Physics: Theses

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A CT Scanner Using Coincidence Techniques
(Houghton College, 2014-05-19) Finch, Victoria
A CT scanner has been designed which uses gamma rays produced by positron annihilation. A low-activity 22Na source produces the positrons, which, when they annihilate, create 0.511 MeV gamma rays travelling in opposite directions. These gamma rays can be used to image an object using NaI detectors that are collinear with the source. Requiring a coincidence between the detectors reduces background. LabVIEW software counted the number of gamma ray coincidences and translated and rotated a robotic table, allowing the attenuation to be measured along multiple beam paths through the object. Ultimately, the attenuation data can be used to reconstruct an image of the object being observed.
A Low-Cost Van de Graaff Accelerator
(Houghton College, 2002-05-08) Winey, Brian Andrew
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 µA were collected in a Faraday cup. The end-point of the bremsstrahlung x-ray energy spectrum has been measured to be between 300 and 400 keV.
A Measurement of the 12c(N,2n)11c Cross-Section for Use as an Inertial Confinement Fusion Diagnostic
(Houghton College, 2014-05-06) Hartshaw, Garrett
In inertial confinement fusion (ICF), nuclear fusion reactions are initiated by bombarding a small fuel pellet with high power lasers. One ICF diagnostic involves measuring the high-energy neutron yield via activation of 12C, requiring an accurate value for the 12C(n,2n)11C cross-section. An experiment to determine this cross-section in the energy range of 20-27 MeV was performed using the tandem van de Graaff accelerator at Ohio University. Monoenergetic neutrons, produced via the T(d,n)α reaction, were allowed to strike targets of polyethylene and graphite. Target activation was determined by counting positron annihilations due to β+ decay using back-to-back NaI detectors and the neutron flux was determined indirectly via protons elastically scattered from the polyethylene target. The cross-section will be determined from the number of 11C present in the target after activation, the number of protons detected during activation, and the geometry of the experiment. Funded in part by a LLE contract through the DOE.
A Measurement of the Muon Magnetic Moment Using Cosmic Rays
(Houghton College, 2002-05-08) Kroening, Daniel
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 positrons 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 results are t = 2.28 ± 0.07 µs (mean decay time) and g = 2.74 ± 0.20. Some possible explanations for the large value of g are discussed.
A Novel 1st Generation Computed Tomography Scanner
(Houghton College, 2003-12-19) Kingsley, Nicholas
A preliminary design for a first generation tomography scanner is being designed and constructed. The scanner uses Na-22 as the radiation source, with annihilation photons being counted by shielded NaI detectors. The novel design of the scanner allows a very weak radiation source to be used by taking advantage of the back-to-back 511 keV annihilation photons emitted after Na-22 B+ decay to improve the signal to noise ratio. The object being scanned will be translated and rotated systematically by computerized motor control using two motors attached to a standard rotary table.
A Parity Violation Experiment for Undergraduate Laboratories
(Houghton College, 2017-05-19) Ganger, Michael
The discovery of parity violation in weak interactions was a foundational discovery of the 20th century, first proposed by Lee and Yang in 1956 and experimentally verified by Wu in 1957. Lee and Yang also proposed a simpler experiment which does not require that the 60Co source be polarized. Randomly oriented 60Co beta decays to an excited state of 60Ni, which then deexcites by emitting two gamma rays. Conservation of angular momentum ensures that the spins of all emitted particles are aligned. Therefore, when a gamma ray and a beta particle have antiparallel momenta they necessarily have opposite helicities. In the proposed experiment, these circularly polarized gamma rays are transmitted through a steel rod magnetized along the axis between two collinear detectors, a germanium detector for the gamma rays and a silicon detector for the beta particles. Due to the slight dependence of the Compton scattering cross-section on the relative orientations of the gamma rays and the electron spins in the magnet, a parity violating asymmetry may be observed by comparing beta particle and transmitted gamma ray coincidence count rates for opposite directions of magnetization. An experiment to observe effect this is currently being prepared at Houghton College using modern techniques suitable for an undergraduate laboratory.
A PARITY VIOLATION TRANSMISSION EXPERIMENT FOR UNDERGRADUATE LABORATORIES
(Houghton University, 2024-05-03) Kennel, Levi
Because there are currently no published weak interaction parity violation experiments specifically for undergraduate laboratories, a simple parity violation experiment is being developed using circularly polarized gamma rays. A 60Co source will be placed on one side of an electromagnet, so that the circularly polarized gamma rays emitted opposite the beta particles will pass through the electromagnet. A NaI detector detects the number of gamma rays that pass through the electromagnet, and a silicon detector detects in coincidence beta particles opposite the gamma rays. The number of 𝛾𝛽 coincidence events will be measured when the electromagnet is polarized both parallel and antiparallel to the gamma rays — an asymmetry between the number of coincidence events for each orientation would show that parity is violated.
