Student Abstracts: Physics at ANL

Improvements and Additions to Support Systems of Atlas ECR Ion Sources. THOMAS CECIL (Murray State University, Murray, KY 42071) RICK VONDRASEK (Argonne National Laboratory, Argonne, IL 60439).
The Atlas facility is a national user facility that provides heavy-ion beams for use in a wide variety of experiments. The facility consists of two ion injector sites, booster linac sites, and several target experimental sites. The facility is capable of producing ion beams from as light as helium to as heavy as Uranium in high charge states. The starting point for any ion beam is the ion source. The positive ion injector has two Electron Cyclotron Resonance ion sources (ECRI and ECRII). Keeping the ECR sources properly running requires numerous support systems. Some of these systems include cooling water, power supplies, support gas supply, and safety controls. My project this summer will involve the upgrade and maintenance of several of these systems. Projects currently in progress are 1) an expanded electrical safety cage for ECRII, 2) a more robust deionized cooling water system for ECRI, and 3) a support gas handling system for both ECR sources. The safety cage on ECRII is being expanded to ensure complete enclosure of the source with the addition of a capture key lock. An increase of cooling power from the existing 45 kW to 125 kW for ECRI involves replacing the existing cooling-water circulation pump and heat exchanger, and installing new water circulation piping. A gas handling system for both ECR sources is to be designed and built. The system will allow for alternating between three support gases without breaking the vacuum of the source.

Construction of a Large Gas-cell Catcher Prototype for the Collection of Fast-recoiling Fragmentation Products. ADAM FRANKEL (Cornell University, Ithaca, NY 60089) GUY SAVARD (Argonne National Laboratory, Argonne, IL 60439).
By incorporating a large gas-cell catcher into a high-power version of a fragmentation-based ISOL, it will be possible to thermalize and extract ions for post-acceleration and thereby attain simultaneously the quality and precise energy of an ISOL system and the universality and short delay time of a fragmentation-based system. A prototype gas-cell catcher along with the circuit that controls it has been constructed for this purpose and preliminary tests of the electronics have been performed. It has been determined that the electronic circuit of the accelerating section of the gas cell behaves according to the specifications (determined from simulations) that will be necessary for it to perform its intended function. The next step will be to test the circuit of the focusing section. Following that, some tests of extraction efficiency and delay time will be performed with the prototype using low-energy ions produced at the ATLAS facility at Argonne National Laboratory. Finally, the prototype will be tested at a higher energy behind the fragment separator at GSI in Germany to determine its viability as a new piece of technology for a next generation radioactive beam facility called RIA.

Ultra-sensitive Atom Trap Trace Analysis of Calcium Isotopes. WILLIAM GRIMES (Monmouth College, Monmouth, IL 61462) ZHENG-TIAN LU (Argonne National Laboratory, Argonne, IL 60439).
Atom Trap Trace Analysis (ATTA) is an ultra-sensitive method capable of trapping, detecting and counting single atoms of long-lived radioactive trace isotopes. The method, based on a magneto-optical trap has been used to trap isotopes of krypton and calcium. 81Kr has a half-life of 2.3 x105 years (and an abundance of 6x10-13) making it the ideal isotope for dating ancient ground water and ice on the order of one million years. 41Ca, with a half-life of 1.03x105 years and an isotopic abundance of ~10-15, has promising applications as a biomedical tool to directly measure the loss of bone mass (osteoporosis). Counting 41Ca ratios in samples of old bone could lead to the dating of archeological findings on the order of 105 years, improving our understanding on the early origins of life. These methods are relatively new and much research is concurring to provide a practical system for real-life applications. This summer I have worked on a daily basis with the ATTA Ca setup. We have been successful in producing a trap sensitive enough to detect single atoms of all stable calcium isotopes. I spent my time working to improve the sensitivity of the trap and therefore increasing the probability of detecting single atoms of the extremely rare isotope, 41Ca. I have been working with our detection system, to continually improve the signal to noise ratio of the fluorescence of a single atom.

. SEAN GRULLON (Florida International University, Miami, FL 33199) TENG LEK KHOO (Argonne National Laboratory, Argonne, IL 60439).
Reconstructing Total Photon Energy and direction in a Germanium Detector. SEAN GRULLON (Florida International University, Miami, FL, 33199) TENG LEK KHOO (Physics Division 203-F145, Argonne, IL, 60439) A photon entering a detector and interacting at different points can be reconstructed using a computer program. The algorithm in the program was made to determine all the valid incoming photon energies and display them on a histogram to give a spectrum. The program tracks gamma rays from specific location and rejects photons not coming from a radioactive source at a specified location. It is important to track the incoming photons and reject the dominant background photons coming from a location other than the radioactive source. The program was done using ROOT, a new data acquisition, visualization, and analysis package with an included C++ interpreter. Artificial data was created with this package as well to test the abilities of the program. The program takes the correctly identified incoming photons, graphs them on a histogram, and graphs the rejected photons on another histogram. The next step in for the program is to analyze data created in a Monte Carlo simulation, and eventually be used in conjunction with an actual experiment.

