Midn Alex Jaqua `17
Over the Christmas break of 2015, approximately 40 LaBr detectors were combined with 50 Ge detectors from Gammasphere to investigate the life times of nuclei produced when 252Cf fissions. This experiment ran for approximately a month and produced nearly 100 different nuclei. The intent of the experiment is to use the good timing characteristics of the LaBr detectors to determine the half lives of the low-energy states in the nuclei produced. Before this can be done, one must know what states were observed, and how strong they are. MIDN Jaqua did that for the series of lanthanum nuclei which spanned 143-147La. MIDN Jaqua learned how to take gates in the coincidence cube, build level schemes, and defend them using the spectra generated. This information will be used to assess whether there is enough counts to produce time spectra such that the life times of the yrast h11/2 band-head state can be determined.
Spring 2016 - Fall 2016
Midn Kenneth Hicks `17 - Bowman Scholar
MIDN Hicks analyzed the data from our 160Eu beta-decay experiment that used the CARIBU radioactive beam facility at Argonne National Laboratory. A beam of mass selected A = 160 nuclei from the CARIBU source was directed onto a moving tape system, and the gamma rays were detected with four Compton-suppressed clover detectors, while the betas were detected with four plastic scintillators. Initially, Kenny learned how to take gates in the gamma-gamma matrix to produce gamma-ray spectra that allowed him to correct and add to the previously known 160Gd level scheme. This nucleus is the daughter of 160Eu after it beta decays. After seeing that the gamma rays could be separated into two different types, he produced time spectra (time at which the gamma ray was observed relative to the tape movement) that indicated the two types of transitions were produced by two beta-decaying states in 160Eu (instead of a single state, as previously reported). He then determined the half lives of these states by fitting the data to an exponential decay curve. This was part of his Bowman project and he presented a poster at the fall Capstone Day ceremony.
Midn Jules Godino `16
The first rotational bands in the doubly-odd nucleus 168Re were recently discovered from an experiment that focused on 169Re. The configurations of these two bands (i.e. the unpaired proton and neutron that are associated with the bands) needed to be determined. Because these structures are strongly coupled, many of the states decay through both magnetic dipole (M1) and electric quadrupole (E2) transitions. The reduced probability ratio, B(M1)/B(E2), is highly dependent on the configuration; thus, Midn Godino determined the experimental ratios, and then compared them to theoretical ratios. The B(M1)/B(E2) is based on the energy of the two gamma rays that decay from the state, and the branching ratio which is simply the ratio of the intensity of the E2 transition over the intensity of the M1. Midn Godino took gates in a coincidence cube to measure these intensities, and then determined the transition strength ratios for many states in both structures. He then learned what the theoretical values were dependent on, and calculated ratios for various possible configurations. He determined that the most intensely populated band was based on the coupling of an h11/2 proton with an i13/2 neutron, while the other sequence is based on the coupling of an h11/2 proton with an h9/2 neutron. His results were used as the basis of his Capstone paper.
Fall 2013 - Spring 2015
Midn Steven Hallgren `15 - Trident Scholar
Steven worked with me for three years on various projects, but his main contribution was performing analysis on some Gammasphere data concerning the odd-odd nucleus 160Lu. This experiment took place in the spring of 2014 where a 45Sc beam was directed onto a 120Sn target to produce 160Lu in the 5n evaporation channel. Steven wrote a code to efficiently sort the data into a database, and a coincidence cube was constructed from that database. He then learned how to perform energy calibrations and correct for detector efficiencies using a 152Eu source, and he performed a correction for the Doppler effect observed from 160Lu emitting gamma rays as it moved through the beam pipe.
Using the coincidence cube, Steven extended the 160Lu level scheme from a highest observed spin in the main decay sequence from 27 to 42 hbar, as well as extending two other structures to higher spin. The focus of the project became the main sequence, which is based on the uncoupled h11/2 proton, i13/2 neutron configuration (p h11/2, n i13/2). This configuration is well known for displaying the phenomenon of signature inversion. That is, this decay sequence is made up of two sequences, one with even spins, the other with odd spins. One would expect the even spin "signature" to be favored in spin for this configuration, but a systematic look at these bands in the mass A = 160 region shows that the odd spin signature is lower in energy at low spins. At higher spins, the normal ordering is observed, and smooth trends can be seen at which spin the normal ordering begins. There are several theoretical explanations for this signature inversion, one of which is that if the nucleus is asymmetrically deformed, inversion is possible. In addition, the cranked shell model suggests that the i13/2 neutron drives the nuclear shape towards asymmetry.