A Preliminary Design for a Small Permanent Magnet Cyclotron
(Houghton College, 2003-01-20) King, Barry
A small cyclotron is being constructed using a 0.5 T permanent magnet and a vacuum chamber containing a single brass RF electrode. In this design the magnetic field strength may be modified by adjusting the separation of two iron pole pieces, which will be sealed to the chamber using vacuum grease. The chamber will be filled with low pressure hydrogen gas which will be ionized by electrons from a cathode at the center of the chamber. The required 3.6 to 11.5 MHz RF power will be supplied by a commercial RF amplifier. A diffusion pump backed by a voluntary forepump and a liquid nitrogen cold trap will be used to evacuate the chamber. Expected energies are 37.5 keV and 87.7 keV for protons and 18.7 keV and 43.8 keV for deuterons.
A Remotely Controlled Electron Gun for a 200 KeV Electrostatic Accelerator
(Houghton College, 2013-12-01) Lipnicki, Alexander
One problem encountered in the design for the Houghton College electrostatic electron accelerator is the electron source, which must be operated while floating at a potential of 200 kV. The simple two-grid electron gun used previously did not have electrodes to provide focusing and positioning of the beam. A new electron gun was constructed using an RCA 3RP1 cathode ray tube. This electron gun may be remotely controlled via an Ethernet-GPIB-RS232-Fiber optic link to a BASIC stamp-2 microcontroller inside the high voltage terminal. This microcontroller controls the intensity, focus, and acceleration grids of the cathode ray tube using a 12-bit four channel DAC7624 digital-to-analog converter, which, after current amplification, drives four EMCO G20 DC to HV DC converters.
A Study of Tailored Oriented Thin Silver Films by X-ray Diffraction
(Houghton College, 2010-05-17) Timian, Lindsay
The transition of crystal orientations in tailored oriented thin silver films were studied; specifically, the transition from fcc(111) to fcc(100) orientations of films ranging in thickness from 1 nm to 1000 nm. The films were deposited via electron beam evaporation onto a silicon substrate in a high vacuum chamber and passivated through sputter deposition. After thickness measurements were taken they were annealed for various times and temperatures. Putting an adhesion promoter layer of titanium on both sides of a thin film of silver sharpened the transition of silver grains between the 111 and 100 orientations. The titanium layer was deposited with a thickness gradient, to determine the thickness at which the adhesive properties of titanium took effect. Also, the percentage of the film’s volume that transitioned to fcc(100) increased with anneal temperature and time.
A Tabletop Apparatus to Measure the Magnetic Moment of the Muon
(Houghton College, 2002-05-08) Ely, David Richard
An apparatus was constructed to measure the magnetic moment of cosmic ray muons using their precession in a uniform magnetic field. A 102.0 x 20.6 x 5.4 cm plastic scintillator was sandwiched between two 102.0 x 20.6 x 1.6 cm scintillators inside a uniform, 42 G magnetic field, which was produced by a large solenoid. A small veto scintillator eliminated events occurring in the non-uniform region of the field at the ends of the solenoid. A logic circuit identified muons stopping in the center scintillator 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 Tabletop Transmission Computed Tomography Scanner
(Houghton College, 2003-11-11) Clifford, Rebekah
A first generation computed tomography (CT) scanner allows for a cross-sectional slice of an object to be analyzed by x-rays passing through the material. These images are created by recording the x-ray energy spectrum at a specified number of translational and rotational steps. Instead of an x-ray tube, 22Na will be used as the radiation source in conjunction with two sodium-iodide scintillation detectors. The source and detectors will remain co-linear and stationary, while the object to be scanned will rotate and translate. During the last two years, the rotation and translation table have been assembled and progress has been made towards a computer code to control the motors that translate and rotate the table on which the object is placed. Once this program has been completed, the source and detectors will be installed and the scanner will be tested.
A Wind Driven Power Generating System: Initial Designs and Construction
(Houghton College, 2004-05-01) Merriam, Donald Jr.
The goal of this study is to design and build a low cost, mechanically efficient wind driven powergenerating system in the 1 to 5 kilowatt range and to predict and improve its performance based on equations derived from fundamental principles. Construction and assembly have begun for a directly coupled, low “rpm” (angular frequency) generator consisting of a disk of copper coils sandwiched between two rotating disks of neodymium (NdFeB) magnets to which the blades will be directly coupled.
A Wind Driven Power Generating System: Preliminary Modeling of Power Curves
(Houghton College, 2003-05-08) Marthai, Sonya
Most power curves for current wind power systems depend on filed measurements. Relationships between the details of the design and power output are therefore often hidden. The overall goal of this project is to design and build a low cost, mechanically efficient wind driven power-generating system in the 1 to 5 kilowatt range and to predict and improve its performance based on equations derived from fundamental principles. A series of theoretical power curves are presented that successively incorporate greater complexity of blade parameters. The aim is to optimize each individual parameter, then design an efficient blade design based on those specifications.
An Ambient Air Scanning Tunneling Microscope to Study the Surfaces of Thin Metal Films
(Houghton University, 2023-05-10) Wilson, Joshua C.
