kini mini
Active Member
Another of my posts from The Alchemist . It's been far too long since I read this mag, it's very good 
. This particular article relates to the practical applications of the techniques you learn about in Q2Q.
http://www.chemweb.com/alchem/articles/1044877175738.html
PDF version attached if you want the links and pics
Though originally mostly a physicist's tool, chemists, biologists, and geologists also use a subatomic particle accelerator called a synchrotron to help unravel the mysteries of their field. Because the synchrotron gives chemists a close-up look at molecules, one geologist uses it to determine whether chemical pollution at some American Superfund sites is dangerous or inert and what should be done about it, writes Jean Thilmany.
Gordon Brown, geology professor at Stanford University in California, uses synchrotron-based spectroscopy to show whether some of America's worst Superfund sites polluted with heavy metals like mercury or chromium should be cleaned up or left alone.
Synchrotron-based spectroscopy
A synchrotron is an oval-shaped subatomic particle accelerator used to determine a molecule's form and function. Scientists siphon extremely narrow, bright X-ray beams from synchrotrons and use that light to take snapshots of biological molecules or charged atoms in water on the surfaces of minerals. Environmental scientists like Brown have discovered they can use synchrotron-based spectroscopy to examine environmental contaminants in greater detail than by other means.
"The bottom line is, we can use synchrotron-based spectroscopy to determine rather quickly what the chemical form of mercury or chromium or other heavy metals is in different environmental settings and therefore determine potential danger, like whether these metals are toxic or bioavailable," said Brown.
The X-rays from a synchrotron are several million times brighter than the X-rays used in a dentist's office, Brown continued. These intense X-ray beams allow for the detection of elements and phases at much lower concentrations than possible with conventional X-ray techniques such as X-ray diffraction, which requires samples to be highly ordered at the atomic levels.
Scientists can tune synchrotron beams through a range of energies from a few electron volts to about 100 000 electron volts. They can use the synchrotron to deliver X-rays of a specific energy and focus on objects as small as 50 nm at the lower energies, about five times the thickness of the metal film on a bag of potato chips. This miniscule thickness is the size of colloids, particles suspended in water that can transport the contaminants Brown studies.
Scientist David Day working on a double-crystal monochromator at an SSRL beamline. Image courtesy of Stanford Linear Acclerator Center.
When six oxygen atoms surround a chromium atom, chromium takes the harmless, trivalent form. When surrounded by four oxygen atoms, however, chromium assumes the hexavalent form that can cause cancer. Whether chromium is benign or malignant comes down to miniscule difference in the distance between atoms and the number and types of atoms surrounding it; differences seen with a synchrotron. The same is true of other contaminants including arsenic, lead, uranium, and plutonium. The distance between atoms helps define a molecule's structure and thus its toxicity in the environment and its behaviour in living cells.
Isolating good from bad chromium
Brown's work with the synchrotron has revealed some surprises. For example, some contaminants occur in the environment in inert form, so it may be better to leave them alone rather than clean them up. Also, some of the geological features of the contaminants might even keep other types of contaminants at bay. Brown's findings could guide cleanup of some of the 1235 hazardous waste sites identified as priorities for clean up under the US Superfund program. Congress established the program in 1980 to give the government authority to clean up or establish individual ways of addressing the nation's most serious hazardous waste sites, called Superfund sites.
To study the molecules, Brown places a sample of a potential pollutant in a holder and shines X-rays on it, gradually increasing the energy until a big jump in absorbed light called the absorption edge signals the excitation of a specific electron in an atom. That jump and associated fine structure form a pattern an atomic fingerprint that reveals the local structure around the atom within a molecule or solid. This technique, called X-ray absorption fine structure spectroscopy, reveals an atom's oxidation state and shows which other atoms the original atom is bound to locally, and in what type of solid the atom occurs.
X-ray absorption fine structure spectroscopy is one of many synchrotron techniques that have given environmental science and other disciplines new analytical teeth, according to Brown.
Speculating on chemical pollutants
With graduate student Jeff Catalano and other scientists, Brown is now determining the form of chromium and uranium sent from underneath the Hanford Tank Farm in the state of Washington to the Stanford Synchrotron Radiation Laboratory, where Brown is faculty chair. About half the US high-level radioactive waste is stored at this tank farm. Chromium used in rods from nuclear reactors has been released from spills during overfilling and from leaks in deteriorating tanks. It's seeping into the groundwater and into the nearby Columbia River.
Brown is charged with discovering if the chromium is the good, trivalent form or the bad, hexavalent form.
He's found through his synchrotron studies that the majority is hexavalent and, further, can be transported great distances in flowing groundwater. The Stanford team did discover that some bad chromium was transformed to good chromium while travelling through a porous layer of sediment and into the groundwater, though not enough to prevent some of the bad stuff from making it into the water table.
"But it turns out it's not as disastrous as you think because the natural background level of radiation coming down the Columbia River is greater than the stuff introduced into it by the leaking Hanford tanks," said Brown. "We're exposed to radioactivity in many places anyway because rocks contain radioactive elements."
Synchrotron-based spectroscopy conducted at the Stanford laboratory has already saved millions of dollars in clean up costs. A group from the US Department of Energy's Los Alamos National Laboratory asked the laboratory in the late 1990s to determine the form of plutonium in contaminated soil and concrete at the former Rocky Flats plutonium processing plant in Colorado. Synchrotron-based spectroscopy revealed the form to be extremely insoluble.
"That knowledge, coupled with how plutonium is distributed saved the contractor and the US taxpayer millions of dollars because they didn't have to do nearly as much as they thought they would in terms of clean up," said Brown.