However, Steven noticed that the spin at which normal ordering occurred in 160Lu did not fit the observed trend. That is, this spin was much higher than that seen in neighboring nuclei. He also found evidence that a pair of neutrons occupying the h9/2 orbital break apart and align their spins with that of the nucleus. We wondered if that could have an effect on the delayed spin of normal ordering. Indeed, we found a theory paper that indicated the addition of the h9/2 neutrons would drive the nuclear shape to larger degrees of asymmetry, thus delaying when the normal ordering would occur. Steven presented his results at the 2015 APS April Meeting in Baltimore, MD. Steven will spend the next two years in England where he will earn two Master's degrees from the University of Oxford!
Fall 2013 - Fall 2014
Midn Matt Benner `15
Matt did a great job on several projects over three semesters! He took the lead in determining the characteristics of a newly purchased LaBr3 detector. This is a scintillating detector that has better resolution than a NaI detector, and has timing characteristics similar to BaF detectors. It will be used in an array at Argonne National Laboratory to study lifetimes of neutron-rich, exotic nuclei. Matt learned how to calibrate the detector with a 152Eu source, and then determined the relative efficiency of the detector with the same source. Next, he used one of the Naval Academy's certified 60Co sources to determine the absolute efficiency at 1332 keV. He also investigated the fact the detector itself is radioactive! Natural lanthanum has a long-lived radioactive isotope (138La) that emits gamma rays. By allowing the detector to count for an extended period of time, he compared the amount of activity related to 138La to that of naturally occurring 40K.
In the fall of 2014, Matt took on an ambitious project to design a new data acquisition system for the Academy's nuclear physics laboratory. He started with the latest version of the commercially available KMax program (from Sparrow Corporation) for Windows. Matt quickly realized that this was not going to work with Windows, so he learned how to install the Linux operating system on the computers in the lab. KMax worked perfectly with the Linux systems, and he set out to edit the basic codes to meet the needs of our lab. Matt created three different programs - one to take and analyze data from a single ADC unit, one to take data from a four-channel ADC, and a final program to analyze the four-channel data - and in particular perform the Add-Back procedure for the Academy's clover detector. His work has made it possible for future Midshipmen to use the nuclear laboratory efficiently.
Fall 2011 and Spring 2012
Midn Jake Cavey `12 - Bowman Scholar
Jake continued the research program started by Eowyn Pedicini (see below) concerning the possibility of finding evidence of an asymmetric shape in the nucleus 171Re. Jake and I went to Argonne National Lab in the fall of 2011 to run the experiment using Gammasphere to collect the gamma-ray information. The data was brought back to the Academy, where Jake carefully processed the information into a form that allowed him to search for structure that would be consistent with a nucleus wobbling (in a manner similar to an asymmetric top spinning). Although he did a thorough search, no such sequence could be found. However, Jake did learn a great deal of nuclear structure physics (and patience) through this project. Jake was accepted into the Nuclear Engineering programs at the Massachusetts Institute of Technology and the University of California, Berkeley with full tuition waivers. Unfortunately, the Navy did not permit Jake to attend either school. He is now an officer on a nuclear-powered submarine.
Fall 2010 and Spring 2011
Midn Eowyn Pedicini `11 – Trident and Bowman Scholar
Eowyn spent a year analyzing Gammasphere data on 171Re that we took during the summer of 2010. She was able to go to Argonne National Lab for the experiment and assisted with the data acquisition. Back at the Academy, she was in charge of preparing the data for analysis which included: looking and correcting gain shifts, detector calibration and efficiency analysis, as well as Doppler correction. Eowyn then created a Blue database from which she built a coincidence cube. She then took thousands of gates in this cube to significantly improve the level scheme of 171Re. In particular, she extended the i13/2 band, that is known to display wobbling in other nearby nuclei. Based on these results, Eowyn conducted a thorough search for any hints of a wobbling band. Unfortunately, none could be observed, but that may be due to a lack of statistics resulting from the fact that this experiment lasted for less than one day. A picture of Eowyn at Gammasphere is shown on the PowerPoint presentation for the Trident committee. Eowyn recognized for her hard work by earning Honorable Mention for the best Trident project. She also presented her results in the oral session of the American Physical Society April Meeting 2011 in Los Angeles, CA.
UPDATE: Eowyn completed her M.S. in Nuclear Engineering at Texas A&M University and is now a submarine officer.
