Active Pixel Sensor Characterization for the STAR Detector. JAKE KING (University of Kansas, Lawrence, KS 66045) HOWARD MATIS (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

The STAR collaboration is studying matter at high temperatures and densities. If a significant improvement to the measurement of particle trajectories can be made, charmed mesons that decay away from the primary collision point could be identified. To achieve this goal, STAR is building a vertex detector consisting of a new technology – active pixel sensors. (APS) An APS is an implementation of standard CMOS technology in which each pixel has a photodiode directly above the epitaxial layer. Incident particles produce electron-hole pairs in the epitaxial layer, and these electrons accumulate on the photodiode. Charge from the photodiode is digitized to identify the position of the incident particle. It is important to characterize the signal to noise, readout time, and resolution on several different pixel sizes so that the vertex detector can be optimized for cost and speed. Larger pixels result in a faster data acquisition, while smaller pixels have better resolution. We will present studies of 5, 10, 20 and 30 µm square pixel geometries that measure charge distribution and collection. We will also display the results of using a field emission scanning electron microscope with energies from 1 to 30 keV. This tool has the potential to probe regions of the APS integrated circuit and contribute to understanding its properties.

Analysis of Neutron Flux in Preparation for Reaction Measurements with Radioactive Targets. KATHERINE BAUER (Smith College, Northampton, MA 1063) MARGARET A. MCMAHAN (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

At the 88-Inch Cyclotron, in the Nuclear Science Division at Lawrence Berkeley National Laboratory in Berkeley, CA, researchers are trying to measure the cross section for the reaction 89Zr(n,2n)88Zr. Knowing this cross-section accurately is important for the US Stockpile Stewardship Program; in addition, neutron cross-sections such as this one, are useful in order to understand nucleosynthesis. A large neutron flux is important for the SSP project because the 89Zr target is radioactive, with a half-life of 78.41 hours. The resulting isotope, 88Zr, is also radioactive with a half-life of 63.4 days. Without a large neutron flux, the material will decay too much, making if more difficult to calculate the cross-section. By replicating the experiment with activation foils that are not radioactive, using identical geometry the neutron flux can be evaluated and energy information can be obtained. The neutrons produced in the bombardment of the activation foils induces radioactivity within the foils. The decay of the radioactive material in these foils can be measured using a Ge-Li counter. The resultant information from counting radioactive decays is used to quantify the neutron flux. These same measurements of decay will also identify which reactions have energy thresholds that are too high to take place in the given beam-line. Neutron flux measurements for these non-radioactive foils will allow researchers to determine an expected neutron flux for the 89Zr experiment—and if it will be high enough to effectively measure the (n,2n) cross-section. Results from this work showed a neutron flux measurement roughly 100 times smaller than expected, at 3 x 10^8 neutrons/cm^2/sec, which indicates that in the current conditions the 89Zr experiment will not be possible. Also indicated from this work is that higher threshold reactions did not occur—reactions with thresholds above 12 MeV. Foils placed at different stances showed a steady and quantifiable difference in flux. These findings will allow future placements to be determined, as flux operates by a 1/r^2 relationship with distance. Future work will include confirming these results related to distance, as well as producing a higher neutron flux, ideally around 3 x 10^10 neutrons/cm^2.

Fingerprint Analysis a the Infrared Beam Line. JORGE SERVIN (West Hills College, Lemoore, CA 93245) DR. MIKE MARTIN (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

Fingerprint Analysis has been around for thousands of years. Samaritans were the first that we know of to use fingerprints as a way to sign a contract. Samaritans were not the only one’s to use fingerprints as a way to do business, in the late 1800 century, Francis Galton used fingerprints in India because the majority of people there were illiterate. The most famous case in the history of fingerprinting occurred in the late 19th century when a man was spotted in the incoming prisoner line at the U.S. Penitentiary in Leavenworth, Kansas by a guard who 'knew' him and had just seen him already in the prison population. Upon examination, the incoming prisoner claimed to be named Will West, while the (not escaped) existing prisoner was named William West. According to their Bertillon Measurement they were essentially indistinguishable. As they were not twins, the Bertillon system came into some question. However, their fingerprints were different, and fingerprint identification received a significant boost in credibility. In our research at Lawrence Berkeley National Laboratory this summer, the Intensive Research Group did fingerprint analysis at the Infrared Beam line. Our project consisted of finding out what kind of chemical components were present in fingerprints. We put our fingerprints on a gold plated slide. Then, we used the FTIR (Fourier Transformation Infrared Red) Spectrometer to analyze the sample. The machine measures the absorbance of infrared radiation by the sample and records a spectrum. Then we search the computer library or known spectra and find the best match to the sample. This tells us the different types of molecules that are presented in the sample fingerprint. Now the boundaries of infrared forensics are being pushed into uncharted territories by researchers at Berkeley Lab, and the results are promising for criminal and antiterrorism investigations as well as for historians and archaeologists.

