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JOHN E. EDWARDS ACCELERATOR LABORATORY INTRODUCTION The John E. Edwards Accelerator Laboratory was established when Ohio University received a one-million dollar grant from the Atomic Energy Commission in the late sixties for an accelerator. As a condition of the grant, the University was committed to maintain the accelerator, which it has done, therefore, enabling original work and an excellent facility to be developed. As other accelerators have been closed down across the country, we find ourselves in a unique position. We have the only MeV ion accelerator in a college or university in Ohio. Many of our individual capabilities are now not available anywhere else in the U.S. The 4.5 million volt tandem accelerator is still being used today and the breadth of research covered now includes materials science as well as nuclear physics. The work encompasses many areas of both pure and applied research. In the field of nuclear physics, the work has covered fields as diverse as medicine and basic nuclear physics. Research has been done for National Institute of Health and others in support of medical uses of neutrons. For many years, work has been done here for the U.S. fusion reactor program. The accelerator and its support facilities are used frequently to test and calibrate particle detection systems used at other higher energy accelerators both in the U.S. and other countries. Fundamental research into the nuclear shell model, a key to our understanding to nucleus of the atom, has been part of the research program. In addition to work solely originated at Ohio University, and because of the unique capabilities found in the laboratory, collaborations are often sought with us by workers at other U.S. universities and national laboratories. Visiting researchers have become a regular feature in our laboratory. With the founding in 1994 of the W.M. Keck Thin Film Analysis Facility, the materials science capabilities of the Accelerator Laboratory have been greatly extended. The materials science research that is performed includes work on diamond films for electronic applications, solar cell materials, materials for fusion reactors and light weight materials for aerospace applications, in addition to basic research to broaden our understanding of these materials. Much of this work is performed through interdisciplinary collaborations at Ohio University involving the Condensed Matter and Surface Science Program (CMSS) or the Center for Advanced Materials Processing (CAMP). Both CMSS and CAMP involve faculty from both the College of Arts and Sciences and the College of Engineering, including the departments of Physics and Astronomy, Chemistry, and Chemical, Electrical and Mechanical Engineering. Just as in the area of nuclear physics, collaborations are undertaken with U.S. universities and national laboratories who wish to use our facilities. The range of materials analysis capabilities here are not found in any other U.S. universities or national laboratories. This facility is now unique in the United States in the extent of both the nuclear physics and materials science research that may be undertaken. Please feel free to contact any of the faculty listed below if you have any questions about the work done in the Accelerator Laboratory. We hope you enjoyed your visit.
NUCLEAR PHYSICS RESEARCH AT OHIO UNIVERSITY History Experimental nuclear physics research at Ohio University began in 1960. Through a grant from the U.S. Atomic Energy Commission, a 150 keV Cockcroft-Walton nuclear accelerator manufactured by Texas Nuclear Corporation was obtained, and this served as the principal research instrument of the Ohio University Radiation Laboratory. This laboratory was housed in the old Dailey garage on Richland Avenue where the new 682 bypass is now located. Many successful research projects were carried out in this laboratory, and the results have been published in numerous scientific journals. With the growth of the physics department in the 1960's, the Radiation Laboratory became inadequate to fulfill the requirements of larger numbers of physics graduate students doing increasingly sophisticated research projects. A proposal for a new 4.5 million volt high current accelerator was submitted to the Atomic Energy Commission in 1967 and Ohio University received $1,000,000 for its purchase. The new accelerator was manufactured by High Voltage Engineering Corporation of Burlington, Massachusetts and is the only one like it in the country. It is a tandem Van de Graaff accelerator which is used to accelerate atomic particles to energies up to 9 MeV (14% of the speed of light) via a large dome charged to high voltage by a moving belt in a manner similar to the charge a person received by walking across a rug on a dry day. This accelerator is unique in that the charged belt is situated perpendicular to the accelerator beam which allows for unusually high currents of atomic particles to be produced. In the years since the O.U. accelerator has been in operation, one other accelerator of this general type has been manufactured and is located in Athens, Greece. These two machines are the only T-shaped tandem Van de Graaff accelerators in the world. The Ohio University Accelerator Laboratory (O.U.A.L.), named as the John E. Edwards Accelerator Laboratory, is located on the Athens campus across from the Clippinger research laboratories in the hillside behind Gordy Hall. The original laboratory building was constructed in 1967 at a cost of $337,288. In 1994, it was expanded to 17,400 square feet with most of the experimental areas located underground. The accelerator itself took 18 months to manufacture and over 10 months to install with the first experiments starting in 1971. The Research Program Many types of nuclear research