Last updated on Friday, March 31st, 2023

Introduction to Geiger Counter

The Geiger counter is used in this experiment, having mainly geiger muller tube that detect the particles. The radioactive source for the experiment is Cesium-137.

The Geiger Muller tube was invented by the German physicists Hans Geiger and Walther Muller in 1928. The tube is in the shape of a cylinder about 1 cm in diameter and about 4 cm long. We carry the Cesium-137 source close to the end of the Geiger-Muller tube.

The main features of the source:

• The half-life for the cesium-137 decay is 30.2 years
• The source activity was 5 micro Curies when new (1 Curie = 3.7 x10¹⁰decays per second)
• The energy of the emitted gamma rays is 661.6 KeV (1 KeV = 1 thousand electron-volts).

Geiger counter Viva Questions

Some Viva questions are listed here related to the Geiger counter:

1Q. What interval did you select to note the counts?

The interval used to note the counts in a Geiger counter is determined based on the desired level of accuracy and the expected count rate of the radiation being detected. For example, if the count rate is very high, a shorter interval may be used to prevent loss of count data, while a longer interval may be used if the count rate is low to improve statistical accuracy.

2Q. What is the minimum number of counts detected in that interval?

3Q. Cesium-137 decays into Barium or Uranium?

Cesium-137 (Cs-137) is a radioactive isotope that undergoes beta decay, meaning it emits a beta particle (an electron) to transform one of its neutrons into a proton. As a result, the Cs-137 nucleus becomes a more stable isotope of Barium, specifically Barium-137m (Ba-137m), which is in an excited state. This excited state is short-lived, and Ba-137m quickly releases gamma radiation to reach a stable state of non-radioactive Barium-137 (Ba-137).

4Q. When Cesium-137 decays, which particles eject?

When Cesium-137 (Cs-137) undergoes radioactive decay, it emits beta particles (electrons) and gamma rays.

The Cs-137 undergoes beta decay, in which a neutron in the nucleus is transformed into a proton, while emitting an electron and an antineutrino. The decay process can be represented by the following equation:

Cs-137 → Ba-137m + e- + ν

Here, e- represents the beta particle, and ν represents the antineutrino.

In addition to beta particles, Cs-137 also emits gamma rays during the decay process. 

The decay of Cs-137 into Ba-137m, along with the emission of beta particles and gamma rays, is used in a variety of applications, including medical imaging and radiation therapy, as well as in industrial and research settings.

5Q.From which excited nucleus photon emits, Cesium-137 or Barium-137  ?

Barium-137m (Ba-137m) is the excited nucleus that emits a gamma ray photon after being formed by the beta decay of Cesium-137 (Cs-137).

The Cs-137 nucleus into Ba-137m. The Ba-137m nucleus is left in an excited state, and it quickly releases the excess energy by emitting a gamma ray photon with a characteristic energy of 662 keV. The decay process of Cs-137 into Ba-137m can be represented by the following equation:

Cs-137 → Ba-137m + e- + ν

Ba-137m → Ba-137 + γ

6Q. Why should you clean the hand after performing the experiment?

It is important to clean your hands after performing the Geiger-Muller (GM) experiment to prevent the spread of radioactive contamination. During the experiment, the GM tube may come into contact with radioactive sources, such as radioactive isotopes, which can contaminate the surface of the GM tube, as well as your hands.

7Q. What precaution you should keep when performing the Geiger-Mueller experiment?

Performing the Geiger-Mueller (GM) experiment involves working with radioactive materials, so it is important to take appropriate precautions to ensure your safety and the safety of others. Here are some precautions to keep in mind:

1. Wear appropriate personal protective equipment (PPE): PPE, such as gloves, lab coat, and safety glasses, can protect you from exposure to radioactive materials. Make sure you know what type of PPE is appropriate for the experiment you are performing.
2. Minimize your exposure: Keep your exposure to radioactive materials as low as possible by working behind a radiation shield or using a remote handling system if available.
3. Work in a well-ventilated area: Good ventilation helps prevent the buildup of radioactive gases or particles in the air.

