In an experiment performed at Lawrence Berkeley National Laboratory’s 88-inch cyclotron, a team of physicists successfully created a new isotope of the human-made element mendelevium.
Mendelevium, a synthetic radioactive element of the actinide family with the symbol Md and atomic number 101, was first created by Berkeley Lab scientists in 1955.
The newly-created isotope, mendelevium-244, is the 17th and lightest form of mendelevium.
“It was challenging to discover this new isotope of mendelevium because all of the neighboring mendelevium isotopes have very similar decay properties,” said team leader Dr. Jennifer Pore, a scientist in the Nuclear Science Division at Lawrence Berkeley National Laboratory.
In total, Dr. Pore and colleagues measured the properties of 10 atoms of mendelevium-244.
They found evidence that the new isotope has two separate chains of decay, each leading to a different half-life: 0.4 second and 6 seconds, based on different energy configurations of particles in its nucleus.
Central to the discovery of mendelevium-244 was an instrument at the 88-inch cyclotron called FIONA (For the Identification Of Nuclide A).
“The most important tool that we had in this discovery was FIONA,” Dr. Pore said.
The team used FIONA to precisely measure the mass number of mendelevium-244.
“We built FIONA to enable discoveries like this one, and it is exciting to see this instrument hitting its stride,” said Dr. Barbara Jacak, Nuclear Science Division director at Lawrence Berkeley National Laboratory.
“Isotope discoveries are cyclical and depend on new accelerators and major advances in experimental equipment development,” added Michigan State University’s Professor Michael Thoennessen.
To ensure that FIONA’s measurements were accurate, the researchers first measured the decay properties and mass numbers of known mendelevium isotopes, including mendelevium-247, mendelevium-246, and mendelevium-245.
“Once we were confident that we were well-versed in the properties of these light mendelevium isotopes, we attempted the experiment to discover the previously unobserved isotope mendelevium-244,” Dr. Pore explained.
“Without the direct confirmation that we had produced an isotope with a mass number of 244, it would have been very difficult to disentangle the results and prove the discovery.”
In addition to discovering mendelevium-244, the scientists found the first evidence for the alpha decay process of berkelium-236, an isotope of berkelium, as it transforms into americium-232, a slightly lighter isotope.
Their results were published in the journal Physical Review Letters.
J.L. Pore et al. 2020. Identification of the New Isotope 244Md. Phys. Rev. Lett 124 (25): 252502; doi: 10.1103/PhysRevLett.124.252502
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