are carried out at the laboratory, but the main emphasis has been on studies of the neutron-nucleus interaction, i.e., the study of the nuclear force and the structure of the atomic nucleus using neutrons as probes. Neutrons, which are a constituent of the atomic nucleus, are generated in the laboratory via nuclear reactions. For instance, high energy protons from the Van de Graaff accelerator are passed through tritium gas, which is an isotope of normal hydrogen, and monoenergetic neutrons up to 8 million electron-volts are produced in collisions between the protons and tritium gas. High intensities of neutrons can be generated in this way. These neutrons are then scattered from various target materials, and their scattering patterns, called cross sections, are measured and analyzed. It is from the analysis of the cross sections that nuclear structure information of the target material can be derived. Part of this research is funded by the U.S. Department of Energy to study the interactions of neutrons with light elements such as lithium, boron and carbon which will be utilized as shielding components of fusion reactor designs of the future. This work is very much related to finding solutions to the problems of safe and abundant sources of energy for the future. Another part of the research is funded by the National Science Foundation and involves the analysis of neutron-nucleus interaction data to gain better theoretical understanding of the nuclear force. Nuclear models are used to predict scattering patterns and then refined to better explain the results gained from actual experiments. Certain applied areas of research have also been studied such as the production of short-lived (radioactive) isotopes for use in medical diagnoses, production of very high neutron intensity to observe possible sputtering effects (material damage from intense radiation) and proton-induced x-ray emission (PIXE) with a microprobe beam which can detect very minute traces of chemical elements as might be required in a scientific criminal investigation. Beginning in 1978, a portion of the effort at the Accelerator Laboratory was directed toward the investigation of new methods in the treatment of cancer. The program was started with the assistance of the Ohio University College of Osteopathic Medicine and has subsequently been supported by the National Cancer Institute of the Department of Health and Human Services. The idea behind this research is that radiotherapy with neutron beams appears to be superior to conventional x-ray and Cobalt therapy in the treatment of certain types of cancer. There are no plans to make Ohio University a clinical center for the treatment of cancer patients, but the unique research capabilities of this laboratory make it an appropriate place to study the basic interaction between neutrons and those elements (carbon, oxygen and nitrogen) which make up the bulk of malignant tissue. New Developments Looking to the future, the laboratory is expanding its current program of neutron cross section measurements of the elements and has significantly upgraded the sophisticated equipment necessary to remain at "state-of-the-art". In 1980, the first architectural change in the building was made since its construction in 1967. A new "time-of-flight tunnel" was placed deeply underground in the vacant land just east of the building. This addition--together with some sophisticated new research equipment--has extended the capability of the laboratory by a significant amount. Just as a higher power microscope gives the botanist a clearer look at the cellular structure of plant tissue, this new facility provides the higher magnification which we need for a clearer look at the vastly smaller structure of atomic nuclei. The laboratory is also well equipped for study of (n,z) reactions, that is, processes in which a neutron strikes a nucleus and releases a charged particle. These (n,z) reactions are of importance in radiation therapy for cancer as well as fusion reactor design. The combination of a high current accelerator, a long neutron flight path in the new tunnel, and a pair of "state-of-the-art" (n,z) spectrometers makes it possible to study at Ohio University problems which include questions as fundamental as how nuclei are held together and as applied as measuring numbers needed for implementing cancer therapy. In physics, as in so many aspects of contemporary life, the computer is a necessity--not a luxury. This laboratory is equipped with a wide variety of computer facilities, most of which were designed and constructed by our own staff. A highly sophisticated data acquisition computer, which was conceived, designed, constructed and programmed in-house by Mr. Donald Carter and his undergraduate assistants, is the heart of the operation. It is directly interfaced to Carter's latest computer--the OU32--a fast, 32-bit word machine with eight independent general purpose registers and auxiliary disk storage. Both of these computers are interfaced to the central university computer as well as four commercially built "in house" computers. Several additional "smart" terminals are located throughout the laboratory to give the researchers the best available computational capability. Impact Because of the capabilities of O.U.A.L., many researchers come from other universities and the national laboratories to do experiments at the laboratory and to collaborate with researchers here. Recently, visiting scientists from Oak Ridge National Laboratory, Los Alamos Scientific Laboratory, Lawrence Livermore Laboratory and Argonne National Laboratory, Ohio State, Kent State and Indiana Universities, UCLA and the Memorial Sloane-Kettering Cancer Research Center have taken advantage of the special research capabilities of the Ohio University laboratory. A measure of the