Research Interests & History

Since 1984, I have been involved in a number of projects to improve science education for both science majors and the general public. During 1984-1985 while at the University of North Texas, I redesigned the electronics courses and laboratories for nonscience majors. Many of the existing labs emphasized vacuum and discrete component technology while completely ignoring superior and simpler linear integrated circuit technology. Furthermore, many of the lab exercises had little or no educational value. in order to improve the quality of the courses, a complete revision of all material was undertaken and more than twenty thousand dollars of new lab equipment was purchased. I have also been involved in the development of demonstration and video resources for the undergraduate curriculum since 1991 both at the University of North Texas and the United States Military Academy. In particular, I have been involved in upgrading both the freshman engineering physics lab and upper level physics major lab materials. Since 1984, I have also involved in programs to increase the interaction of various physics departments and the general public by both judging local science fairs and by giving physics demonstrations at local area schools. From 1984-1994 I was involved in the University of North Texas’ Annual Physics Olympics. The Physics Olympics is an annual contest between high school students from Texas, Oklahoma, and Arkansas that is held each spring at UNT. Students compete in a wide variety of team contests including a) bridge building, b) mouse car races, c) egg drops, d) Fermi questions, and e) physics problem solving. I was active in both the actual operation of the Physics Olympics as well as being on the rules committee.

Of special interest is the use of accelerators both for teaching advanced undergraduate physics and secondary school students. From 1984-1994, I was involved with Dr. Jerome L. Duggan to provide advanced accelerator and atomic physics labs for visiting student groups from small colleges. The response to these visits were very favorable and several students choose to attend graduate school at UNT. To expand our capabilities, we began developing a dedicated accelerator user facility in 1993 with a $300,000 grant from NSF and over $75,000 worth of equipment contributions from various companies including ORTEC and Tennelec. In addition, we expanded our user base to include both science and nonscience groups from community colleges as well as high school students. During this time, I designed and built several complete student labs including the development of all the written and visual materials that accompanied the labs. Among the labs developed were labs on Rutherford scattering, x-rays, measuring the speed of light using positron annihilation, charged particles in magnetic fields, conservation of momentum, measuring nuclear reactions. By providing instructors with both written and visual material of the labs prior to their arrival in Denton, instructors could choose the experiments that best suited their classes and prepare their students so as to maximize the learning experience. These labs were ran by students from several area high schools and community colleges as well as several colleges from Tennessee, Arkansas, New York, Oklahoma, and Texas. In all, more than 150 students visited the lab during its first year of operation and has the number has continued to increase during 1995.

After joining the physics department faculty at the United States Military Academy in 1994, I began working to develop an accelerator user facility by repairing the department’s 400 kV Van de Graaff accelerator. This machine which had been inoperable since the mid 1980’s is now completely renovated and operating up to terminal potentials of 600 kV. The facility has been expanded from 400 sq ft to 2000 sq ft to enable the accellerator to be used by visiting students from local high schools and colleges. These visits include both short lab classes as well as cooperative student research projects with some of the colleges. Furthermore, the LC-400 Van de Graaff is presently being used by West Point cadets in their senior experimental physics laboratory class as well as in individual research classes in both the physics and electrical engineering departments. During AY1997, I redesigned the senior nuclear physics class for to make extensive hands on use of the LC-400 accelerator. This included labs to measure the size of the nucleus, calibrate magnets using nuclear reactions and a lab to show the equivalence of mass and energy. Although the USMA accelerator facility still requires a considerable capital equipment investment to become a research grade material analysis facility, considerable progress has been made. During the past four years, over $50K in Army Research Office and internal funds along with more than $75K of transfered and donated equipment has been directed toward improving both the teaching and materials characterization capabilities of the facility. Finally, several initiatives are presently underway to continue upgrading the facility in the future. These include proposals to both the Army Office of Graduates and the Army as requested by the Dean for $1.1 million each to upgrade the facility both for teaching and increased research opportunities for departmental faculty, cadets and four new NRC post-docs. Plans to expand the accelerator lab by another 3000 sq ft in order to house a 1.7 MV Tandetron accelerator and beamline has also been submitted.

