U-238 equilibrium in granite ??

[Chi-Chang Liu <chichang@ma.kswan.org.tw>]

Dear radsafers,

I had a problem when I tried to identify U-238 concentrations in granite and
other building materials. The gamma spectroscopy results the specific
activities of Pa-234m and Bi-214 are quite different. Since all samples had
been pretreated by tightly packed of thin PE film to reduce radon exhalation
and idled for one month before counting. The peaks for Pa-234m and Bi-214
are 1.001MeV and 0.609 Mev, respectively. Peak area handling, efficiency
calibration and brach ratio correction are done by CABERRA Genie PC system.

The results of 50 granite samples show that the correlation between specific
activities of Pa-234m and Bi-214 are:

[Bi-214]=0.52*[Pa-234m] with R-square=0.7

The results of 30 tile samples show that the correlation between specific
activities of Pa-234m and Bi-214 are:

[Bi-214]=0.50*[Pa-234m] with R-square=0.8

If refered to Radium-226 at peaks 186.21 keV, the specific activities of
Ra-226 in samples are some little more then specific activities of Pa-234m.

I can figure out why U-238 in granite is so disequilibrium ? Would any one
give me some suggestions about how should I express the U-series
concentration in granite and how to explain the disequilibrium phenomenon ?

Thank you very much !!

ChiChang Liu,
Engineer
Radiation Monitoring Center
chichang@ma.kswan.org.tw

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html