REU Projects for 2008
Nuclear Data Review and Evaluation of Ground State Particle Decaying Nuclei
Advisor: Dr. John Kelley
The 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 for ground-state particle decays will be evaluated using
standardized techniques in order to obtain the best values for decay
properties and associated structure parameters. Activities will include
searching databases of published articles, 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.
Measurements of 187Re(n,2n γ)186mRe cross-section
Advisors: Dr. John Kelley and Anton Tonchev
The aim of this project is to measure partial (n,2n γ) cross sections
that lead to population of levels above a very long-lived state in
186mRe (T1/2=2.0x105y). These data are needed
in order to evaluate the production (and destruction) cross sections of
187Re, and hence, to reduce the nuclear physics uncertainties for the
187Re/187Os cosmochronometer that is used to date the age of the r-process
nucleosynthesis. In addition, rhenium has one of the highest melting points
of all elements (exceeded only by tungsten and carbon) and it is used to
make parts of jet engines, and in space reactor technologies. Therefore, the
accurate knowledge of neutron induced reaction cross-sections for this
element is of vital importance to these applied technologies. We will study
the 187Re(n,2n γ)186mRe reaction using monoenergetic neutron beams in
the 5-15 MeV energy range at the TUNL accelerator facility.
A suite of high-resolution Ge detectors will be used to detect prompt
gamma-rays above the 186Re isomer in both singles and coincidence modes. The
nuclear model codes TALYS and EMPIRE will be utilized in reconstructing the
total 187Re(n,2n)186mRe reaction cross-section.
Plant Physiology Studies With Short-Lived Radioisotopes
Advisors: Drs. Calvin Howell and Alex Crowell, and Matt Kiser
In the last few years a collaboration of physicists from
TUNL and biologists at the Duke Phytotron have begun a
program to study various aspects of plant physiology using
short-lived radioisotopes as tracers. Positron-emitting
radioisotopes such as 11C (20 min half-life) and
13N (10 min half-life) have been produced in the tandem lab
at TUNL and transported to the Duke Phytotron via underground
conduits. An array of scintillators have been utilized to
detect the 511-keV gamma rays from positron-electron
annihilation and time-lapse images can be constructed that
show metabolism on the sub-cm scale. One goal of the 11C
studies is to provide information on short time- and
small spatial-scale processes that will complement large
scale studies performed in Duke Forest (FACE) on the effects
of elevated CO2 on plants.
An REU student will be involved with the assembly and testing of new scintillation detectors and will participate in experiments performed during the summer run period.
Nuclear Fusion using the Pyroelectric Effect
Advisor: Dr. Werner Tornow
The REU student will join a small research group that is following up on work
published by Naranjo et al. (Nature 453, 115 (2005))
and J. Geuther et al. (Phys. Rev. Lett. 96, 054803 (2006)) who
used pyroelectric crystals to initiate
the fusion reaction 2H(d,n)3He in a dilute gas of deuterium.
In 2006 and 2007
we tried to reproduce these results, but we were not successful. We detected
neutrons, but at a much lower rate as found in the published work.
For 2008 we plan to change our approach. Rather than looking for neutrons from the 2H(d,n)3He reaction we will try to detect protons from the 2H(d,p)3H reaction. The REU student will participate in the associated measurements.
Building a Source Manipulator for the miniCLEAN Detector
Advisors: Dr. Reyco Henning and Dr. Michael Ronquest
The search for dark matter is currently one of the most active fields in the
fundamental physics today. While the existence of dark matter is quite
persuasive given current astrophysical evidence, the exact identity remains
a complete mystery. With the experiments at the LHC years away from having
detectors which can indirectly detect SUSY particles, which remain the
leading candidate for dark matter, it remains for the direct detection experiments
to solve this mystery.
The miniCLEAN experiment is an innovative and ambitious experiment which will look for low energy interactions within liquid Argon and liquid Neon which are the signal of dark matter particles. The miniCLEAN concept is a simple one: use scintillation light from Liquid Noble gasses in order to detect nuclear recoils and reject other backgrounds. Without the need for large Time Projection Chambers, this method allows an experiment to be scaled up quite easily, thus allowing higher sensitivities to be reached.
The REU student will work at the Triangle Universities Nuclear Lab and help develop and build a source manipulator arm that will insert a variety of radioactive sources into the miniCLEAN detector in order to study and calibrate the experiment's energy and position resolution. This work will involve many aspects nuclear and experimental physics in general, including work with radioactive sources, particle detectors, cyrogenic liquids, Radon mitigation, robotics, data analysis and data acquisition using LabView.
3He Injection Test for the Neutron Electric Dipole Moment (nEDM) Experiment
Advisors: Dr. Haiyan Gao and Dr. Xiaofeng Zhu
Precision measurements of the properties of the neutron present an
opportunity to search for violations of fundamental symmetries and to make
critical tests of the validity of the standard model (SM) of electro-weak
(EW) interactions. Recently, a new experiment is underway on a search of the
neutron electric dipole moment (EDM) aiming at an unprecedented sensitivity.
The new search will have a two orders of magnitude improvement over the
current experimental limit on this quantity. A search for a non-zero value
of the neutron EDM is a direct search of the time reversal symmetry (T)
violation. A direct search for T symmetry violation such as the search for
the neutron EDM is a unique way of search for CP violation because of CPT
invariance.
