Geiger-Muller tubes

Figure 5.2 Geiger-Muller tube. The tube is filled with an ionizable gas mixture, such as neon and argon, and a voltage applied across the electrodes. Ionization of the gas by incident radiation causes a current to flow between the electrodes.

If the voltage applied to a Geiger-Muller tube is increased from zero, no response to radiation is detected despite the presence of a radioactive isotope... 

Figure 5.3 A Geiger-Muller tube for measuring the activity of liquid samples.

Lost counts correction is necessary because Geiger-Muller tubes have a dead-time in their operation. 

The sensor is a crystal of Nal(TI) that transforms the 7 photon into luminescence whose intensity is proportional to the energy of the photon (assuming that the 7 photon is entirely absorbed by the crystal). The principle is similar to that of liquid scintillators used to measure 14C. If a Ge(Li) crystal is used, it behaves like the support gas in a Geiger-Muller tube. 

Another method of radiation detection that has value in biochemistry is the use of gas ionization chambers The most common device that uses this technique is the Geiger-Muller tube (G-M tube). When j8 particles pass through a gas, they collide with atoms and may cause ejection of an electron from a gas atom. This results in the formation of an ion pair made up... 

Neon In advertising signs, because it glows red when electricity is passed through it In the helium-neon gas laser (Figure 11.11) In Geiger-Muller tubes, which are used for the detection of radioactivity... 

In-line detection. In the treatment of solutions containing americium the americium 241 content of solutions leaving the chromatography columns is continuously monitored. The gamma detector is a miniature Geiger-Muller tube placed in contact with the solution outlet pipe. The unit is shielded from ambient irradiation by lead. 

Figure 10.5 Diagram of a Geiger-Muller tube (a) and photograph of a liquid scintillation counter (b).

The typical response of a Geiger-Muller tube is shown below. Explain the shape of this curve. 

When using a Geiger-Muller counter to measure radioactivity, one must maintain the same geometrical orientation between the sample and the Geiger-Muller tube to compare different measurements. Why ... 

Fig. 6. The experimental arrangement for measurement of enhanced radioactivity. GM is a Geiger—Muller tube. (From ref. 179.)...

The experimental arrangement consisted of a Geiger-Muller tube which monitored a catalyst over which were passed pulses of radioactive gas in a flow of H2. The rise and fall of radioactivity in the catalyst chamber was compared with the rise and fall of radioactivity generated by the same stream of molecules in a space of known capacity. The Occupancy Principle states that the ratio of occupancy to capacity is the same for all parts of the system and equals the reciprocal of entry flow. From this the population of molecules on the catalyst could be determined. The time history of a radioactive tracer passing over the catalyst was investigated at the same time. 

These measure the radiation in units of dose rate and normally contain an ionisation chamber or Geiger-Muller tube. They are usually used to monitor P and Y radiation fields. Special instruments are used for measuring neutron radiation dose rates. 

These measure the surface activity of radioactive contamination in counts per unit time. They normally contain a Geiger-Muller tube or scintillation counter. For a contamination, the detector normally employed would be a scintillation counter. The efficiency depends on the particular radionuclide being measured and the instrument should be calibrated for each radionuclide of interest. 

Geiger-Muller tube A radiation-detection device operating on the principle that ions form when radiation passes through a tube filled with low-pressure gas. 

Counter tubes. A few popular types of Geiger-Muller tubes are illustrated in Figure 13.5(B). The choice of counter tubes to be used depends on the nature of the sample to be counted (whether the sample is soUd or liquid whether it is soft or high energy -emitter etc). 

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