direction as a function of decay time. The tentative results are t = 2.12 ± 0.03 m s (mean decay time) and g = 2.79 ± 0.06, where the uncertainty does not include systematic effects.
 

Determining the Depth of a Buried Object Using Gamma-ray Spectroscopy

Jessica Gary, Dr. E. Naessens, C. Ross Schmidtlein, Brian Moretti, U.S. Military Academy, West Point

We propose a method of determining the depth of buried objects by directing gamma-ray from a known source towards the object and using gamma-ray spectroscopy to observe the uncollided energy peak from Compton scattering from the object. From the known source/detector geometry and the measured uncollided photon energy, we can calculate the round trip distance that gamma rays have traveled from the source to the detector. We will present both simulations and experimental data to validate our approach. Monte Carlo calculations of scattering from disks of various materials buried in several different media at various depths give a small systematic shift that depends on both the material and the thickness of the disk. Possible source of this systematic shift will be discussed,

Magnetorotational Instability of Liquid Metal Couette Flow

Jason Nordhaus, University of Rochester, Prof. S. Colgate, Los Alamos National Laboratory, NM

Despite the importance of the magnetorotational instability (MRI) as a fundamental mechanism in magnetized accretion disks, it has yet to bedemonstrated in the laboratory. A liquid sodium alpha-omega dynamo experiment at the New Mexico Institute of Mining and Technology provides an ideal environment in which one might study the MRI in a rotating metal annulus (Couette flow). Local stability analysis is performed while taking into account the formation of an Ekman layer against the rigidly rotating cylindrical boundaries. Stability conditions are presented and unstable regions are identified in terms of magnetic field strength and shear flow. Unstable conditions for the sodium experiment are compared with another proposed MRI experiment with liquid gallium.
 

THE 2001 OUTBURST OF BLAZAR 3C 279

Jeyhan Kartaltepe, Prof. Thomas J. Balonek, Colgate Univesity

This study looks at the long and short time scale variations of the blazar 3C 279 throughout the 2001 optical outburst, but concentrates on the intra-night and night-to-night variations during the intense outburst. This outburst was the most violent outburst (with variations in brightness of over three magnitudes) seen in thirteen years of study at Colgate University. Observations were conducted at Colgate’s Foggy Bottom Observatory using a sixteen-inch Cassegrain telescope and CCD camera. The outburst began in March, after 3C 279 had faded to its faintest level, R = 15.5, in four years. The source was still active in early August, at its brightest level, R = 12.5, in the thirteen years of our study, at which time it became unobservable due to its proximity to the Sun. Since becoming observable again in mid-November, 3C 279 has fluctuated between R=14.0 and R=14.5. The source exhibited numerous week-long flares of approximately one magnitude during the six-month outburst period. Superposed on these flares were night-to-night variations of up to one half magnitude and intra-night microvariability of 0.2 magnitude in five hours. We compare the optical light curve to an x-ray light curve for this same time period to look for possible correlations.
 

Optical Variability of the Blazar BL Lacertae

Meredith Tanguay, Prof. Thomas J. Balonek, Colgate University

BL Lacertae, a complex, highly variable blazar, has been observed at optical wavelengths for 13 years with Colgate University's Foggy Bottom Observatory 16"± telescope. Data reduction is accomplished in IRAF with the aid of Colgate-specific scripts. Investigation of the variability allows us to probe the physical processes of this object, the prototype for the BL Lac category. This study focuses on R-filter CCD data taken between summer 2000 and spring 2002. The variability timescale and profile of flares during this outburst period are examined in both magnitude and flux. The effects of overlapping flaring events on the observed light curve are also explored
 

Elementary Climate Modeling

Laura Schmidt, Profs. H.L. Helfer and R.S. Knox, University of Rochester

Complete climate models are very complicated and emphasize hydrodynamics, obscuring the underlying physical energy fluxes. Our simpler model attempts to gain a qualitative understanding of global energy transfers without the added complexity. This model is an extension of a 2-temperature climate model that uses globally and annually averaged parameters to one that uses local parameters adapted to perform computations on a monthly as well as yearly basis. The local parameters are stored in grid of 864 cells representing areas on the globe and the energy balance is carried out on each cell individually. The two temperature model solves energy balances for steady-state on the surface and atmospheric layers, taking into account reflection and absorption of the solar radiation in the UV region, the emission of the layers in the IR region, and a term included for non-radiative transfer between the layers. The steady-state assumption breaks down at monthly level because the non-radiative term must compensate for lack of inclusion of a phase lag between the solar flux and the surface temperature time variations. Investigating this phase lag by comparing monthly zonal averages of the non-radiative energy flux to the surface temperature is the current focus.
 
