Neutron activation of soils: Does anyone know the source of 161.8 keV gammas seen at 5-10 minutes after short neutron irradiation (<10 secs)?

I see a photopeak build in, with a maximum after 8 mins, disappearing by 12 mins. This was found in desert soils and in flyash standard material. Energy matches Se 77m 17 second, but I cannot...

14 March 2013 5,633 13 View