REU Projects for 2005
Neutron-Deuteron Analyzing Power Data at 26 MeV
Advisors: Werner Tornow and Gary WeiselFor neutron-deuteron (nd) elastic scattering, the nuclear physics community has found that there is a large discrepancy between experimental data and theoretical calculations for the analyzing power, an important polarization observable. This discrepancy has been shown to be about 25% below 19 MeV and to be absent above 50 MeV. The present REU project is part of TUNL's effort to determine at what energy the discrepancy becomes insignificant. Such information will help theorists identify shortcomings of three-nucleon computations or the shortcomings of the nucleon-nucleon force models on which the computations are based. This project will produce the first high-precision nd analyzing power data at 26 MeV. The REU student will help set up the target area and associated electronics and will participate in the first experimental run. The student also will gain experience in data analysis, using a Linux-based software package. At this relatively-high energy, removing unwanted background counts from the detector spectra will be especially important and challenging.
Measuring 3He Cell Density Using a Tunable Laser
Advisors: Haiyan Gao and Kevin KramerThe High Intensity Gamma-ray Source (HIGS) program at the Duke Free Electron Laser Laboratory(DFELL) has an active program using a polarized 3He target. A polarized target aligns the spins of the target material, in this case 3He nuclei, so that some of its electromagnetic properties can be isolated. This target will be used to study neutron and 3He structure by measuring the spin-related observables from gamma-ray scattering. Construction of this target is nearly completed with a production run occurring in the summer.
A polarized target of this type uses high-pressure 3He gas that is sealed in glass cells. Since the glass cells cannot be opened and no pressure sensor can be put inside the cell, the various characteristics of the cell, which must be known for experimental accuracy, have to be done using external, non-intrusive techniques. Fortunately, one of the most important quantities, the 3He density, can be measured using a well-known optical technique.
The technique used for polarizing the 3He nuclei requires a small amount of rubidium to be placed inside the cell. The range of frequencies of light that rubidium electrons can absorb is sensitive to changes in pressure of the gases that surround it. In other words, the higher the pressure of 3He the broader the spectrum of light the rubidium sample can absorb. Therefore, if one shines a tunable laser through one of our glass cells and scan over an appropriate band of frequencies, one can determine the density by looking at the absorption spectrum.
The student working on this project will set-up and perform this measurement on several cells. Most of the work will be setting up the optical elements and writing LabView software to record and analyze the output data. Additional work will be needed to modify some of the pre-existing equipment so that it can be used. This project is ideal for a self-motivated student interested in a hands-on, table-top experiment dealing with optics and computer software.
The Solar Neutrino Problem
Advisor: Yannis Parpottas, Henry Weller, and the Capture GroupThe 3He(α,γ)7Be reaction is of great interest in nuclear astrophysics. It is a key reaction in the solar proton-proton chain, being one of the terminating branches of this chain [1]. It produces 7Be in our Sun, which is destroyed by either the capture of an electron or a proton. In both cases high-energy neutrinos are generated which are observable by terrestrial detectors.
Accurate reaction rates at the most effective solar energies ( ≈ 20 keV) could reduce uncertainties and consequently help resolve the existing discrepancy between the predicted and experimental neutrino flux (solar neutrino problem). Cross section measurements down to 100 keV energies are feasible. Extrapolation of the reaction rates at solar energies can be also obtained.
At TUNL, the Radiative Capture group is working on these measurements. 3He-implanted targets have been fabricated and test-runs with α-beams have begun. This REU project gives the opportunity for the student to be involved with the preparation and execution of these measurements. Analysis of the data obtained using High-Purity Germanium γ-ray detectors and calculations of the reaction rate using a direct-capture model computer code are also included in the project. [1] C. E. Rolfs and W. S. Rodney, Cauldrons in the Cosmos (The University of Chicago Press, Chicago, 1988, p.328).
Double-Beta Decay Studies to Excited States
Advisors: Werner Tornow and James EsterlineThe double-beta decay of nuclei is a very rare process with half-life times of larger than 1019 years. TUNL is currently operating a double-beta decay experiment on 100Mo in the basement of the Duke Physics Building. A 1 kg sample of 100Mo is sandwiched between two high-purity germanium detectors surrounded by a NaI anti-coincidence annulus. The interest is in double-beta decay transitions to excited states in the daughter nucleus 100Ru. In order to extend these measurements to 150Nd, where only small amounts of isotopically enriched 150Nd exist worldwide, the present apparatus has to be moved to a much deeper underground location in order to reduce the cosmic-ray induced background. The REU student will join activities related to the relocation of the TUNL double-beta decay apparatus to the Kimballton mine in Virginia. The main focus is on the optimization of the experiment in the new undergound environment.
Scintillation light detection using VLPCs for the neutron electric dipole moment experiment
Advisors: Dipangkar Dutta and Haiyan GaoThe electric dipole moment (EDM) of the neutron is a fundamental quantity which is predicted to be on the order of 10-31 e.cm by the Standard Model of electroweak interaction. This quantity is a direct probe of violations of the time-reversal symmetry, thus providing insight into understanding the origin of CP (C: charge conjugate symmetry, P: parity) violation. The current experimental limit on this quantity is 6 x 10-26 e.cm. At present a new search is underway aiming at a two orders of magnitude improvement over the current limit. This new experiment will have important impact on the search of New Physics beyond the Standard Model.
Detection of the scintillation light in superfluid 4He is at the heart of the new proposal to measure the Neutron EDM. Prof. Gao's Medium Energy Physics Group at TUNL is actively engaged in this new search and is embarking on a R & D effort devoted to using novel high quantum efficiency photon detectors. The new scheme involves using wavelength shifting fibers to collect the scintillation light in superfluid 4He, these fibers then transports the light out of the detection region. The fiber terminates in a visible light photon counter (VLPC). The VLPCs are doped silicon based solid state photo multipliers with quantum efficiency as high as 85%, they are also very fast and have very low dark counts. Moreover, they are insensitive to magnetic fields and operate at temperatures of 6.5~K.