Precaution part-2

1. Label and store radioactive materials properly: Proper labeling and storage of radioactive materials help prevent accidental exposure and contamination.
2. Follow proper handling and disposal procedures: Follow established protocols for handling and disposing of radioactive materials to minimize the risk of exposure and environmental contamination.
3. Use a radiation survey meter: Use a radiation survey meter to monitor the level of radiation in the area and ensure that it is within safe limits.
4. Clean up after the experiment: Clean any contaminated surfaces or equipment using appropriate decontamination procedures and dispose of waste according to established protocols.

By following these precautions and any additional guidelines specific to the experiment you are performing, you can minimize the risk of exposure to ionizing radiation and ensure safe handling of radioactive materials.

READ ALSO: Ionization Potential Experiment Viva

Questions working of Geiger-Muller Tube

1Q. In which region the GM TUBE cannot distinguish between different type of radiations and why?

The Geiger-Muller (GM) tube is a type of gas-filled radiation detector that is widely used to detect and measure ionizing radiation. However, there is a region of operation for the GM tube where it cannot distinguish between different types of radiation, and this region is known as the “dead time.”

Dead Time Definition

The dead time of the GM tube is the period of time during which the tube is unable to respond to incoming radiation. It happened due to the ionization process that takes place inside the tube. When a particle enters the tube and ionizes the gas inside. It creates a pulse of electrical charge that can be detected and counted by the electronics attached to the tube. During the dead time, the tube is still processing the previous pulse, and it cannot respond to any new incoming radiation. Until it has finished processing the previous pulse. As a result, if two particles enter the tube during the dead time, the second particle will not be detected and will be missed.

2Q. A metal wire that is stretched at the axis of the cylinder (GM TUBE) is Anode or Cathode?

In a typical Geiger Muller tube (GM Tube), the metal wire that is stretched along the axis of the cylindrical tube is the anode.

Construction of Geiger Muller Tube

The GM tube consists of a cylindrical metal housing that is filled with a gas, such as argon or helium, at low pressure. The metal wire is located at the center of the cylinder and acts as the anode. The cathode is usually the metal housing itself, which is coated with a layer of a special material, such as graphite or cesium. It is to enhance its ability to emit electrons when ionized by incoming radiation.

When ionizing radiation enters the GM tube, it ionizes the gas atoms, creating a cascade of electrons. This cascade of electrons are attracted to the anode and create a pulse of electrical charge. It is detected and counted by the electronics attached to the tube. The metal wire is designed to be thin enough to create a high electric field. Which accelerates the electrons towards the anode, creating a detectable pulse.

3Q. What type of gases and volatile compounds are filled in the GM Tube?

Geiger Muller tube is typically filled with a gas at low pressure. The choice of gas depends on the specific application of the GM tube, but commonly used gases include argon, helium, and neon.

In addition to the gas, some GM tubes may contain small amounts of volatile compounds, such as halogens or organometallics. It added to improve the performance of the tube. For example, a small amount of halogen gas, such as iodine or bromine, can be added to the gas mixture. That will increase the probability of electron multiplication, which enhances the sensitivity of the tube.

4Q. What order of minimum potential difference between the anode and cathode of the tube is kept to detect the particles?

The potential difference between the anode and cathode of a Geiger-Muller (GM) tube depends on the specific design and application of the tube. However, typically the potential difference applied between the anode and cathode, is in the range of hundreds to thousands of volts.

The high voltage is required to create a strong electric field inside the tube. It accelerates the charged particles created by ionizing radiation towards the anode, resulting in a measurable electrical pulse. The exact voltage required depends on factors such as the type of gas used in the tube, the diameter of the anode wire, and the distance between the anode and cathode.

5Q. What type of particles this detector can detect?

