Month: March 2020

Radiation Damage Spreads

Radiation Damage Spreads Among Close Neighbors

X-ray absorption cascade
Direct hit. A soft x-ray (white) hits a holmium atom (green). A photo-electron zooms off the holmium atom, which releases energy (purple) that jumps to the 80-carbon fullerene cage surrounding the holmium. The cage then also loses an electron. (Courtesy of Razib Obaid)

 – Kim Krieger – UConn Communications

A single x-ray can unravel an enormous molecule, physicists report in the March 17 issue of Physical Review Letters. Their findings could lead to safer medical imaging and a more nuanced understanding of the electronics of heavy metals.

Medical imaging techniques such as MRIs use heavy metals from the bottom of the periodic table as “dyes” to make certain tissues easier to see. But these metals, called lanthanides, are toxic. To protect the person getting the MRI, some chemists wrap the lanthanide inside a cage of carbon atoms.

Molecular physicist Razib Obaid and his mentor, Prof. Nora Berrah in the physics department, wanted to know more about how the lanthanides interact with the carbon cages they’re wrapped in. The cages, 80 carbon atoms strong, are called fullerenes and are shaped like soccer balls. They don’t actually bond to the lanthanide; the metal floats inside the cage. There are many similar situations in nature. Proteins, for example, often have a metal hanging out close to a giant organic (that is, mostly made of carbon) molecule.

So Obaid and his team of collaborators from Kansas State University, Pulse Institute at Stanford, Max Planck Institute at Heidelberg, and the University of Heidelberg studied how three atoms of the lanthanide element holmium inside of an 80-carbon fullerene reacted to x-rays. Their initial guess was that when an x-ray first hit one of the holmium atoms, it would get absorbed by an electron. But that electron would be so energized by the absorbed x-ray that  it would fly right out of the atom, leaving a vacant spot. That spot would than get taken by another of the holmium’s electrons, which would have to jump down from the outer edge of the atom to fill it. That electron had formerly been partnered with another electron on the outskirts of the atom. When it jumped down, its lonely ex, called an Auger electron, would zoom away from the whole molecule and get detected by the scientists.  Its distinctive energy would give it away. 

It sounds complicated, but that would have been the simplest (and thus most likely) scenario, the physicists thought. But it’s not what they saw.

When Obaid and his colleagues zapped the holmium-fullerene molecule with a soft x-ray (about 160 electron-volts), the number of the Auger electrons detected was too low. And too many of the electrons had energies much less than the Auger electrons should have. 

After some calculating, the team figured out there was more going on than they’d guessed.

First, the x-ray would hit the holmium, which would lose an electron. The vacant spot would then be filled by the outer edge electron from the holmium atom. That much was correct. But the energy released by the jumping electron (when it jumps ‘down’ from the outskirts of the atom to the interior, it also jumps ‘down’ in energy) would then be absorbed by the carbon fullerene cage or another of the neighboring holmium atoms. In either case, the energy would cause an additional electron to zoom away from whatever absorbed it, the fullerene cage or the holmium atom.

Losing these multiple electrons destabilized the whole molecule, which would then fall apart entirely.

The end result?

“You can induce radiation damage just by striking one atom out of 84,” says Obaid. That is, a single x-ray strike is  enough to destroy the entire molecule complex through this energy transfer process involving neighboring atoms. It gives some insight into how radiation damage occurs in living systems, Obaid says. It was always thought that radiation damaged tissue by stripping away electrons directly. This experiment shows that interactions between an ionized atom or molecule and its neighbors can cause even more damage and decay than the original irradiation.

The work also gives medical physicists an idea of how to limit patient’s exposure to heavy metals used as dyes in medical imaging. Shielding all parts of the body from the radiation except for those to be imaged with heavy metal dyes can potentially restrict the heavy metal exposure as well as the radiation damage, the researchers say. The next step of this work would be to understand exactly how fast this interaction with the neighbors occurs. The researchers expect it to take place in just a few femtoseconds (10-15 s). 

The work was funded by Department of Energy, Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences, and Biosciences, under Grant No. DE-SC0012376.

RESCHEDULED: Professor Donna Strickland , Katzenstein Distinguished Lecturer, October 8, 2021

The next Katzenstein lecture has been rescheduled to October 8, 2021. More information to follow.

Dear Friends of UConn Physics,

Due to the current health situation and concerns surrounding the Corona virus, we are canceling the Katzenstein Lecture and Banquet scheduled for Friday, March 13, 2020.

It was an agonizing decision to cancel, but our first priority is the health of all who would have been attending, our special guest Professor Strickland, and the UConn community. I extend an extra apology for those of you who have planned to travel a considerable distance and will need to change plans. For those who have signed up for the banquet, we are working to arrange refunds.

If all goes well, the current health crisis will be behind us soon and we will see if we can reschedule Professor Strickland for another, safer time.

Again, my apologies and best wishes,

Barry Wells

Barrett O. Wells
Professor and Head, Department of Physics

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The University of Connecticut, Department of Physics, is proud to announce that on March 13, 2020, Professor Donna Strickland of the Department of Physics and Astronomy at the University of Waterloo will be presenting the 2020 Distinguished Katzenstein Lecture. Prof. D. Strickland Prof. Strickland is one of the recipients of the 2018 Nobel Prize in Physics for developing chirped pulse amplification with Gérard Mourou, her PhD supervisor. They published this Nobel-winning research in 1985 when Strickland was a PhD student at the University of Rochester in New York State. Together they paved the way toward the most intense laser pulses ever created. The research has several applications today in industry and medicine — including the cutting of a patient’s cornea in laser eye surgery, and the machining of small glass parts for use in cell phones.

Prof. Strickland earned a Bachelor in Engineering from McMaster University and a PhD in optics from the University of Rochester. She was a research associate at the National Research Council Canada, a physicist at Lawrence Livermore National Laboratory and a member of technical staff at Princeton University. In 1997, she joined the University of Waterloo, where her ultrafast laser group develops high-intensity laser systems for nonlinear optics investigations. She is a recipient of a Sloan Research Fellowship, the Ontario Premier’s Research Excellence Award and a Cottrell Scholar Award. She received the Rochester Distinguished Scholar Award and the Eastman Medal from the University of Rochester.

Prof. Strickland served as the president of the Optical Society (OSA) in 2013 and is a fellow of OSA, the Royal Society of Canada, and SPIE (International Society for Optics and Photonics). She is an honorary fellow of the Canadian Academy of Engineering as well as the Institute of Physics. She received the Golden Plate Award from the Academy of Achievement, is in the International Women’s Forum Hall of Fame, and holds numerous honorary doctorates.

Livestream of the talk: March 13 2020, 4:00 EST, https://www.youtube.com/channel/UCBv2Kp9wAsjHDfEHhIRc0pg

Reception: at 3pm in the Gant Light Court