biodex ATOMLAB 500, Operation And Service Manual, Page: 198 / 212

susceptible to errors caused by low energy photon absorption. In cases where a container has a
wall thickness or material significantly different from the NIST standards used above, it is
recommended that a correction factor or corrected dial value be used to correct for the
difference in absorption between the NIST configuration and the configuration used in clinical
practice. Whichever container and configuration issued in clinical practice, it is strongly
recommended that such configuration be standardized and used every single time.
Determining Personal Dial Values
Dial values can be determined by the user for isotopes for which no published dial value exists.
In order to do this, a sample for which the value is known is required. The activity value may be
provided by the isotope producer or pharmacy, or it may be measured by a method
independent of the dose calibrator. The accuracy of the dial value will depend upon the
accuracy of the known activity value of the sample used. Because of this, it is best if an
estimate of the accuracy of the isotope calibration is available.
To determine the dial value for the isotope, select the Co-60 isotope key and measure the
isotope sample in the same container and geometry that will be used to measure the isotope in
clinical practice. The dial value can be calculated by the following formula:
𝑁𝑒𝑤 𝐷𝑖𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 = 5 . 0 ×
!"#$%$#&
!"#$%&"!"'(
Where :
The activity is the known activity of the source and the measurement is the displayed activity
when measured on the Co-60 isotope key. Remember to decay correct the source’s activity for
the time elapsed since the sourced activity calibration.
Once the new dial value has been calculated, a new isotope name should be created on the
display for the isotope with the dial value as calculated above. The source should be measured
again and compared with its known time-decayed activity in order to verify that the calculation
is correct. It may be necessary to adjust the dial value slightly in order to match the known
activity.
When the dial value has been determined by means of comparison to a source of known
activity, it should not be changed unless access to a source with an activity known to have a
higher accuracy allows determination of a more accurate dial value. Dial values should never be
adjusted daily to make a source match daily isotope measurements. The dial value should only
be determined with a calibrated isotope of known accuracy.
References
1. National Nuclear Data Center, Nudat 2.2 Database , Upton, NY: Brookhaven National
Laboratory, 2007.
2. Browne, Edgardo, and Richard B. Firestone, Table of Radioactive Isotopes, New York: John
Wiley and Sons, Inc., 1986.
3. David C. Rayburn, Determination of the Response Characteristics of the Atomlab Re-Entrant
Ionization Detector, Melbourne, FL: Florida Institute of Technology, 2007.