A new initiative is to use advances in computer networks and the internet to allow larger numbers of visiting students and cadets to use the accelerator facility while ensuring that students work in the small groups that facilitate active learning. In the fall of 1997, a classroom with full networking and internet capability was constructed and eight personnel computers with multichannel analyzer boards and networking cards have been purchased. All eight MCA’s are capable of simultaneous real time data acquisition from a single detector using the USMA network. Software for additional computer MCA’s will be purchased in AY98 to further take advantage of this capability. Presently the accelerator facility is capable of hosting 32 cadets or high school students working in groups of four from a single experiment. Using additional resources already present in the lab, the facility can easily host visiting student groups of 50 or more students. The physics department is also presently involved in both the implementation and investigation of the use of video, hyper-text and hyper-media techniques in conventional classes. Although I think that hyper-text and especially hyper media shows great promise in promoting an active learning environment in the traditional lecture class, I believe that its real impact could be in integrating lecture and laboratory classes together. I am presently interested in the combined use of the LC-400 Van de Graaff accelerator, laser disk technology and computer hyper-media teaching techniques to develop virtual accelerator laboratory material for other schools as well as classes at West Point. Accelerators provide an extremely effective manner for teaching a wide range of basic and advanced physics concepts as well as injecting both enthusiasm and an appreciation for science into students. However, most smaller colleges have access to advanced accelerator experiments only through user facilities such as the ones at UNT and West Point due to equipment costs. In addition, safety considerations involving both radiation and high voltage place additional difficulties on most institutions especially high schools. A third difficulty is budgeting enough class time to perform useful experiments. Even freshman physics labs often take longer than expected and many experiments involving nuclear reactions may take several hours depending on the accelerator beam current, interaction cross sections etc. By using the LC-400 Van de Graaff accelerator to produce a large data base of experimental results, many of these difficulties could be solved. The data could be accessed from a file server in near real data acquisition time or even compressed data acquisition time. By integrating laser video technology, the student could see the physicist actually setting up the experiment just as if they were in the lab. Such an approach has several pedagogical values including interactive learning using hyper media and the ability of the instructor to assign each student their own unique individual data set. Since the student doesn’t have to leave class to perform the experiment, such experiments could be integrated into the actual lecture class and the run time of the experiment adjusted by the instructor to match available class time. Finally, there is no health-safety issues or accelerator equipment operation and maintenance issues involved in the lab.

Since joining the faculty of Tarleton State University in August of 1998, I have began working to develop an accelerator based teaching program at the university using a 400 kV Van de Graaff accelerator which I brought with me from USMA. This program will largely be delayed until the new science building is finished in the spring of 2000.

Since 1985, I have been involved in the characterization of both thin films and bulk materials using ion beam techniques. In addition to collaborating with scientists in academia, this research has also included collaborations with scientists from both private industry and government laboratories including Drs. Mark Anthony, Bruce Gnade, and Joe Keenan of Texas Instruments, Dr. Syd Wilson of Motorola, Dr. Joe Kirchhoff of Charles Evans and Associates and Drs. Robert Pfeffer, J. Derek Demaree and James Hirvonen of the Army Research Laboratory.

Upon coming to West Point in 1994, I began developing a characterization lab in the Department of Physics by repairing and improving their existing 400 kV Van de Graaff accelerator as well as upgrading the nuclear electronics. My primary goal is to develop the capability to analyze materials using both Heavy Ion Backscattering Spectrometry (HIBS) and the related technique of low energy Time-of-Flight Elastic Recoil Detection (TOF-ERD). These techniques developed independently by Drs. Barney Doyle of Sandia National Laboratory and Robert Weller of Vanderbilt University are promising new techniques for detecting extremely low impurity concentrations in semiconductor materials. Furthermore both techniques are very surface sensitive. Both techniques take advantage of the increase in the scattering cross section for both decreasing ion beam energy and increasing atomic number of the incident ion. Thus, a smaller accelerator than that used in conventional IBA techniques is required. My work has centered on improving the energy stability of the machine that will limit its mass resolution and hence its applicability as an analytical tool along with upgrading the vacuum system to allow for surface science measurements. When completed, this machine will be used to compliment existing IBA techniques ant other Army Labs. In particular, TOF-ERD will be used to complement on going research in detecting hydrogen in ferroelectric materials and wide-band gap semiconductors (SiC, GaN, etc.).

