Experimental nuclear physics

Overview

By bombarding targets with intense beams of high-energy ions, we induce nuclear reactions that yield radiation and radioisotopes, which can be used for a wide range of research applications. The nuclear data generated by these experiments informs our understanding of nuclear astrophysics, stockpile stewardship, nuclear safeguards, and nuclear nonproliferation, as well as fundamental nuclear science. These measurements often take the form of nuclear cross sections—valuable experimental data used to support our national security mission.

The experiments conducted at CAMS provide data on a wide range of radioisotopes, from nuclei just off stability to short-lived fission products. In addition, the experiments enable scientists to pursue direct measurements of actinides to determine cross sections that are otherwise difficult to measure.

New experimental approach developed to study nuclear reactions

A gamma spectrometer. — At LLNL’s Nuclear Counting Facility, researchers used gamma spectrometers to capture measurement data regarding isotopes produced during their experiments at CAMS.

LLNL scientists study nuclear reactions that are similar to those found in astrophysical environments, such as reactions that take place when supernovae explosions seed the galaxy with heavy elements. It is difficult to make these measurements in a laboratory due to the low probability that the nuclear reactions will occur.

To make these complex measurements possible, LLNL researchers developed a novel experimental approach. At CAMS, they irradiated a natural strontium target with helium-4 ions, producing zirconium-91, a stable isotope. CAMS instruments offer the sensitivity needed to detect the zirconium-91 produced during the reaction, enabling researchers to measure how much of it was generated during irradiation. In addition, they used gamma spectrometers at LLNL’s Nuclear Counting Facility to capture unstable isotopes created when the helium-4 particles reacted with the strontium isotopes.

What’s next: Researchers are studying the nuclear reaction data produced during these initial proof-of-concept experiments to better understand reactions that play a key role in nuclear astrophysics. In addition, scientists can use the new technique to study other mission-critical nuclear reactions to support the Lab’s nuclear forensics and stockpile stewardship research.

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Nuclear safeguards

Researchers take a selfie while working in a laboratory. — LLNL scientists study alpha-induced nuclear reactions at CAMS—research that supports the Lab’s nuclear safeguards and nonproliferation mission.

Alpha emission is a common decay mode for actinide materials. These energetic particles can induce secondary nuclear reactions in neighboring materials, thereby producing neutrons and gamma rays, which have a distinct isotopic signature that can be used to identify materials within a bulk sample.

At CAMS, we can study these alpha-induced nuclear reactions at precise and accurate bombarding energies. By varying the irradiation energy in very fine steps, we can map out how the nuclear cross section changes. These experiments produce rich data sets, providing researchers with the tools they need to screen and identify nuclear material.

For example, we measure alpha-induced reactions on isotopes of oxygen and aluminum that are commonly found in bulk samples. By measuring these reactions at CAMS, we can improve the efficiency and reliability of activities focused on detecting actinide materials in nuclear fuel matrices. As such, this research capability supports LLNL’s nonproliferation mission.