Geiger-Muller (GM) tubes are capable of detecting ionizing radiation, which includes several types of particles. These particles include:

Alpha particles: These are positively charged particles consisting of two protons and two neutrons, and are typically emitted by radioactive isotopes such as uranium, radium, and polonium. Alpha particles are relatively large and heavy, and are easily stopped by even a thin layer of material such as paper or skin.

Beta particles:

These are high-energy electrons or positrons that are emitted by some radioactive isotopes, such as strontium-90 and tritium. Beta particles are smaller and lighter than alpha particles and can penetrate further into materials before being stopped.

Gamma rays: These are high-energy photons that are emitted by radioactive isotopes during the decay process. Gamma rays are similar to X-rays and can penetrate deeply into materials before being absorbed.

X-rays: These are high-energy photons that are produced by man-made sources, such as X-ray machines, or by natural sources, such as the decay of radioactive isotopes.

6Q. Can we detect the counts of radiation without the ionization inside the tube?

No, it is not possible to detect ionizing radiation using a Geiger-Muller (GM) tube without ionization occurring inside the tube. The basic principle of operation for a GM tube is that ionizing radiation passing through the tube ionizes the gas inside the tube, creating a brief electrical pulse that is detected by the tube’s electronics.

7Q. Does the cylindrical geometry of the tube play any role to define the electric field in the tube? If yes, where it will be maximum?

Yes, the cylindrical geometry of a Geiger-Muller (GM) tube plays an important role in defining the electric field inside the tube. The electric field is created by applying a high voltage difference between the central wire (anode) and the outer tube (cathode).

The electric field is strongest near the anode wire, and decreases as the distance from the anode increases. The cylindrical geometry of the tube means that the electric field is radially symmetric, and the strength of the field is greatest along the central axis of the tube.

Overall, the geometry of the GM tube is designed to produce a uniform electric field inside the tube, which allows for consistent detection of ionizing radiation.

Part -2 of working

1Q. The Townsend avalanche created due to the high electric field, where it takes place?

In a Geiger-Muller (GM) tube, the Townsend avalanche occurs in the region of the tube where the electric field strength is high enough to cause ionization of the gas molecules. This occurs in the vicinity of the anode wire, where the electric field strength is highest.

If the electric field strength is high enough, the free electrons can ionize additional gas molecules, creating more free electrons and positive ions. This creates a chain reaction, known as the Townsend avalanche, where the number of free electrons and positive ions increases rapidly, resulting in a large electrical pulse that can be detected by the GM tube’s electronics.

2Q. For the second avalanche which particle is responsible within the G M TUBE?

When a photon of sufficient energy is absorbed by the metal surface of the GM tube’s anode, it can cause the emission of a photo-electron. The photo-electron is then accelerated towards the positively charged electrode in the center of the tube.

As the photo-electron moves through the gas in the tube, it can ionize gas atoms, creating a small number of free electrons and positively charged ions. If the voltage applied across the tube is high enough, the free electrons can undergo a chain reaction, causing a large number of ionizations and creating a cascade of free electrons. This cascade is the second avalanche and produces a detectable electrical pulse that can be used to measure the incident radiation.

3Q. What is Geiger’s discharge?

Geiger’s discharge, also known as a Geiger-Müller discharge, is a type of electrical discharge that occurs in a gas-filled tube. When a high voltage is applied across it. The GM discharge was discovered by physicist Hans Geiger and his student Walther Müller in 1928.

If a high voltage is applied to the tube, it can create an electric field that accelerates the free electrons towards a positively charged electrode (anode) in the center of the tube. When the electrons collide with gas atoms on their way to the anode, they can ionize additional gas atoms, creating more free electrons.

If the voltage is high enough,

a chain reaction can occur, and the number of free electrons in the tube can rapidly increase, resulting in a visible electrical discharge. This is the Geiger’s discharge, which produces a characteristic “click” or “tick” sound and a pulse of electrical current that can be detected and counted by a measuring device.

