[ RadSafe ] Energy Shift

Cary Renquist cary.renquist at ezag.com
Fri Jun 5 14:14:03 CDT 2009

Hi Elaine,

I looked at some old data sheets we had on Ce-141 (I found two) -- one cited Ce-139 impurity 
at ~0.1% and the other was ~0.3% (of course, it will increase as the 141Ce decays...)
@ 0.3%, you would have ~15 nCi of C-139 in your sample.
That might be enough to extend the upper tail of your 145 keV peak out to the 165 keV Ce-139 line and hence shift your peak.
Are the low and high activity samples from the same batch?

Best regards,

Cary Renquist
Radiation Safety Officer
Manager, Health Physics
Eckert & Ziegler Isotope Products
Direct:   +1 661-309-1033
cary.renquist at ezag.com

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf Of Marshall, Elaine
Sent: Friday, 05 June 2009 10:49
To: radsafe at radlab.nl
Subject: [ RadSafe ] Energy Shift

We have been observing something interesting.


We are working with Ce-141 in varying concentrations.   We counted two
samples yesterday on three different pieces of equipment - LSC, gamma
counter and also ionization chamber connected to a MCA.  With the lower
activity (about 3000 cpm), we see nice peaks on the MCA at 36 keV and
145 keV as expected.  In this instance, the relative intensity of the 36
keV peak is about 2X that of the 145 keV peak.  However with the higher
activity samples (5 uCi) in the same geometry, the higher energy peak is
shifted to 158 keV and the 36 keV peak can not be distinguished from the
significant scatter.  Count rates in the first 30 channels are orders of
magnitude greater than the 158 keV peak.  


I am confused as to why we would see the energy shift (from 145 to 158)
on the MCA for the higher activity samples and wonder if anyone can shed
some light on this.




Elaine T. Marshall, CHP

Radiation Safety Officer

Lovelace Respiratory Research Institute

2425 Ridgecrest Drive SE

Albuquerque, NM  87108

(505) 348-9578

emarshall at lrri.org


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