Having problems with message search?
The classic college physics experiment is to find out the "age" of thorium mantles by Gamma spectrometry. Although it may take 25 years for all the daughters to grow back in, in only 7 years the ratio of Ra-228 to Th-228 is already stable. This ratio during the first 7 years can give a very accurate "age" of a mantle. Unfortunately, all ours are now older than that, and won't be made in U.S. any more. In practice, Ac-228 is measured with a Gamma Spec, to indicate the Ra-228 activity, and Pb-212 is measured to indicate the Th-228 activity. After the energy correction is made, and background stripped, the ratio indicates the Ra-228/Th-228 ratio and therefore the age( 0-7 Y) according to a standard chart. http://www.qsl.net/k0ff/index_files/ThoriumMantle%20Age%20small.jpg
Reference:
"Experimental Gamma Ray Spectroscopy" R.S. Peterson ©1996
Reference:
Am. J. Phys., Vol. 51, No. 6, June 1983 Pages 538 - 542
Determining the age of gas lantern mantles using gamma-ray analysisJohn Luetzelschwab
(Received 12 April 1982; accepted for publication 2 August 1982)
The thorium used in gas lantern mantles is a naturally radioactive element. Using the buildup and decay of the daughters in the thorium decay series, the age of a gas lantern mantle can be determined. "Have funGeo
Offline 
Send Email