Uranium isotope
While studying the atoms of heavy elements, physicists in Japan discovered a previously unknown isotope of uranium, with atomic number 92 and mass number 241, i.e. uranium-241.
The finding refines our understanding of nuclear physics. What shapes the large nuclei of heavy elements take and how often (or rarely) defines the boundaries of models that physicists use to design nuclear power plants and models of exploding stars.
“The discovery of a new neutron-rich uranium isotope is the first since 1979,” Toshitaka Niwase, a postdoctoral fellow with the KEK Wako Nuclear Science Centre (WNSC), Japan, and a member of the study, wrote in an email to The Hindu.
“This is because of the extreme difficulty of synthesising a nuclide in this region by general reaction.”
Why does a new isotope matter?
The arrangement of protons and neutrons in an atomic nucleus follows some rules. We know what these rules are based on the nuclei’s properties and structure.
“In general, an atom’s mass is slightly lower than the sum of the masses of protons, neutrons, and electrons,” Michiharu Wada, head of the WNSC and another member of the group, explained via email.
So systematically measuring the mass of “uranium and its neighbourhood elements yields essential nuclear information to understand the synthesis of such heavy elements in explosive astronomical events”.
How was uranium-241 found?
The researchers accelerated uranium-238 nuclei into plutonium-198 nuclei at the KEK Isotope Separation System (KISS). In a process called multinucleon transfer, the two isotopes exchanged protons and neutrons.
The resulting nuclear fragments contained different isotopes. This is how the researchers identified uranium-241 and measured the mass of its nucleus. Theoretical calculations suggest it could have a half-life of 40 minutes, according to Dr. Niwase.
The team used time-of-flight mass spectrometry to estimate the mass of each nucleus depending on the time it took to reach a detector. “Precise mass value is a good fingerprint of atomic nuclides,” Dr. Wada said.
“Our results are an experimental demonstration that the combination of the multinucleon transfer reaction and KISS can open up this area,” Dr. Niwase said.
“This approach is expected to lead to the discovery of more neutron-rich actinide nuclides, and to the elucidation and understanding of the stability of nuclides and the process of astronomical nucleosynthesis.”
What are ‘magic numbers’?
There is particular interest in ‘magic number’ nuclei: containing a number of protons or neutrons such that the resulting nucleus is highly stable. The heaviest known ‘magic’ nucleus is lead (82 protons). Physicists have been trying to find the next such element.
“We’d like to extend the systematic mass measurements towards many neutron-rich isotopes, at least to neutron number 152, where a new ‘magic number’ is expected,” Dr. Wada said.
Their work is a “first step” in this direction, he added.
Their paper was published by Physical Review Letters on March 31.
- While studying the atoms of heavy elements, physicists in Japan discovered a previously unknown isotope of uranium, with atomic number 92 and mass number 241, i.e. uranium-241.
- The finding refines our understanding of nuclear physics. What shapes the large nuclei of heavy elements take and how often (or rarely) defines the boundaries of models that physicists use to design nuclear power plants and models of exploding stars.
- There is particular interest in ‘magic number’ nuclei: containing a number of protons or neutrons such that the resulting nucleus is highly stable. The heaviest known ‘magic’ nucleus is lead (82 protons). Physicists have been trying to find the next such element.
