Overview

Our group uses electrons and light for investigations in several areas.

    1. Determination of the mass of the electron antineutrino by beta decay of T₂
    2. Detection of Ultra-High-Energy Cosmic Neutrinos (≈10²⁰eV)
    3. Applied Physics, Raman spectroscopy
    4. Development of intensive positron sources

Thus, our research extends from astro-particles to biology with a significant emphasis on applying our know-how applied problems.

Faculty Collaborators

    Philip Varghese, Professor, Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin
    Jacek Borysow, Professor, Department of Physics, Michigan Tech University
    Hermann Wellenstein, Professor, Physics Department, Brandeis University

Graduate Students

    Jeremy Johnson

Current Research Projects

1 The Determination of the Mass of the Electron Anti-Neutrino

There are two convincing arguments for determining the rest mass of the neutrino. First, the standard model predicts the mass to be zero mainly due to its one component helicity. Thus, our experiment is one of the many searches to go beyond the standard model. Second, there is little doubt today that the majority of the mass in the universe is non-luminous. Since the baryons contribute only at most 10% of the mass of the universe, this dark matter must be WIMPS (weak interacting massive particles). The only members of the elementary particles, which fit this description and are known today, are neutrinos. If these leptons have a mass, which can now be expected due to neutrino oscillation measurements, then we may find answers to many current astronomical questions. The only technique known today to measure the Dirac mass of the neutrino directly is based on the shape of the endpoint of the electrons forming the beta-decay spectrum of tritium. Three experiments have produced results for m_v by recording very well the spectral shape of the electrons in the neighborhood of the endpoint of the beta spectrum. Our experiment is also based on the T₂ beta decay. The lowest mass value quoted today is an upper limit of 2.8eV. We expect to achieve much higher resolution and to avoid many systematic problems. Our T₂ gas will be housed in a magnetic field-free environment. Currently we reach 1.5 eV combined resolution with our electron spectrometer system. However we know the spectrometer functions well enough to de-convolute the data and reach 0.5 eV (3σ).

2 Detection of Ultra - High Energy Cosmic Neutrinos in a Salt-dome

The results of several recent experiments revealed many new properties of neutrinos. We know now that they have mass and they oscillate between flavor states in both vacuum and matter. Our research will explore this newly gained knowledge to gain insight into the astrophysical processes, which emit the neutrinos.

We propose feasibility studies using the unique properties of salt domes to collect data from ultra high-energy neutrinos (≈10²⁰eV). Salt domes grew during 150 million years from the Louann Salt in a monolithic, polycrystalline structure. Most domes are 6 km deep and have diameters of 1-10 km. There are three major sources of information for a variety of domes: the salt mining industry, petrochemical research and studies related to the use of salt domes for depositories of nuclear waste. The salt domes are studied in detail by the department of Geophysics here at UTA.

There are several properties the salt domes have to possess to quantify them as high quality detectors. We need to know the mean free path of electromagnetic radiation and ultrasound in the polycrystalline material, the intrinsic stability of the salt at great depths, the radioactive backgrounds and those introduced by impurities in the surrounding rock and the flux of cosmic high-energy neutrons. These quantities set the precision for determining the direction and energy of the neutrinos to be detected.

A salt dome detector will be a more sensitive second generation ultra high-energy neutrino detector than the Ice-Cube project at the South Pole. Depending on which suitable dome is available, the active volume can be as large as 3x3x5 km³. The water equivalent volume is then over 90 km³, because of the 2.1 times larger salt density than ice. Drilling cores from several oil companies show that most salt domes are homogeneous in composition and crystallization down to 3 km. The dome structure moves by about 0.01mm a year, making them very quiet from an ultrasound point of view. There are hundreds of domes to search for the optimal detector location.

The interaction of an ultra-high energy neutrino with a quark leads to a lepton of the same flavor as the incident neutrino and a recoil quark. The total energy and momentum are transferred to the exiting particles. The lepton starts a strong shower beginning as a narrow bundle, which broadens as the kinetic energy is shared by higher tiers of secondary particles. This plasma filament emits polarized electromagnetic radiation (Cherenkov radiation) and a coherent ultrasonic boom. The recoil quark will lead to a short track. The determination of the flavor of the lepton and the incident energy require detailed and reliable "GEANT4" calculations.

