biodex ATOMLAB 500, Operation And Service Manual, Page: 197 / 212

Figure G.1. Atomlab Photon Sensitivity Curve.
The accuracy for dial value calculation depends upon not only the accuracy of the sensitivity
curve and the photon emission intensity data, but also upon the sample configuration, due to
low energy photon absorption. The photon sensitivity curve displayed in Figure G.1 is for
sources with configurations similar to the NIST ampoule configuration discussed above. All
Atomlab Dose Calibrators are calibrated with NIST traceable Co-60, Ba-133, Co-57, and Cs-137
sources. Each dose calibrator is certified to measure the correct activity of the calibration
sources to within the specified accuracy.
The following factors can affect measurement accuracy and should be taken into consideration
when using the Atomlab Dose Calibrator:
Lead Shield: A lead shield is necessary to protect personnel from exposure to the radiation
produced by radioactive isotopes. This lead shield is integrally installed as part of the Atomlab
dose calibrator. However, photon backscatter occurs from the lead shield resulting in increased
detector sensitivity in the 88-200 keV photon energy range. The increase in sensitivity is
already included in the sensitivity curve illustrated in Figure G.1 and can be seen in the peak at
88 keV. However, if for any reason, the dose calibrator is operated without the integral shield,
the sensitivity curve will be incorrect in this energy range resulting in incorrect measurements
for isotopes that emit photons in this range. It is recommended that the dose calibrator always
be operated with the lead shield in place.
Radioisotope Container: The style and the type of container for a radioisotope can affect the
measurement. Users should have a standard procedure, container, and solution volume for
measuring radioisotopes. Plastic syringes are often used as a standard container because they
are usually the means of delivery to the patient in a clinical environment. The dial values
generated using the photon sensitivity curve above should be appropriate for most plastic and
thin glass syringes. Glass vials may require a correction factor for some isotopes.
The wall thickness of the container is especially important when measuring isotopes that emit
low energy photon and/or high energy Beta radiation. I-125, I-123, and Xe-133 are especially