Fundamental nuclear decay data measurements using metallic magnetic calorimeters

Atomic particle

Work developed on an EMPIR project has made important progress on the knowledge of electron capture decay and subsequent atomic relaxation processes

Radioactive isotopes have been of significant scientific and technological interest ever since their discovery. Completed EMPIR project Measurement of fundamental nuclear decay data using metallic magnetic calorimeters (17FUN02, MetroMMC) has improved novel detection techniques and theoretical models to understand better the behaviour of radioactive elements undergoing electron capture decay. They undergo change in a variety of ways, electron capture decay being one such pathway. 

The project has made important progress with source and absorber preparation, which is a critical aspect of measurement with metallic magnetic calorimeters (MMC). The use of nano-porous gold, for example, has shown promising improvements over solid gold used in a preceding EMPIR project. High-resolution measurements obtained during the project have also highlighted spectrum features linked to source details that are not well understood. The need for developing high quality thin sources is recognised in several applications of modern radiation metrology including electron spectroscopy and high-resolution alpha spectrometry.

Additional achievements of the project include:

  • Theoretical models of electron capture and atomic relaxation have been developed for selected isotopes (54Mn, 65Zn, 109Cd) beyond the state-of-the art, and toward a more realistic modelling of the decay process. These include coupling of atomic and nuclear states and the inclusion of fine details of atomic structure. The model improvement realised are also important to extend calculations to other radionuclides, work that has already started within this project.
  • The first ever successful particle detection via a microwave-coupled resonator system has been achieved. Although the performance of the technology does not match that of MMC detectors, it has potential to be complementary to some low-temperature detectors with several potential advantages such as the ease of operation and the higher operational temperature.
  • Studies with iodine-125, which is an important isotope used in medical imaging, radiation therapy including prostate cancer, uveal melanomas, and brain tumours. It is also used for radiobiology assay and research. Results have shown that 125I capture probability is almost 5% different from the accepted value based on a measurement prior to 1964, which is an important difference.
  • New data on both electron capture and X-ray emission of nickel-59, which are important for nuclear decommissioning research and development of a robust metrology route for this isotope. This is a long-lived isotope produced in thermal-nuclear reactors as activation product of Ni cladded control rods and other steel structural components. It is present in nuclear waste and its detection is very difficult because of its long half-life and no g-rays emission.

Project Coordinator Dirk Arnold, from PTB, said

‘With this EMPIR project and the precursor project MetroBeta we made a big step forward to establish the MMC-technique with its unique energy resolution and extremely low energy threshold for the measurement of radionuclide decay data. And the development continues with the follow-up EMPIR project PrimA-LTD.’

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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