at Kansas State University we recently dealt with this. We calibrated with Cs-135, but Kansas regulations changed to require Tc-99 and another isotope I am drawing a blank on right now, as well as energy error in calibration. We quit doing detector calibrations because the extra requirements weren't worth what we charged. As far as a "response check" by definition, all you need is a response, not a quantitative value. If you have a source for an instrument, it's safe to assume it's calibrated with that source (generally CS-135) so if you know what the source is, you can figure the dose pretty quick.
Internal sources are kind of hit and miss. If the instrument has cal based on the check source reading, It's only calibrated to that isotope. If the detector reads in REM, it has to be calibrated to at least 3 sources of different energies.
Generally for portable units with pancake probes, you don't give "much of a concern" when it comes to energy, you're looking for total counts. "friskers" don't care what energy it is, if it clicks, it's there. CS-135 is used because it's a relativly mid range energy decay for a long half life isotope. Friskers only tell you if there is something there, not what it is. If you're frisking trash and you get high counts on everything you don't know if it's natural radon or real contamination unless you scan each item individually. If something is "hot" you don't know what it is with a pancake probe.
The way we scan trash at K-State is a "rough" frisk with a pancake probe. It's time consuming because we scan everything in a trash can. if it's over 100 over background we don't pass it. after that, we use a germanium detector to ensure the isotopes we release are below the limits. At our facility we do not release anything less than 1/10 the limit.
