IEC 61577-2:2000 pdf download
IEC 61577-2:2000 pdf download.Radiation protection instrumentation – Radon and radon decay product measuring instruments – Part 2:Specific requirements for radon measuring instruments.
3.5
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time delay between initial exposure of the detection assembly to a given value of the measurement quantity and the attainment of 90 % of the equilibrium reading. or for integrating (slope) assemblies, 90 % of the equilibrium value of the first derivative of the indication, with respect to time
4 General characterIstics
To measure radon volume activity, several methods of measurement can be used and many different instruments are commercially available. General aspects of the physical principles involved and of the instrument performances have been summarized in IEC 61577-1
The methods of measurement normally used are the ionization chamber, scintillation flask or solid state detector with electrostatic precipitation.
Most of the measurement methods require the air to be filtered to remove radon decay products before entering the detector.
For instantaneous measurement of radon volume activity, grab sampling methods are used. A sample of the air to be measured may be collected by filling a container, either one that has been previously evacuated or a flow4hrough type, and resealing the container. The radon from the sampler is then transferred to the measuring chamber, which may be an Ionization chamber or a scintillation flask. In some cases, scintillation flasks themselves are used as samplers.
To measure the variation of radon volume activity, continuous measurement methods are used. In most continuous monitors, the air is drawn through a scintillation flask or a flow-through ionization chamber or the air diffuses into the detector. Solid state detectors may also be used to monitor radon volume activity continuously.
The determination of the radon concentration may be affected by changes in the flow rate. The air humidity may affect the efficiency of some detectors and the instruments can be provided with air drying systems.
Instrumentation that is intended to be used in field monitoring shall be simple to operate. portable and protected against hostile environmental conditions.
4.1 Range of measurement
The radon measurement instrument shall give a result of airborne radon volume activity. The range of measurement of airborne radon volume activity within which the requirements of this standard are met shall extend from 102 Bq m3 to iO Bqm’3 at least.
Whatever the measurement conditions (outdoor, indoor, underground), the instrument shall be able to measure all the ranges of activity it is designed for.
4.2 Minimum detectable volume activity
The required minimum detectable radon volume activity will depend on the particular application. It shall, therefore, be agreed between manufacturer and purchaser.
4.3 Reference source
The reference source shall be radon source or radon atmosphere (STAR) which is traceable to a recognized standard.
5 TechnIcal characteristIcs
The instrument shall Include one or more radiation detection units and, where appropriate, some or all of the following function units:
— radiation detection unit;
— air-pumping device;
— aerosol retention device:
— air-drying device;
— provisions for operational testing;
— signal processing unit;
– measurement display device;
– power supply sub-assembly;
— operational indicators;
— alarm threshold to give a signal when a predetermined radon volume activity level is exceeded.
Where instruments include the function units listed above, they shall conform to the following requirements.
5.1 Radiation detection unit
The geometrical efficiency of the detection unit shall be as high as possible. Contamination of the detector with naturally occurring alpha emitting radionuclides (mainly long-lived daughter products of radon) may result in higher background. Precautions shall be taken to protect the detector surface from airborne contamination when the nstrument Is not In use.
5.2 Air-pumping device
The air-pumping circuit shall provide a total air flow adequate for the measurement method. The air pump shall be capable of withstanding the variations of pressure induced by operating conditions, sampling time, filter types. atmospheric dust mass contributing to blockage, etc. Hoses and connections shall be suflicientty tight to maintain a stable flow rate and prevent leaks. Where an air pump is an integral part of the assembly it is recommended that the air pump be capable of continuous operation between scheduled maintenance operations. The flow rate should be stabilized or measured.