We invite REU students to join us in this exciting and challenging experiment this summer at TUNL. The project wil involve helping helping assemble the experimental apparatus inside a cryostat, testing the apparatus, collecting data with alpha and beta sources, and analyzing the data. Interested students please contact Prof. Haiyan Gao at gao@tunl.duke.edu and/or Dr. Dipangkar Dutta at ddutta@tunl.duke.edu. Please also visit our group's web page at http://www.tunl.duke.edu/~mep, which links to the web page of the EDM experiment as well as other experiments that our group is working on.
Nuclear & Nucleon Compton Scattering at the High Intensity Gamma-Ray Source (HIGS) and Commissioning of the Neutral Meson Spectrometer (NMS)
Advisors: Mohammad W. Ahmed, Henry R. Weller & the Capture Group at TUNLIn a simple, non-relativistic picture when an external electric and magnetic field is applied to a collection of charged particles, a charge-mass separation occurs in response to these fields. This process, commonly referred to as polarization, also occurs in nuclei (where protons and mesons act as charged particles) and nucleons (where quarks are massive charged objects). Different wavelengths of the applied electromagnetic field (or a photon) are required to study polarization in nuclei or nucleons.
The first-order study of polarization phenomenon consists of measuring electric and magnetic polarizabilities. The low-energy theories, such as Chiral Perturbation Theory (CPT), predicts them via energy expansion of the Compton scattering amplitude.
Scattering Amplitude = A0 + alpha F(omega) + beta G(omega),
Where A0 is a constant (depends on parameters such as charge and mass of the particle), alpha is the electric polarizability, and beta is the magnetic polarizability. The expansion is in terms of the energy based functions F and G.
At HIGS, we plan to perform precision measurements of alpha and beta. The experiment requires a polarized photon beam, a target (a nucleus or a nucleon), and a set of detectors to measure the scattered photon and the recoil nucleon(s). The beam will be provided by HIGS; various targets such as protons (liquid hydrogen), deuterons (liquid deuterium), and He-3 are in production; a spectrometer, the neutral meson spectrometer (NMS), is available to detect the scattered photons.
This REU project will focus on understanding the basics of the Compton Scattering on nuclei and nucleons (including calculations of count rates, and limits on experimental measurements), and commissioning of the NMS. The commissioning of the NMS will include testing of various detector elements, such as CsI and BGO scintillators using cosmic-ray background. The project will aid the student in developing strong skills in Compton Scattering theory, methods of photon detection, and hands-on experience in collecting, analyzing and organizing data from scintillating detectors.
Nuclear Data Review and Evaluation of neutron-capture reactions
Advisor: John KellyThe Nuclear Data Evaluation Group is responsible for maintaining a database of nuclear structure properties in the atomic mass range of A=2-20. Our group surveys published literature and provides summary reviews to the nuclear data user community. In this project, publications with relevant information from thermal neutron-capture reactions will be evaluated using standardized techniques in order to obtain the best structure parameters. Activities will include searching databases of published articles for neutron-capture reaction data, familiarizing oneself with the information that can be obtained from these measurements, and evaluating the published data sets to deduce a set of "best values". The student will develop a web interface for presenting the information. As time permits, the student may choose to develop discussion about specialized topics. In addition the student will become familiar with useful experimental procedures that are relevant to measurements with High-Purity Germanium gamma-ray detectors.
Data Acquisition Software Development
Advisor: John KelleyA Data Acquisition software package based in Tk/Tcl and C++ is being evaluated at TUNL. The programs Spectrodaq and SpecTcl are interfaced to provide data acquisition and data analysis capabilities in a Linux OS environment. In this project a student will develop skills in evaluating detector setup, analog and logic signal electronics, signal processing and analysis software setup. The student will gain experience with various gamma-ray detectors (NaI-scintillator and HPGe-Semiconductor) and neutron detectors (liquid scintillator). In addition the student will summarize the findings in a short user's manual and in sample distributions codes that will be used by others to aid in future experimental setups.
Precision Alignment and Vibration Studies of Accelerators for High Intensity Gamma Source (HIGs)
Advisor: Ying WuThe High Intensity Gamma Source (HIGS) is a world-class nuclear physics facility operated by the Triangle Universities Nuclear Laboratory (TUNL) and Duke Free Electron Laser Laboratory (DFELL). The high intensity, nearly monochromatic gamma beam is produced by colliding a high energy electron beam (from 270 MeV to 1.2 GeV) with the high power FEL light in the Duke storage ring via a process called Compton scattering. The HIGS facility is currently undergoing a major upgrade with the development and installation of a booster synchrotron accelerator. This new accelerator will replace the lost electrons in the storage ring at any operational energy to enable the continuous production of gamma beams at HIGS.
Under the guidance of a Duke faculty and a DFELL alignment expert and mechanical engineer, the REU student will assist in the installation and alignment of this booster synchrotron accelerator utilizing a state-of-the art laser tracker system. The laser tracker operates on the principle of spherical coordinate measurements system with the aid of a laser interferometer. The student will be involved in monitoring minute settlements and vibrations on and around the floor of the booster vault to better characterize the mechanical stability of the booster floor. In addition to the laser tracker, the student will gain hands-on experience with a variety of sophisticate experimental apparatus including ultra sensitive vibration sensors and various optical alignment instruments. Furthermore, the student will get a chance to master advanced data analysis tools such as Matlab.