A second material research thrust involved a joint collaboration with Dr. Robert Pfeffer of the Physical Sciences Directorate (formerly ETDL) of the Army Research Laboratory and now with Drs. J. Derek Demaree and James Hirvonen of the Weapons and Materials Directorate to develop a Nuclear Reaction Analysis system for profiling hydrogen in metals, semiconductors, and ferroelectric materials using NRA. This research has centered around the designing and building of a beamline, target chamber and detection system for measuring hydrogen in materials using the1H(15N,ag )12C nuclear reaction. Ferroelectric materials show great promise in a) developing uncooled planar arrays for night vision, b) radiation resistant memory devices and c) variable capacitors for integrated circuit technology. The primary methods of producing ferroelectric thin films are sol-gel deposition, pulsed laser deposition, RF sputtering, and CVD. Of these methods sol-gel deposition and CVD are the most useful. Sol-gel deposition is the easiest manner in which to produce high quality laboratory films. CVD, although extremely difficult to set up, is the best for scaling up to industrial sizes and quantities. Both of these methods, however, are know to produce films with significant hydrogen contents. Hydrogen incorporated in bulk ferroelectric crystals has been shown to affect the mobility of domain walls as well as to alter their dielectric spectra. Because of its high diffussivity and reactivity and the hygroscopic nature of perovskites, it may well be that hydrogen contamination is responsible for a good deal of the variability plaguing ferroelectric thin film device structures, commonly attributed to “uncontrolled processing parameters.” Wide band gap materials including SiC and GaN have superior materials properties as compared to conventional silicon devices. Unfortunately, such materials are plagued by materials difficulties in producing materials of sufficient quality to manufacture actual devices. Recent processing techniques to overcome these difficulties including hydrogen cleaving and sputtering of SiC and the use of hydrogen to vary the emission wavelength of GaN lasers all show promise but have the potential for hydrogen contamination with possible detrimental effects. NRA will provide a bulk depth profiling technique for ARL as well as providing a means to standardize data taken at ARL using SIMS. During the summer of 1997, I constructed a new high sensitivity hydrogen detector system at ARL in collaboration with Drs. Hirvone and Demarree of ARL and Drs. Illa and Zimmerman of Alabama A&M as part of an ARO funded project. This detector system uses a coincidence configuration between the first escape peak from the primary gamma ray and the 511 keV escape gamm ray to reject cosmic ray background. It is believed that this detector should also be useful for high sensitvity detection of other light impurities using lower energy (p,g ) reactions with the higher currents obtained by the USMA LC-400 accelerator. During the summer 1998, the system was used to profile hydrogen in a wide variety of materials including wide band gap semiconductors, metals, and polymers in conjunction with the Naval Surface Warfare Center at Carderock. Collaboration with ARL on the effect of boron at grain boundaries in metals using NRA to profile boron is presently underway.

Prior to 1994, I was involved in a variety of research efforts involving both the use and development of material characterization techniques at the University of North Texas This research grew significantly in 1987 with the building of the Ion Beam Modification and Analysis Laboratory (IBMAL) at UNT and again in 1992 with the formation of a National Science Foundation research center : Industry/University Cooperative Research Center for Nanostructural Materials. In the center, a wide range of techniques are available including Rutherford Backscattering Spectrometry (RBS), Particle Induced X-Ray Emission (PIXE), and Accelerator Mass Spectrometry (AMS).

Rutherford Backscattering using both helium and heavy ions was performed on a wide range of samples. Research using X-Ray Photoelectric Spectroscopy (XPS) and RBS with Baylor College of Medicine and Texas Instruments showed that oxide films on dental tooth amalgams were unstable and did not prevent the migration of mercury and other metals as previously thought. RBS and channeling was also performed on buried oxide layers in silicon after annealing to determine crystal quality. This research has demonstrated that Silicon-on-Insulator (SOI) materials formed by high dose oxygen ion implantation and subsequent epitaxial grown silicon layers are far superior to conventional Silicon-on-Sapphire (SOS) materials and therefore SOI is a leading candidate for Very Large Scale Integrated (VLSI) circuit applications. RBS was also performed on ZnS, diamond and GaAs wafers.

