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1. Filling in Some Age-Old Blanks: Physicists Calculate a Fundamental Property of the Rare Earths |
by Marcia Goodrich, senior writer
Physics Professor Don Beck's research team, including Research Associate Steven O'Malley, has filled in some longtime blank spaces on the periodic table. They have calculated electron affinities for the lanthanides, a series of 15 elements commonly known as rare earths.
"Electron affinity" is the amount of energy required to detach an electron from an anion, or negative ion (an atom with an extra electron orbiting around its nucleus). Elements with low electron affinities (like iron) give up that extra electron easily. Elements with high electron affinities (like chlorine) do not.
"I remember learning about electron affinities in 10th grade chemistry," said O'Malley. "When I began working as a grad student in atomic physics, I was surprised to learn that many of them were still unknown."
Among them were the lanthanides, which are used in the production of lasers and sunglasses. In terms of their atomic structure, lanthanides are among the most complex elements on the periodic table, which is why no one had been able to calculate their electron affinities before.
Here's what makes them so tricky. Electrons orbit in shells around an atom's nucleus, something like the layers of an onion, but in stranger shapes. Within each shell are a number of subshells. A subshell is like an egg carton: it can hold from one to a certain number of electrons, but no more.
Typically, as you work your way down and across the periodic table to larger and larger atoms, the inner shells fill up with electrons, and then new shells and subshells are formed and fill up pretty neatly.
That's not what happens with the lanthanides. Before their so-called 4f subshell fills up, the additional electrons begin making new shells. Then, gradually, as you move across the periodic table to heavier atoms in the lanthanide series, that 4f subshell finally fills up with its maximum number of 14 electrons.
Why would this matter for electron affinity? A number of forces hold electrons in their orbits around the atom's nucleus. Two simple ones are electrons' attraction to protons in the nucleus and repulsion away from their fellow orbiting electrons, what Beck calls "the B.O. effect."
The forces exerted by a full shell on the electrons orbiting farther from the nucleus are pretty constant, which had made it relatively easy to calculate the electron affinities of most elements. But if there are vacancies in the shell--as there are in the lanthanides--the electrons in that shell can move around, playing musical chairs, as it were.
The forces an electron exerts from each spot in the shell are different. And, in addition to simple electrical factors, there are other complex variables to contend with at the subatomic level, including relativistic and many-body effects.
"It's a nightmare," says Beck. With several electrons bouncing around in those 14 slots, over 200 different arrangements of electrons of the 4f subshell are possible in some of the lanthanides.
In 1994, the Beck research group, supported by the National Science Foundation, began work on one of the simpler lanthanide atoms, cerium. Then they started to approach the "nightmare" middle of the lanthanide row from both ends, one anion at a time. The most difficult anion treated was neodymium (Nd-) which took about six months of effort.
Then, in 2007, O'Malley and Beck began a final push to complete the remaining lanthanides (promethium through erbium) by
(1) carefully examining exactly what variables to include in the calculations; and
(2) writing scripts and auxiliary computer codes to automate much of the calculation.
As a result, they cut the overall work time by about 85 percent. In just 18 months, they found electron affinities for all the lanthanides, including electron affinities for high-energy, excited states of the anions. All in all, they discovered 118 lanthanide anion states, 63 of which were new.
What's next? The team's theoretical results have already been partially verified by experimentalists, but they are still working to better understand the lanthanides theoretically, to help identify just what is being measured experimentally.
In the meantime, they are turning their attention to the next row in the periodic table.
"We expect to have electron affinities for a portion of the actinides--actinum through plutonium--available sometime this summer," Beck said.
For more in-depth information, including article citations and corroborating findings from other institutions, visit www.phy.mtu.edu/~donald/lanea.html . |
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2. The Deadline for BRC Travel Grants is Mid-April |
The Biotechnology Research Center (BRC) at SFRES announces its spring 2009 travel grants, which provide financial assistance to undergraduate and graduate students and postdoctoral scientists who present their research at scientific meetings.
The grants promote biotechnological research and achievement.
To apply, complete the application form available at www.biotech.mtu.edu . Send the application to Mary Tassava, staff assistant in BRC, at mltassav@mtu.edu . The deadline is Wednesday, April 15.
The awards are merit-based and are offered twice per year. The fall 2009 deadline is Oct. 15. Incomplete applications will not be considered.
The spring awards will be announced at the end of April, the fall awards at the end of October. |
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3. Club Indigo Shows "The Dead," Serves Irish Fare |
Mu Beta Psi music fraternity brings John Huston's adaptation of James Joyce's greatest short story, "The Dead," to the Calumet Theatre's Club Indigo Friday.
The movie is at 7:15 p.m., preceded at 6 p.m. by an optional Irish buffet from Chef Cormac Ronan, Irish Times, Laurium. The cost for both is $18; the movie alone is $5. For the buffet, call the theater at least a day in advance: 337-2610.
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4. New Staff |
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Kenneth Leivdal joins Human Resources as a data analyst. He comes to Tech from Citizens Bank, where he was a loan systems administrator. He lives in Houghton with his wife and three children. |
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