[ RadSafe ] 4.4 billion year old crystal
EMERDF at nv.doe.gov
Mon Feb 24 18:07:45 CST 2014
They don't actually need the U-238 concentration as they look at the in-growth of Pb-206 from U-238 in a zircon crystal. The structure of Zircon (ZrSiO4) allows it to readily contain a uranium impurity but excludes a lead impurity. So once the zircon is formed (cooled and crystallizes) it starts the clock with all Uranium and no Pb.
The age is then determined by the Pb/U ratio.
National Security Technologies, LLC (NSTec)
National Center for Nuclear Security
Nevada National Security Site, Mercury, Nv
U.S. DOE Contractor
email: emerdf at nv.doe.gov
P.O. Box 98521
M/S NNSS 980
Las Vegas, Nv 89193-8521
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Kulp, Jeffrey (DOH)
Sent: Monday, February 24, 2014 2:58 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] 4.4 billion year old crystal
I have a question about a news story I just read; it said that scientists in Australia had discovered a 4.4 billion year old zircon crystal.
The article went on to say that they had dated it using uranium decay to lead.
My question is how do they know what concentration of uranium the crystal started with? At present the concentration of uranium in the
earth's crust varies
quite a bit (two orders of magnitude or more?). Was the U concentration more uniform back when the crust just formed?
Given that the half-life of U-238 is roughly 4.4 billion years, how can they be so sure of its age?
Thanks in advance for the information
Jeffrey Kulp, RRPT
Radiation Health Physicist
Washington State Department of Health - ORP
16201 E. Indiana Ave. Suite 1500
Spokane Valley, WA 99216
(509) 329-2138 (Office)
(509) 329-2154 (Fax)
"Public Health - Always Working for a Safer and Healthier Washington"
You are currently subscribed to the RadSafe mailing list
Before posting a message to RadSafe be sure to have read and understood the RadSafe rules. These can be found at: http://health.phys.iit.edu/radsaferules.html
For information on how to subscribe or unsubscribe and other settings visit: http://health.phys.iit.edu
More information about the RadSafe