Initial Studies of 238UO22+ and 248Cm3+ Complexation by Potentiometry and Time Resolved Laser Fluorescence Spectroscopy (TRLFS). KRISTINA SVENSSON (College of Marin, Kentfield, CA 94904) HEINO NITSCHE (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

Understanding the chemical behavior of actinides’ aqueous chemistry is necessary for designing cleanup and containment methods, predicting transport rates and preventing further contamination of areas to which actinides have been introduced. The determination of stability constants via potentiometric titrations or TRLFS provides fundamental chemical information which supplements data used for modeling actinide behavior in the environment. TRLFS was used to analyze micromolar concentrations of UO22+ and Cm3+ complexed with simple carboxylic acids of varying carbon chain lengths as well as with phosphoenol pyruvate (PEP) to attain fluorescence lifetime information. The modeling software Hyperquad 2000 aided in the determination of the stability constants of PEP, but additional experimentation is needed. The results show no correlation between carbon chain length and fluorescence lifetime. A blue shift is evident from that of free uranyl at pH 3.9 in the presence of 0.05M propionic acid. These shifts are evidence of a second fluorescent species in solution, but further characterization is required for identification. At pH 3, both UO22+ and Cm3+ show a red shift in the presence of 0.045M PEP. These shifts are evidence of a second fluorescent species in solution, but further characterization is required for identification.

Investigating Low Gamma-Ray Spectrum Analysis in Soil and Rock Samples at Lawrence Berkeley National Laboratory (LBNL). DONICHE DERRICK (Medgar Evers College, Brooklyn, NY 11216) AL SMITH (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

About fifteen billion years ago the universe was created by a theory which scientists called the big bang. When the earth was created, matter along with radioactive elements were produced. The main radioactive elements found on earth are Uranium, Thorium, and Potassium. However, after world war two due to the fall- out from nuclear weapons testing long life Cesium was created and deposited on the earth’s surface. Natural radioactivity is present around us whether it may be in the earth or the atmosphere. During the summer my objective was to study low gamma-ray emission from Uranium, Thorium, Potassium and Cesium present in soil and rock samples taken from around the hills of Berkeley at the LBNL site. In addition, calculations were performed to determine our annual dosage rate from these various radioactive elements. To perform this experiment we used a high-resolution germanium detector. So far, our results have shown that the amount of natural radioactive elements present in the samples is low in concentration and in effective dosage.

Studying the 11C + dn + 12N Reaction for its Astrophysical Significance. THAZIN WIN (University of Illinois at Chicago, Chicago, IL 60607) JOSEPH CERNY (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

After the Big Bang there were only light nuclei up to boron in the early stages of development. For stars about the size of our sun, energy is produced primarily by direct fusion of a sequence of reactions involving four hydrogen atoms into helium which is known as the p-p chain. However, for larger stars, the higher temperature and density occurrence allows for energy production by hydrogen burning of heavier elements. The CNO cycle is a hydrogen burning chain of proton reactions that can produce higher rates of energy generation in such massive stars [1]; however the Big Bang did not directly produce CNO nuclei. One way this CNO cycle could have started is the creation of 12C nuclei from a process beginning with hydrogen nuclei. Professor Cerny’s group has led the effort to develop a radioactive ion-beam capability at the 88" Cyclotron via the Berkeley Experiments with Accelerated Radioactive Species (BEARS) initiative. Upon completion of the BEARS activity-handling system in August 1999, this coupled-cyclotron facility produced 1x108 11C ions/sec on target for nuclear experiments [2]. The current experiment that the group is working on is to study 12N by bombarding a CD2 target with a 11C (t1/2 =20 min) radioactive beam at 150 MeV. This d(11C,12N)n experiment requires the assembling of Si-strip detectors and a set up of nuclear electronics and the data acquisition system. The purpose of this reaction is to produce 12N (T1/2 = 11ms) which will rapidly ß decay to stable 12C [3]. Through this process, the group is hoping to contribute to the understanding of the production of 12C in early generation stars. The d(11C,12N)n experiment at the 88-Inch cyclotron is completed; however, the detailed calculations of the differential cross section are continuing.

The Intensive Research Institute. KEO CHHIM (California State University Fresno, Fresno, CA 93740) TOM KNIGHT (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

The Intensive Research Institute consisted of four workshops: Natural Terrestrial Radioactivity, Cosmic Ray Detection, Neutron Activation Analysis, and Fingerprint Analysis. Each workshop was designed to expand knowledge in a certain area of science and guide in applying this knowledge to the classroom. The objective of Natural Terrestrial Radioactivity is that radioactivity is naturally occurring in our environment. Soil samples from different areas around the Berkeley lab were collected and analyzed. Yearly dosages of gamma ray exposure from Uranium, Thorium and Potassium were measured and compared to LBNL limits. Results showed that this exposure is insignificant. Primary cosmic rays are protons which react with the atmosphere and become secondary cosmic rays called muons. In the Cosmic Ray Detection workshop, we learned that the Earth is constantly being bombarded by cosmic rays. We built a cosmic ray detector that used scintillation paddles. By comparing count rate at different angles, we found that most muons come from directly above. By comparing count rate at different elevations, we found that as elevation increased, the number of muons detected increased. This shows that most muons have decayed at before reaching the Earth’s surface. In the Neutron Activation Analysis workshop, stable isotopes of an element were bombarded with neutrons resulting in a radioactive isotope. Our objective in this workshop was to identify the elements present in an unknown pottery sample. Thirty-one of the 35 elements were found. Applications of NAA include: airplane/automobile part testing, forensics, and medical research. The objective in the Fingerprint Analysis workshop was to learn about the infrared spectrum and its use in infrared spectroscopy. One can analyze the chemical properties of a given sample such as different fingerprints using infrared spectroscopy. We found that the chemical compounds in different people’s fingerprints could be characterized. IR fingerprint analysis is still in early development, but looks promising for forensic identification.