Nuclear Reaction Analysis (NRA) was used to detect and profile trace impurities of hydrogen, carbon, and fluorine in materials. NRA was used to detect hydrogen in steel, silicon, diamond, ZnS, and solar cell samples using both the 1H(15N,ag )12C and 1H(19F,ag )16O nuclear reactions. Hydrogen impurity levels to 100 ppm were measured using a BGO detector along with plastic scintillator and fast timing electronics acting as a veto detector to reduce cosmic ray noise. I developed software to enable hydrogen profiling of samples by complete computer control including control of the accelerator. Flexible analysis software was also produced in collaboration with Dr. Grygory Viskelethy of Idaho State University. The results have been compared favorably with depth and sensitivity to low energy ERD for hydrogen profiling. Fluorine profiling using an inverse reaction has also been performed to settle a patent infringement case for 16 Meg DRAMS. Low level carbon concentrations in BaSrTi on Pt on ZrO2 structures have measured using both 12C(p,p)12C nuclear reaction and the 12C(a ,a )12C nuclear reaction at 4.29 MeV.

A unique feature of IBMAL is its stable isotope accelerator mass spectrometry system (AMS). The UNT AMS system which was built in collaboration with Texas Instruments is presently the only stable element accelerator mass spectrometry system in the world. When fully completed this system will allow for part per trillion impurity determination in semiconductors. I was involved in the retrofitting of the existing accelerator hardware, in the design and implementation of the computer control hardware, development of a new ultraclean ion source, and the design and implementation of the primary ion beam rastering and imaging systems. The AMS system has already exceeded the present capabilities of static Secondary ion Mass Spectrometry (SIMS) machines. Samples that have been analyzed by AMS include HgCdTl, GaAs, and Si wafers. Carbon rods from POCO Graphite have also been analyzed for sulfur contamination.

Finally, I have been involved in a wide variety of other research projects including: single event upsets (IBIC) in semiconductors using an extracted helium beam with Dr. Tom Aton of Texas Instruments, X-Ray Fluorescence of steel turbine rotor blades with both synchrotron and radioactive light sources, Particle Induced X-Ray Emission (PIXE) studies of a wide variety of samples and ion implantation with Dr. Joe Kirchhoff of Charles Evans and Associates.

Since 1984, I have been involved in a wide range of experiments in both basic ion-atom interaction physics and in applying this information to solve unique problems in non-traditional physics research fields. My primary interests have been involved in both the study of heavy ion-atom collisions and medium energy collisions (incident ion scaled energy < 1 MeV/u) where present theories of x-ray cross sections for these ion-atom collisions deviate from experimental results. This is due partly to the difficulty of solving this quantum mechanical many body process in a region where the simplyifing assumptions used in fast and slow collisions asymmetrical are no longer available. Additionally, many additional physical process such as charge exchange, multiple ionization and molecular orbital ionization further complicate theoretical interpretation of the data mostly due to a lack of good experimental data caused by instrumentation limits. Theoretical improvements are essential to the development of PIXE on heavy ion microprobes such as the one being funded by the State of Texas and NSF for development at the University of North Texas. Heavy Ion PIXE would provide superior sensitivity to impurities that conventional proton based PIXE systems due to increasing cross section with the atomic number of the incident ion. Unfortunately, the technique is presently not feasible due to poor quantitative capabilities caused by the lack of a comprehensive theory to account for the complex nature of the physical processes including chemical effects, multiple ionization. However, recent improvements in x-ray detector technology for the semiconductor industry may provide the necessary tool to overcome these problems. These new detectors built for scanning electron microscopes have resolutions of less than 10 eV and efficiencies approaching that of Si(Li) detectors. If appropriately modified for ion-atom collisions, these detectors could provide a wealth of experimental results that were previously unattainable and greatly simplify data interpretation.