international stature of the laboratory can be found in the fact that scientists from Vienna, Tokyo, Warsaw, Peking and Edinburgh have joined the O.U.A.L. staff for extended periods. Casual visits of scientists from many countries--but particularly China, Germany and France--are a common feature of life at the Accelerator Laboratory. O.U.A.L. has been very prolific in the number of scientific articles published in leading research journals in the field with typically 10-15 major articles per year. The laboratory is represented - frequently with invited papers - at virtually all national and international conferences dealing with neutron physics and other aspects of nuclear physics. In 1984, Ohio University served as host to the International Conference on Neutron-Nucleus Collisions at Burr Oak State Park. In 1992, 1993 and 1994, the Burr Oak facilities were again used for a series of one-day retreats on current research topics. The Retreats started as a joint OU-OSU informal get-together, but their popularity has grown, and the most recent retreat had visitors from several regional research universities. As of June 1994, 43 Ph.D. dissertations have been written on experimental nuclear physics research at Ohio University. Graduates are located at major national laboratories, leading research universities, small colleges and major medical research facilities. The present laboratory staff include five permanent faculty, two or three postdoctoral research associates, two professional engineers, one secretary and about a dozen graduate/undergraduate students working on various research projects. Through the years, the laboratory has been a source of considerable outside income to the University through research grants from agencies such as the former Atomic Energy Commission, which provided the initial money for the accelerator, the former U.S. Energy Research and Development Administration, the present U.S. Department of Energy, the National Science Foundation and the National Cancer Institute as well as other smaller sources. Since 1973 over $11,000,000 have been awarded to faculty and staff of the laboratory for research in nuclear physics. Current funding levels are over $600,000 per year for the experimental program while our colleagues in nuclear theory bring in another $180,000 from their related but independent research grants. Since the late 1980's, it has been clear that much of the future of nuclear physics has been moving away from the types of problems that we had been addressing with our Tandem Van de Graaff facility and toward those facilities that had been previously considered to be parts of Intermediate Energy and High Energy Physics communities. In response to this trend, faculty at O.U.A.L. have moved with the tide, and we now have important programs at Los Alamos, Fermilab, Brookhaven National Laboratory, Indiana University Cyclotron Facility and other leading research facilities. To assist with the adjustment to these changing times, Ohio University has established the Institute of Nuclear and Particle Physics to include both theorists and experimentalists, both Van de Graaff experiments and Fermilab experiments. The Institute is an administrative structure that enables the faculty to start new research initiatives, invite visiting scientists, sponsor Burr Oak retreats and otherwise remain at the leading edge of our rapidly changing field. All of this growth, progress and change has not been without its problems. For many years, a critical problem was the severe overcrowding of the Edwards Accelerator Laboratory. The recent renovation of the building has not only relieved the overcrowding, it has provided an opportunity for a second career for our venerable accelerator, materials science. MATERIALS SCIENCE IN THE ACCELERATOR LABORATORY History In 1987 the Board of Regents of the State of Ohio recognized the Ohio University program in Condensed Matter and Surface Science (CMSS) for an Academic Challenge grant. The interdisciplinary CMSS program has been administered by physics faculty but has major involvement from the Chemistry, Electrical, Mechanical and Chemical Engineering departments. To date, the program has received funding of well over $2,000,000. In 1992, the final year of the Academic Challenge grant, the CMSS program's funding was absorbed into the general funding of the University. The funding level has been maintained at the present level, as it has been for all other successful Academic Challenge programs. The CMSS program has provided two new faculty positions in physics, new postdoctoral and graduate student appointments, and significant start-up funds for the new faculty as well as over $400,000 in equipment to support the projects of its faculty members. The accelerator laboratory was recognized as a key facility for materials research at Ohio University. One the faculty positions in CMSS was for someone with a background in the use of accelerators and materials science to exploit the capabilities of the accelerator and make them available to other members of CMSS. The accelerator is now a major component of the CMSS program. Ion beams in the range 1 to 10 million electron volts (MeV) are being used in the analysis and modification of materials. The accelerator has been used extensively by members of the CMSS group to study hydrogen in diamond, the stoichiometry of high superconducting materials, and the composition of chalcogenide thin films. The accelerator has also been used to modify oxidation barrier coatings on polyimides used in spacecraft. In addition to work from Ohio University, collaborations have been developed with U.S. and foreign universities, national laboratories and private companies who need access to a facility such as this. New Developments Chemical and Mechanical Engineering were successful in