 

Neutron-Duetron Scattering as a Probe of the Three-Nucleon

Pete Brady, Rachael DeYoung, Daniel Kroening, S. Tuminaro, and Prof. M. Yuly, Houghton College

Previous experimental and theoretical studies are unclear regarding the existence and role of the three-nucleon force in nuclear interactions. An experiment is being performed at the Los Alamos Neutron Science Center (LANSCE) to measure the d(n,dn) cross-section for incident energies of 100 MeV to 700 MeV and deutron angles of 24º, 30º, 36º, 42º, 28º, and 54º to the incident beam. These results will eventually be compared to theorectical predictions for this reaction with and without inclusion of the three-nucleon force.
 

Using the (n,2p) Reaction to Ssearch for a Preexisting Nuclear D⁺⁺ Component

Rachael DeYoung, Prof. M. Yuly, Houghton College

The ³He(n,2p)2n and the ⁴He(n,2p)3n cross-sections are being measured as a means to explore the D⁺⁺ contribution to the nuclear wave function. The incident neutron beam ranged between 200 and 500 MeV. Scattered protons passed through magnetic spectrometers centered 45º to the right and left of the beam line. Each spectrometer consisted of a thin D E scintillator, a wire chamber, a permanent bending magnet, a wire chamber, and a detection barrier of three stacked scintillators.
 
 

Double Pump-Probe Laser Transmission through an Organic Dye

Dennis Mackin, Jason Choi, Dr. M. Donovan, U. S. Military Academy, West Point

We are using a versatile, new material characterization technique that measures the time-resolved change in optical transmission of a substance due to a sequence of two intense, ultrashort (40 ps) laser pulses. With this technique, we are able to simultaneously determine several excited state parameters of an organic dye. Ultimately, the data that we gather will be used in the development of a new class of materials called reverse saturable absorbers. The method is based on the concept of using the pump laser to produce a nonlinear change in the transmission of light through the dye while using the probe laser to monitor this change. The probe pulse is made to arrive at a sequence of delays, from arriving simultaneous with the first pump pulse to arriving well after the second pump pulse. This allows us to plot sample transmission versus time, which we then match to a set of rate equations developed by our collaborator Dr. Timothy Pritchett. Our immediate aim is to validate the improvements in the rate equations over the original double pump-probe experiments.
 

Spin Precession in a Two-Level System

David Etlinger, Prof. J. Eberly, University of Rochester

Many systems in physics can be approximately modelled by an idealized system of just two energy levels. For example, an electron has two spin states which, in the presence of external fields, possess different energies. In isolation, such a system will exhibit limited dynamics, at most precessing about one or the other energy level. In the presence of an external pump,such as a laser, the system will oscillate between the two states. A standard approximation gives a surprisingly simple result for this model.

The results are most easily derived through the Heisenberg picture of dynamics, which is equivalent to other formulations of quantum mechanics but is not often taught at the undergraduate level. The main goal of our research is to couple such a system to random environments of varying dimensions and investigate the resulting decoherence times.
 

Rotating Tractor Beams: Controlled Rotation of Microorganisms in an Optical Trap

Adam Weiss, Prof. E. Galvez, Colgate University

Using a modified single beam gradient trap, we can trap, translate, and rotate yeast cells. A laser that produces transverse modes is used in a laser tweezers setup to control the rotational orientation of irregular objects, including microorganisms. This capability could be very useful to biologists in the study of microscopic life. Our system allows for full control of objects in two dimensions.
 

Alzheimer’s Disease: Inhibiting the Aggregation of the Amyloid b Peptide

Hunter Karmel, Binghamton University, David Callaway, Picower Institute

The widespread deposition of plaques within the brain parenchyma and vasculature is one of the hallmarks of Alzheimer’s disease. These protease resistant fibrillar sediments are constituted primarily by a 39-42 amino acid residue peptide referred to as the b -amyloid. For this reason the Amyloid- b peptide (Ab ) seems to play a central role in the neuropathology of Alzheimer’s disease. Ligands with the capability of inhibiting the process by which the b -amyloid polymerizes into these plaques could provide a powerful tool for the creation of therapeutic agents. To choose these ligands, an explicit knowledge of the polymerization process and the molecular conformation of the peptides is critical. X-ray crystallography and NMR have not been capable of providing the structural details required for ligand design. We approach the problem theoretically by constructing a three dimensional model of the Ab molecule such that it will be possible to choose compounds for the inhibition of amyloidogenesis which then can be experimentally validated.
 

Electronic Structure of Mn₁₂-Acetate

S. M. Oppenheimer, Binghamton University, A. B. Sushkov, and J. L. Musfeldt, University of Tennessee, Knoxville

We report transmittance and polarized reflectance measurements of crystalline Mn₁₂-acetate over a wide frequency range (600-50,000 cm^-1) to investigate the electronic structure of this prototypical molecular magnet. Overall, the spectral features are quite diffuse down to 10 K, although a number of Mn inner -> outer d -> d and outer p -> Mn d charge transfer excitations are observed and assigned. The two lowest energy excitations (at 13,500 and 15,900 cm^-1) are polarized perpendicular to the easy magnetization c axis. Optical gaps are estimated at 8,750 cm^-1 (1.08 eV) and 14,000 cm^-1 (1.75 eV), corresponding to minority and majority gaps, respectively.

