European center explores new territory in nuclear fission.
announced Monday the discovery of an unexpected new type of asymmetric nuclear
fission, which challenges current theories.
"The surprising result opens the way for new nuclear structure models and
further theories to elucidate the question," said CERN in a press release.
Resonance Ionization Laser Ion Source (RILIS) in action at ISOLDE, it said,
adding that RILIS was instrumental in providing the pure beam necessary for
the successful nuclear fission experiment.
Nuclear fission is exploited in power plants to produce energy, it pointed
In nuclear fission, the nucleus splits into two fragments (daughter
nuclei), releasing a huge amount of energy, it said.
From the fundamental research point of view, fission is not yet fully
understood decades after its discovery and its properties can still surprise
nuclear physicists, it said.
The way the process occurs can tell us a lot about the internal structure
of the nucleus and the interactions taking place inside the complex nuclear
structure, the release said.
In particular, processes in which fission is observed at an energy just
above the minimum required are the most likely to tell us which quantum
corrections should be applied to the liquid-drop model (classical description)
to fully understand nuclear behavior, it added.
At ISOLDE, an international collaboration involving scientists from nine
countries has been studying the 180Tl isotope, it said.
Via radioactive decay, the thallium isotope transforms into the 180 isotope
of mercury (180Hg), which subsequently fissions, it said.
"According to previous experiments and related theoretical models, we were
expecting a symmetric mass distribution of the fission fragments," says A. N.
Andreyev, the principal investigator from the team.
"However, we measured an asymmetric mass distribution of the fission
fragments. This discrepancy is leading us to rethink our theories on the
interplay between the macroscopic liquid-drop model and the microscopic
single-particle shell corrections to apply in the description of these nuclei,
" he added.
The result follows other attempts to understand similar fission processes
that were made about 20 years ago by scientists in Dubna.
"Previous experiments had to deal with huge amounts of contaminants in the
samples of the parent element. Using ISOLDE's unique laser ion source that
makes it possible to selectively ionize elements, we can obtain a high-purity
sample of 180Tl (T1/2=1.1 s). This allows us to determine with an
unprecedented accuracy the different branching ratios of the various decays,"
The unexpected result of ISOLDE's experiment will stimulate the development
of new theoretical approaches to the fission process.
"We have worked on a new description of the internal structure of the Hg
nucleus, which is able to predict the asymmetric mass splits that we have
observed. Further experiments and new theories are needed to elucidate the
dynamics of the fission processes, at least for nuclei located in the region
around thallium in the nuclei chart," concludes Mark Huyse, another member of
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