receiving a peer reviewed competitive grant of $400,000 from the W.M Keck Foundation for an integrated ultra high vacuum (UHV) thin film deposition and characterization facility. By the provision of a UHV integrated facility in the accelerator laboratory, we now have access to several analysis and deposition facilities operating under highly-controlled environments. The most difficult task faced by a material scientist is knowing how the environment can affect the material being made or analyzed, and if in moving a sample from one facility to another, e.g., deposition to analysis, a change has taken place. This is the only facility of its type in a U.S. university or national laboratory. The W.M. Keck Thin Film Analysis Facility integrates several techniques within a set of coupled UHV chambers to provide analysis and preparation facilities for research on surfaces and thin films. Rutherford Backscattering Spectroscopy (RBS), Nuclear Reaction Analysis (NRA), Elastic Recoil Spectroscopy (ERS) and Proton-Induced X-Ray Emission (PIXE) may be used directly on materials problems at UHV or to support other techniques by providing accurate, repeatable and standardless calibrations. These techniques can be applied in conjunction with ion channeling in a six-axis goniometer designed to allow transmission channeling with ERS. Also present in the base of the MeV ion scattering chamber will be facilities for physical vapor deposition of thin films. Provision is being made for unbalanced magnetron sputtering and electron beam evaporation. The chamber will also have provision for Photo-Emission Electron Microscopy (PEEM) and Low Energy Electron Diffraction (LEED). Samples may be transported into additional chambers via a UHV sample transfer system. In one of the additional chambers will be Auger Electron Spectroscopy (AES) and X-Ray Photon Spectroscopy (XPS). In another connected chamber will be facilities for chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD). There will also be provision for ion beam-enhanced deposition. The key to the successful exploitation of these analytical techniques is their integration with the deposition techniques within one UHV facility. Under conventional high vacuum conditions, where the pressure is one billionth of the standard atmospheric pressure, the arrival rate of background gas molecules is similar to or exceeds the rate of arrival of material for the deposited film, about one layer of molecules per second. Under UHV conditions, however, where the pressure is a thousand times lower, the arrival rate of material making the required film typically exceeds the gas arrival rate by 100 to 10,000 times, for the growth techniques used by the CMSS faculty. This is especially critical for materials sensitive to hydrogen, oxygen, water vapor or hydrocarbons, e.g., Ti, Al, Mg. What makes this facility unique is the provision of the MeV ion beam analysis techniques with the more usual electron spectroscopy and diffraction techniques. This will enable structural, composition and chemical information to be gathered efficiently on a sample without exposure to atmosphere in order to achieve the analysis. Among the proposed research for this facility is extensive work on diamond. With this facility we will be able to study nucleation of diamond by bias-enhanced nucleation. For this work, it is essential that early stages of the nucleation process be examined in a continuous vacuum environment so that the surface of the substrate exposed to the bias nucleation process can be examined by a variety of techniques. In addition to nucleation studies, it is proposed to study the trapping of hydrogen in diamond. Hydrogen is the major impurity in both natural and synthetic diamond. It is proposed to use ERS ion channeling to locate the position of the trapped hydrogen in the diamond lattice. The commitment of Ohio University to materials research was recently emphasized by the establishment by the Board of Trustees of Ohio University of a Center for Advanced Materials Processing (CAMP). CAMP has located a UHV unbalanced magnetron sputtering facility in the Accelerator Laboratory. This will enable in-situ analysis of deposited coatings under UHV conditions. Light-weight high-strength aerospace alloys of aluminum, magnesium and titanium will be deposited in this new facility. It has been designed to enable in-situMeV ion beam analysis of deposited coatings. Of particular concern is how to prevent oxygen and hydrogen from being incorporated in these alloys. The analysis will be done using elastic resonance-enhanced backscattering for oxygen and ERS for hydrogen. This will be the first time these alloys will have been deposited by unbalanced magnetron sputtering in UHV conditions. SUMMARY It is the nature of university-based research equipment that it must also provide for future research needs. The facilities of the Edwards Accelerator Laboratory are unique and have been well maintained by Ohio University. The scientific requirements of such a facility are not absolutely predictable but the development of new materials technologies will require such facilities as these in order to characterize the new materials and to develop new material deposition techniques. It is an essential feature of a university with graduate programs that it must be able to train research scientists and engineers for their future careers. We believe that the materials research of the future will require facilities such as these and that industrial development of new materials technologies will depend on having scientists who have been trained with such facilities. FIGURE CAPTIONS Fig. 1 Cross sectional view of the Ohio University Tandem Van de Graaff Accelerator. Fig. 2 first floor plan view of the Edwards Accelerator Laboratory including the recent addition to the building. |
