Profile
Settings
Refer your friends
Sign out
A Geiger counter (also known as a Geiger-Muller tube) is a device that detects and measures all forms of radiation, including alpha, beta, and gamma radiation. It is made up of a pair of electrodes that are surrounded by a gas. A strong voltage is applied across the electrodes. Helium or Argon are the most common gases used. Radiation can ionise the gas when it enters the tube. The ions (and electrons) are drawn to the electrodes, resulting in an electric current. A scaler counts the current pulses, and a “count” is obtained everytime the gas is ionised by radiation.
The tube and the (counter + power supply) are the two pieces of the equipment.
The Geiger-Mueller tube is typically cylindrical and has a wire running through it. Voltage controls and timer settings are available on the (counter + power supply). As indicated on the figure page, a high voltage is established across the cylinder and the wire.
Geiger Counter Principle
- The Geiger counter would include a Geiger-Müller tube, a sensory element that detects radiation, and electronics that process the information to produce the result.
- The Geiger-Müller tube is filled with a gas such as helium, neon, or argon at the lowest pressure possible, where a high voltage is applied. When a particle or photon of incident radiation ionises the gas, it causes conduction of the electrical charge on the tube.
Geiger Counter Types
The Geiger counter is totally determined by the tube’s architecture and can be divided into two types:
- End Window:
 One of the tube’s ends would have a small window. This window would be useful for ionising particles that move quickly.
- Windowless:
 As the name implies, this type of tube would have no windows and a thickness of one to two mm. This tube is used to detect high-penetrating radiations.
Units of Geiger Counters
Particles are measured in a variety of units, the most common of which is the Counts Per Minute (CPM). Micro-(μSv/hr) – Sieverts per hour and (μmR/hr) milli-Roentgens per hour would be used to measure radioactivity.
Geiger Counter Equation
For a variety of reasons, the Geiger counter has been the most widely used beta particle detector. First, whether made in the lab or as a commercially available component, it is reasonably inexpensive. Second, unlike scintillation or solid-state detectors, it requires little in the way of specific circuitry to operate. Third, the halogen-filled variants have a rather extended working life. A window must be provided to allow beta particles to enter the detector in order to detect them.
The relationships between the many parameters that determine the effectiveness with which a specific radioactive source is detected by a specific Geiger counter have been widely explored. In an early publication, Zumwalt (1950) established the essential conclusions that have since been cited in later books and papers by Price (1964) and Overman and Clark (1960). In general, the equation can be used to link the observed counting rate R with the corresponding disintegration rate A.
R=YA
where Y is a factor that represents the efficiency of counting.
What is a Safe Level of Radiation on a Geiger Counter
The microsievert/hour (Sv/hr) is the standard unit of radiation dose in a region. To get the corresponding uSv/hr radiation exposure for this tube, multiply its CPM by 0.0057. So, in my office, the background radiation level varies from 0.05-0.10 Sv/hr, which is a normal and safe level of background radiation (see Radiation Units below).
Conclusion
Ionising radiation, such as an alpha, beta, or gamma particle, can ionise some of the gas molecules in the tube when it enters. An electron is knocked out of these ionised atoms, leaving a positively charged atom in its place. The tube’s high voltage generates an electric field inside it. The positively charged ions are drawn to the negative electrode, whereas the electrons that were knocked out of the atom are attracted to the positive electrode. This causes a current pulse in the cables connecting the electrodes, which can be counted. The charged ions are neutralised once the pulse is counted, and the Geiger counter is ready to record another pulse. A gas is introduced to the Geiger counter tube in order for it to swiftly return to its former state after radiation has entered.
The adequate voltage across the electrodes is required for proper operation of the Geiger counter. The electric field in the tube is too weak to create a current pulse if the voltage is too low. If the voltage is too high, the tube will discharge continuously, perhaps damaging it. The correct voltage to use for the tube is usually recommended by the manufacturer. To create the appropriate electric fields inside the tube, larger tubes require higher voltages.
