True Coincidence Summing Correction in Gamma Spectroscopy

For the radionuclide under consideration, the total effect with respect to γ-line g can
be described by a coincidence correction factor COI g
COIg = (1 - Lg).(1 + Sg)
(3.1)
From the observed peak area, the corrected peak area (N’ p.g ), can be computed
using the equation:
p,g
N
p,g
COI
g
N' = (3.2)
In case of simple decay schemes, the problem of coincidence correction is well
understood for the point sources as can be seen in the section 2.10 (mathematical
summing correction) while general formulae for complex decay schemes have been
given by ANDREAV et al (1972, 1973) 11,12 . However, for a more general case such
as voluminous sources e.g. Marinelli beakers and bottles, the correction for
coincidence summing is more complicated due to the complexity of self-absorption
and the subsequent cascade summing with partial peak energies, and the formulae
given in section 2.10 are no longer valid.
3.2 Estimation of True Coincidence Corrections for Voluminous
Sources
The coincidence summing depends on the position within the source volume. To
calculate summing correction for voluminous sources the quantities ε and ε t (defined
for the whole source) become useless due to the contribution of the individual source
volume elements to the peak areas. The summing effects should therefore be
calculated for each volume element dV from the full-energy peak efficiency ε(r) and
the total efficiency ε t (r) for the specific position r of dV. So equation (2.3) is replaced
by
1
1
Similarly, ε t1 in eq. (2.5) is replaced by
/ C1 = 1 ε
t
ε ( r)
dV.
(3.3)
− ∫ 1(
r)
ε
2
( r)
dV / ∫
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