Condensed Matter Physics
Annular Resonator to Measure the Speed of Fourth Sound in Liquid Helium
In this experiment, we measured the velocity of fourth sound, a pressure wave which propagates only through the superfluid component of liquid helium II, in an annular resonator packed with Al2O3 powder by inducing fourth sound waves in the helium within the resonator at frequencies between 200 Hz and 10 kHz and observing the resonance frequencies of the system which correspond to the frequencies of standing waves within the resonator. The velocity of the fourth sound waves was calculated from the location of the resonant frequencies along with the known dimensions of the resonator at each of ten temperatures between 2.17 K and 1.5 K. We were able to observe values for the speed of fourth sound which showed the correct overall trend as a function of temperature; however, they were systematically lower than the theoretically calculated values.
Cosmic Ray Experiments
Characterizing the Low Energy Response of the FOXSI silicon X-Ray Detectors
The purpose of our experiment was to improve the characterization of the energy response of the Focusing Optics X-ray Solar Imager (FOXSI) silicon X-ray detectors below 5 keV, as there have been observed discrepancies in this regime. We did so by using a 5.9 keV Fe-55 X-ray source to measure the variation in transmission of low energy X-rays through the detectors' nonuniformly crinkled thermal blanketing. We found that at 5.9 keV, a smooth blanket had an average transmission of .83 +/- .03 and a crinkled blanket had an average transmission of .83 +/- .02, indicating that there was no significant change in transmission with crinkling and that the crinkling cannot have caused the observed discrepancy
Daylight Experiment for Teaching Stellar Interferometry
A quasi-monochromatic, spatially incoherent light source was used to simulate star light. A telescope fitted with masks containing pairs of pinholes was used to observe the simulated star, producing interference patterns. Increasing the pinhole separation produced a change in the degree of coherence of the light and fringe visibility of the interference patterns. Relating pinhole separation to fringe visibility using the van Cittert-Zernike theorem, the diameter of the light source was determined to be 2.33 ± 0.18 mm. This diameter agrees with the actual diameter of 2.31 mm with an error of 1.12% or 0.14sigma, though the data does not fit to the predicted equation.
Measuring the Refractive Index Using and Extended Cavity Diode Laser
In this experiment, the index of refraction of a thin glass slide was measured using an Extended Cavity Diode Laser (ECDL). This was done using saturated absorption spectroscopy of a Rubidium cell combined with a change in optical path length inside the extended cavity. Using Snell's Law and trigonometry, the index of refraction of a thin piece of BK7 glass was related to path length changes in the laser. Using a least squares fit, the index of refraction was measured to be n=1.52±0.032. This value agrees with the index of refraction of BK7 glass found literature, 1.51.
Efficiency Measurement of thin Plastic Scintillator as an Electron Target
We measured the detection efficiency of thin target scintillator for
minimum ionizing particles in order to find the feasibility of an electron
event trigger design for the Light Dark Matter eXperiment (LDMX)
detector. Cosmic muons were used in place of high energy electrons
since they have comparable energy scales. The detection efficiency was
determined by comparing the energy deposited in the target scintilla-
tor at the time of trigger, which is created by looking at the energy
in two thick layers of scintillator on either side of the target scintilla-
tor. An efficiency was taken for two scintillators with thicknesses of
3.0+/-0.1 mm and 2.2+/-0.1 mm. We measured efficiencies of 0.88+/0.01
and 0.78+/0.02 for each respectively. Preliminary results of our attempt
to determine the location of the muon event in the plane by looking
at the differences in energy in each SiPM are also shown. Our results
from this experiment will determine if such an electron event trigger
will be used in the final LDMX detector.
Electrodynamics and Mechanics of the Thomson Jumping Ring
The purpose of our experiment was to construct a model for the motion of an aluminum ring as it undergoes an accelerating force due to a magnetic field from a solenoid coil. We achieved this by measuring a series of height dependent auxiliary functions, and then using second order Euler approximations and Newton's second law of motion to generate a model of the expected motion. We found that our model described the motion of the ring to within 0.42 standard deviations in the regime where the magnetic force is driving the motion.
Electron-Positron Pair Production
The rate of detection of positron annihilation photons as a function of the thickness of a lead target slab was investigated. A Co-60 gamma ray source provided high energy photons for pair production. Coincidence detectors placed 180° apart on either side of the target were used to identify simultaneous 511 keV photons produced by annihilation. The detection rates were measured for slab thicknesses ranging from 1 mm to 15 mm, and were found to be in agreement with the theory.
Exploration of the Ball-Rod Physical System Using an Optical Interferometer
We use a Michelson interferometer with a 633 nm HeNe laser to investigate the motion of two steel rods of lengths 39.8 cm and 55.1 cm after being struck by a steel ball. The collision launches an elastic wave through the rod with observable displacements of the end mirror by interferometry. The speed of sound in thin, steel rods was found to be consistent with literature at 4830 ± 10 m/s for the 39.8 cm rod and 4870 ± 10 m/s for the 55.1 cm rod by observing rod lengths traveled within 43 round trip times of the induced compression wave. The evolution of the rod’s motion with time is also analyzed with position and velocity vs. time graphs for the two rods. The rods initially experience start-stop motion due to compression wave dominated movement with no gross rod motion between bursts and evolve to include gross motion as the compression wave transfers energy to the rod. Rod friction is neglected for short timescales less than 1 ms but play a significant factor in slowing the rod subsequently.
Analysis of a Vibraphone Bar Using Speckle Interferometry
In this experiment, an electronic speckle pattern interferometer was built, then used to find the nodes of a vibrating vibraphone bar. The interferometer was tested by bending a metal plate and observing the number of fringes seen. The speckle pattern was created by diverging a laser beam and reflecting it off of the object in question and a reference object. To view the nodes or fringes, an image of the unaltered object was subtracted from the object while it was deformed or vibrating. After testing the interferometer by bending a plate, we found the observed number of fringes to match the predicted number quite well, with most predicted points lying within the observed points’ uncertainties. With the vibraphone bar, we calculated the fundamental node locations (as fractions of the total bar length) to be 0.224 ± 0.009 and 0.786 ± 0.004 from left to right. The left node lies within four standard deviations of the value of a tuned bar from literature (0.1929), and the right node lies within five standard deviations (0.8034).
Gamma Ray Spectroscopy
Using a high-resolution, high-purity germanium (HPGe) detector, spectra of gamma ray emissions from radioactive isotopes in sediment samples from Lake McCarrons were taken. By comparing the spectra of sediments from different depths, it was found that there is no significant time dependence of natural radiation over the time frame the sample covers. In addition, no (unnatural) radiation from the fallout of nuclear testing could be detected.