Analysis of the Characteristics of the Electron Cloud Build-Up in High Energy Particle Accelerators Using the Java Programming Language.. LAURA LOIACONO (Loyola University Chicago, Chicago, IL 60626) DR. KATHERINE HARKAY (Argonne National Laboratory, Argonne, IL 60439).
A phenomenon, known as the "Electron Cloud Effect", has become important for accelerator physicists to understand in an effort to increase the efficiency and quality of particle beams. A result of the photoelectric effect, the "electron cloud" is comprised of photo- and secondary electrons that can interfere with an electron or positron particle beam circulating in the storage chamber. At the Advanced Photon Source (APS) at Argonne National Laboratory, data have been collected on the characteristics of this electron cloud using detectors designed and constructed by researchers at the APS. The data show high densities of electrons comprising the cloud under specific conditions. One theory that suggests that this phenomenon can be explained by a resonant electromagnetic interaction between electrons in the cloud and the charged particle beam, known as "beam-induced multipacting", only partially accounts for the data. In an effort to fully explain the high densities of cloud electrons shown in the data, an "alternate resonance" theory was developed that suggests the secondary electrons play an important role in the resonant interactions. To determine validity of the latter theory, several computer programs that provide a quantitative analysis of the cloud-beam interactions were developed. By examining the energy imparted to the cloud electrons by the charged particle beam and their resulting motion, resonant beam-cloud interactions can be determined. Preliminary results suggest that an alternate resonance condition among secondary electrons exists in the storage ring at the APS for a variety of beam parameters.

Experimental setup for Zircaloy Fuel Rod Cladding Experiments; Spike Oxidation Kinetics and Auto-ignition.. CASSIDY LUDLOW (Lafayette College, Easton, PA 18042) KEN NATESAN (Argonne National Laboratory, Argonne, IL 60439).
With recent terrorist attacks, concern about the safety of the nuclear industry is understandable. Because of this, it is important to study the temperature rise, pressure buildup, and possible explosion of uncontrolled spent nuclear fuel in the United States. By simulating the conditions of high temperature (up to 1300 degrees Celsius) and high internal pressure (both from helium gas and expanding ceramic pellets), one can look at the changes that a Zircaloy nuclear fuel cladding undergoes as it approaches burst conditions. This set of experiments, to be carried out in the future, will do just that.

Creating a Strong Electric Field in a High Vacuum. LUKE LUGINBUHL (Illinois State University, Normal, IL 61790) ELAINE SCHULTE (Argonne National Laboratory, Argonne, IL 60439).
As a part of an Electric Dipole Moment (EDM) measurement, a set of high voltage electrodes must be designed and tested. These electrodes (also called field plates) are a prototype of those to be used in a measurement of the atomic EDM of Radium-225 (225Ra). To reduce the amount of unwanted gas molecules, the electrodes are set up in the presence of a high vacuum system. There is a tendency under the conditions of high voltage, small gap length between the field plates, and low pressure to produce electric breakdown, which is an undesirable effect. Electric breakdown occurs when an arc of electricity jumps across the gap between the electrodes dissipating the stored energy in the electric field. The goal of this project is to setup up a strong electric field in a high vacuum system between the prototype field plates. The electric field needs to be extremely stable. Once this is set up without any malfunction, a new set of electric field plates must be designed or the original plates must be modified so the 225Ra can be introduced into the electric field and tested for an Electric Dipole Moment. The electric field was not set up in the given time period because of some unexpected delays. However, the vacuum system worked properly and obtained a pressure of 1.4 x 10-5 Torr. In conclusion, the experiment was successfully setup and is almost ready to establish the electric field between the electrodes.

Ion Release Curves for Isotope Separation On-Line Targets. DANIEL PETERSON (University of Notre Dame, Notre Dame, IN 46556) BRAHIM MUSTAPHA (Argonne National Laboratory, Argonne, IL 60439).
When an isotope is created in an isotope separation on-line (ISOL) target, the time it takes to leave the target is given by the sum of the diffusion and effusion times. The effusion can only be given by a statistical distribution, but the diffusion process can be described by a known formula. A simple parameterization of the effusion time distribution generated by the GEANT-4 simulation of the Radioactive Ion Source Test (RIST) target at CERN was found. Combined with the analytical formula of the diffusion time distribution, the parameterization produced a complete analytical model for the release process. This allowed computerized statistical fits of release data to be performed, replacing the manual fits used in earlier studies. This analytical formula gave the expected statistically relevant fits, which in turn provided values for the release parameters such as the diffusion coefficient and the sticking time for the studied nuclei. These values can be used to predict the release of the same nuclei from different target geometries without building and testing them.

Temperature Calculations for a Rotating Target Wheel Under Intense Beams for Super-Heavy Element Production. JENNIFER WELSH (University of Illinois at Urbana-Champaign, Urbana, IL 61801) JOHN P. GREENE (Argonne National Laboratory, Argonne, IL 60439).
Intense beams are needed in the production of the heaviest elements as a consequence of very small fusion cross sections. Thus, the targets used will have shortened lifetimes as the beam current is increased. When a tightly focused beam hits a stationary target of modest melting point and/or a high sputtering yield material, the target will eventually melt or be destroyed. Using a rotating target wheel can help to overcome target melting and adding a thin covering of a low sputtering rate material will help to protect the target. This allows for higher beam currents to be applied. Using a defocused or a "wobbled" beam can enhance target survival as well. The purpose of the calculations done for this work is to attempt to predict the safe range of beam currents that produce a heat load below the melting point of the target material. Calculations of the target temperature after beam exposure will show the safe limits to which they may be exposed without being destroyed.