Introduction of detection of cosmic ray particles
In this particular article Introduction of detection of Cosmic Ray particles, we are going to discuss coincidence counter, the photographic emulsion method, advantages of photographic emulsion method, limitations, and drawbacks of photographic emulsion method.
For the detection of cosmic ray particles, many types of detectors such as gold leaf electroscope, ionization chamber, GM counter, cloud chamber, scintillation counter, coincidence counter, photographic emulsion technique etc are used. We will discuss only coincidence counter and photographic emulsion technique here used for detection of cosmic ray particles.
For the detection single charged particle which can ionize the gas, Geiger-Mueller counter a very useful device. It can also be used in the detection of cosmic ray charged particles. But using single GM counter it detects cosmic rays charged particles as well as other charged particles or radiations present in the atmosphere. In order to remove the false GM pulses produced by the background radiations generally coincidence counter is used.
In coincidence counter three GM counters C1, C2 and C3 are arranged above the other as shown in. The output signal of all the three GM counters is fed into an electronic circuit which sends the signal to the counter only when single cosmic ray PQ passes through all the counters. If background radiations pass through all the three counters even then it will detect the cosmic ray. This possibility is very small and it is called chance coincidence. This chance coincidence can be detected separately.
The arrangement is shown in is also called cosmic ray counter telescope. It can detect the cosmic ray coming in a particular direction. It is found from this device that cosmic rays are falling in equal amount directions on the top of the earth atmosphere.
Photographic emulsion method-
The principle of photographic emulsion method of the same as that of ordinary photographic plate i.e. When a photographic emulsion plate, during traversing a photographic emulsion it interacts with tiny silver halide crystals and produces a latent image of its track. When a plate is developed and fixed, the track of charged particles can be observed as a permanent record of track in the form of black metallic silver grains.
The ordinary optical photographic emulsion is not suitable for tracking of charged particles as the density of the emulsions is low and the developed crystals are too large and widely spaced. Due to this reason that photographic emulsion is used in which the proportion of silver bromide to gelatin is higher than that of optical emulsions by about 10 times. The length of tracks printed by the charged particles on such emulsions can be measured precisely.
The size of these grains is from 0.5 μm to 0.1 μm and the type of emulsions categorized A, B, C, D etc according to the size of the grains. The thickness of the emulsion is ordinarily about 100 μm. Which are many times thicker than the emulsions used in the ordinary photographic plate.
The track printed by the charged particles in the emulsions depends upon the ability. To produce ionization in a unit length of particle track and density of black grains. If the tracks recorded by an α-particle. And a proton of equal energy is compared then being ionization by α-particle more in comparison of a proton. The density of black grains in the track of α-particle is greater than that of a proton. As a result, the track of α-particle is more black and thicker in comparison of the track of the proton. The track electron appears as of least density, thinner and dotted track.
The stopping power of photographic emulsion is about 1700 times more than that of air (Emulsion of 1 μm thick is equivalent to 0.i7 cm of air thickness.)
The track produced by the charged particles in a photographic plate is three dimensional.
The track produced by the collision of a cosmic ray of energy about 10⁹ eV with silver nuclei. In photographic emulsion appears as star-like tracks as shown in.
Advantages of photographic emulsion method-
- It remains sensitive every time.
- And It is simple, less expensive and more convenient for observation at a greater height.
- It can analyze one single cosmic ray particle and its decay products.
- Its recording is permanent.
Limitations and drawbacks of photographic emulsion method-
- The main drawback of the photographic emulsion is that their sensitivity. And thickness is affected by temperature, humidity, an age of the emulsion. And the conditions under which emulsion plate is developed.
- If the length of track of charged particle is small, then it is difficult to measure the radius of curvature of the track in the magnetic field. And so the energy and momentum of the charged particle cannot be determined.