My main research focus is in stellar nucleosynthesis. Stars sustain themselves by fusing together atomic nuclei, which are composed of protons and neutrons, in very hot and dense environments. This is called nucleosynthesis – the formation of heavier nuclei – and depending on the energetics of the stellar environment – how hot and dense the star is – different processes are favored. For example, the s-process, which occurs on the time scale of billions of years, is a very slow way for elements heavier than iron to form by capturing a few free neutrons then beta-decaying up to the next-heaviest element. There is also the r-process, which occurs on the time scale of milliseconds and in extremely hot, neutron-dense, environments like collapsing stars and supernovae. Because each nucleus encounters, on average, more neutrons in the same amount of time, the nuclei capture many more of these free neutrons before beta decaying, resulting in the synthesis of even heavier elements. Understanding these and numerous other processes gives scientists greater insight into the inner workings of stars and the material building blocks throughout the universe.
The nucleosynthesis process I’m currently researching is proton evaporation. When two nuclei collide with enough energy, they occasionally form a compound nucleus, which can either persist – we call that fusion – or quickly separate into any number of product nuclei. One such separation is when a proton “boils off” extremely rapidly after compound nucleus formation, which is appropriately called proton evaporation. The energy at which two nuclei collide is very important, as it affects which exit channels are accessible and energetically favored in that environment. As such, it is very important to accurately measure the energy level density of nuclei, because this directly impacts how they interact at different energies. The angular momentum and parity of the nuclei also most be kept track of.
Together with my collaborators at the Edwards Accelerator Laboratory at Ohio University, my student research group has written a pair of programs to sort and analyze data from a proton-evaporation experiment run at EAL. This data was recorded from an experiment in which a carbon-12 particle beam was incident on an aluminum foil, creating the compound nucleus potassium-39 from which a proton evaporates, leaving behind argon-38. The reaction can then be written as 27Al(12C,p)38Ar. When an experiment is run, detectors are positioned radially around the target to measure where the scattering angle of the product nuclei, as seen in the top-center figure [1]. The time-of-flight and energy data from these detectors is then sorted, calibrated, and then plotted to identify the nuclei in each detection event, as shown in the top-right figure. Because of the intrinsic relationship between time-of-flight and energy, this particle identification plot generates different curves that correlate to particles of different masses. Because these curves look like a bunch of bananas, we call figures like the one in the top right banana plots. We can use this to isolate the particle of interest in our experiment – protons, because they signify that proton-evaporation occurred. From there, we can calculate the differential cross section with respect to scattering angle and energy. My students have also been using standard nuclear reaction code software programs Talys and EMPIRE to model what we should expect the differential cross section to look like, an example of which my students have done on another reaction is shown in the top-left figure. Such simulation modeling is crucial when extracting information from a measured cross section. Once the differential cross section has been fully calculated, we can then use it to calculate energy level densities for the compound nucleus, potassium-39. Nuclear level densities are essential to better understanding astrophysical reaction rates, since they directly impact the likelihood that a particular reaction can occur.
In addition to nuclear level density and astrophysical reaction studies, I have also worked on understanding nuclear structure, primarily the clustering structure of atomic nuclei. This is also experimental work, though I closely collaborate with theorists on the systems I'm measuring. I'm particularly interested in how some nuclei can be successfully modeled as a collection of α (alpha) particles. An α particle, consisting of two protons and two neutrons, is the nucleus of the helium atom. Since α particles are very stable structures, it's not a surprise that one can model a larger nucleus as a collection of α particles. For example, carbon-12 contains six protons and six neutrons, which can thus be described as three α particles. Any model is only as good as its predictions, so it's vital to measure observable quantities to discern whether or not the clustering of α particles inside of a nucleus can improve our understanding of nuclear structure.