An ambient–air scanning tunneling microscope (STM) is being built at Houghton University to study the crystal growth and transformation of thin metal films. The STM operates by maintaining a constant current between a piezoelectrically–controlled scanning probe and the thin metal film sample while recording the height of the probe relative to the sample stage. This current is produced when electrons from the sample quantum tunnel through the ~10-10 m air gap to the probe, aided by a small bias voltage of ~-1 V applied to the sample. In order to achieve a tunneling gap of this size, the STM uses stepper motors to perform a rough approach of the probe to the sample. The STM is suspended on a dual-stage vibration isolation system which uses springs with eddy current damping to protect the STM from background noise. The STM is controlled by a user interface written in Processing and a Teensy 4.1 microcontroller via Arduino, along with a control circuit. The data collected by the STM are used to create an intensity plot that will act as an atomic resolution “image” of the film surface. All hardware, electronics, and programs have been completely and successfully tested.
An Electron Gun Controller for a Small Electrostatic Electron Accelerator
(Houghton College, 2009-05-08) Thomson, Stephen
The Houghton College electrostatic electron accelerator uses a small Van de Graaff generator and an accelerator column made from alternating high-density polyethylene and aluminum rings to create a uniform electric field. The accelerator column is evacuated to about 10-6 torr by a rotary forepump and a diffusion pump. To produce the electrons, an electron gun made from a 3RP1 CRT is located inside the high voltage terminal. The electrodes of the electron gun require user-controlled voltages for the anode, focus and intensity grids. Since the gun is located inside the HV terminal, a microcontroller/amplifier circuit was designed to produce the required voltages and communicate with the user via a non-conducting, fiber optic RS232 link. The remote control system has been tested with the electron gun attached to the vacuum system.
An Evaporation Deposition System for the In-Situ Study of Thin Metal Films
(Houghton College, 2013-08-23) Mertzlufft, Joshua
Thin films have been the subject of study for years by research groups both in academia and the semiconductor industry. With applications primarily in microelectronics and also emerging applications in the energy industry, it is desirable to have a greater understanding of the underlying characteristics of the films. This project is focused on the construction of a deposition system that may be used to produce thin films for study at Houghton College, a small Christian liberal arts institution. The system will also enable researchers to study the effects of annealing in-situ.
An Experiment to Simulate the Trapping and Detection of Radioactive Isotopes Produced In ICF Implosions
(Houghton College, 2022-01-28) Christensen, Micah J.
It may be possible to measure the low energy nuclear cross sections of light ion reactions by trapping the reaction products from an ICF implosion and detecting their beta decays. To test this idea, an “exploding wire” experiment has been designed to simulate the expanding gas released in an ICF event. A copper plated tungsten foil was inserted into a vacuum chamber and activated with a deuteron beam via 65Cu(d,p)66Cu. A current pulse then vaporized the copper to create an expanding radioactive gas, simulating the gas behavior in the ICF target chamber following the laser shot. Attempts were made to capture some gas and detect the 66Cu beta decays using two trap designs, one using a getter foil and the other a turbopump. Results were obtained with both trap designs, using the Short-Lived Isotope Counting System (SLICS) consisting of plastic scintillator phoswich detectors and fast electronics to identify and count the beta particles.
Astrometry from Space: An Overview of the European Space Agency’s Hipparcos Satellite
(Houghton College, 2008-06-14) Runyon, Kirby
The European Space Agency’s Hipparcos satellite was launched in 1989 to provide a high-precision catalogue of stellar astrometric data, including parallaxes and luminosities, from above Earth’s dimming and distorting atmosphere. Despite the satellite failing to reach its intended geosynchronous orbit, its mission successfully measured astrometric characteristics of 120,000 stars and photometric and less accurate astrometric properties of approximately one million stars. Since the mission’s end, the data have been reduced into several catalogues that have proven useful in determining other astrometric and astrophysical properties of stellar phenomena. This report will describe the motivation for and details of the Hipparcos mission, the data reduction, the applications of these data, and the prospects for future space-based astrometry missions.
Automatic Control of an Inertial Electrostatic Confinement Device
(Houghton University, 2023-05-10) Condie, Micah K.
The Houghton University Farnsworth-Hirsch fusor is an inertial electrostatic confinement device designed for the purpose of studying plasmas, D-D fusion, and as a source of x-rays and neutrons for other experiments. It operates via two concentrically arranged wire spheres with a voltage difference between them of up to 30 kV, ionizing a low-pressure gas to form and confine a plasma. The voltage across the two spheres is measured using a voltage divider circuit allowing an Arduino at the bottom of the chain to measure a lower proportional voltage. The current from the HV grid to the power supply flows through an LED, floating at high voltage, the light from which is then measured at the end of a fiber-optic cable using a phototransistor circuit. The previous fusor remote operating system used LabVIEW and Digi TS4 Port servers to communicate with the high voltage power supply, pressure gauge, and mass-flow controller via ethernet, RS-232, and RS-485. It was redesigned using a python code running on a remote computer to communicate with the instrumentation directly over USB and RS-485. Furthermore, the python code implemented a PID controller so that the pressure in the chamber could be adjusted automatically, maintaining the plasma while raising the voltage. The fusor was tested using air as the ionized gas with limited success using the PID controller. Future experiments will correct the automatic system and test the system with hydrogen then deuterium.

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