My research effort at West Point was in measuring L-shell and K-shell x-ray cross sections for 200-600 keV protons on selected targets including among others Fe, Cu, Ni, Rb, U, and Bi. At present, the West Point accelerator has been upgraded and a new multipurpose target chamber and beamline has been designed and constructed by an undergraduate student using equipment donated by both Dr. James Lambert of Georgetown and the Army Material Command as well as equipment purchased through internal funds from an Army Research Office account at West Point. This research was being performed in collaboration with Dr. Richard Wheeler of SUNY Cortland. The work supplements our previous work with 100-225 keV protons as well as that of other researchers at higher proton energies > 750 keV. The previous experimental work has shown that present theoretical methods such as the ECPSSR theory correctly calculate x-ray cross sections for protons on targets at proton energies > 1 MeV. These proton cross section measurements may be of use in future improvements in material characterization using PIXE if lower proton beam energies are required. Such beam energies may be necessary in order to be able to analyze contaminants in thin films without interferences from the bulk material in future semiconductor applications where film thickness will continue to decrease. This is in fact the driving force behind the development of new x-ray detectors where electron beam energies will have to be lowered substantially. Finally, these studies could be greatly expanded with the acquisition of the new high resolution detectors.

Since 1984, I have been involved in numerous other collaborations to measure x-ray production cross sections including research with Drs. R. Wheeler and R. Chaturvedi of the State University of New York at Cortland, Dr. Michael McNeir of the Army Research Laboratory in Aberdeen Maryland, Dr. V. Zoran of the Central Institute for Atomic Physics Research in Bucharest Romania, Dr. R. Mehta of Central Arkansas, Dr. G. Lapicki of East Carolina State University, Dr. Jack Price at the Naval Surface Warfare Laboratory in Silver Springs Maryland, as well as my former colleagues at the University of North Texas. One of the experimental problems that has plagued this field is the development of ultrathin and ultraclean solid targets that could provide single collision measurements. Such targets are essential for accurate charge transfer measurements without x-ray interferences from ppm level trace impurity elements. We developed a new method for producing ultraclean target foils with thickness less than 1 m g/cm2. In the process, we discovered that many previous measurements at Oak Ridge and other facilities were flawed due to the use of peak fitting routines to remove the Na impurity peak from their spectra based on the detector’s response to a characteristic x-ray. X-rays from electron bremsstrahlung also fall in this region of the spectra. The bremsstrahlung peak has a broader width than a characteristic Na x-ray peak. Also, the bremsstrahlung peak differs in its dependence on the incident ion’s energy and atomic number than does the sodium photopeak. Using new windowless Si(Li) x-ray detectors and ultraclean, ultrathin targets, a new method was developed to obtain accurate x-ray cross sections for low energy x-ray energies, < 1.2 keV.

I have also been involved in both the experimental measurement and theoretical prediction of chemical effects (multiple ionization) on x-ray cross section measurements using high resolution Si(Li) c-ray detectors. Si(Li) x-ray detectors and other energy dispersive spectrometers are superior to crystal spectrometers for most x-ray measurements due to their larger efficiencies. However, since they have poorer resolution, Si(Li) detectors are unable to resolve sub-multiplets and other detail information in x-ray spectra. Unfortunately, the probability that an x-ray is produced in a heavy-ion collision depends on the number of electrons available since the atom may also deexcite by auger electron emission. The number of electrons available depends on the kinematics of the collision as well as chemical environment seen by the target atom. Thus, in order to properly compare experimental x-ray cross section measurements to theoretical ionization probabilities, corrections must be made for multiple ionization. In the past, these effects have been ignored or accounted for by simple binary collision techniques that have been shown to be inaccurate. With improved windowless Si(Li) detectors, attempts have been made to extract multiple ionization information from x-ray spectra by noting the shift in the energy of the x-ray photopeak. This is extremely difficult in the case of low energy x-ray peaks due to bremsstrahlung and other artifacts. This work as stated previously is important in the application of the new heavy ion microprobe as PIXE system. Furthermore, with the development of new high efficiency and high resolution detectors, this field shows greatly improved possibilities for important new discoveries and external funding.