Clusters of α particles can take many geometric shapes within a nucleus. In carbon, there are various predictions including triangular shapes and even linear-chain structures, in which the three α particles form a perfectly straight line. This one-dimensional behavior has been predicted since at least the 1950s [2], and evidence of it has been highly sought-after ever since. There have been predictions that adding additional neutrons to carbon may help stabilize the linear-chain structure. One of my recent publications [3] involves the study of 14C. In this work, my colleagues and I identified a rotational band of excited states that has close agreement with an antisymmetrized molecular dynamics model [4] that predicts linear-chain structure in 14C. We are continuing our studies of 14C and related systems to further understand the nature of linear-chain α-structure in nuclei.
I'm always looking to take on an interested and motivated student, so please contact me if you're interested!
[1] A. P. D. Ramirez, Study of nuclear level density from deuteron induced reactions on 54,56,58 Fe, and 63,65 Cu, Ph.D. thesis, Ohio University (2014)
[2] H. Morinaga, Phys. Rev., 101, 254 (1956)
[3] Fritsch et al., Phys. Rev. C 93, 014321 (2016)
[4] T. Suhara and Y. Kanada-En’yo, Phys. Rev. C 82, 044301 (2010)
Recent Group Presentations and Publications
P Thompson †, December 1, 2023. Understanding Stellar Nucleosynthesis by Measuring Nuclear Level Densities via Proton Evaporation, 6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan, Hilton Waikoloa Village, HI.
A Fritsch, November 29, 2023. Level Density Studies via Proton Evaporation, 6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan, Hilton Waikoloa Village, HI.
P Thompson †, November 11, 2023. Understanding Nucleosynthesis in Stars by Measuring Reaction Rates in Lab, 32nd Annual Murdock College Science Research Program, Vancouver, WA.
M Bair †, November 13, 2021. Proton Energy Dampening Framework (PEDF) for a Time Projection Chamber, 30th Annual Murdock College Science Research Program, Vancouver, WA.
A Fritsch, November 9, 2021. Invited seminar. Nuclear Structure and Nuclear Astrophysics, Physics Colloquium, Wabash College, Crawfordsville, IN.
The nucleosynthesis process I’m currently researching is proton evaporation. When two nuclei collide with enough energy, they occasionally form a compound nucleus, which can either persist – we call that fusion – or quickly separate into any number of product nuclei. One such separation is when a proton “boils off” extremely rapidly after compound nucleus formation, which is appropriately called proton evaporation. The energy at which two nuclei collide is very important, as it affects which exit channels are accessible and energetically favored in that environment. As such, it is very important to accurately measure the energy level density of nuclei, because this directly impacts how they interact at different energies. The angular momentum and parity of the nuclei also most be kept track of.
Together with my collaborators at the Edwards Accelerator Laboratory at Ohio University, my student research group has written a pair of programs to sort and analyze data from a proton-evaporation experiment run at EAL. This data was recorded from an experiment in which a carbon-12 particle beam was incident on an aluminum foil, creating the compound nucleus potassium-39 from which a proton evaporates, leaving behind argon-38. The reaction can then be written as 27Al(12C,p)38Ar. When an experiment is run, detectors are positioned radially around the target to measure where the scattering angle of the product nuclei, as seen in the top-center figure [1]. The time-of-flight and energy data from these detectors is then sorted, calibrated, and then plotted to identify the nuclei in each detection event, as shown in the top-right figure. Because of the intrinsic relationship between time-of-flight and energy, this particle identification plot generates different curves that correlate to particles of different masses. Because these curves look like a bunch of bananas, we call figures like the one in the top right banana plots. We can use this to isolate the particle of interest in our experiment – protons, because they signify that proton-evaporation occurred. From there, we can calculate the differential cross section with respect to scattering angle and energy. My students have also been using standard nuclear reaction code software programs Talys and EMPIRE to model what we should expect the differential cross section to look like, an example of which my students have done on another reaction is shown in the top-left figure. Such simulation modeling is crucial when extracting information from a measured cross section. Once the differential cross section has been fully calculated, we can then use it to calculate energy level densities for the compound nucleus, potassium-39. Nuclear level densities are essential to better understanding astrophysical reaction rates, since they directly impact the likelihood that a particular reaction can occur.
