SensitivityThe sensitivity S is defined as the inverseof the calibration coefficient NUsing decade resistances, larger detectorvolumes or detector gases underhigher pressures, a wide range ofequivalent dose rates can be covered withionization chamber based survey meters
Energy dependenceSurvey meters are calibrated at one ormore beam qualities, but are oftenused in situations in which the radiationfield is complex or unknown. Thesesurvey meters should hence have a lowenergy dependence over a wide energyrange
Directional dependenceBy rotating the survey monitor about itsvertical axis, the directionalresponse of the instrument can be studied.A survey monitor usually exhibitsisotropic response, as required formeasuring ambient dose equivalent,within±60º to ±80º with respect to the referencedirection of calibration
Survey meters may cover a range from nSv/h to Sv/h, but the typicalrange in use is mSv/h to mSv/h.Dose equivalent range
Overload characteristicsSurvey meters must be subjected to doserates of about ten times themaximum scale range to ensure that theyread full scale rather than near zeroon saturation.
Response timeThe response time of the survey monitor isdefined as the RC timeconstant of the measuring circuit, where Ris the decade resistor used and C thecapacitance of the circuit.
Long term stabilitySurvey meters must be calibrated in a standards dosimetry laboratorywith the frequency prescribed by the regulatory requirements of the country,typically once every three years; they also need calibration immediately afterrepair or immediately upon detection of any sudden change in response.The long term stability of survey meters must be checked at regularintervals using a long half-life source in a reproducible geometry.
Discrimination between different types ofradiationEnd window GM counters have aremovable buildup cap to discriminateb from g rays. For b measurements the endcap must be removed to allow bparticles to enter the sensitive volume.
Uncertainties in area survey measurementsThe standards laboratory provides, along with the survey monitorcalibration, the uncertainty associated with the calibration factor.Subsequentmeasurements at the user department provide a type A uncertainty. Theuncertainties due to energy dependence and angular dependence of thedetector, andthe variation in the user field conditions compared with calibrationconditions,contribute to type B uncertainties. These two types of uncertainty areadded inquadrature to obtain the combined uncertainty associated with the surveymeter measurement
Film and thermoluminescence dosimetrybadges can measure equivalentdoses as low as 0.1 mSv and up to 10 Sv;optically stimulated luminescent andradiophotoluminescent dosimeters aremore sensitive, with a lower detectionlimit of 10–30 mSvSensitivity
The uncertainty in measurements withEPDs is about 10% for low doserates (2 mSv/h) and increases to 20% forhigher dose rates (<100 mSv/h) inlaboratory conditions.Uncertainties In personal monitoringmeasurements
Equivalent dose rangePersonal monitors must have as wide adose range as possible so that theycan cover both radiation protection andaccidental situations
Film dosimeters can identify and estimatedoses of X rays, g rays, bparticles and thermal neutrons. TLDs andoptically stimulated luminescent andradiophotoluminescent dosimetersgenerally identify and estimate doses of Xrays and g and b radiation.Discrimination between different types ofradiation