Midn Eowyn Pedicini `11
Eowyn focused on learning basic nuclear structure models (such as the shell and deformed shell models) as she was preparing to apply for the Trident Scholar program. She also independently learned about asymmetric nuclei and wobbling such that she could present the reasons for our experiment on 169,171Re. These nuclei have two more protons that the Ta nuclei that previous students explored, but have a neutron number near 94, where wobbling is likely to be centered. We performed the experiments in March at Gammasphere and the data are now at the Academy waiting to be analyzed. Eowyn did a fantastic job with her proposal and her defense of the proposal in front of the Trident committee. She was indeed selected as a Trident and Bowman Scholar! Eowyn will complete her research in the 2011 academic year.
Fall 2008 & Spring 2009
Midn Ryan Pifer `09 – Bowman Scholar
Ryan picked up from where Sandy finished for the 167Ta project. We performed an experiment at Gammasphere to produce high-spin state in 167Ta so that we could look for evidence of wobbling in this nucleus. The most recent theory suggested that wobbling would NOT likely be observed, but that’s why we do experiments. Ryan sorted the data, and using a coincidence hypercube he greatly extended the level scheme for 167Ta. Most importantly, Ryan pushed the i13/2 band to higher spin and found a sequence of transitions feeding into it that had the key signatures of a wobbling band. However, there were some peculiarities that were not quite consistent with a wobbler. With some help from Stefan Frauendorf (Notre Dame), it is our belief that those abnormalities are a result of the i13/2 structure evolving from a symmetric shape to an asymmetric shape as spin increases. Ryan made a great poster which can be seen on the Wobbling Mode in Tantalum-167 document.
Ryan has earned his Master’s degree at the Naval Postgraduate School in Monterrey, CA and is now a Submarine Officer.
Fall 2007 & Spring 2008
Midn Evan Seyfried `08 – Bowman Scholar
Evan was given Gammasphere data resulting from a reaction where a beam of 30Si bombarded a 181Ta target. This creates a compound nucleus of 211Fr which would lead to neutron-deficient, trans-lead nuclei. These nuclei are traditionally under-studied due to the fact 98% of the time, the 211Fr fissions, which leads to a huge background of gamma rays from the fission products. However, these data were taken with the Washington University HERCULES detector working in conjunction with Gammasphere. HERCULES measures the energy and time-of-flight of the recoils following the reaction. The fission products have significantly different characteristics than the fusion products, therefore, HERCULES can identify the fusion products and their associated gamma rays. Using the gamma-ray data, Evan built the first ever high-spin level schemes for 205,206,207Fr and 204At. In particular, he found a sequence of low-energy transitions in both the odd-odd nuclei 204At and 206Fr. After doing some reading of papers focusing on nearby nuclei, Evan determined that these were likely “Shears Bands.” As described in his American Physical Society April Meeting talk, Shears Bands result from the closing of the angular momenta vectors from the protons and neutrons onto the total momentum vector. This produces a decay similar to classic nuclear rotation, even though the nucleus is not actually rotating. As stated above, Evan and I went out to St. Louis where he presented his data in a session with graduate student, post-docs, and professor from other universities and national laboratories. A picture of Evan at Gammasphere is shown below.
Evan finished his commitment as a submarine officer and is now looking to attend graduate school.
Midn Alexander (Sandy) Ludington `07 – Bowman Scholar
Sandy continued his research (see below) by building the full level scheme of 167Ta. In fact, he was able to identify all the previously known transitions and even add a few more. This is impressive as we only used nine detectors whereas the previous study used 29 detectors. One transition was of particular interest as it was previously suggested to be a linking transition from the h9/2 band to the d3/2 band. Such a transition would have an E1 character, and the earlier study had evidence that it was indeed a dipole; however, their array could determine the electromagnetic character. The Yale array, which uses Clover detectors, allows for polarization analysis which can determine whether gamma rays are electric or magnetic. Therefore, Sandy first constructed a DCO (directional correlation of oriented states) matrix to verify the dipole character of the linking transition. Following this, he spent six weeks coding to properly perform polarization analysis. This took a lot debugging and patience, but he was able to sort the data into perpendicular and parallel scattering. Using the asymmetry ratio, Sandy tested his spectra with known electric and magnetic transitions. As seen in the figure electric transitions have positive asymmetry ratios, while magnetic transitions have negative ratios. Sandy then determined that the linking transition had a positive ratio, and is thus an electric dipole. Sandy also delivered a talk at the National Conference for Undergraduate Research (NCUR 2007) concerning his fall semester research.
Sandy earned a Master’s degree in Nuclear Engineering from the Massachusetts Institute of Technology. He is now a submarine officer.