In addition to nuclear level density and astrophysical reaction studies, I have also worked on understanding nuclear structure, primarily the clustering structure of atomic nuclei. This is also experimental work, though I closely collaborate with theorists on the systems I'm measuring. I'm particularly interested in how some nuclei can be successfully modeled as a collection of α (alpha) particles. An α particle, consisting of two protons and two neutrons, is the nucleus of the helium atom. Since α particles are very stable structures, it's not a surprise that one can model a larger nucleus as a collection of α particles. For example, carbon-12 contains six protons and six neutrons, which can thus be described as three α particles. Any model is only as good as its predictions, so it's vital to measure observable quantities to discern whether or not the clustering of α particles inside of a nucleus can improve our understanding of nuclear structure.
Clusters of α particles can take many geometric shapes within a nucleus. In carbon, there are various predictions including triangular shapes and even linear-chain structures, in which the three α particles form a perfectly straight line. This one-dimensional behavior has been predicted since at least the 1950s [2], and evidence of it has been highly sought-after ever since. There have been predictions that adding additional neutrons to carbon may help stabilize the linear-chain structure. One of my recent publications [3] involves the study of 14C. In this work, my colleagues and I identified a rotational band of excited states that has close agreement with an antisymmetrized molecular dynamics model [4] that predicts linear-chain structure in 14C. We are continuing our studies of 14C and related systems to further understand the nature of linear-chain α-structure in nuclei.
I'm always looking to take on an interested and motivated student, so please contact me if you're interested!
[1] A. P. D. Ramirez, Study of nuclear level density from deuteron induced reactions on 54,56,58 Fe, and 63,65 Cu, Ph.D. thesis, Ohio University (2014)
[2] H. Morinaga, Phys. Rev., 101, 254 (1956)
[3] Fritsch et al., Phys. Rev. C 93, 014321 (2016)
[4] T. Suhara and Y. Kanada-En’yo, Phys. Rev. C 82, 044301 (2010)
Recent Group Presentations and Publications
P Thompson †, December 1, 2023. Understanding Stellar Nucleosynthesis by Measuring Nuclear Level Densities via Proton Evaporation, 6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan, Hilton Waikoloa Village, HI.
A Fritsch, November 29, 2023. Level Density Studies via Proton Evaporation, 6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan, Hilton Waikoloa Village, HI.
P Thompson †, November 11, 2023. Understanding Nucleosynthesis in Stars by Measuring Reaction Rates in Lab, 32nd Annual Murdock College Science Research Program, Vancouver, WA.
M Bair †, November 13, 2021. Proton Energy Dampening Framework (PEDF) for a Time Projection Chamber, 30th Annual Murdock College Science Research Program, Vancouver, WA.
A Fritsch, November 9, 2021. Invited seminar. Nuclear Structure and Nuclear Astrophysics, Physics Colloquium, Wabash College, Crawfordsville, IN.
