Accuracy of external standardization systems in two commercially available spectrometers using gamma sources of high or low energy
✍ Scribed by Françoise Gogan; Paul Gogan
- Book ID
- 102625611
- Publisher
- Elsevier Science
- Year
- 1974
- Tongue
- English
- Weight
- 477 KB
- Volume
- 60
- Category
- Article
- ISSN
- 0003-2697
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✦ Synopsis
The use of a high energy source ('"Ra) instead of a low one YCS) for external standardization, appears to give more constant and accurate results when changing sample parameters like quenching, volume, isotopic activity, and vial material. The most import,ant effect is a large decrease, over many hours, of the counting efficiency computed by external standardization, when using polyethylene vials and the 13'Cs source. No changes were observed when using a *"Ra source.
During the past year, discrepancies of unknown origin appeared in some of our experimental results obtained by liquid scintillation counting of tritiated material (sex hormones or neurotransmitter substances). Careful examination of the experimental set-up led us to suspect that these discrepancies could be relevant' to systematic errors introduced by the external standardization system in one type of spectrometer we used in our work. More particularly, it appeared that a continuous drift in external standardization might occur during the 8-12 hr interval of our counting sessions, when using our polyethylene vials concurrently with a 137Cs source as the external standard. In effect, samples had been counted on two different spectrometer types, one using a 2"GRa source for ext.ernal standardization, and the other a lB7Cs source, according to availability at the time the samples were ready.
Recently we had the opportunity to verify in detail our hypothesis, since we could dispose entirely during 2 mo of spectrometers of each type, for comparison purposes. Apparatus were first compared with regard to efficiency, to be sure that sample parameters as quenching, volume, and vial material, affected the results similarly for both types. Then, external standardization systems were compared for sensitivity, accuracy, volume dependance, sample activity, vial material, and stability in time.
Results of this comparison are presented hereafter. It appears that a greater error is effectively introduced by the spectrometer using la7Cs as 363