Geiger Muller Counter for Radiation Measurement

Introduction

A Geiger-Mueller counter is an instrument used for the identification and measurement of levels of radiation. The main particles that can be detected by the device are beta and gamma radiation that could be emanating from any radioactive object. There have been instances where some of the counters are able to discover gamma particles or radiation (Brownell, 28). Although not widely used for the purposes of detecting alpha particles the device is favored as an instrument for rating dosage and portable radioactive pollution.

Components of a Geiger Mueller Counter

The counter is comprised of a gas discharge tube that encompasses a wire that is center conducting and it is located within a conducting cylinder. The cylinder is further potted with insulators at both ends. One of the insulators within the cylinder is for the admission of beta particles into the gas tube (Dashiki, 72). The gas used within the tube is used for the intention of ionizing gas and conduction on manipulation from a particle. Normally the preferred gas for this purpose is either Argon or Helium gas. The process of deionization is further catalyzed in the cylinder by employing a trace of halide which could be in the form of chlorine. The trace of halide is also used in the extinguishing of ions which ensures that the tube is ready for the next radiation occurrence. The process of counting is done by using a pulse amplifier in conjunction with a counting circuit whose purpose is to assess the exposure to an amount of radiation over a given period of time. The counter also produces a characteristic click sound to signify the passage of a radioactive event (Meloan, 102).

Operation

The ionizing gas enclosed inside the tube acts together with the radiation that leads to a knock effect of electrons from molecules of the gas enclosed. As we have discussed, this gas is the ionizing gas and the resultant electron is made to increase in velocity towards the positively charged electrode (Dashiki, 89). All this is influenced by the difference in high voltage that runs across both electrodes of the tube. While on transit, the electron collides with other gas molecules hence producing even more electrons which are accelerated to the opposite direction i.e. towards the direction where the negatively charged electrode is located. The resultant net effect of the whole process culminates in an avalanche effect that “soaks” the discharge tube into a high state of electrical conduction (Brownell, 25). A voltage drop within the confines of the tube is realized after the scale of conduction is minimized by the effect of having a load resistor lie in series with the tube. The function of this resistor is to also produce a pulse utilized for the sole basis of amplification and later counting by the electronic circuit. It is at this point that a trace of halide is used to enable faster restoration of the ionizing gas to a position that can allow radiation events to be detected.

Application of Geiger- Mueller Counter

The counter is normally used in the sensing of cosmic rays and the location of minerals that could be possessing radioactive characteristics. The devices have also been found to be very useful in the medical field where they are used for tracing malignancies in the human body. They are also used in the tracking of radioactive tracers that could be used in researching the body and the complex organisms that form it. In chemistry, the counters are also used to track radioactive isotopes during an event following a chemical reaction (Brownell, 60). Its use is important as we know that the process of radioactivity is invisible and cannot be detected by the natural five senses that we possess. The device is normally used in a laboratory setting where conditions can be changed to suit research and experimentation.

Advantages of the Geiger Mueller Counter

Generally, Geiger counters are cost-effective when compared to other devices used for the same purpose such as scintillation counters. They are also very durable and can withstand very harsh terrain and conditions in order to ensure that accurate reading are collected and recorded. The device is also portable thus making it the equipment of choice used in forensics and in other fields that require the detection of radiation. The device has the characteristics of detecting all the ranges of radiation i.e. beta, gamma, and alpha particles (Brownell, 45).

Disadvantages of Geiger Mueller Counter

A problem identified by the counter is the issue of the resolution time which is described as the period before the counter resets itself before measuring another radioactive event. After recording a radioactive event, the counter takes a certain period in order t reorganize itself to take down the next event (Meloan, 110). The counter remains inactive while in this period and hence some events can go unrecorded as the counter is inactive at this time as it is busy resetting itself. The counter also does not have the capacity to distinguish the types of radiation it is detecting and also the extent of the energy radiated off by the object being measured. Lastly apart from the counts of the radioactive events, Geiger Muller counters have very low efficiency as they are not able to give an exact reading and the margin for error is high (Dashiki, 56).

Works Cited

Brownell, Gordon. Radiation dosimeter. Wash: Academic Press, 1956. Print.

Dashiki, Ashak. Introduction to Nuclear and Particle physics. New York: Wiley, 1994. Print.

Meloan, Clifton. Problems and experiments in instrumental analysis. London: C.E. Merrill Books, 1963. Print.