The GM tube is commonly used in radiation detection and measurement devices, such as Geiger counters and radiation dosimeters.

4Q. What do you understand from photo-electron in the tube and how they emit?

In a GM (Geiger-Müller) tube, photo-electrons are electrons that are emitted from a material, usually a metal, when it absorbs a photon of electromagnetic radiation, typically in the ultraviolet or visible range.

The photo-electrons are emitted through the photoelectric effect, which is the process by which a photon is absorbed by an electron in the metal, giving the electron enough energy to overcome the binding energy holding it to the metal and escape from the surface. The energy of the emitted photo-electron depends on the energy of the absorbed photon and the properties of the metal.

In the context of a GM tube, photo-electrons are generated when ionizing radiation, such as alpha or beta particles, or gamma rays, enters the tube and interacts with the gas atoms inside. The radiation can ionize the gas atoms, creating free electrons and positively charged ions.

If the radiation is energetic enough

it can also cause the emission of photo-electrons from the metal surface of the anode. The photo-electrons that are emitted from the anode are accelerated towards a positively charged electrode (cathode) in the center of the tube, creating a pulse of electrical current that can be detected and counted.

The number of photo-electrons generated in a GM tube is proportional to the energy of the incident radiation. So by measuring the number of photo-electrons produced, it is possible to determine the intensity of the radiation. This property makes GM tubes useful for detecting and measuring ionizing radiation. Such as in radiation monitoring, nuclear physics experiments, and medical imaging.

5Q. Does photo-electron initiate the second avalanche?

Yes, photo-electrons can initiate the second avalanche in a Geiger-Müller (GM) tube. In fact, the GM tube is designed to detect ionizing radiation, including photons, by using the photoelectric effect to produce photo-electrons that can initiate the discharge process.

6Q. In the G M TUBE does every avalanche initiate the next avalanche, if yes what is the main point behind it?

In a Geiger Müller tube, not every avalanche initiates the next avalanche, but one avalanche can initiate many subsequent avalanches.

When ionizing radiation enters the GM tube, it can ionize gas atoms, creating a small number of free electrons and positively charged ions. If a high voltage is applied across the tube, the free electrons can be accelerated towards a positively charged electrode (anode) in the center of the tube.

When the electrons move through the gas, they can ionize additional gas atoms, creating more free electrons. If the voltage is high enough, this can result in a chain reaction, where the number of free electrons in the tube rapidly increases, and a large number of ionizations occur in a short time. This is the first avalanche.

During the first avalanche,

a large number of positive ions are also created. These positive ions can quickly neutralize some of the free electrons, reducing their number in the tube. However, if the voltage across the tube is still high, some of the remaining free electrons can continue to ionize gas atoms, creating a second avalanche.

Eventually, the number of free electrons is reduced to a level where another avalanche cannot be initiated, and the GM tube enters a quenched state until the voltage across the tube is reset or the radiation intensity increases again.

7Q. From mass points of view, at a constant potential difference does two different massive particles will move at the same speed?

In a GM (Geiger-Müller) tube, the velocity of charged particles is primarily determined by the applied electric field. Two different massive particles at the same potential difference will not necessarily move at the same speed in a GM tube.

The magnitude of the electric field in the GM tube depends on the applied voltage and the geometry of the tube. The electric field strength is typically a few hundred volts per millimeter, and the voltage across the tube is set to ensure that the tube operates in the proportional or Geiger-Müller regime.

The velocity of a charged particle

in the tube is determined by the electric field strength and the particle’s charge-to-mass ratio. The greater the electric field strength, the greater the acceleration of the particle, and the higher the velocity it attains. However, the particle’s mass also affects its velocity, since a more massive particle will be less easily accelerated than a lighter one.

8Q. A space charge produces near to the central wire during the avalanche process, is this space charge created by the electrons or by the positive ions?

During the avalanche process in a Geiger-Müller (GM) tube, a space charge is created near the central wire due to the accumulation of positive ions. The space charge is not created by electrons, but rather by the positively charged ions that are produced during the ionization process.