Midn Alexander (Sandy) Ludington `07 – Bowman Scholar
In August 2006, Sandy and I took a trip to Yale University to investigate the products of the 51V + 120Sn reaction. This reaction is of interest as one of its main products is 167Ta. The isotones of 167Ta (163Tm and 165Lu) have strongly deformed bands which are believed to be triaxial. However, only 165Lu shows evidence for wobbling bands. Stefan Frauendorf (a nuclear theorist at Notre Dame) has postulated that the density of proton levels is a key factor as to whether wobbling will be observed or not. To test his theory, 167Ta must be investigated to look for signs of wobbling. However, the reaction leading to high-spins states in this nucleus had never been run before. So the optimal energy for producing 167Ta was not known. Therefore, Sandy and I performed an excitation function of the reaction with the help of the Yale professors, plus FSU and Yale grad students.
The reaction was run at three different beam energies (228, 235, and 240 MeV) and nine clover detectors (see picture of Sandy standing in front of the array) were used to measure the gamma rays emitted by the excited nuclei. Sandy brought the data back to the Academy and sorted through over 3400 spectra to check for gain shifts. He corrected these shifts, performed an energy calibration and determined the energy dependent efficiency for the detectors, and calculated the proper Doppler shift. Sandy then built coincidence matrices for the data taken at the three different beam energies. By measuring the intensity of the gamma rays produced by each nucleus, we could determine the relative production of each at the different energies. These relative abundances were then compared with calculations from a program called PACE. It was found that good agreement between experiment and theory achieved when the calculated values were shifted by 7 MeV. We now know that 235 MeV appears to be the optimum beam energy for a proposed experiment at Gammasphere. Sandy delivered a fantastic talk at the end of the semester and his PowerPoint presentation can be downloaded here.
Midn Timothy Fitzgerald and A.J. Storrs (`07)
Tim continued (see below) to look through the data for new bands in 160Tm. Although he found many candidates, all of these sequences were later associated with other nuclei formed in the reaction (such as 158,159Er). We then focused on interpreting the bands that Tim found last semester. Tim learned about the Nilsson model and determined possible proton and neutron orbitals near the Fermi surface for 160Tm. He determined the h11/2 and g7/2 protons were likely candidates along with i13/2 and h9/2 neutrons. Next, he learned how to calculate aligned angular momentum and made plots of these values versus rotational frequency for the bands in an Excel spreadsheet. This gave us our first clues to which orbitals were responsible for the bands. For instance, the first i13/2 neutron crossing was blocked in one of the bands, which indicates this neutron is likely involved in the configuration. Tim then determined the branching ratio for each of the bands, and then calculated the B(M1)/B(E2) ratios. These experimental values were then compared with theoretical values to positively identify the two strongest bands as having the h11/2 proton coupled to the i13/2 and h9/2 neutrons, respectively. Once again, Tim presented his research to the faculty at the end of the semester.
A.J. Storrs was responsible to determine whether any new information on the nucleus 159Tm could be mined out of the same data Tim Fitzgerald was working on. This nucleus is part of the famous chain of N = 90 nuclei that lie between vibrational and well-deformed nuclei. A.J. was able to find the two strongest bands in 159Tm, but could not extend them to higher spin. There were not enough statistics to allow for new information. However, he too learned how to calculate aligned angular momentum and determine the likely configurations of the bands based on these plots.
Midn Timothy Fitzgerald and Billy Mohr
Unfortunately, the accelerator at Yale University had some major problems, so Tim and I were not able to perform an experiment on 167Ta that we had planned. However, I had just participated in a Gammasphere experiment with my colleagues at Florida State University in the summer. High-spin states were populated in 161Tm to search for evidence of a wobbling sequence which would indicate stable triaxial deformation in the nucleus. While the FSU folks took the lead on 161Tm, there was a good amount of data on the odd-odd nucleus 160Tm. So, Tim got a chance to sort the data into a Blue database and build his own gamma-gamma-gamma coincidence cube. This took some time as we battled the extra information in the data stream resulting from the use of a spinning target wheel during the experiment. Then it was time to start setting gates and Tim quickly extended the two known bands to much higher spins (from 26 to 44). In addition, two new bands were found and linked into one of the previously established bands. At this point, the semester ran out and Tim gave a 20-minute presentation to the faculty. He also agreed to come back the following semester to interpret the configurations of these bands.