The new nEDM experiment relies on the spin dependence of the nuclear absorption cross section: n + 3He → p + t + 764keV. Therefore, polarized 3He is important to the success of the nEDM experiment. The purpose of the 3He Injection test is to make sure that the number of 3He atoms collected should be big enough in the collection volume, while the polarization loss should be small enough. During the test, 3He atoms with nuclear polarization of nearly 100% from Atomic Beam Source will pass through a transfer tube of 1.5 meters of length first and then be injected into collection volume which is a pyrex cell partially filled with superfluid of 4He. The collection volume with superfluid 4He will be operated around 400 mk. A passive film burner will be implemented along the transfer tube to reduce effectively the evaporation of superfluid helium film along the wall. A superconducting solenoid coil will provide magnetic field along the 3He injection path. A superconducting tricoil system will provide a vertical magnetic holding field of 1.2 KGauss for the collection cell, which is 45 degrees to the injection path. The 3He spin direction will rotate by 45 degrees, aligning with the magnetic field. Due to low concentration of 3He in the collection volume, the NMR signal is expected to be small. A magnetic holding of 1.2 Kgauss will be used to enhance the NMR signal and we plan to use pulsed NMR for the measurement.
An REU student will have the opportunities to test various components of the injection test apparatus at Duke this summer and perhaps make one trip to Los Alamos National Lab. For detailed information, please contact Prof. Gao at gao@tunl.duke.edu and Dr. Xiaofeng Zhu at xfzhu@tunl.duke.edu.
A high-pressure polarized 3He target
Advisors: Drs. Haiyan Gao and Xiaofeng Zhu, Xing Zong
The 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.
A first experiment using this target is expected to take data this April.
The technique used for polarizing the 3He nuclei requires a small amount of alkili metal (for example, 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. There has also been new laser technologies developed which allow one to further improve the 3He target polarization.
The student working on this project will set-up and perform measurements of target densities from the target cells used in the upcoming experiment and also carry out systematic study of the target polarization using a linewidth narrowed laser. Most of the work will be setting up the optical elements and working with 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 lasers, optics and nuclear magnetic resonance (NMR) technique.
Measurements of 11B + p and Related Reactions for Nuclear Fusion Power Reactors
Advisors: Drs. Sean Stave, Ralph France, Henry Weller and the Capture Group
There is a renewed interest in practical power generation using nuclear fusion. In the past, fusion reactors have been designed using radioactive fuels such as tritium, and produce high fluxes of unwanted neutrons. A new possibility is being proposed and evaluated which uses Boron-11 (a stable isotope). This isotope undergoes neutron-free fusion via the 11B(p,α)2α reaction. In order to estimate the power generation, accurate values of the cross section of this reaction at various low energies are needed. This past summer, we performed measurements of the 11B(p,α)2α reaction. Since the alpha particles which are produced will also interact with the 11B, additional measurements of the elastic scattering of alpha particles from 11B are needed. In addition, there is some concern about the gamma-rays which could be generated via the 11B(p,γ)12C reaction, so measurements of this reaction will also be performed.
The REU student involved in this project will take part in setting up both the elastic scattering and the (p,γ) experiments, and be involved in acquiring, analyzing and interpreting portions of the resulting data.
The CLEAR Experiment
Advisor: Dr. Kate Scholberg
Coherent neutral current neutrino-nucleus elastic scattering is a process in which a neutrino interacts with a nucleus, giving it recoil kick. Although the probability for such a process to occur is relatively high, the process has never before been detected because typical nuclear recoil energies are very small. However, detection of the process may be within the reach of the new generation of low-threshold detectors. Because the rate of the process can be quite precisely predicted, a deviation of measurement from prediction could indicate new physics beyond the Standard Model. A promising prospect for the first detection of this process is the CLEAR (Coherent Low Energy A(nuclear) Recoil) experiment at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee. This planned experiment comprises a liquid xenon time projection chamber inside an instrumented water shield.
This project will involve participation in design, simulation and background evaluation work for the CLEAR experiment. The project will include simulation studies for design optimization and analysis of background measurements at the SNS using scintillation detectors. The student will gain experience with a variety of simulation and data analysis software tools. Programming experience will be useful but is not required.
Radon reduction in laboratory air
Advisor: Dr. Henning Back
Radioactive radon in the air can create radioactive surface contamination on detector components, because radon decay products are solids and can plate-out on surfaces. Although it is possible to create gases with a very low radon concentration, human contact with a detector during construction, assembly, and operation requires an air atmosphere. It has been suggested that some underground laboratories (SNO-Lab and DUSEL) will want radon removed from the laboratory air. The data from this project will be used to develop the technology needed to create a radon scrubber for removing the radon from air, and for establishing the limitations to this technology. Knowing the radon reduction limits will allow experimenters to develop protocols for minimizing the effects of radon daughter plate-out.
This REU project will focus on creating radon absorption columns based on activated charcoal and study the effect of column geometry on the radon reduction efficiencies. The REU student will take part in designing and building absorption columns, learning to run an off-the-self radon detector, and develop experimental techniques to determine radon scrubbing efficiencies. If time permits the student may also participate in developing a highly sensitive radon detector.