2023 TUNL REU Projects

Nuclear Physics Projects

1. High-precision Neutron-induced Cross-section Measurements on Iridium

Advisor: Alex Crowell

Student: Andres Gonzalez

Studies of neutron-induced reactions are of considerable significance, both for their importance to fundamental research in nuclear physics and astrophysics and for practical applications in nuclear technology, medicine, and industry [Fessler, Nucl. Sci. Eng. 134, 171 (2000)]. One such practical application is the development of dosimetry materials, also referred to as radiochemistry diagnostics, which can be used to determine neutron fluence by measuring the transmutation of the initial isotopes into product isotopes in the neutron environment.

Iridium (Z = 77) is widely used in various medical and industrial applications, ranging from cancer treatment to activation detectors. The two isotopes of natural iridium constitute a well-known neutron fluence detector and have also been part of historical nuclear explosive device performance. The student on this project will be involved in cross-section measurements on iridium using the tandem accelerator to acquire neutron activation data, as well as analyzing data from previous measurements at TUNL.

2. Deconvolution of Detector Response in Prompt Fission Gamma-Ray Spectra

Advisor: Sean Finch

Student: Brody Beskar

Nuclear fission is the process fundamental to some of nuclear physics' most famous applications. Detailed measurements of all the observables in fission is necessary to benchmark theoretical models and expand our knowledge of this extremely complex process. The prompt fission gamma-ray spectra (PFGS) are important for telling us how the two newly formed nuclei de-excite post scission. PFGS were recently measured during an experimental campaign at the High Intensity Gamma-ray Source (HIγS). In this dataset the true PFGS is obscured by the response function of the LaBr and CeBr detectors used. The student will work on models to deconvolute these spectra from the intrinsic detector response and report the true PFGS. This would be the first measurement of PFGS from photofission. The student will also assist with various experiments over the summer and gain familiarity with HIγS and TUNL's tandem accelerator.

3. Developing the 3He Polarization System and SQUID Magnetometry for the nEDM@SNS SOS Apparatus

Advisors: Thomas Rao, Robert Golub, Ekaterina Korobkina

Student: Mikolaj Konieczny

The nEDM@SNS experiment will measure the time reversal symmetry violating electric dipole moment of the neutron (nEDM). To do this, the trajectory correlation functions of polarized 3He must be understood. The Systematic and Operation Studies (SOS) apparatus at TUNL will determine the trajectory correlation functions of 3He by measuring the B2 frequency shift in the Lamour precession and the T2 relaxation of polarized 3He in a superfluid helium filled cell. Two projects are available related to this endeavor.

The first project is the development and testing of a 3He polarization system, utilizing metastability exchange optical pumping (MEOP), that will act as a source of polarized 3He for the SOS experiment. This project will involve finishing the assembly of the gas handling system, and demonstrating the system can be used to produce 70-80% polarized 3He.

The second project is the testing of Superconducting Quantum Interference Device (SQUID) magnetometers that will be used to measure the precession of the 3He in the SOS experiment. The SQUID magnetometers must be able to operate in vacuum with a cryoswitch capable of turning off the input signal to the SQUID. This project will involve setting up and performing tests of the operation of SQUIDs in LHe and in vacuum.

4. Neutron/Gamma Pulse Shape Categorization with Machine Learning

Advisor: Forrest Friesen

Student: Natalie Figueroa

Measurement of neutrons using scintillators is an important technique in experimental nuclear physics in general. When a neutron scatters from the sensitive volume of a detector, it deposits a probabilistic amount of energy up to the energy of the neutron, which is then converted to visible light by the scintillator and recorded digitally. However, these detectors are also sensitive to gamma rays, which constitute a significant background in some experiments. To help combat this, some scintillators produce subtly different pulse shapes depending on whether they were struck by a neutron or a photon.

Traditionally, some simple pulse processing is performed to estimate the probability that a given waveform came from a neutron vs. a gamma ray. However, it becomes increasingly difficult to separate these two populations at low pulse heights. The student will leverage modern machine learning techniques to design, implement, and evaluate a neutron/gamma waveform classifier for our detectors. This will help support our broader efforts to use existing equipment to accurately measure neutrons with energies lower than would typically be possible. Programming experience would be useful but is not required.

5. Elastic Scattering Measurements on 88Sr

Advisors: Caleb Marshall, Thanassis Psaltis, and David Gribble

Student: Tali Lansing

We propose to measure 88Sr(α, α) elastic scattering at several beam energies in order to test the applicability and effectiveness of a spherical α optical model potential (αOMP) for the astrophysically relevant 88Sr(α, n) cross section. The measurement would use the 52° beamline and the scattering chamber, instrumented with several silicon surface barrier detectors (SSBs).

A measurement of 88Sr(α, α) elastic scattering in the Tandem lab will require a fair amount of experimental effort that would greatly benefit from an undergraduate student. We have access to a large collection of silicon detectors, but their performance would have to be tested. Stands exist for these detectors, but they would need to be assembled and tested (a determination of solid angle would also need to be made). Strontium targets would need to be fabricated using the evaporator. Finally, a simple DAQ system will be setup. Depending on the level of engagement, the student will gain experience with silicon detectors, basic data analysis, target fabrication, and general laboratory skills.

On the theoretical side, we could envision the student becoming familiar with the nuclear optical model, and possibly acquiring the ability to carry out basic fitting procedures to extract parameters from the data.

