[ RadSafe ] Neutron activation used to date gold from volcanic eruptions in trees

[John Jacobus]

I orginally received this through an announcement by
the National Science Foundation at
http://www.nsf.gov/publications/pub_summ.jsp?ods_key=PR05099

The Penn State University article is at
http://live.psu.edu/story/12203
---------------- 
 Nuclear approach may help climate researchers
pinpoint volcanic eruptions 
 
University Park, Pa. –There's gold in them thar rings.
Tree rings that is, and Penn State researchers are
using the Breazeale Nuclear Reactor to measure gold
and link the rings to volcanic eruptions.

"Initially, when we began this work at Cornell
University, we were simply looking to see what
elements in tree rings could be measured using neutron
activation analysis," says Dr. Kenan Unlu, professor
of nuclear engineering and associate director for
research of Penn State's Radiation Science and
Engineering Center. "We can see a lot of elements, but
it is easy to see the gold peak."

When Peter I. Kuniholm, professor of archaeology and
dendrochronology and director of the Malcolm and
Carolyn Wiener Laboratory for Aegean and Near Eastern
Dendrochronology at Cornell, saw which tree rings held
the highest gold levels, he quickly recognized that
they dated to years of known volcanic eruptions.

Because trees add a ring a year to their trunks, if
researchers know the cutting date of a tree or can
calibrate the tree's rings against a previously dated
tree, researchers can assign each ring accurately to a
specific year. By isolated wood from just one ring,
neutron activation analysis can measure the gold that
the tree took up during that year with parts per
billion sensitivity.

Neutron activation analysis uses the neutrons produced
by a nuclear reactor to create temporary radioactive
isotopes in a sample. Because each isotope has its own
gamma radiation signal, the gamma radiation signal
strength indicates the amount of that element present.

When Cornell's nuclear reactor at the Ward Center for
Nuclear Sciences was shut down, Unlu moved the
project, which was funded in part by the National
Science Foundation, to Penn State's Breazeale Nuclear
Reactor. The preliminary results of analysis of one
tree for the years 1411 through 1988 were presented in
a recent issue of the Journal of Radioanalytical and
Nuclear Chemistry.

Working with Kuniholm and John J. Chiment, another
researcher at the dendrochronology laboratory, and
Corrnell undergraduate students Pam Sullivan, Meg
Underwood and Danielle Hauck, Unlu analyzed 577 rings
from a Bosnian or palebark pine from Greece. 

"We are looking at the last 500 to 600 years to gain
confidence in the procedure," says Unlu. "The volcanic
eruptions during that time are known, so we can make
correlations. Then we will go back and look at the
past 6,000 years."

Six thousand years into the past is the depth of the
samples currently at Cornell's dendrochronology
laboratory. The lab has already dated approximately
4.5 million tree rings to this time.

The researchers found that they successfully matched
gold peaks to volcanic eruptions beginning with an
eruption of the Soufriere Hills volcano in 1440 and
including a 1480 eruption of Mt. St. Helens. However,
the researchers also had high gold peaks for a number
of years between 1480 and 1580 when there were no
known volcanic eruptions.

"When we see major gold peaks but no volcanoes, it
could be forest fires," says Unlu. "We cannot really
tell if we are seeing a global signal or a regional or
local signal when we are looking at only one tree."

How can a forest fire be confused with a major
volcanic eruption? If the researchers are correct,
easily. Unlu believes that the increased gold uptake
during volcano years occurs because the volcanoes put
large amounts of particulate matter into the
atmosphere and change the environmental acidity as
well as the rainfall, sunshine and temperature
patterns creating a stressful situation for trees. The
trees, to compensate for a lousy year, try to take up
more nutrients, including copper, an essential element
for tree growth and health. The gold is
indiscriminately absorbed along with the copper, but
the copper is used for tree metabolism while the gold
remains in the new growth.

Another possible cause of the increased gold uptake
could be through the leaves because of direct fallout
from the volcanic eruptions, but Unlu believes it is
the darkness and stress that push the trees to search
for copper among other elements.

To eliminate forest fires and other local events, the
researchers want to look at other trees from other
areas. They are currently looking at two dated trees
from Turkey and one from California.

"The main problem in atmospheric science is they do
not have enough data," says Hauck, now a graduate
student in nuclear engineering at Penn State. "We want
to correlate tree ring data with climate cycles to get
a much better indication of what is natural and what
is anthropogenic. Tree rings can help."

Large volcanic eruptions put particles into the wind,
into the jet stream and have a global, rather than
only local effect.

Unlu would also like to go back and check the samples
with high gold for other elements. Because neutron
activation analysis is nondestructive, and the samples
are no longer radioactive after about a month, this
reanalysis for other elements is possible. Unlu now
has a Nuclear Engineering Education and Research grant
from the U.S. Department of Energy to continue his
analysis of tree rings and correlation to volcanic
activity and other climate events. 

Photos Available at:
http://www.psu.edu/ur/2005/treeringgoldphotos.html 

Contact
  A'ndrea Messer
  aem1 at psu.edu
  http://live.psu.edu
  814-865-9481
  
Contact
  Vicki Fong
  vfong at psu.edu
  http://live.psu.edu
  814-865-9481 

+++++++++++++++++++
"Every now and then a man's mind is stretched by a new idea and never shrinks back to its original proportion." -- Oliver Wendell Holmes, Jr.

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com


		
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