Physics Students

The Society of Physics Students (SPS)

We are a group of students interested in physics and we hold physics/science related events to promote interest in the sciences.  This semester we became an offical organization and we held a movie/pizza night.  Anyone interested within the Trinity community is welcome.

Characterization of PACVD Diamond Films

Matthew Bermudez '09
Faculty Sponsors: Barbara Walden, Ann Lehman
The unique properties of diamond have long been known, and significant study has been done to investigate these properties in diamond films. Diamond film coating is applicable in countless fields because of the hardness, thermal conductivity, and inertness of the crystal. In order to fully take advantage of these properties, diamond growth will have to be more versatile than it is now. When growing films of greater than a few microns in thickness, intrinsic stresses develop, reducing the strength and integrity of the film. These features are closely related to the manner in which the crystals are grown, and onto what type of surface. In the nineteen-eighties, a method called chemical vapor deposition was applied to the manufacture of thin diamond films. Plasma-assisted Chemical Vapor Deposition (PACVD) has been used recently to grow thin films of the crystal with structure on the order of nanometers. Different growth conditions yield different film structures, and thus different levels of stress. Films have been prepared under different plasma temperatures, pressures, and from different mixtures of gasses.
Scanning electron microscope images of the films have shown a variety of surface features that indicate the different conditions under which they are formed. This study will link the different film features to their original deposition conditions. The next step in our research will be Raman spectroscopy on the films. It provides a characteristic signature for carbon materials, and thus is used to evaluate the micro and nanostructural properties of CVD diamond films. Shifts and changes in size and shape of the peaks in the spectrum generated by the diamond indicate flaws and stresses. These spectrums, along with the visual data from the microscopy, will help to further characterize films based on their deposition conditions.

Quantification of Ultra-Fine Magnetic Grains in Soil

Tamara Machac '06
Faculty Sponsor: Christoph Geiss
Our research investigates an alternative inexpensive, fast and sensitive method initially developed by Horst Worm (1999) to quantify the abundance of very small magnetic grains (diameter smaller that 20 nm) near the SP-SSD boundary in natural soil samples and relates these abundances to modern climate in the Midwestern US.
The amount of these ultrafine magnetic grains in soils is thought to vary with changes in climate, especially precipitation. By comparing the physical properties of modern soils and older, buried soils we intend to shed light on past climatic changes. We designed a small field coil that can produce a magnetic field between approximately 100 to 6000 A/m. Using this simple device, we expose samples to a magnetic field for about 0.02s, by dropping the sample through the vertically oriented coil. Exposure to the same magnetic field for longer time periods is possible by placing the sample in the pipe for the specified amount of time. We measure the magnetic remanence of the samples after we expose the samples to the coil’s magnetic field for first 0.02, and then two seconds, using a JR6 Spinner Magnetometer. Then, we calculated the normalized difference ((IRM2s-IRMpulse)/IRM2s) of the two remanence measurements to estimate the abundance of ultrafine magnetic particles.
We have found that in general, the abundance of ultrafine magnetic (SP) particles increases dramatically for soils in the upper soil horizons, and then decreases with depth. Also, their abundance is generally greater in soils that formed under humid climatic conditions. However, the correlation between SP particles and climate is not particularly strong. SP-abundance is unlikely to yield a useful climatic proxy.

Self-Organized Criticality in Cellular Automation as a Possible Model for Evolution

Bao Pham '06
Faculty Sponsor: Mark Silverman
The Theory of Self-Organized Criticality (SOC) describes nature as a complex dynamic system, perched at a poised critical state. This state is characterized by scale free behaviors in which small disturbances can cause responses, call avalanches, of all sizes. A complex system becomes critical without forcing from any outside agents. The critical state comes into existence as a consequence of interactions among individual elements of the system. In other word, the critical state is self-organized. The key mathematical characteristic of SOC is the power laws relation, which is characterized by the line on the double logarithmic plot. SOC appears in a range of biological, earth and human systems. One interesting model that was observed to be critical is the ‘Game of Life’ developed by John Conway. This computer game is a cellular automaton, made up of a square lattice system with a specific set of rules that govern the state of each square. Earlier studies found that realizations of the game organize into the critical state from which scale-free structure emerged. The power law was applicable for both the distribution of ‘clusters’ of size s and the distribution of durations of perturbations. In this study we looked at previous research carried out on the Game of Life. We found that the rules established in this game were critical within a large length scale. We extended the study by creating our own cellular automaton on a hexagonal lattice governed by a unique set of rules. We hope that by studying the dynamics of cellular automata we will gain some insight into the dynamics of a society of living organisms and how these systems evolve.

Study of the Climatic Influence on the Loessic Soils in the Midwestern United States

Saroj Aryal '09
Faculty Sponsor: Christoph Geiss

Soil formation is controlled by five major factors: climate, time, vegetation, topography, and parent material. In our research we studied the effects of the se factors on the magnetic characteristics of the soil. Most of our sites in Nebraska and some parts of Iowa and Minnesota have almost the same age and developed under similar topographic conditions. Also, most of our sites developed in late-Pleistocene or Holocene loess ranging from SE Minnesota through SW Nebraska and Kansas, so they have the same parent material. For our study we measured magnetic susceptibility, ARM, IRM, hysteresis loops and Curie temperatures. In addition, have also studied several non-magnetic components such as the determination of the soil mineral content, soil color and textural changes.
The parameters were measured against the depth of the soil. The soil in the upper horizons seems to have higher concentrations of magnetic minerals as shown by the measurements of Magnetic Susceptibility, ARM, IRM and ARM/IRM. It was also observed that these changes in magnetic properties are dependent upon the climatic conditions under which the soil forms. The average ARM, IRM, ARM/IRM and Magnetic Susceptibility were somewhat proportional to the mean annual precipitation.

