IEC 61562 pdf download – Instrumentation pour la radioprotection – Equipement portable de mesure de l’activité massique de radionucléides émetteurs bêta dans les aliments
b) Radiation meters for liquid and loose solid samples allowing measurement in approximately
4 T geometry, containing a detector with wrapping surface
Liquid sources are poured into a detector cell and may be in close contact with the detector.Loose solid samples may have protective cover packages, cuvettes,etc.
Measuring geometry and sample volume in this type of detector are fixed.
4.2General description of instrument
Radiation meters for specific beta-activity measurements in foodstuffs can comprise thefollowing main parts:
detection sub-assembly;- measuring sub-assembly.
These parts may be either integrated or realised as separate units.
Radiation meters should be provided with a terminal for an external precision pulse generatorconnection which can be used for instrument adjustment, calibration and test.
4.3Detection sub-assembly
Detection sub-assemblies may be interchangeable. Through the detection sub-assemblyconnection, the device shall automatically set the appropriate operating mode.Construction ofthe instrument shall be such that an incorrect detection unit connection is impossible.
Detection cell construction should allow quick and simple substitution of one measured sampleby another.
4.4Measurement sub-assembly
The measurement sub-assembly should in general provide the following radiation meterfunctions:
to convert the measured value information coming from the detection sub-assembly anddisplay it in appropriate units;
to integrate the background value over time，in order to increase the accuracy of thebackground measurement;
to automatically take into account the radiation meter background value;- to automatically determine the number of counts and display their value;
– to automatically set the appropriate operating mode at the connection of the specific
detection subassembly;
to maintain the power supply condition during monitoring and in case of its breakdown, toswitch off the display of the radiation meter;
to accept in digital form coefficients or parameters used for information processing(calibration factors, energy range，alarm thresholds, etc.);
to activate sound and/or light alarms when the specific activity level exceeds the presetthresholds.
The device should be provided with visual signalling of radiation meter overload and a lowbattery indicator.
4.5Complementary equipment
The following complementary equipment may in general be part of the radiation meter system:- removable cups or insertion pieces for holding and positioning foodstuff samples in
sufficient quantities;
simulators of samples under test for radiation meter background determination;- funnels,measuring cups for pouring liquid samples into the detector cell;
– scissors, graters, mills, for grinding or adjusting samples shapes;
other materials and tools necessary for sample preparation;
equipments necessary for decontamination;
checking sources, and special holders for these checking sources to hold the sources atfixed positions with respect to the detector.
4.6Decontamination
The instrument design， especially with regard to the detection unit, should be implemented insuch a way that the probability of radioactive contamination is minimized.
The materials used for constructing the instrument should possess minimum absorption ofcontamination and allow decontamination by routine means.
5Main characteristics
5.1 Measured nuclides
The radiation meter shall, as a minimum, measure the specific activities of these radionuclides:
89sr, 90sr+90y,1311,134Cs,137Cs.
5.2 Measurement range
The measurement range of the radiation meter for the above radionuclides should have amaximum lower bound of 1 x 102 Bq/kg and a minimum upper bound of 1 x 106 Bq/kg， theexternal gamma dose rate not exceeding 2,5 uGy/h.
NOTE The operation manual for the radiation meter should specify the time required to perform the measurementsat the lower limit of detection. This value should not include the time for sample preparation and of that fordetermination of background.
5.3Energy measurement range
The energy measurement range of the instrument shall provide for the measurement of thenuclides mentioned in 5.1.This range shall be at least from 150 keV to 2 300 keV.
5.4Instrument background
Radiation meter background originates from internal and external sources.
The internal sources consist of electronic noise and radioactivity of contaminated materials ofinstrument construction，primarily in the detector sub-assembly. The external sources arenaturally occurring radioactive materials and cosmic radiation. Instrument background maydepend heavily on the selected energy range of measurement.
IEC 61562 pdf download – Instrumentation pour la radioprotection – Equipement portable de mesure de l’activité massique de radionucléides émetteurs bêta dans les aliments
