Vp. Kolotov et al., ESTIMATION OF TRUE COINCIDENCE CORRECTIONS FOR VOLUMINOUS SOURCES, Journal of radioanalytical and nuclear chemistry, 210(1), 1996, pp. 183-196
To analyze a voluminous radioactive source with the highest possible s
ensitivity, it is necessary to use both a high efficiency detector and
an optimal measurement geometry. The ''optimal'' geometry implies pos
itioning the source as close to the detector as possible. It also impl
ies selection of the shape of the source in order to reach the highest
efficiency possible (e.g., Marinelli beaker). Under such conditions o
f measurements, true coincidences may cause systematic errors that can
reach levels of more than ten percent for some radionuclides. A metho
d for estimation of the effect of these coincidences was developed. It
is based on direct computation of the effect by means of integration
of a function which involves the experimentally obtained detection eff
iciency for the place around the detector it was found that for the te
sted detector with a relative efficiency of 15%, the so-called intrins
ic peak-to-total calibration may be used in the course of such an inte
gration: It has been shown that the P/T-ratio for the given energy in
the working space around the detector may be considered a constant val
ue. Some results from a peak-to-total calibration study in the presenc
e of scattering material are also given.