Currently we are most interested in the mean free path of ultrasound as a function of frequencies. Next, we plan to setup 4 detectors to monitor continuously for 6 months the noise in the salt dome to learn if there are internal crack formations and if there are natural background sources to be considered in the detector design. All these measurements will be carried out at the Hockley mine 25 miles north-east of Houston, close to highway 290.

3 Applied Spectroscopy

Raman spectroscopy is becoming the prevalently applied spectroscopic tool in science, technology and medicine for the following reasons: (1) the spectra are very simple (scarce line density) and thus free of interferences, (2) the lasers needed are small, highly efficient, and affordable, and (3) and the photo-avalanche diode detectors have high quantum efficiencies to record very dilute gas mixtures. In our laboratory we have developed a Raman system which is particularly focused at the determination of the isotope ratios in molecules made of CO₂. The ¹³C to ¹²C ratio is 0.01 for all natural products. However, if one digests a compound which is enriched with ¹³C the breath will reflect this with a higher carbon isotope ratio; if the compound chosen is decomposed at the specific site in the body (human or beast). The increase of 13C in the breath reveals the biological activity of this site. Currently ten different diseases can be analyzed by this technique. Our instrument is an inexpensive and reliable diagnostic technology to be used by a nurse in a physician's office. Our method will detect Lactose sensitivies in newborn babies quickly enough to avoid major harm. The most common application will be the detection of Helicobacter Pylori viruses in the stomach, which initiate ulcer, and eventually cancer.

4 Development of an intense positron source

Positron annihilation spectroscopy is a well established research tool to characterize the surface and bulk electron distributions of any chosen material. However, the impressive results obtained with this technique have not yielded positron investigations and monitoring in an industrial environment. The greatest hindrance is the lack of sufficiently intense positron sources to record a simple Doppler distribution function with good statistics within minutes at a fabrication line. In general, most positron spectrometers are equipped with radioactive sources which produce at best only modest intensities of 10⁶ e⁺/s. An improvement by at least a factor of at least 100 is needed to become viable for on-line positron metrology. High-energy accelerators or nuclear reactors are not the answer due to their size and costs.

We propose to use standard technologies to generate an e+ beam with good electron optical properties, such as a small diverging angle, a small diameter and with a flux of 10⁸ e⁺/s. Beta positrons from a 10Ci source will be moderated with a 12-times folded W-mesh network. The low energy positrons will be accelerated into an electron optic focusing device which forces the positron trajectories to cross at a small (1-2 mm²) area above the electrodes. A second moderator (solid rare gas) will form the source for a gun to generate a beam of mono-energetic positrons of any desired energy.

The positron will be used to research the new dielectrics in MOSFETs with HfO₂ doping and to studies of micro-voids in plastic membranes, which are used in industry to separate gases mixtures.

Recent Publications

J. Haeger, M. Fink and H. Walther, "Molecular beam scattering of NO from graphite surface at cryogenic temp.", Surface Science, <550>, 35-45 (2004)

J. Borysow and M.Fink, "NIR Raman spectrometer for monitoring protonation reactions in gaseous hydrogen", J Nucl. Materials, <341>, 224-230, (2005)

M. Fink and J. Campell, "An all-quartz gas cell for a multi-pass cavity", Rev. Sci. Instr. <77>, 036113-1-036113-3, (2006)

T. F. Roland, J. Borysow and M. Fink, "Surface mediated isotope exchange reactions between water and gaseous deuterium", J. Nucl. Materials, <535>, 193-201, (2006)

J. Borysow and M. Fink, "Ultra high resolution NIR Raman spectrometer", Appl. Spectrosc. <60>, 54-56, (2006)

M. Fink, H. Wellenstein and S. Nguyen, "A New Positron Source with High Flux and Excellent Electron Optical Properties, Nucl. Instr. and Meth. B, <261>, 819-821, (2007)