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Blurring the Boundaries of Existence

A team of researchers led by the nuclear physics groups at the University of Liverpool, STFC’s Daresbury Laboratory and the University of Jyväskylä in Finland have discovered that nuclei can exist in special states that blur the boundaries of existence. This research highlights how UK technology and expertise is enabling research into the behaviour of isotopes that are so very rare they might only exist momentarily during stellar explosions. Until now, these could have only been predicted through theoretical calculations; but the reality is proving to be very different to the theory.

In a paper published in Physical Review Letters, the team, which was supported by STFC, report the experimental discovery of an isomer of tantalum with a structure that allows it to live longer than expected before decaying.

Jurogam
  (Credit: University of
Jyväskylä)

The research was carried out at the nuclear physics research facility at the University of Jyväskylä in Finland, where some of the key technology, including the highly powerful GREAT and JUROGAM spectrometers were designed and developed by STFC’s Nuclear Physics Group and UK Universities, including Liverpool.

Identifying the full extent of the nuclear landscape – essentially how many isotopes exist – is a long-standing issue of fundamental importance for nuclear physics. Beyond the stable nuclei that we find on Earth, there are many unstable nuclei that are formed in stellar events such as supernovae, but which are short-lived. There is a limit to how many protons and neutrons a nucleus can hold – too many and the excess literally ‘pop out’. These limits are known as the proton and neutron ‘drip lines’.

The University of Liverpool’s Professor Robert Page, who led the research, said: “We usually think of nuclear ground states as being the most stable, but these results show that certain excited states have enhanced stability and could extend the range of observable nuclei far beyond the drip lines.”

Although these drip lines can be calculated theoretically, experimental results rarely agree. Finding them experimentally is a difficult prospect, and the research outlined in this paper was only made possible by instrumentation designed and realised in the UK, and is now running successfully in Finland.

Professor John Simpson, Head of STFC’s Nuclear Physics Group, said: “Nuclear physicists look to create and study the very rarest isotopes predicted to exist. It is really exciting to see technology developed by the Nuclear Physics Group at STFC and UK Universities contribute to this research that challenges theories that, until now, we have only been able to predict. These scientific advances that are now emerging are the result of years of innovative technical development and investment by the UK and a strong and fruitful collaboration with the University of Jyväskylä".

 
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