Microfabricated Striplines for Measuring the High Frequency Response of Carbon Nanotubes

Michael S. Fine, Dr. Beth Parks, Colgate University

Carbon nanotubes are ideal one-dimensional conductors that are being developed as elements in molecular electronics. Understanding their high frequency electrical properties is instrumental to this development. In this study, transmission lines are utilized to measure these high frequency properties. Using a mode-locked, ti-sapphire laser, short pulses are created and detected as they propagate down each transmission line. The absorption of specific frequencies in these pulses by single nanotubes will provide information about the tube’s high frequency characteristics. This project is ongoing. Microfabrication was completed at Cornell’s Nanofabrication Facility
 

Assembly and Calibration of a Vibrating Sample Magnetometer for Magnetic Measurements

Eric Holt, Sunil Labroo, Joshua Vanderpool, Chung Wong, SUNY at Oneonta, Dale Zych, SUNY at Oswego

We report on the assembly and calibration of a vibrating sample magnetometer (VSM). This VSM uses a 1.0 Tesla electromagnet, a mechanism for sample vibration, and a signal detection system that utilizes a Stanford Research SR530 lock-in amplifier. Currently this VSM is configured for a variable temperature range from room temperature to about 900 K using a Lakeshore model 330 temperature controller. Data is acquired by a PC with an IEEE-488 interface. In this study we will present some preliminary data on standard magnetic samples and an estimate of the sensitivity of the VSM.
 

Borated Tungsten as a Potential Material for Kinetic Energy Penetrators

Troy D. Scribner, Philip D. Sacks, Anthony W. Clark, Morgan D. Greene, Dr. Lee E. Harrell, A.K. Pallone, U.S. Military Academy, West Point

During US involvement in the Gulf War, depleted uranium (DU) weapons proved to be more effective than rounds used in previous conflicts due to DU’s high ductility which causes self-sharpening on impact. However, the environmental concerns associated with the use of DU led to the search for an alternative material. One alternative under investigation is tungsten. Although tungsten possesses many of the same desirable physical characteristics as DU, its low ductility causes tungsten rounds to mushroom on impact decreasing their armor piercing effectiveness. By doping tungsten with boron atoms at 10-30 ppm, there is reason to believe that we can increase the ductility of tungsten to overcome the problem of mushrooming.
 

Determination of the Diffusion Constant of Boron Along Grain Boundaries in Polycrystalline Tungsten

Anthony W. Clark, Morgan D. Greene, Philip D. Sacks, Troy D. Scribner, A.K. Pallone, Dr. Lee E. Harrell, U.S. Military Academy, West Point

In order to better engineer future boron-doped tungsten rounds, the diffusion behavior of boron in polycrystalline tungsten needs to be understood. To study this behavior, boron is first deposited on the surface of polycrystalline tungsten samples. Then the samples are annealed at known temperatures for a known periods of time. Through nuclear reaction analysis, the depth profile of boron concentration in the annealed samples can be determined. Through application of Fick’s laws, theoretical curves for the depth profile can be generated. By fitting the theoretical curves to the data, the activation energy and the temperature independent diffusion coefficient of boron along the grain boundaries of polycrystalline tungsten can be determined.
 

Application of Nuclear Reaction Analysis to Depth Profiling of Boron Concentration in Polycrystalline Tungsten

Philip D. Sacks, Troy D. Scribner, Anthony W. Clark, Morgan D. Greene, Dr. Lee E. Harrell, A.K. Pallone, U.S. Military Academy, West Point

B can combine with a proton to form ¹²C plus an energetic photon. While the reaction can occur for any proton energy, a resonance exists for absorption of the proton at 163 keV. This reaction can be used to find the concentration of boron in tungsten as a function of depth. The rate at which a proton loses energy as it passes through polycrystalline tungsten is well understood. By irradiating samples of boron-doped polycrystalline tungsten with protons of known incident energy, one can calculate the depth at which the resonance occurs. The number of characteristic photons detected is directly proportional to the concentration of boron at that depth. Coincidence techniques used to reduce background events will be discussed.
 

Study of Depressed Melting in Thin Film Multilayers

Elisa Pueschel, E. J. Cotts, Binghamton University

Lower melting temperatures have been observed in particles of small radii than are observed in bulk samples of the same materials. We observed the melting of thin film multilayers using a differential scanning calorimeter. Multilayers of aluminum and tin were produced by vapor deposition. Aluminum and tin were chosen because they form a simple eutectic system. The nominal thickness varied from 80 angstroms for a fifty-fifty stoichiometry to 120 angstroms for an eighty-twenty tin-rich composition. High angle x-ray diffraction was used to verify that the samples were composed of pure metals, without significant amounts of alloy. Calorimetric scans recorded three melting signals. Two of the peaks occurred at temperatures close to the accepted values for tin melting and aluminum/tin eutectic melting. The third peak was observed as many as ten degrees lower than the eutectic melting temperature. This result points to a correlation between small particle size in a eutectic system and decreased melting temperature.