REU Projects for 2006
Neutron-Deuteron Analyzing Power Data at 22.5 MeV
Advisors: Dr. Werner Tornow and Dr. 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 22.5 MeV,
completing measurements that were begun during the summer of 2005. 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.
The study of 3He nuclear spin relaxation time at 500 mK
Advisors: Dr. D. Dutta, Dr. Haiyan Gao and Q. Ye
The 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
time-violating symmetry breaking, 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 × 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.
The neutron electric dipole moment can be determined employing the
spin-dependent nuclear reaction _n +3 _ He ? p + T. In addition, polarized
3He nuclei are served as a co-magnetometer in the EDM experiment.
Therefore, minimizing the depolarization effect of the 3He under the
operating conditions of the EDM experiment is crucial. Prof. Gao's Medium
Energy Physics Group at TUNL is actively engaged in this new search and is
embarking on understanding and minimizing the depolarization effect of
polarized 3He nuclei in superfluid 4He at a temperature of around 500 mK,
which will be the operating temperature for the EDM experiment.
A first study has been carried out using spin-exchange optical pumping of
3He atoms and subsequent measurements of the 3He polarization using the
nuclear magnetic resonance (NMR) technique down to a temperature of 1.9 K
in a deuterated tetraphenyl butadiene (dTPB) coated acrylic cell. The
neutron storage cell will be made of dTPB coated acrylic for the neutron
EDM experiment. Currently, we are planning a new experiment to extend
these measurements down to a temperature of about 500 mK using a dilution
refrigerator in collaboration with Profs. Huffman and Golub at NC State
University.
We invite REU students to join us in this exciting and challenging
experiment this summer at TUNL. Specific projects may involve building a
magnetic cell transport system, polarizing a detachable 3He cell using
optical pumping technique, carrying out 3He relaxation time measurements,
and many others.
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.
Investigation of neutron induced background reactions of importance for
the next generation of neutrinoless double-beta decay experiments
Presently planned neutrinoless double-beta decay experiments are aimed at
determining the absolute electron neutrino mass through discovery of the
neutrinoless double beta decay. If neutrinos are their own antiparticles,
neutrinoless double-beta can occur in nature, resulting in a violation of
lepton number. The Majorana Collaboration plans to use High-Purity
Germanium detectors enriched to 85 % in Ge-76 as source and detector for
the two beta particles from the neutrinoless double-beta decay. These
detectors are surrounded by lead to reduce the effects of external
background radiation. However, neutrons generated by cosmic-ray muons are
a source of background, even deep underground.
This project will involve two REU students: One student will be
investigating the interaction of neutrons in the 4 to 20 MeV energy range
with natural germanium, while the other student will do the same for
natural lead. The experiments will take place in TUNL's Shielded Neutron
Source Area using the equipment and electronics currently used for TUNL's
National Nuclear Security Administration (NNSA) Studies. Therefore, the
REU students will work closely with the NNSA group (Drs. Anton Tonchev,
John Kelley, Gary Weisel, and Werner Tornow and their students).
Nuclear & Nucleon Compton Scattering at the High Intensity Gamma-Ray Source (HIGS) and
Commissioning of the HIGS NaI Detector Array (HINDA)
In 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 the High Intensity Gamma-Ray Source (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 system HINDA will be 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 detector system. The commissioning of HINDA will
include testing of NaI detectors and their shields using radioactive sources and
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.
Measurement of 11B and Proton Capture Reaction for Nuclear Fusion Power Reactors
Advisors: Dr. Mohammad Ahmed, Dr. Ralph France , Dr. Henry Weller & the Capture Group
There is a renewed interest in practical power generation using nuclear fusion.
In the past, these methods have explored standard fusion fuels such as tritium.
This method is not ideal due to the use of long half-life radioactive materials
(tritium) and the high fluxes of neutrons produced in this reaction.
A new possibility is being proposed and evaluated which uses Boron-11
isotope (stable) which undergoes neutron-free fusion via 11B(p,alpha)2alpha.
In order to estimate the power generation, accurate values of the cross section
of this reaction at various energies are needed. TUNL is involved in measuring
this cross section. We have recently performed a preliminary test run and plan to
take significant data this summer. We are also planning to study the reaction using
a polarized proton beam. If a polarized beam can enhance the cross section, there
is a possibility of using this to enhance the energy produced in this reaction.
The REU student involved in this project will take part in setting up the experiment, d
oing calibrations of the Si detectors using alpha emitting radioactive sources,
and acquiring and analyzing parts of the data.
Nuclear Data Review and Evaluation of beta-decay reactions
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 from beta-decay reactions 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 for beta-decay 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.
Development of A Digital Imaging System for Beam Diagnostics
Advisors: Dr. Yujong Kim, and Dr. Ying Wu
The Duke Free Electron Laser Laboratory (DFELL) operates and
continues to develop accelerator based light source facilities,
including the storage ring based UV-VUV FEL, High Intensity Gamma
Source (HIGS), and an infrared FEL. Many important electron beam
properties, such its size, position, and emittance need to be
measured using a high-quality digital imaging system. In addition,
this system can be used as a diagnostic tool for the
free-electron laser beam. A research program will be in place to
develop such an image system. The REU student will be involved
in designing and setting up the optical system with lens, mirrors,
and apertures, in testing and adjusting the digital camera, and
in integrating the both systems with computer controls.
We invite a REU student who is familiar with PC/Window and PC/Linux
systems and has some basic programming skills.
High Precision Alignment of Accelerators Using A Laser Interferometer
Advisors: Mark Emamian, and Dr. Ying Wu
The REU student will assist the Duke FEL alignment/mechanical engineer
in the high precision alignment of part of the magnetic optics of our
1.2 GeV storage ring and the survey and alignment of our booster
synchrotron utilizing a Leica laser tracker alignment system. This system
operates on the principle of spherical coordinate measurements system
with the aid of a laser interferometer. The student will also help our
engineers in monitoring minute settlements and vibrations on and around
the floor of the booster vault and the optical stations for the
free-electron laser cavity to better characterize the mechanical
stability of the floor. He/she will gain hands on experience on a
variety of our sophisticate tools such as a laser tracker,
ultra sensitive vibration sensors and other optical alignment instruments.
Background Studies for a Coherent Neutrino-Nucleus Scattering Experimen
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 an experiment at a high
flux stopped-pion neutrino source such as the Spallation Neutron
Source in Tennessee.
This project will involve work on simulation studies to understand
whether the signal of tiny neutrino-induced recoils in new detector
technology will be observable above various backgrounds. The student
will also help with preparation for a measurement of beam-related
background neutrons at the SNS using scintillation detectors, and will
analyze data from this measurement. The student will gain experience
with a variety of simulation and data analysis software tools.