All of the work previously mentioned has been necessary so that accurate cross section measurements could be performed. Over the last ten years, we have checked the accuracy of several theoretical models for ionization using a wide range of target and projectile combinations over a wide range of incident ion energies. In particular, we have examined the accuracy of the Nikolev formalism for predicting the electron capture contribution to the x-ray cross section. We have also examined the direct ionization and molecular orbital (Pauli excitation) contributions to the cross section. Experimental measurements of slow symmetrical collisions performed over the past five years at UNT and Bucharest have shown that the simple Nikitin model of molecular orbital ionization is

valid for many ion-atom systems. This model which had previously been disregarded as incorrect, allows for the accurate calculation of x-ray cross sections for many ion-atom systems that would have been impossible using more sophisticated models.

A separate interest has been the in the use of atomic and nuclear physics techniques to solve problems in other branches of physics. One of the more successful of these ventures has been as a consultant on a project with Dr. Floyd McDaniel of the University of North Texas and Drs. Collin Nicholls, Ralph Hill and Mr. Derwin King of Southwest Research Institute at San Antonio Texas to demonstrate the feasibility of detecting of detecting plastic explosives in real time using gamma ray absorption. Gamma rays were created using the 13C(p, g )14N nuclear reaction. Since plastic explosives contain nitrogen, the absorption of the gamma ray from the reaction will be enhanced when the sample is at an angle where the energy of the gamma ray is Doppler shifted to match an energy level transition in the nitrogen nucleus. By measuring the dip in the transmitted gamma rays as a function of angle, the nitrogen concentration in the sample can be determined. A new proprietary technique is now being developed to distinguish plastic explosives from other nitrogen containing materials by determining the chemical environment on the nitrogen nucleus. Thus, the need to independently measure the carbon, oxygen and nitrogen concentrations would be eliminated allowing for real time analysis for airport use. A second project has been in the dating of flint archeological artifacts (arrow heads, etc..) by the amount of fluorine present. Preliminary studies in Paris have shown that fluorine concentration may be used as a reliable dating technique for arrow heads found in Europe. Such research was initiated while I was at UNT under the guidance of Dr. Sam Matteson of the Physics Department and Dr. Reed of the Archaeology Department using the 19F(p, a g )16O nuclear reaction to date artifacts from North America and Europe. This work has recently succeeded in obtaining external funding and a new accelerator is being dedicated to the project at UNT. Since the lower energy reactions can be performed on smaller machines, I am presently interested in attempting to follow up on this work at West Point using its lower energy accelerator to look at the large number of artifacts in the historically rich Hudson Valley region and nearby Mohawk Indian reservation.

A new interest that I have developed recently is in the study of energy losses that an ion experiences when traveling through a solid. My main interest is in experimentally determining the energy loss of ions in the 100-500 keV region in compound materials especially ferroelectric, superconductors, and phosphor materials used in flat panel displays. Although considerable energy loss information information exists for the use of many species of lower energy ions in ion implantation and the energy loss of ions at all energies in silicon, little data exists for nonstandard IBA ion energies for these new novel materials. Such information will be needed to fully exploit the usefulness of the new low energy ion beam techniques such as heavy ion backscattering and time-of-flight elastic recoil detection. Since the Bragg scaling law is known to be inaccurate for many compounds, it would be surprising if it should work for these materials. At present, there appears to be very little literature in this area except for a couple of papers at the most recent Ion Beam Analysis conference.

Accelerators provide excellent research opportunities for students of all academic levels including undergraduates. The basic principles of accelerators require only freshman level physics to understand and are an excellent method of combining many of the concepts taught in first and second semester physic class in a hands on manner that makes the students classes come alive. Furthermore, an undergraduate student who does research with accelerators will need to learn a number of experimental techniques including electronics, computer programming, interfacing of instrumentation, and vacuum technology. These same skills are required to perform research in all most any field of physics. In addition, they are excellent job skills for a career outside of physics.