9Q. The Geiger discharge repeated at fix interval of time, what is the reason for it?

The Geiger discharge, also known as the avalanche process, is a phenomenon that occurs in a Geiger Müller tube. A high-energy particle, such as a gamma ray or a beta particle, ionizes gas molecules in the tube. it create a cascade of additional ionization events that can result in a measurable electrical signal.

In a properly operated GM tube, the Geiger discharge should occur only once for each incident particle. However, if the tube is operated at a high voltage. If the gas pressure is too high, the discharge may not stop after the initial ionization event. And the tube can go into what is known as the “continuous discharge” mode. In this mode, the tube produces a steady stream of electrical pulses, even in the absence of incident radiation.

Proportional Region

To prevent the tube from entering the continuous discharge mode, the GM tube is typically operated in the “proportional region,”. In which the applied voltage is set to a level such that the ionization events are proportional to the number of incident particles. In this region, each incident particle produces a single Geiger discharge event. That is followed by a period of quenching, during which the electrical signal returns to its baseline level.

The time interval between successive Geiger discharge events

is determined by the time required for the ionization events to be quenched and for the electrical signal to return to its baseline level. This time interval is typically a few microseconds and is dependent on the specific design of the GM tube and the operating conditions, such as the applied voltage and the gas pressure.

So, the Geiger discharge occurs at fixed intervals of time because the GM tube is operated in the proportional region, where each incident particle produces a single ionization event that is followed by a period of quenching. The time interval between successive Geiger discharge events is determined by the time required for the ionization events to be quenched and for the electrical signal to return to its baseline level.

10Q. What is the concept of voltage drop, and how it helps to detect the rate of ionizing radiation?

The voltage drop

is a concept that is used in the operation of Geiger-Müller (GM) tubes to detect the rate of ionizing radiation. In a GM tube, a high voltage is applied between the anode and cathode, creating an electric field that is used to accelerate the free electrons and positive ions that are produced by the ionizing radiation.

In addition to the pulse amplitude, the shape of the pulse can also provide information about the ionizing radiation. In particular, the voltage drop, or the time it takes for the electrical pulse to return to its baseline level after the ionization event, can be used to distinguish between different types of ionizing radiation.

The voltage drop (V D) is determined

by the gas fill and the geometry of the GM tube, as well as the applied voltage and the rate of ionizing radiation. When an ionizing event occurs, a large number of free electrons are created, which can form a space charge near the anode wire. This space charge can reduce the electric field strength in the region, leading to a slower rate of electron acceleration and a longer voltage drop.

So VD is dependent on the rate of ionizing radiation, with higher radiation rates leading to a shorter voltage drop. This is because the space charge created by the ionization events can be neutralized more quickly by subsequent ionization events, leading to a faster recovery of the electric field and a shorter voltage drop.

11Q. What do you mean by the characteristic curve for the counter? What it reflects?

The characteristic curve of a radiation counter is a plot of the output signal of the detector (usually the number of counts per unit time) as a function of the applied high voltage. The curve typically shows a plateau region, in which the output signal is relatively constant over a range of high voltages, and a breakdown region, in which the output signal begins to rise rapidly as the high voltage is increased beyond a certain threshold.

The plateau region

of the curve is important because it indicates the voltage range over which the detector is operating in the “proportional mode”, in which the output signal is directly proportional to the energy deposited by the incident radiation. In this region, the detector is able to accurately measure the energy of the incident radiation and can distinguish between different types of radiation based on their energy.

The breakdown region of the characteristic curve

is also important, as it indicates the voltage at which the detector enters the “Geiger mode”, in which the output signal is no longer proportional to the energy of the incident radiation. In this mode, the detector produces a high output signal for each ionizing event, regardless of the energy of the incident radiation, and is typically used for counting applications.

If you want to know more about the Geiger-Muller tube and its working, let me know. You can write your question in the comment box below.

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