BS-IEC-61577-2-2000 pdf free download -Radiation protection instrumentation — Radon and radon decay product measuring instruments — Part 2: Specific requirements for radon measuring instruments.
4General characteristics
To measure radon volume activity,several methods of measurement can be used and manydifferent instruments are commercially available.General aspects of the physical principlesinvolved and of the instrument performances have been summarized in lEC 61577-1.
The methods of measurement normally used are the ionization chamber,scintillation flask orsolid state detector with electrostatic precipitation.
Most of the measurement methods require the air to be filtered to remove radon decayproducts before entering the detector.
For instantaneous measurement of radon volume activity, grab sampling methods are used.Asample of the air to be measured may be collected by filling a container，either one that hasbeen previously evacuated or a flow-through type, and resealing the container.The radon fromthe sampler is then transferred to the measuring chamber,which may be an ionization chamberor 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.ln most continuous monitors， the air is drawn through a scintillation flask or a flow-throughionization chamber or the air diffuses into the detector. Solid state detectors may also be usedto monitor radon volume activity continuously.
The determination of the radon concentration may be affected by changes in the flow rate.Theair humidity may affect the efficiency of some detectors and the instruments can be providedwith 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. Therange of measurement of airborne radon volume activity within which the requirements of thisstandard are met shall extend from 102 Bq-m-3 to 105 Bq-m-3 at least.
Whatever the measurement conditions (outdoor,indoor,underground), the instrument shall beable 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 particularapplication. It shall, therefore, be agreed between manufacturer and purchaser.
4.3Reference source
The reference source shall be radon source or radon atmosphere(STAR) which is traceable toa 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 instrument 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 sufficiently 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.BS-IEC-61577-2 pdf download.