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Snapshot of a nuclear reaction showing a high-energy neutron causing a carbon-12 atom to break apart into three alpha-particles, leaving a low-energy neutron (left). This is the reverse of how the process would occur in nature (right).
Snapshot of a nuclear reaction showing a high-energy neutron causing a carbon-12 atom to break apart into three alpha-particles, leaving a low-energy neutron (left). This is the reverse of how the process would occur in nature (right).
Image courtesy of Jack Bishop

The Science

Advances in technology have enabled scientists to produce extremely precise snapshots of nuclear reactions. Time Projection Chambers (TPCs) enable scientists to study the interactions of rare nuclei that are accelerated to a fraction of the speed of light and that then collide with gas. Researchers then study the resulting nuclear reactions with exotic nuclei and observe rare radioactive decay. These studies give us insights into the nuclear force, the strongest and least-understood of the four fundamental forces in the standard model of particle physics. Many experiments that can now be performed with a TPC were impossible or very difficult with previous technologies. 

The Impact

Researchers are using TexAT, a TPC at Texas A&M University, to study important reactions in stars by measuring the “time-reverse” scenario of nuclear processes. This process involves studying a mirror image version of extremely high-speed processes in stars. This reverse sequence is easier to observe. While firing a beam of neutrons into the TPC, researchers looked at the breakup of carbon in carbon dioxide gas into three radioactive alpha particles in the form of helium-4 nuclei. Measuring the likelihood of this reaction tells us how something scientists call the ‘triple-alpha process’ can increase stars’ production of carbon. These studies help us understand whether stars create carbon during their normal lives, or whether they also create carbon during nucleosynthesis in supernovae or neutron star collisions. Researchers have also used the TexAT TPC in experiments involving the exotic nuclei carbon-9 and beryllium-13. These studies help us understand how nuclear structure changes as we add more protons or neutrons to already exotic and unstable nuclei. 

Summary

TexAT is a gas-filled Time Projection Chamber. Sending radioactive nuclei into the detector causes them to interact with the gas. Any products from the reaction that are charged (i.e. protons, deuterons, or alpha particles) will produce electrons as they interact with the gas. Researchers can then record images of the nuclear reactions that occur and can reconstruct a three dimensional image of any products created from these reactions. This allows for sensitive studies of the different reactions that are important for understanding how stars live and die.

Contact

PI: Grigory Rogachev 
Department of Physics and Cyclotron Institute, Texas A&M University
rogachev@tamu.edu
 
Communication: Jack Bishop
Cyclotron institute, Texas A&M University
jackbishop@tamu.edu

Funding

This work was supported by the Department of Energy Office of Science, Office of Nuclear Physics; by the National Nuclear Security Administration through the Center for Excellence in Nuclear Training and University Based Research; and by the Nuclear Solutions Institute at Texas A&M University. 

Publications

Koshchiy, E., et al., “Texas Active Target (TexAT) detector for experiments with rare isotope beams.” Nuclear Instruments and Methods in Physics Research Section A 957, 163398 (2020) 
[DOI: 10.1016/j.nima.2020.163398]

Hooker, J. et al. “Structure of 9C through proton resonance scattering with the Texas Active Target detectorPhysical Review C 100, 054618 (2019) [DOI: 10.1103/PhysRevC.100.054618]

Bishop, J. et al., “Beta-delayed charged-particle spectroscopy using TexAT.” Nuclear Instruments and Methods in Physics Research Section A 964, 163773 (2020) 
[DOI: 10.1016/j.nima.2020.163773]

Bishop, J. et al., Almost medium-free measurement of the Hoyle state direct-decay component with a TPC" Physical Review C 102, 4 (2020). [DOI: 10.1103/physrevc.102.0410303]

Related Links

Texas A&M-Led Experiment Uses Novel Particle Detector to Track Alternate Theory Behind Carbon Creation in Stars, Texas A&M University College of Science News