CAPINTEC, INC CRC
®
-25R
The assay of radioisotopes having a significant abundance of low- energy gamma-, x-,
and/or high-energy beta-ray radiation may be affected by changes in the sample
configuration used to assay the radio-pharmaceutical if the samples are severely different
from the standard source. In such cases, an independent check or determination of a
calibration appropriate to a user's needs is advised. Fortunately, most radioisotopes can be
accurately assayed independently of the sample size.
Effects of Impurities
An Ionization chamber itself does not have intrinsic energy- discrimination capability. The
presence of radioisotope impurities will affect the reading of the instrument unless the effect
of impurities is eliminated by photon filtration as is done with Mo99 breakthrough in Tc99m.
However, the presence of low-level radionuclide impurity does not negate the usefulness of a
radioisotope calibrator, if the user is aware of its presence and has an independently
determined calibration including photons arising from the impurities.
June 09 APPENDIX I A1 - 7
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