REU Projects for 2001
Nuclear Astrophysics
Advisors: Art Champagne and Christian IlliadisOur basic nuclear astrophysics program interests are in the areas of stellar evolution and explosions. In both cases, we look at particular nuclear signatures that can be observed and often find that some further work must be done before a connection can be made between these nuclear observables and something in the interior of a star. For example, we're looking at the origin of the Na (sodium) and Al (aluminum) abundance anomalies in globular clusters that hint at some modification of basic stellar structure. However, in order to make the connection with a stellar model, we have to measure the rates of some key reactions (for example, 26Mg(p,gamma)). Another reaction, 14N(p,gamma), plays a role in age estimates of clusters and has a big impact on structure and nucleosynthesis (because it limits the rate of energy production). We believe that the current rate used in models is 40% too large, but we have to be more quantitative than that.
First Experiments at the LENA Facility - Stellar Evolution Reaction Rates
To do these astrophysically relevant measurements, we've built LENA (Laboratory for Experimental Nuclear Astrophysics), which is one of 3 purpose-built facilities in the world. It consists of 2 small accelerators and construction is nearly complete. In addition, we are building a detector array to count gamma-rays from the above mentioned reaction rate experiments.
During the summer of 2001, the LENA facility will turn on and the first beams will be analyzed. It is likely that we will be troubleshooting the accelerator system and fixing whatever bugs come along as we try to get the first measurement going. We will have a small gamma-ray detector array in place, but we're switching to a new hardware standard for the readout electronics (VME from CAMAC) and that will take some time to figure out. The data acquisition software is written in Java and this is what is used to communicate with the VME modules. This is an area that still needs quite a bit of work.
Explosive Nucleosynthesis Reaction Studies for Novae
On the explosions side, we have a program underway to do realistic models of novae. A nova is a thermonuclear explosion triggered when mass is transferred from a star onto the surface of a white dwarf. We have to explain the observed features of the explosion, such as the light curve (luminosity vs. time), and spectral lines. We hope to be doing measurements at TUNL to see if novae can produce certain radioactive nuclei that could be observed with gamma-ray satellites. There is work to be done, both on the theoretical side (predicting the isotopes made in the explosion) and the experimental.
Few Nucleon Studies of the Strong Interaction
Advisors: Hugon Karwowski and Ed LudwigTUNL has a windowless high density recirculating gas-jet target for use in experiments where solid targets become problematic. Especially at low energies, solid targets suffer from problems such as substantial energy loss effects and background effects deriving from the backing material of thin targets. Static gas cells have been used as alternatives to alleviate these problems, but at very low energies energy losses through the cell foil, in addition to energy and angle straggling, preclude the use of such cells. A windowless high density gas jet has none of these problems, and allows high precision measurements of cross sections and polarization observables at low energies.
When running the target with expensive gasses or with high flow-rates, the gas consumption becomes expensive. We are going to install a gas compressor / gas-cleaning recirculation system, that will greatly cut down on our gas consumption. The project would involve helping graduate students design, build, and test parts of this system, including all the relevant monitoring apparatus. The REU student would be particularly involved in the development of the safety interlocks, and testing of the resulting purity of the recirculated gas.
Cryogenic Polarized Targets for Investigations of the Nucleus
Advisors: David Haase and Diana Markoff The forces between nucleons depend strongly on the relative spin orientations of the particles. These forces can be studied in experiments that use a beam of polarized neutrons (that is the majority of the magnetic moments are aligned in the same direction) and a target in which the nuclei are similarly aligned. The Polarized Target Group at TUNL produces such targets using low temperatures (T < 1 kelvin), high magnetic fields (2.5 tesla) and some black magic with microwaves.We are looking for two REU students that would like to spend long hours taking data for a polarized-n-on-polarized-deuteron measurement, help in the testing of a new target refrigerator (0.2 kelvin) and test drive a new 2.5 tesla superconducting magnet system. By the end of the summer the student will have learned a lot about nuclear and solid state physics and much practical cryogenics which can be applied in many fields of science and technology.
Development of A Low-Energy Electron Spectrometer
Advisor: Calvin HowellThe 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.
Development of Real-time Data Acquisition System
Advisor: Calvin HowellExperimental nuclear physics research requires high-speed real-time data acquisition (DAQ) systems. As the complexity of experimental apparatuses and the sophistication of experimental techniques are increased to gain deeper insights about nuclear phenomena, greater demands are placed on the data acquisition rates and the data management capabilities of data acquisition systems. Modern data acquisition systems used for nuclear physics research are built from high-speed intelligent network components. The basic components in such DAQ systems are the run controller (RC), the readout controller (ROC), the event builder (EB), the data distributor (DD), the event recorder (ER) and the event analyzer (EA). The RC provides the user interface for configuring the DAQ and starting and stopping data accumulation. The ROCs read the raw data words from the digitizers and counters in the hardware crates and ships them to the EB. The EB collects event fragments from the ROCs and puts them together to make complete events. The events are distributed to the ER for storage and to the online EA for data inspection by the researchers.