A Faster, Cheaper Circuit for Detection of Coincident Photons

Sagar Bhandari '09, Nabil Imam '08, Valentina Zhelyaskova '08, Doug Goodman '06
Faculty Sponsors: David Branning, David Ahlgren, Mark Beck (Whitman College)
Our experiment involves the creation and detection of coincident photon pairs. In our lab, a Single Photon Counting Module (SPCM) is used to detect each photon. Each SPCM sends an electronic pulse corresponding to an incident photon. As we are concerned with the photons arriving simultaneously at two detectors, the pulses from the detectors should be checked for simultaneity. Traditionally, the pulses from each detector (named start and stop) are sent to a Time to Amplitude Converter (TAC) that converts the delay time between those two pulses into a voltage. This voltage is then analyzed by a Single Channel Analyzer which sends a new pulse every time the voltage from the TAC falls within a certain range (this voltage range corresponds to a time window set manually on the SCA module). And therefore, each of these new pulses corresponds to a coincidence count. However, this method of counting coincidences turns out to be inefficient since a lot of coincidence counts are missed due to the long conversion time of the TAC and it is expensive too. It was realized that simple “AND” gates (contained in cheap integrated circuits) that have a much shorter conversion time could be used to check for coincidence. The initial design of this new Coincidence Counting Circuit was proposed by Professor Mark Beck at Whitman College which was later improved upon by Professor David Ahlgren, Professor David Branning, Sagar Bhandari’09 and Nabil Imam ’08 at Trinity College. The prototype circuit board was fabricated by PCB Express and completed in the Trinity College Engineering Department. It was tested in the lab and significant improvement in the coincidence counting rate was observed. In fact, at high counting rates the new coincidence counting circuit was twice as efficient as the traditional TAC/SCA method.

Quantum Optics

Nabil Imam '08
Faculty Sponsor: David Branning
The goal of our research is to test the supposedly intrinsic randomness of quantum theory. When a photon is incident on a BBO crystal, a quantum mechanical process called parametric downconversion causes the crystal to emit a pair of photons. The process of parametric downconversion is thought to be random. The photons coming out of the crystal will be detected and a comprehensive statistical random number test will be carried out on the data to see whether or not the downconversion process is truly random. A second test will also be carried out to investigate the randomness associated with the quantum bits themselves. The two photons coming out of the crystal will be passed through a polarizer which will cause the photon to make a choice between two directions of polarisation, vertical or horizontal. Quantum theory’s prediction is that this choice is random. By running similar statistical tests on the data, the randomness of this process will be investigated. These tests will have significance in current cryptography research since the research is based on the assumption that the entire procedures mentioned above are truly random. If our data indicates non-randomness, it is possible that a hidden source of bias is present in the optics or electronics which can be exploited by hackers. If that is the case, our illumination of the problem will help cryptographers avoid such biases.

The Radon-220 Problem

Terrance Kessler '04 and Jeffrey Peo '03
Faculty Sponsor: Al Howard
Radon has long been known to be a health hazard to humans. Inhalation of radioactive radon gases can lead to harmful a-decay inside the lungs. Two isotopes of radon currently still exist in Nature: 222Ra with a half-life of 3.9 days and 220Ra with a half life of 55.9 seconds. Terrance and Jude measured the emission of 220Ra from small samples of gneiss and found emissions that far exceed current EPA limits. Their study establishes that 220Ra escapes from maximum depths of approximately 1 cm, a factor of 2 x 106 larger than previously assumed.
The quantities of 220Ra released from granite countertops are thus far greater than previously assumed and can easily exceed current EPA limits.

Paleomagnetic Investigation of Cave Deposits

Tamara Machac '06
Faculty Sponsor: Christoph Geiss
Tamara analyzes cave deposits from central Missouri to characterize variations in the Earth's magnetic field over the last 130,000 years.  Since the specimens under investigation are extremely weakly magnetized most of Tamara's  measurements are performed at Lehigh University where we have access to a 2G cryogenic magnetometer, but many of the basic sample characterization is done right here at Trinity College using the facilities in the Physics and Chemistry Departments.

Development of Electric Furnace for Rock-magnetic Analyses

Terrance (Jude) Kessler '04
Faculty Sponsor: Christoph Geiss
Jude developed an electric furnace capable of heating geologic specimens to 700°C within 30 minutes. To avoid chemical alteration of the samples they are heated in an inert gas atmosphere (helium or argon). The furnace is located in a magnetically shielded space and surrounded by a field coil allowing heating and cooling in well characterized magnetic fields.  This arrangement allows us to simulate the acquisition of thermal remanent magnetization of igneous rocks such as the lava flows on the west side of campus.  Jude used his furnace and the equipment of the rock-magnetism laboratory to reconstruct the direction and magnitude of the Earth's magnetic field during late Triassic time.