Billy decided to tackle a new project that would contribute to the search for wobbling bands in the A = 165 region. A wobbling band decays through ΔI = 1 transitions that are dominated by an E2 component (rather than the usual M1 character). As discussed above in Tim Fitzgerald’s first project, the electromagnetic character of a gamma ray can be determined by a polarization measurement. Although Gammasphere does not contain clover detectors, many of the detectors have been electrically split such that one may determine whether the gamma ray hit on the left or right side of the detector. This was done primarily to well with Doppler correction to effectively reduce the opening angle of the detector. This information is written as a low-resolution signal called the “side channel” energy. We can use this side channel information to also do a poor-man’s polarization measurement. If both sides of the detector fired, this likely means the gamma ray Compton scattered parallel to the plane. If only one side fired, either the transition was completely absorbed in the detector when it first hit, or it Compton scattered perpendicular to the plane. Although this method is not nearly as sensitive as a clover, we may gain some idea of the electromagnetic character of a given transition. Billy was able to lay the groundwork for codes that use a double gate and project the resultant side channel information. However, as his research course was only a one hour course, we were not able to determine whether this is a reliable polarization method. More work will be performed in the future.
Midn Timothy Fitzgerald `06
In the spring of 2005, Tim picked up on the Clover project where Jack Hathaway left off (see below). We want to determine the electromagnetic character of gamma rays emitted by excited nuclei with the Clover. First, Tim had to construct a new target chamber for use of the Clover with the U.S. Naval Academy tandem accelerator. He successfully completed this project in about a month and picture of him installing the chamber is shown. Next we ran an experiment of bombarding protons on magnesium oxide foil. Magnesium emits a high-energy gamma ray that is an electric quadrupole. Tim is edited the code developed by Jack Hathaway to sort the Compton scattered data into two spectra: one spectrum has gamma rays that scattered parallel to the reaction plane, the other has gamma rays that scattered perpendicularly to the plane. Whether the gamma ray emitted by magnesium favors scattering parallel or perpendicular will signify if it is dominated by an electric or magnetic character. Tim gave a 10-minute presentation to the faculty at the end of the semester.
MIDN Billy Mohr `06
In the fall of 2004, Billy got to go on a field trip to Argonne National Lab and use the best gamma-ray spectrometer in the world – Gammasphere. A picture of Billy in front of Gammasphere is shown. The experiment produced high-spin states of 171Ta, where we were looking for evidence of triaxial deformation. After learning how to operate the data acquisition system and the basics of scanning data stored on 8 mm tapes, Billy returned to the Academy and learned how to process a large data set (~250 GB worth of information). Billy determined the calibration and efficiency of Gammasphere for our experiment. He then determined the average recoil velocity of the 171Ta nuclei through analysis of the observed Doppler shift in the gamma rays. Once this was accomplished, the data was sorted into a database, from which a coincidence cube was extracted. Billy analyzed this cube and added substantial amounts of new gamma rays in the level scheme of 171Ta. While doing this, he learned about the shell structure of the nucleus, the pairing between nucleons, and the electromagnetic characteristics of gamma rays. Billy even began an analysis of the rotational alignment properties of the different decay sequences. All of his work was put together in a nice PowerPoint file which you can download. This work was presented at the National Conference of Undergraduate Research in April of 2005.
UPDATE: Billy earned his Master’s degree in nuclear physics from the University of North Carolina and is now flying jets for the Navy.
MIDN Christopher (Jack) Hathaway `04
In the spring of 2004, Jack did some incredible work to integrate the Naval Academy's new Clover germanium detector with the nuclear physics lab. I will give a summary of his work, put you can download his entertaining PowerPoint presentation here.
The Clover has four separate germanium crystals within the casing which detect gamma rays. An advantage of the Clover over other germanium detectors is that contains four times as much germanium (which makes it more efficient for detecting gamma rays), but because the crystals are separated from each other, the detector does not lose its resolution. In order to maximize the results from the Clover, Jack had to write some code to perform an Add-back routine. When a high-energy gamma ray enters one crystal, it may not deposit all of its energy into that crystal. Instead a lower energy gamma ray may leave and enter a neighboring crystal. This process (called Compton scattering) is demonstrated here (thanks to Dave Campbell!). If this occurs, we can add back the two energies to get the correct energy of the original gamma ray. After a few wrong starts, Jack successfully did this and then checked that the high-energy efficiency working in this Add-back mode was indeed better than if we used the Clover as four separate detectors. Jack used 56Co, 60Co, and 152Eu sources to perform this experiment, and he was successful.
UPDATE: Jack was selected to go to Test Pilot School in the UK!!