Quality Control Of Dose Calibrators

Test  Frequency Regulatory Agency
Accuracy Annually NRC/State
Dept Of Nuclear Safety
Constancy  Daily  NRC/State
Dept Of Nuclear Safety
Linearity Quarterly NRC/State
Dept Of Nuclear Safety
Geometry Tinstallation NRC/State
Dept Of Nuclear Safety

ACCURACY: This test is designed to show that the calibrator is giving correct readings throughout the entire energy scale that we are likely to encounter. Low, medium, and high energy standards (usually Co-57, Ba-133 or Cs-137, and Co-60, respectively), are measured in the dose calibrator using appropriate settings. Standard and measured values are compared.


Standard  Energy (keV) Expected Value (mCi) Measured
Value (mCi)
Co-57  122 2.48 2.51
Cs-137 662  3.38 3.29
Co-60 1,332 1.55 1.52

CONSTANCY: This test measures precision and is designed to show that a long-lived source, usually 30 y Cs-137, yields reproducible readings on a daily basis on all isotope settings we are likely to use. The Cs-137 source is placed in the dose calibrator. Activity is then measured on the Cs-137 setting and all other settings used on a daily basis. Values are recorded in the dose calibrator logbook and are compared with recent values to determine if instrument is maintaining constancy on a daily basis.

LINEARITY: This test is designed to prove that the dose calibrator readout is linear for sources varying from the mCi range through the mCi range. A high activity Tc-99m source (50-300 mCi) is measured at T0 and at predetermined time intervals up to 48 hours. Expected and actual measurements are compared (and may be analyzed graphically) to determine if the instrument is linear throughout the activity range we are likely to encounter.

GEOMETRY: This test is designed to show that correct readings can be obtained regardless of the sample size or geometry. One ml of Tc-99m in a 10 ml syringe (activity 25 mCi) is measured in the dose calibrator and the value obtained is recorded. The activity is then diluted with water to 2 ml, 3 ml, 5 ml, and 10 ml. At each of these points a reading is taken and the value recorded. Data are then evaluated to determine the effect of sample geometry on the dose calibrator reading. If instrument is geometry-dependent, it may be necessary to routinely correct readings obtained when using calibrator.

1. Deviation from standard or expected values must be within + 10%.

2. If Deviation > 10%, then obligation is to record value, note repair or recalibration of instrument, retest, and record new values.

3. In addition to the above steps, every dose must be corrected mathematically until the instrument is repaired. There is NO LONGER a reporting requirement.

Determines ability of a sodium iodide (thallium) or solid state crystal to resolve gamma ray energies. Measures only resolution, not sensitivity.

For NaI(Tl), Normal Value is 6-10%

For Ge(Li) Crystal, typical value is <1% across entire energy spectrum.