ResearchGate Profile
Research Lab: Herak 256A (tours given upon request)
Research Assistants (Gonzaga students unless otherwise indicated)
Fall 2023 - Pierce Thompson
Project Title: Understanding Nucleosynthesis in Stars by Measuring Reaction Rates in Lab
Summer 2023 - Sean Pierce, Pierce Thompson, Binyu Tony Yang, and Kiyah Young-Wilson
Project Title: Understanding Nucleosynthesis in Stars by Measuring Reaction Rates in Lab
Spring 2023 - Megan Hill and Pierce Thompson
Project Title: Nuclear Reaction Analysis of Stellar Nucleosynthesis Processes
Fall 2022 - Matthew Bair, Megan Hill, and Pierce Thompson
Project Title: Nuclear Reaction Analysis of Stellar Nucleosynthesis Processes
Summer 2022 - Matthew Bair and Pierce Thompson
Project Title: Nuclear Reaction Analysis of Stellar Nucleosynthesis Processes
Spring 2022 - Sam Carryer (Ohio University)
Senior Thesis Project Title: Nuclear Level Density Determinations via 12C + 27Al Proton Evaporation Spectra
Summer 2021 - Ethan Bailes, Matthew Bair, and Austin Rambo
Project Title: Proton Energy Dampening Framework (EB and MB) and Gamma Ray Detection and Time Projection Chamber Simulations Using Geant4 (AR)
Summer 2020 - Andrea Bracamonte and Lauren Fisher
Project Title: Gamma Ray Detector Simulation Using Geant4
Summer 2019 - Nathan Magrogan and Brennan Watkins
Project Title: Gamma Ray Spectroscopy Simulations with Geant4
Summer 2018 - Andrew Clusserath and Bryce Makela
Project Title: Gamma Detection Simulations in Nuclear Isomers
Summer 2017 - Henry Thurston
First Project Title: 3 Body Nuclear Kinematic Modeling
Second Project Title: Finding a Relation Between Galactic Redshift and Radial Distance
Summer 2016 - Joey Gutierrez and Jourden Simmons
Project Title: Monte Carlo Acceptance Simulations for the Prototype Active-Target Time-Projection Chamber
Summer 2015 - Michael Wolff (College of Wooster)
Project Title: Measurement of Gain and Drift Velocity of the Prototype AT-TPC, presented at the 2015 Fall Meeting of the APS Division of Nuclear Physics
Research Lab: Herak 256A (tours given upon request)
Research Assistants (Gonzaga students unless otherwise indicated)
Fall 2023 - Pierce Thompson
Project Title: Understanding Nucleosynthesis in Stars by Measuring Reaction Rates in Lab
Summer 2023 - Sean Pierce, Pierce Thompson, Binyu Tony Yang, and Kiyah Young-Wilson
Project Title: Understanding Nucleosynthesis in Stars by Measuring Reaction Rates in Lab
Spring 2023 - Megan Hill and Pierce Thompson
Project Title: Nuclear Reaction Analysis of Stellar Nucleosynthesis Processes
Fall 2022 - Matthew Bair, Megan Hill, and Pierce Thompson
Project Title: Nuclear Reaction Analysis of Stellar Nucleosynthesis Processes
Summer 2022 - Matthew Bair and Pierce Thompson
Project Title: Nuclear Reaction Analysis of Stellar Nucleosynthesis Processes
Spring 2022 - Sam Carryer (Ohio University)
Senior Thesis Project Title: Nuclear Level Density Determinations via 12C + 27Al Proton Evaporation Spectra
Summer 2021 - Ethan Bailes, Matthew Bair, and Austin Rambo
Project Title: Proton Energy Dampening Framework (EB and MB) and Gamma Ray Detection and Time Projection Chamber Simulations Using Geant4 (AR)
Summer 2020 - Andrea Bracamonte and Lauren Fisher
Project Title: Gamma Ray Detector Simulation Using Geant4
Summer 2019 - Nathan Magrogan and Brennan Watkins
Project Title: Gamma Ray Spectroscopy Simulations with Geant4
Summer 2018 - Andrew Clusserath and Bryce Makela
Project Title: Gamma Detection Simulations in Nuclear Isomers
Summer 2017 - Henry Thurston
First Project Title: 3 Body Nuclear Kinematic Modeling
Second Project Title: Finding a Relation Between Galactic Redshift and Radial Distance
Summer 2016 - Joey Gutierrez and Jourden Simmons
Project Title: Monte Carlo Acceptance Simulations for the Prototype Active-Target Time-Projection Chamber
Summer 2015 - Michael Wolff (College of Wooster)
Project Title: Measurement of Gain and Drift Velocity of the Prototype AT-TPC, presented at the 2015 Fall Meeting of the APS Division of Nuclear Physics