Cosmic Rays or Cosmic Radiation

Image via Wikipedia

Soon after 1900 it was shown by scientists that the air in an ionisation chamber, which was completely protected against penetration of α , β and γ rays, by surrounding it with thick lead walls, was still conductive; and it was thought that the inns causing this conductivity were produced by some rays coming from an unknown source. In 1911, Hess and Kolhoster, by placing ionization chambers in balloons and sending then to great heights established the existence of penetrating radiations coming from above. These radiations are now called Cosmic Rays

Improvements of Physics of Cosmic Radiations: East West Effect

Further investigations on these rays were begun by Millikan in 1925 by means of sounding balloons carrying a recording electroscope, thermometer and barometer; and also by lowering measuring instruments deep into lakes. It was found that the intensity of the penetrating rays (i.e., Cosmic Rays) increases with the height, reaching a maximum at a height, equivalent to 9 meter of water, above earth, which shows that most of the rays must actually be produced there , and much of the cosmic radiation observed at lower level is a secondary radiation, produced by the impact of the original radiation with air molecules.

It has also been noticed that the intensity of cosmic rays is greater for higher magnetic latitudes than for lower latitudes. This seems to be due to the fact that the magnetic field of the earth deflects the cosmic ray particles, although some of then are still able to reach the earth , while others do not. Also it has been observed that the number of particles coming from the west is greater than from the east , and the effect is known as The East West Effect.

Types of Cosmic Radiations

The cosmic radiations are of two types:



Those which penetrate about 10 cm of lead are called Hard Cosmic Radiations and those which are absorbed within this thickness of lead are soft.

The great penetrating power of the cosmic rays was at first believed to show that the rays must be photons of the same nature as γ rays. In 1926, Bothe and Kolhoster showed that the cosmic rays consist largely of electrically charged particles and the primary or original cosmic rays consist of α particles, protons and electrons.

Cosmic Rays made it happen! Discovery of Positron

In 1932 Anderson used Wilson cloud chamber and powerful magnetic field to bend the path of the cosmic ray particles. He discovered that there was present a new type of particle, which has the same mass as an electron but has positive charge equal to that of an electron. This particle is called positron, the name negatron is sometime given to the ordinary electron to distinguish it from a positron as stated.

Do you know?

A photon can be broken into an electron and a positron. This process is called Pair Production.

Cosmic Ray Showers

Cosmic rays have been investigated by means of Wilson cloud chambers and tracks which are due to secondary radiations have been obtained. There tracks show that they originate from the same point and many goog-ring particles emanate from the same point. Such a group of particles form a shower, a Cosmic Shower. A theoretical explanation of their showers has been given by Dr. Homi Bhabha & Heitler.

It is assumed that the shower producing raw is a fast moving electron. When it passes close to the nucleus of an atom at A (see image), a photon radiated which consequently passes close to the nucleus of another atom as at B and produces a +ve & a -ve electron(?), i.e., a positron and a negatron(electron). Meanwhile the original electron produces another photon at C, which in turn produces another electron pair at D and so on, thus producing fresh chains, constituting what is known as the Cascade Process. This process continues so long as the energy of the electron and photon is greater than a critical value & performes showering. Cosmic Ray ShowerNote that A, B, C, D…are nuclei. And a high energy γ ray / photon passing close to the nucleus of an atom is annihilated and electrons/positrons are produced.


Feel free to ask questions, send feedback and even point out mistakes. Great conversations start with just a single word. How to write better comments?
Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

You May Also Like

Rayleigh- Jean’s Law

Lord Rayleigh on classical limes made an attempt to explain the energy distribution in black body radiation, which was completed by Jeans in 1900. The result obtained by then is known as Rayleigh – Jean’s Law. Black body emits radiation of continuously variable wavelength right from zero to infinity. This radiation can be imagined as broken up into monochromatic waves.…
Read More

Statistical Physics: Ensembles

Ensembles As a system is defined by the collection of a large number of particles, so the “ensembles” can be defined as a collection of a number macroscopically identical but essentially independent systems. Here the term macroscopically independent means, as, each of the systems constituting an ensemble satisfies the same macroscopic conditions, like Volume, Energy, Pressure, Temperature and Total number…
Read More

Entropy and Disorder

In science, we look for patterns to discover nature’s laws. What is the pattern common to all spontaneous changes? To find a pattern, it is often best to start with very simple examples, because then the pattern is likely to be more obvious. So let’s think about two simple spontaneous changes — the cooling of a hot metal and the…
spiral galaxy sample
Read More

Meet A1689B11 : The oldest spiral galaxy ever discovered

In a collaborative attempt, astrophysicists from different institutions have found success in discovery of A1689B11 – a spiral galaxy that’s said to be the oldest discovered. The research reports an integral-field spectroscopic (IFS) observation of this gravitationally lensed spiral galaxy. It is the most ancient one till date and is calculated to be 11 billion years old, which means it existed…
Read More

How to Revise Physics syllabus for JEE Main in Just 1 Month?

With JEE Main 2019 is scheduled to be conducted from 6th – 20th January 2019, you have just one month left to give your one-year preparation a sure-shot success. If you are wondering how to start your revision for JEE Main Syllabus for Physics section in order to crack the JEE Main exam 2019 in 1 month, we are here…

Statistical Physics: Macrostates and Microstates

Consider some (4, say) distinguishable particles. If we wish to distribute them into two exactly similar compartments in an open box, then the priori probability for a particle of going into any one of the compartments will exactly 1/2 as both compartments are identical. If the four particles are named as a , b, c and d and the compartments…