This dialog is used to calculate the Scan Minimum Detectable Concentration (MDC) for an instrument that takes continuous, or scanning, measurements. Scanning instruments can reduce the time and cost of collecting field measurements, but they must be able to adequately detect an elevated area of radiation (hot spot). The MDC is the lowest concentration that the instrument can detect during normal scanning operation. This MDC must be at or below the Derived Concentration Guidance Level for Elevated Measurement Concentrations (\(DCGL_{EMC}\)) in order to successfully detect hot spots.
This dialog encapsulates the methodology described in MARSSIM section 6.7.2.1, and contains the following controls:
Nuclide grid |
Use this grid to enter the Instrument Scan Efficiency and Surface Efficiency for each nuclide. Instrument Scan Efficiency is the proportion of nuclide disintegrations (between 0.0 to 1.0) that is detected by the instrument. Surface Efficiency is the proportion of disintegrations (between 0.0 and 0.5) that allow energy to escape the surface of the material to be detected by the instrument. These efficiency values are obtained through calibration processes that are outside the scope of this document. |
Background Activity |
If the background has already been specified in the main design page (via Material Specific Background in the Mean and Standard Deviation Table) it is displayed here. If not, you can enter the background activity here. |
True Positive Proportion |
This is the complement of the false negative rate of an ideal (perfect) surveyor (all human error removed). |
False Positive Proportion |
This is the false positive rate of an idea (perfect) surveyor (all human error removed). |
Observation Interval |
This indicates how long a source will remain under the detector probe. A shorter interval indicates the probe is being moved faster. |
Surveyor Efficiency |
The efficiency of the human surveyor as compared to an ideal (perfect) surveyor. Typical efficiencies are between 0.5 and 0.75. |