Cryogenic Microcalorimetry: New Tool for Nuclear Dating

Researchers develop ultra-sensitive technique to precisely measure the age of nuclear materials.

Apr. 3, 2026 at 3:18am

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A highly structured abstract painting in soft, flat colors depicting sweeping geometric arcs, concentric circles, and precise spirals, conceptually representing the complex scientific forces and measurements behind a new nuclear dating method.An abstract visualization of the precise quantum measurements at the heart of a new cryogenic technique for dating nuclear materials.Livermore Today

Scientists at Lawrence Livermore National Laboratory and collaborators have developed a novel approach using cryogenic microcalorimetry to precisely measure the age of nuclear materials. This new technique, called decay energy spectrometry (DES), can determine the age of a 100-day old plutonium sample weighing just 26 trillionths of a gram by measuring the decay-rate ratio of plutonium-241 to its decay product americium-241. DES offers advantages over traditional mass spectrometry and radiation-based methods, providing faster analysis, increased cost-efficiency, and the ability to work with extremely small sample sizes.

Why it matters

Accurate nuclear age-dating is crucial for verifying the origin and history of nuclear materials, which is important for nuclear forensics and safeguards efforts. Organizations like the International Atomic Energy Agency can use these results, along with other measurements, to confirm whether nuclear materials match what states have declared under international safeguards or to identify any undeclared activities.

The details

The DES technique relies on ultra-sensitive quantum sensors called Magnetic Microcalorimetry (MMC), which are cooled to near-absolute zero. When a radioactive decay occurs, the released energy causes a tiny temperature rise and corresponding change in the material's magnetism. These magnetic changes are measured by a quantum magnetometer with extreme precision. By embedding the plutonium sample directly in the microcalorimeter, the team was able to measure each decay event individually and use the ratio of plutonium-241 to americium-241 as a "radioactive clock" to date the age of the sample with an uncertainty of only a few days.

  • The plutonium sample used in the study was 100 days old.
  • The microcalorimeter detector is cooled to 0.02 K within 12 hours for rapid sample analysis.

The players

Lawrence Livermore National Laboratory (LLNL)

A U.S. Department of Energy national laboratory that conducts research in various scientific and engineering fields, including nuclear science and technology.

University of New Mexico

A public research university located in Albuquerque, New Mexico, that collaborated with LLNL on this research.

University of Michigan

A public research university located in Ann Arbor, Michigan, that also collaborated with LLNL on this research.

Geon-Bo Kim

An LLNL staff physicist who worked on the development of the cryogenic microcalorimetry technique.

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What they’re saying

“Mass spectrometry is extremely precise, but it can require complex preparation and careful laboratory work.”

— Geon-Bo Kim, LLNL staff physicist

“It's a new approach directly counting individual nuclear decays with 100% efficiency. We believe that it can complement today's state-of-the-art methods by providing an independent, orthogonal measurement for added confidence.”

— Geon-Bo Kim, LLNL staff physicist

What’s next

The researchers plan to continue developing the cryogenic microcalorimetry technique and exploring its potential applications in nuclear forensics and safeguards.

The takeaway

This new cryogenic microcalorimetry approach offers a highly precise and efficient method for determining the age of nuclear materials, which can provide critical information to support global security efforts and verify the origins of nuclear samples.