. This particular article relates to the practical applications of the techniques you learn about in Q2Q. http://www.chemweb.com/alchem/articles/1044877175738.html
PDF version attached if you want the links and pics
Though originally mostly a physicist's tool, chemists, biologists, and geologists also use a subatomic particle accelerator called a synchrotron to help unravel the mysteries of their field. Because the synchrotron gives chemists a close-up look at molecules, one geologist uses it to determine whether chemical pollution at some American Superfund sites is dangerous or inert and what should be done about it, writes Jean Thilmany.
Gordon Brown, geology professor at Stanford University in California, uses synchrotron-based spectroscopy to show whether some of America's worst Superfund sites polluted with heavy metals like mercury or chromium should be cleaned up or left alone.
Synchrotron-based spectroscopy
A synchrotron is an oval-shaped subatomic particle accelerator used to determine a molecule's form and function. Scientists siphon extremely narrow, bright X-ray beams from synchrotrons and use that light to take snapshots of biological molecules or charged atoms in water on the surfaces of minerals. Environmental scientists like Brown have discovered they can use synchrotron-based spectroscopy to examine environmental contaminants in greater detail than by other means.
"The bottom line is, we can use synchrotron-based spectroscopy to determine rather quickly what the chemical form of mercury or chromium or other heavy metals is in different environmental settings and therefore determine potential danger, like whether these metals are toxic or bioavailable," said Brown.
The X-rays from a synchrotron are several million times brighter than the X-rays used in a dentist's office, Brown continued. These intense X-ray beams allow for the detection of elements and phases at much lower concentrations than possible with conventional X-ray techniques such as X-ray diffraction, which requires samples to be highly ordered at the atomic levels.
Scientists can tune synchrotron beams through a range of energies from a few electron volts to about 100 000 electron volts. They can use the synchrotron to deliver X-rays of a specific energy and focus on objects as small as 50 nm at the lower energies, about five times the thickness of the metal film on a bag of potato chips. This miniscule thickness is the size of colloids, particles suspended in water that can transport the contaminants Brown studies.
Scientist David Day working on a double-crystal monochromator at an SSRL beamline. Image courtesy of Stanford Linear Acclerator Center.
When six oxygen atoms surround a chromium atom, chromium takes the harmless, trivalent form. When surrounded by four oxygen atoms, however, chromium assumes the hexavalent form that can cause cancer. Whether chromium is benign or malignant comes down to miniscule difference in the distance between atoms and the number and types of atoms surrounding it; differences seen with a synchrotron. The same is true of other contaminants including arsenic, lead, uranium, and plutonium. The distance between atoms helps define a molecule's structure and thus its toxicity in the environment and its behaviour in living cells.
Isolating good from bad chromium
Brown's work with the synchrotron has revealed some surprises. For example, some contaminants occur in the environment in inert form, so it may be better to leave them alone rather than clean them up. Also, some of the geological features of the contaminants might even keep other types of contaminants at bay. Brown's findings could guide cleanup of some of the 1235 hazardous waste sites identified as priorities for clean up under the US Superfund program. Congress established the program in 1980 to give the government authority to clean up or establish individual ways of addressing the nation's most serious hazardous waste sites, called Superfund sites.
To study the molecules, Brown places a sample of a potential pollutant in a holder and shines X-rays on it, gradually increasing the energy until a big jump in absorbed light called the absorption edge signals the excitation of a specific electron in an atom. That jump and associated fine structure form a pattern an atomic fingerprint that reveals the local structure around the atom within a molecule or solid. This technique, called X-ray absorption fine structure spectroscopy, reveals an atom's oxidation state and shows which other atoms the original atom is bound to locally, and in what type of solid the atom occurs.
X-ray absorption fine structure spectroscopy is one of many synchrotron techniques that have given environmental science and other disciplines new analytical teeth, according to Brown.
Speculating on chemical pollutants
With graduate student Jeff Catalano and other scientists, Brown is now determining the form of chromium and uranium sent from underneath the Hanford Tank Farm in the state of Washington to the Stanford Synchrotron Radiation Laboratory, where Brown is faculty chair. About half the US high-level radioactive waste is stored at this tank farm. Chromium used in rods from nuclear reactors has been released from spills during overfilling and from leaks in deteriorating tanks. It's seeping into the groundwater and into the nearby Columbia River.
Brown is charged with discovering if the chromium is the good, trivalent form or the bad, hexavalent form.
He's found through his synchrotron studies that the majority is hexavalent and, further, can be transported great distances in flowing groundwater. The Stanford team did discover that some bad chromium was transformed to good chromium while travelling through a porous layer of sediment and into the groundwater, though not enough to prevent some of the bad stuff from making it into the water table.
"But it turns out it's not as disastrous as you think because the natural background level of radiation coming down the Columbia River is greater than the stuff introduced into it by the leaking Hanford tanks," said Brown. "We're exposed to radioactivity in many places anyway because rocks contain radioactive elements."
Synchrotron-based spectroscopy conducted at the Stanford laboratory has already saved millions of dollars in clean up costs. A group from the US Department of Energy's Los Alamos National Laboratory asked the laboratory in the late 1990s to determine the form of plutonium in contaminated soil and concrete at the former Rocky Flats plutonium processing plant in Colorado. Synchrotron-based spectroscopy revealed the form to be extremely insoluble.
"That knowledge, coupled with how plutonium is distributed saved the contractor and the US taxpayer millions of dollars because they didn't have to do nearly as much as they thought they would in terms of clean up," said Brown.