The determination of 235U in environmental samples from its 185.72 keV
photons may require the deconvolution of the multiplet photopeak at ~186 keV,
due to the co-existence of the 186.25 keV photons of 226Ra in the spectrum.
Successful deconvolution depends on many parameters, such as the detector
characteristics, the activity concentration of the 235U and 226Ra in the
sample, the background continuum in the 186 keV energy region and the
gamma-spectrometry computer code used. In this work two sets of experimental
test spectra were constructed for examining the deconvolution of the
multiplet photopeak performed by different codes. For the construction of the
test spectra, a high-resolution low energy germanium detector was used. The
first series consists of 140 spectra and simulates environmental samples
containing various activity concentration levels of 235U and 226Ra. The
second series consists of 280 spectra and has been derived by adding 137Cs,
corresponding to various activity concentration levels, to specific first
series test spectra. As the 137Cs backscatter edge is detected in the energy
region of the multiplet photopeak at ~186 keV, this second series of test
spectra tests the analysis of the multiplet photopeak in high background
continuum conditions. The analysis of the test spectra is performed by two
different g-spectrometry analysis codes: (a) spectrum unix analysis code, a
computer code developed in-house and (b) analysis of germanium detector
spectra, a program freely available from the IAEA. The results obtained by
the two programs are compared in terms of photopeak detection and photopeak
area determination.
HIGH BACKGROUND AREA FOR RADIATION EDUCATION