6. Simulation and data analysis for COHERENT

Advisor: Kate Scholberg

Student: Nubia Udoh

Coherent neutral current neutrino-nucleus elastic scattering (CEvNS) is a process in which a neutrino interacts with a nucleus, giving it a recoil kick. Although the probability for such a process to occur is relatively high, the process is difficult to detect because typical nuclear recoil energies are very small. Because the rate of the process can be quite precisely predicted, a deviation of measurement from prediction could indicate new physics beyond the Standard Model. The COHERENT experiment has made the first measurements of this process at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee, and is currently pursuing further

measurements. There are additional interesting possibilities for studies of inelastic interactions of neutrinos with nuclei. This project may include design, simulation, background evaluation, and data analysis work. The student will gain experience with a variety of simulation and data analysis software tools. Programming experience will be very useful but is not required.

7. Improving Reconstruction for Low Momentum Pions at CLAS12

Advisor: Anselm Vossen

Student: Joseph Thompson

The CLAS12 spectrometer is used at Jefferson Laboratory to study the quark-gluon structure of the proton. One issue with using the spectrometer is that low momentum pions, for example from lambda decays, show a degradation of their resolution with the current reconstruction software due to the non-trivial fringe magnetic fields. The purpose of this project is to explore if Machine Learning (ML) or Bayesian methods can improve the resolution of the pion reconstruction.

The student on this project should have some programming experience and ideally some previous exposure to ML/AI.

8. Understanding Sodium Production in Stars Using Proton Transfer

Advisor: Richard Longland

Student: Qijia Zhou

Sodium is difficult to make in stars, and once made it should be easy to destroy by nuclear reactions. Why, then, is it found with such a high abundance in some globular clusters? To answer this question, we turn to nuclear physics to definitively measure the probability that sodium is destroyed by proton capture to produce magnesium. In particular, we need this destruction probability at temperatures present in a rare type of red giant stars. However, measuring this is exceedingly difficult since the cross section of the reaction is so small.

In this project, the student will develop and perform a proton transfer reaction measurement using the world-leading Enge split-pole spectrograph at TUNL. Data from this measurement will be used with our sophisticated statistical analysis pipeline to answer key questions about the structure of magnesium. Those results will be used to calculate the probability that sodium is destroyed in red giant stars. Along the way, we will test the validity of nuclear reaction models and will investigate disagreement between other reaction studies.

9. Construction of a 4-Paddle Flux Monitoring System

Advisors: Calvin Howell and Kent Leung

Student: Sarah Estupinan-Jimenez

During the summer program, the student will be assisting with the construction, wiring, and testing of the new 4-Paddle flux monitoring system. This process will involve the assembly of predesigned parts,

thermal molding and polishing of acrylic light guides, working with scintillating materials, testing PMT’s, and wiring the system logic. The PMT logic will provide a basic understanding of NIM modules and experience working with digitizers. Additionally, the student will also be involved in the assembly of the 4-paddle elevator mounting system. Testing the system will involve calibration of the 4-paddle. This will require an understanding of cosmic ray spectra and will put into practice all previously learned skills. Secondary projects involve calibration of the HINDA detectors.


High-Energy Physics Research Projects

1. Automating ITk Stave Testing for ATLAS

Advisor: Mark Kruse

Student: Albrun Johnson

The ATLAS experiment at the Large Hadron Collider (LHC) at CERN conducts searches for violations of the Standard Model, antimatter imbalances and dark matter, as well as research into the fundamental forces and the conditions of the early universe. There is a planned upgrade of the LHC that will increase the center of mass energy and the luminosity of the proton beam. The material currently used in the ATLAS detector cannot withstand radiation this intense, which requires the detector to be upgraded. A part of this upgrade are the silicon Inner Tracker (ITk) strips. Before installation, the detector components require intense testing, a process that is currently quite complicated. To facilitate the testing, the student on this project will update the ASIC register converters and design a graphical user interface (GUI) to create the necessary configuration files for the tests.

2. System Tests and Quality Control Procedures for ATLAS ITk strips

Advisor: Mark Kruse

Student: Greta Goldberg

The ATLAS experiment at the LHC is an ongoing experiment that explores the fundamental components of matter on a subatomic scale. The goal of this experiment is to find evidence for particle physics theories, some of which go beyond that of the Standard Model. Recently, the ATLAS experiment has begun undergoing an upgrade in order to achieve higher luminosity of the proton beam and higher center of mass energy of the individual protons, which will result in larger amounts of data to be taken. Due to the higher luminosity, there will also be greater radiation created by the accelerating particles, which the current detectors are not able to withstand. Thus, silicon detector strips are replacing the current detectors. These strips must undergo multiple tests and be calibrated in order to be deemed fit for implementation. The student on this project will create a graphical user interface to facilitate comparison of test data taken at the factory and at CERN of the silicon strip detectors.

3. Searching for Dark Matter at the LHC Using Graph Computing Algorithm

Advisor: Ashutosh Kotwal

Student: Michelle Kwok

A major instrumentation upgrade is planned for the LHC at CERN. The instrumentation upgrade provides the opportunity to use an algorithm that can be programmed directly onto silicon-based integrated circuits using field-programmable gate array technology. This algorithm uses graph computing to detect charged particles that decay invisibly with one of the decay products possibly being dark matter. The algorithm requires the hits recorded by the detectors to be partitioned in specific ways. In this project, the student will evaluate new methods of partitioning the data.

4. Machine Learning Model for Track Extrapolation in ATLAS

Advisor: Ayana Arce

Student: Aishi Guha

In the ATLAS detector, the trigger system uses particle flow algorithms to make decisions on which events to keep, and which to discard in order to prevent the build-up of overwhelming amounts of uninteresting data. The performance and speed of current particle flow algorithms are limited. Machine learning has been identified as a possible solution to speed up particle flow. This project (TExAS) represents a step towards full machine-learned particle flow reconstruction (Flowaii). The student will train a neural network model to extrapolate tracks from the inner detector to the calorimeter with low residual mean error. The performance of this model will establish an appropriate upper-bound for the performance of future Flowaii software in track extrapolation.