In the past, I have been involved in numerous student research projects at both the graduate and undergraduate level. Many of these have resulted in presentations by the students at regional meetings and conferences as can be seen in my list of abstracts contained within this document. Since the Spring of 1995, I have been involved in supervising student research projects for classes in both the Department of Physics and the Department of Electrical Engineering and Computer Science at the United States Military Academy and in training junior faculty members of the Department of Physics to do research with students using accelerators. A situation somewhat unique to the Military Academies is the limitation on the time that a student can be involved in a research project. A cadet can only be required to spend a maximum of 120 hours a semester on a project with only 80 being in the lab. Included in this time period is preparation of both a formal write up in journal format and presentation of a colloquium to the department. If a project occupies more than one semester, the cadet is required to perform these functions each semester in addition to a talk at either the Conference on Undergraduate Research or the Rochester Symposium on Undergraduate Research during the Spring. These time constraints are necessary especially for seniors due to additional military leadership responsibilities that these cadets must undertake in directing the Corps of Cadets and the Honor System. Thus, a special challenge is to develop research projects that are both exciting but limited in scope that they can be completed in the allotted time frame. Below is a synopsis of some of the research projects performed by cadets over the past 2 1/2 years.

Fall1998-Spring 1999: Jacob Schwartz and Lance Tidwell – Freshman Physics Majors Jacob Schwartz and Lance Tidwell worked on a project to determine the optimum detector material and geometry of the primary gamma ray detector for a hydrogen detection system. Recent work by a team of researchers from ARL, Alabama A&M, and Tarleton have demonstrated part per million detection of hydrogen by nuclear reaction analysis without the need for massive passive sheilding to remove cosmic ray background. This novel detection system uses a coincidence detector scheme to obtain more than a 2 order of background reduction. Previous research suggested that the standard 3″x3″ BGO primary gamma detector may be less than optimum for this type of detection scheme. Our research compared BGO, NaI, and HpGe detectors of various geometries. Results show that NaI is a superior material to BGO in this scheme for the same geometry. Furthermore, NaI’s low absorption coefficient for 511 keV escape gamm rays allows for larger NaI detectors as compared to BGO detector’s. This allows for the use of a larger well detector which improves both solid angle and efficiency. A 5″x4″ NaI well detector can improve primary gamma ray detection efficiency by over a factor of 6 compared to a standard 3″x3″ BGO. Since the coincidence scheme completely removes cosmic background, increasing the primary gamma detector size does not significantly increase background. The larger well

detector will also allow for beam rastering and sample cooling. Thus allowing for increased beam current and the analysis of samples which are more beam sensitive. It is believed that these improvements along with small environmental radiation sheilding will lead to IBA compatible, quantitative hydrogen detection below ppm levels with a surface depth resolutions of approximately 5 nm.

Summer 1997:CDT Lyncoln Smith – Senior Nuclear Engineering Major CDT Simith conducted research on the detection of hydrogen in materials using nuclear reaction analysis under my direction at ARL’s new materials facility at Aberdeen, Maryland. This included construction of an NRA detection system and target holder as well as installation and necessary improvements on ARL’s existing 1.7 MV tandem accelerator following the accelerator’s move from Wilmington, Delaware to Maryland.

Fall 1996 and Spring1997:CDT Cassandra Ralls – Senior Electrical Engineering Major Upon the request of Col Sayles in the electrical engineering and computer science department, I developed special EECS-489 classes for Cadet Ralls for the fall of 1996 and spring of 1997. Cadet Ralls was required to rewire the LC-400 Van de Graaff accelerator control console following the accelerator’s move in the summer of 1996 and to trouble shoot the accelerator’s slit energy stabilizer system. Cadet Ralls then installed a set of beam slits and Faraday cups to improve beam monitoring and diagnostics. Finally, Cadet ralls was required to design and build a beam position monitoring system for the slits using integrated circuit and printed circuit board technology. Cadet Ralls successfully designed, built and tested a beam monitor prototype using a circuit board.

Spring 1996: CDT Cassandra Ralls – Junior Electrical Engineering Major Cadet Ralls took a special EECS-489 class in place of the traditional Electrical Power Systems class in the Electrical Engineering and Computer Science Department. She was assigned to design and build an improved target chamber for both scattering and x-ray experiments using parts obtained from Dr. James Lambert of Georgetown University. The chamber was to be used both to analyze semiconductor materials for film thickness , stoichiometry, and impurity information using RBS, ERD, and PIXE as well as being used for both teaching labs and ion-atom collision studies. After constructing the chamber, CDT Ralls tested the system using samples of several phosphor materials for flat panel displays that have been provided by Texas Instruments.