This summer we will complete the development and installation of a modern network based DAQ system at the TUNL. The system will use two computers that communicate with each other over a dedicated network using standard Internet protocol. The ROC program will run on a single-board computer that resides in a VME crate. Both CAMAC and VME digitizers and counters will be used. The ROC is interfaced with CAMAC crates using a special VME-based CAMAC branch driver module. The RC, EB, DD, ER and EA programs will run on the host DAQ computer. In the first release of the DAQ, the host computers will be Ultra workstations by Sun Microsystems. If time permits, the system will be ported to PCs running the Linux operating system. The code for the DAQ is written mostly in C and FORTRAN. This project requires one REU student. The student will write software for the online data analyzer and will help develop software drivers that interface hardware to the ROCs. The student should have some experience in one computer programming language, either C, C++ or FORTRAN.
Detector Array Simulations
Advisor: John KelleyMany nuclear physics experiments consist of a beam of incoming particles impinging on a target material and the particles that are scattered or produced in the target are then counted in detectors. In order to interpret the data recorded in the detectors, the experimenter must understand the properties and limitations of the device counting the particles. Quantitatively, this problem becomes one of estimating the detector response function, which includes the detector efficiency. The detector response function, e.g. for gamma-ray detectors, is sensitive to the detector geometry and the energy of the detected gamma rays.
This project will involve acquiring familiarity with existing, internationally known, computer program codes that simulate the interaction of gamma rays with various materials. The student will develop the computer program input data to simulate the interaction of gamma rays in different detector configurations relevant to the experiments performed here at TUNL. The student will then create an on-line user's guide that will provide TUNL scientists with a simplified method of generating detector simulations and estimating detector efficiencies.
An additional component of this project is connected to the KamLAND collaboration (Japan) in which TUNL participates. The KamLAND detector consists of a large volume of scintillation fluid that detects neutrinos. Because the photo-multiplier tubes that detect the neutrino-induced scintillations are sensitive to the earth's magnetic fields, it has been necessary to construct a large array of coils that surrounds the experimental setup with the aim of canceling the earth's magnetic field to produce a "nearly" magnetic-field free region. It is necessary to verify that the net magnetic-fields will not affect the performance of the detector.
Cosmic-Ray Detectors
Advisor: Werner TornowPrimary cosmic rays are particles with very high energies whose origins in the cosmos are still largely unknown. They consist mainly of energetic nuclei which travel to us through large cosmic distances both within our galaxy and in intergalactic space. The energies of these particles are huge. The detectable cosmic rays begin at energies of about 1 GeV (109 eV) and extend up to 1020 eV. The highest energy cosmic ray detected on Earth had an energy of about 50 J - a macroscopic energy carried by a microscopic particle. The lower cut-off energy of about 1 GeV is due to the outward flow of the solar wind which is too strong to allow lower energy particles to penetrate the heliosphere. The wide energy spectrum of cosmic rays is believed to result from acceleration processes involving progressive acceleration in magnetic fields such as are found in supernova shells. When the primary comic rays arrive at our atmosphere, they interact with atmospheric nuclei and produce cascades of particles. The most important components at ground level are:
ONE student will setup and study a Cerenkov-light based cosmic-ray detector in the TUNL building using a 20" diameter photomultiplier tube in a water-filled tank. A SECOND student will do the same in the adjacent main Physics building. If the detectors operate successfully, their output signals will be coupled to study coincidence events.
These cosmic-ray detectors are considered as prototypes for a possible school-based network in the Triangle area.
Radiative Capture Group - TUNL
Advisors: Henry Weller and John KelleyOne of the projects of the Radiative Capture group involves developing experiments at the High Intensity Gamma Ray Source (HIGS) located in the Duke Free Electron Laser Laboratory. In the early part of the summer, the HIGS collaboration will make measurements on the photodisintegration of the deuteron using the 100% linearly polarized gamma-ray beam of HIGS. This is an important experiment both for BIG BANG nucleosynthesis (at near threshold energies) and for determining the value of the "GDH Sum Rule" for the deuteron. The latter quantity is ultimately connected to the internal (quark) structure of the nucleons. Following this, we will begin assembly of an experiment to determine the "polarizabilities" of the nucleons at HIGS. The detectors for this experiment need to be assembled, tested, calibrated, and installed. In addition, a device to remotely insert different targets needs to be designed, constructed and installed.
REU students will be expected to participate in all aspects of this project, but will concentrate on the development of the "new" experiment. In addition to the hardware development, computer simulations of various aspects of the experiment will be done under the guidance of faculty, post-docs, and graduate students. REU students will also be invited to attend weekly lunch meetings of the Capture Group, where progress will be discussed and reviewed.