The MIMOSA-5 Active Pixel Sensor for Studying Quark-Gluon Plasma. LARA PIERPOINT (University of California, Los Angeles, Los Angeles, CA 90024) FABRICE RETIERE (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

51 universities are working in collaboration to study quark-gluon plasma (QGP) with the Solenoidal Tracker at RHIC (STAR) device at Brookhaven National Laboratory. Characterization of QGP, if it exists, can be accomplished by studying charm-quark hadrons in STAR, but more precise measurements are needed than those currently possible with the detectors in place. The relativistic nuclear collisions group (RNC) at Lawrence Berkeley Lab is designing a new detector that will utilize active pixel sensing (APS) technology to take data in STAR. Advantages of the active pixel sensor include high-speed readout capability and high pixel density. One disadvantage is that the technology employed by the sensor is new and requires characterization. We use as a baseline for our characterizations the MIMOSA-5 chip designed by LEPSI/IreS (Strasbourg, France), which represents a full-scale prototype at 512x512 pixels in a 2x2 cm area. The chip’s properties render it inadequate for use in the final detector, but we utilize it for studying our data readout system and for comparison to the next-generation active pixel sensor expected to meet our detector specifications.

The mystery of cosmic rays is one of the few samples of matter that come from outer space. JOSE GARCIA (Reedley College, Reedley, CA 93654) DR. PEGGY MCMAHAN (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

In 1912, a scientist named Victor Hess did an experiment with an electroscope and a balloon to understand where cosmic rays came from. He used an electroscope to detect charged particles. An electroscope works with two pieces a very thin foil suspended inside a glass jar. There is a brass ball on top, and a brass bar going down from it to the foil, the brass carries electricity to the foil, which becomes equally-charged. Since, like charges repel, the two foils will become separated. Victor Hess noticed over time the foil came back together, which meant that there must be charged particles hitting the electroscope and depolarizing the foil. As he increased his altitude the intensity of particles increased on his electroscope. Therefore, he concluded these particles came from outer space and not from Earth, so he called these particles cosmic rays. In 1936, he won the Nobel Prize for this scientific discovery. Here at the Lawrence Berkeley National Laboratory (LBNL), the Intensive Research Institute (I.R.I.), a group of Pre-Service Teachers wanted to prove Hess’ experiment in a different way. The I.R.I built a detector to better understand the mystery of cosmic rays. Peggy McMahan, my mentor, explained how the muons came from a reaction in the atmosphere with the primary of cosmic rays. These muons hit a target, or one of the two scintillator paddles on the detector, and photons are created. Then, the photons bounce around into the next target, the photomultiplier tubes. The function of the photomultiplier tubes is to convert the photon signal to an electric signal and multiply it by a factor of 10,000. Then, the electric impulse goes to the circuit board which counts the number of cosmic rays per minute. After building the detector, the I.R.I. conducted an experiment at different locations as well as at different altitudes such as Berkeley Marina and Mt. Del Diablo. The results clearly illustrated that as the altitude increases, so does the number of cosmic rays detected. In conclusion, we supported Victor Hess original experiment.

Using Neutron Activation Analysis to Identify Elements in an Unknown Sample. CLAUDIA ROBLEDO (California State University Fresno, Fresno, CA 93728) ERIC NORMAN (Lawrence Berkeley National Laboratory, Berkley, CA 94720)

In 1936, neutron activation analysis (NAA) was discovered when a rare earth element became highly radioactive after exposure to a source of neutrons. NAA is a technique used to identify elements in unknown sample. For decades, NAA has been performed on art and historical artifacts to identify concentrations of chemical elements in the sample and to help confirm authenticity or origin of the art. During my time at Lawrence Berkeley Laboratory, my research objective was to identify elements in a sample of pottery. The sample was bombarded with neutrons in the core of the McClellan nuclear reactor, which made some of the nuclei radioactive. The process of neutron capture is necessary because a stable isotope gives no energy; therefore we are not able to identify the elements in a sample. When the isotope is radioactive it is unstable, thus emitting gamma rays which we can detect through a tool called a germanium detector. This allowed us to interpret the energies of the gamma rays emitted. Through NAA, my research group was able to identify thirty-two different chemical elements in the pottery sample.