•The Assessment of radiation levels at different locations in the vicinity of the radiation installation is known as Area Monitoring or Radiation Survey.
•If the radiation level are found to be higher than the permissible levels, suitable remedial measures can be taken.
AIM & OBJECTIVE
To detect various types of radiations especially ionizing radiation.
To ensure Radiation safety and minimize radiation exposure.
To keep records of monitoring over a long period of time.
IDEAL AREA MONITOR
•An ideal area monitor should have uniform response to X & gamma radiation over the range of 15 keV To 3 meV .
•It should cover a wide range of exposure rates from 0.25 mR /h to 10 R/h.
• should be able to assess beta radiation levels.
•Should be operable with battery cells.
AREA MONITORING DEVICES
•Devices/instruments used for aforesaid purpose are called area monitoring devices /radiation survey meters. These are;-
•Gas molecules get ionized when energetic charged particles propagate through a gas.
•A metallic cylinder filled with a suitable gas at atmospheric pressure consisting of two electrodes (cathode and anode).
•Cathode is(– ive) and the Anode is(+ ive).
•In most Detectors, cathode is the wall of the cylinder that holds the gas and the anode is the wire inside the container.
•Ionization radiation produces ion pairs in the gas .
• Cation’s and Anion’s are attracted towards respected electrodes .
•Depending upon the no. of particles entering into the cylinder, An electric pulse of proportional magnitude is Developed.
•Which is then displayed on the deflection needle.
•Deflection needle meter measures doses in the format of mR/h.
A GM Counter is an area monitoring Device.
A GM counter is an instrument used for detecting and measuring the ionizing radiation.
It is used in application such as:-
- Radiation dosimetry
- Radiation protection
- Nuclear industry
It detects radiation such as alpha particle, beta particle and gamma rays.
•GM counter consist of cylindrical cathode wall with a thin wire made of Tungustun acts as anode.
•The device is filled with the mixture of Gas (Ar ) with a pressure of 10mmhg.
•When radiation passes through the counter ,ion pairs are formed.
•The electrons are accelerated towards central electrode or wire due to large positive potential on the wire.
•These electrons in turn produces large amount of secondary electrons or a group of electrons,thus a large amplification of charge by incident electron is produced.
•GM counter works at high applied voltage (500-1500 volt).
The modern electronic scintillation detector counter was invented in 1994 by Sir Samuel curran (UK).
TYPES OF SCINTILLATOR
Cesium iodide (CsI) detection of photons and alpha particles
Sodium iodide (NaI) containing a small amount of thallium detection of gamma waves
Zinc sulphide (ZnS) detectors of alpha particles Zinc sulphide is the material Rutherford used to perform his scattering experiment.
Lithium iodide (LiI) is used in neutron detectors.
Scintillation counter is an instrument that is used for detect and measuring ionizing radiation.
It comprises of the Scintillator that generates photons by excitation effect in response to incident radiation and detecting the resultant light pulses.
radiation strike the crystal – photoelectron emitted by scintilator – the electron move cathode to anode through diode – electric pulse delivered to PM tube.