European center explores new territory in nuclear fission.

The European Centre of nuclear researches (CERN)

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

out.

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,"

explains Andreyev.

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

the team.

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Publication:	Kuwait News Agency (KUNA)
Date:	Jan 17, 2011
Words:	499
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