Spring 1996: CDT Geoffrey Bull – Senior Physics Major Cadet Bull measured the nuclear scattering cross section for 250 keV-450keV protons on carbon at a variety of angles. The experimental scattering cross sections for protons off carbon were then compared against screened Rutherford (Electrostatic) scattering cross sections. Unlike for higher atomic number targets, proton’s at these energies are capable of entering the carbon nucleus and interacting with the nuclear potential as seen by a resonance in the experimental scattering cross section around 450 keV. The experimental cross sections shows that the nuclear potential may constructively or destructively interfere with the electric potential causing large deviations from the usual Rutherford scattering cross sections. Since their is no simple universal formula for nuclear scattering as compared with Rutherford scattering, the nuclear cross section must be experimentally determined. CDT Bull then used his experimental measurements will provide a data base to modify the commercial material analysis program (RUMP) used by both USMA and ARL. This allows RUMP to accurately simulate and analyze spectra for materials that contain carbon for lower energy energy proton beam spectra for HIBS. In the future, a series of samples with varying amounts of carbon on silicon substrates will be made and analyzed using the West Point accelerator. The results of the analysis will be compared with SIMS work at ARL to determine the accuracy and maximum sensitivity of the West Point accelerator system. This data from this project is also planned for a future theoretical nuclear physics cadet research project to obtain information about the nuclear potential for this scattering event.

Fall 1996: CDT Geoffrey Bull – Senior Physics Major &CDT Cassandra Ralls – Junior Electrical Engineering Major CDT Bull was assigned to finish the repairs of the LC-400 Van de Graaff accelerator and to build an experimental beamline to be used during the Spring for both the senior experimental physics class and his own research project. His second objective was to learn three RBS packages: 1) the Texas Instruments Analysis software supplied by Dr. Joe Keenan; 2) Rump which is a commercial RBS package RUMP that is used in the Army Lab system; and 3) GISA a free software program that was obtained from Dr. Pfeffer of ARL. CDT Bull was to compare the results obtained from the three separate software packages using a common set of RBS spectra obtained from Dr. Joe Keenan as well as that obtained from the West Point accelerator. CDT Ralls volunteered to work in the laboratory on the project in her spare time.

Spring 1995: CDT Brad Smith – Senior Physics Major & CDT Cassandra Ralls – Sophomore Electrical Engineering Major CDT Smith was charged with both learning the necessary theory behind Rutherford backscattering spectrometry and with rebuilding the 400 kV Van de Graaff accelerator that had been inoperative since the mid 1980’s so that it could be used to perform these types of experiments. CDT Ralls volunteered to work in the lab following a departmental laboratory tour given to all Sophomore students taking the Core Physics Class. The project required the cadets to spend a considerable amount of time learning vacuum technology and basic DC and AC electronics which they had not previously dealt with in their course work. The project included constructing new accelerator console and rewiring the accelerator system. It was determined that many of the wires were either incorrectly connected, broken, or unnecessary. Furthermore, the entire vacuum system had to be replaced. The system contained large amounts of plastics, rubber, silicon, glue and other non vacuum compatible materials. Both diffusion pumps were defective and the seals on the mechanical roughing pumps had to be replaced. Both the accelerator tube and the ion source bottle required cleaning to remove pump oil contamination. Several components in the accelerator terminal were also found to be faulty including the belt, focus resistor, column resistor, and gas control rod. New charging and collection screens were also added. At the end of the project, the vacuum was improved from 10-1 to 10-7 torr and the accelerator produced a 200 m A ion beam in a 1 inch spot with 400 kV on terminal. It was also determined that the focus power supply was intermittent and that it was causing loading on the alternator. Unfortunately, it took five months for the supply to arrive from the manufacture so the corrective procedure was not completed till the next Fall.

To complete his training, CDT Smith was required to set up a charged particle detection system using an 241Am radioactive source as his source of ions and to also perform RBS analysis on a series of semiconductor samples using an RBS analysis package that along with the samples was provided by Dr. Joe Keenan of Texas Instruments.