The cosmic rays
it has been proved that extremely penetrating radiations consisting of charged and uncharged particles a photons are reaching the earth. The source these radiations lies beyond the sun or the other stars orour galaxy The radiations which reach the top of the atmosphere of the earth consist of mostly protons of high energy and a few nuclei such as helium, lithium and beryllium These radiation which reach the top of the atmosphere of the earth from remote sources consist of merely protons and called primary cosmic rays When their primary cosmic particles cnter the atmosphere, they interact with nuclei o the atmosphere gases and produces new particles and protons Theu secondary particles consist of protons, electron, neutrons, poritron, merones and photons Their partic and photons which are produced in the earth’s atmosphere are called secondary cosmic rays scientist Wilron During the year 1895, it was found by hat the divergence of the leave of a charged clectroscope slowly decreased in spite of the best insulations showing that the charge of the leave could be due to the presence of ions around the leaves. The ions which camed charge opposite that of leave could slowly neutralized the charge of the electroscope, might have been produced by some kind of rays The rays were called cosmic rays, because their source was found to be from outside the earth and the atmosphere of the Earth, because there was very little change in the intensity o their rays when the electroscope was taken at different heights above the surface of the earth Had the source of rays been inside the earth there would have been a great change in the intensity of their rays with a distance from the earth There was also found only a small change in t ntensity of their rays
during solar and lunar eclipses that showed that the source of cosmic rays was somewhere beyond our galaxy In 1913, a scientist carried bus electroscope upto a betr of about three m and observed that the rate of di was increased In 1915, Hers found that the rate of dischar increased with heights and so he suggested that some unknown penetrating radiation was entering the atmosphere from outer space For this reason, Hers was the credit for the discovery of this mysterious radiation calka cosmic rays and he was granted the Nobel Prize in Physa for the year 1937 Milikan studied the intensity of cosmic rays at different altitude His observations indicated lhat the intensity wi constant at all altitude. This led him to think 1933 that the primary cosmic rays which enter our atmosphere are high energy Gamma rays. This view was found to be wrong TThe measurement of the ionization in air at different heights with the help of acroplane and balloon flights shows that the intensity of cosmic rays Lncreases with heights, reaches the nmaximum and then decreases The height at which cosmic rays intensity becomes maximum depends upon the altitude For example the maximum is found at a height of 16 km al altitude of 51″ and the maximum intensity is 170 times as greater as sea level The variation of cosmic rays
intensity with altitude is called altitude effect In 1940, Clay measured the cosmic rays intensity at vanous altitude during his voyage from Amsterdam to Batavia His observation indicated that the cosmic rays intensity remains constant at greater than 45 but appreciably decreases at the magneuc equator Le the intensity has a maximum value at the equator This is called the latitude effect The altitude and latitude effects can be explained by supporting that the pnmary cosmic rays which come from thr outer space are almost entirely composed of high energy positively charge particles which are mostly proteins Before reaching the surface of the earth, the particles have to pass through the earth’s magnetic field The positively charged particles moving towards a pole travel parallel to the direction of the earth’s magneti field and so experience no force The particles moving towards a pole can reach the surface of the particles moving normally to the canh The positive charged surface of the earth of the magnetc equator and particles experience a force perpendicular to their direction of motion, which makes them move in circular areas If the velocity of particles is sufficiently slow, it will be rurned back and so it will not reach the earth at the equator It is obvious that some of the particles moving towards the equator will not be able to reach the earth, and so the cosmic rays intensity is expected to be loss at the equator that at the poles This explains the latitude effect At a height of about 20 km the density of air is appreciable and so several collision take place between primary cosmic rays and atomic nuclei Such collision produces number of nuclear fragments and highly penetrating gamma rays, which are called secondary cosmic rays as a single primary cosmic ray particle can produce a number of secondary rays and the late can also produce fresh secondary ray by further collisions with atomic nuclei, the intensity of cosmic rays come nearer the earth’s surface, the intensity of air rapidly increases and so the rays distance of cosmic rays from the surface of the earth goes on decreasing This explains the altitude effect. Primary cosmic rays are high energy particles. It is found that some primary cosmic ray particles possess energy as high as mev, How and where such high energy particles are produced in the universe is still a mystery.