RE Activation of concrete

[R.Ryder@dl.ac.uk]

To all radsafers,

I recently posted a question about finding Eu154 in concrete activated by 43 
MeV electrons.
Several people replied saying Eu154 (and Eu152) are formed by neutron 
capture on their stable isotopes.

At first, these production routes with high cross sections and long lived 
isotopes did indeed look like  probable production processes but after more 
investigation, I'm not so sure!

I would expect a (gamma,neutron) reaction to dominate.  The number of 
thermal neutrons in this radiation environment must be almost insignificant. 
The activity is in direct line with the main momentum analysis collimators. 
High energy photons would be the most probable particle.

This doubt led me to look again at the spectrum I had measured. The analysis 
software had posed Eu154 but with poor statistics. When I analysed the 
spectrum by hand I came to think that the identity of Eu154 was spurious. 
 There was no good correlation for the strong lines of Eu154 Lines could 
have errors in the energies of up to several keV. The only isotope I am now 
confident is there is Co60! There could be others but to resolve them will 
take more work. There could also be Eu 152 and 154 but better analysis of 
the spectra is required before I can be certain.

In future, I will  not place as much faith in gamma spectroscopy software 
without looking at all the available information.

Thanks for all the replies,

Roy Ryder