What are cosmic rays? Where do they come from? These are the common question that come in one’s mind but no answer, but it’s really very easy to understand this concept. Basically cosmic radiations are defined as high energy radiations that strike on earth, coming from outer space or can also be defined as the fragments of atom raining down on earth. This is also background radiation definition, as their source is also unknown. These rays are responsible for the electronic problem in satellites and other machineries. Cosmic radiations are composed of charged nuclei which are heavier than helium and are called HZE ions (high energy nuclei component of cosmic rays with charge greater than two, charge on nucleus is the charge of ion as there are no electrons revolving).
90 percent portion of the cosmic radiations that strike earth’s atmosphere are protons (hydrogen nuclei), remaining 9 percent is taken by alpha particles and remaining one percent is of electrons.
Types of cosmic rays
Primary cosmic-radiation: they are produced from the outer region of solar system or Milky Way. They consist of stable charged particles, stable means their lifetime is greater than millions of years. Their energy range is from 109 eV to 1020 eV. A major factor that affects the path of cosmic radiations is magnetic field. It causes difficulty in finding source of cosmic rays.
Secondary cosmic-radiation: when primary cosmic rays strike and interact with earth’s atmosphere, then secondary rays are generated. As they enter earth’s atmosphere, then they collide with atoms and molecules (mainly oxygen and nitrogen) present in air, this interaction causes a cascade of lighter particles including x-rays, muons, protons, alpha particles, pions, electrons and neutrons i.e. air shower of secondary radiations.
The particles that are usually produced in such collisions are neutrons and charged measons (+ve and –ve pions and kaons). Some of them decay with time into muons and neutrinos, which have ability to reach on earth’s surface. Some muons from them penetrate into shallow mines and some neutrinos cross earth without interaction. Remaining particles decay into photons which cause cascades. These particles are detected by the particle detectors like cloud and bubble chambers and scintillation detectors.
What are cosmic rays made of?
When carbon and oxygen nuclei collide with inter-stellar matter then they cause production of lithium, beryllium and boron, under a process known as cosmic radiations spallation. This process is responsible for the abundance of titanium, vanadium and manganese ions in cosmic radiations, which are produced by collisions of iron and nickel nuclei with inter-stellar matter. Some satellite experiments have proved that there are positrons and a few anti-positrons in 1% amount, in primary cosmic rays. These positrons in cosmic radiations reach with no direction and they reach on earth with energy of 500 GeV. While the anti-positrons also have higher energy as compared to normal matter (protons). They reach on earth with the energy of 2 GeV showing that they are produced by different process from cosmic radiations photons. Still, there is no evidence for the presence of antimatter atomic nuclei like anti-helium, in cosmic radiations.
Properties of cosmic rays
- They have very high energy ranging from 100 to 1000 TeV.
- Their intensity increases with altitude which is an indication that it is coming from outer space.
- Their intensity alters with latitude (an angle ranging from 0 degree at equator to 9o degree at poles), which is a proof of presence of a few charged particles which get affected by magnetic field of earth.
- Cosmic radiations may cause shower of secondary particles which can penetrate and even can impact the atmosphere of earth.
Flux of cosmic radiations
At upper atmosphere, the flux of incoming cosmic-rays depends upon solar wind, magnetic field of earth and energy of cosmic radiations. At the distance of about 94 AU from sun, solar wind undergoes a change from supersonic to subsonic speeds, called termination shock. Region b/w termination shock and heliopause acts as a hurdle/barrier to cosmic rays, thus decreasing their flux at lower energies of 1 GeV, by about 90%. Since strength of solar wind is not constant so cosmic ray flux also keeps on changing with solar activity.
Secondly, the magnetic field of earth tries to deflect cosmic rays from its surface, proving that flux is dependent on latitude (an angle ranging from 0 degree at equator to 90 degree at poles), longitude (a geographic co-ordinate specifying east west position of a point of earth’s surface) ad azimuth angle (angular measurement in spherical co-ordinate system).
In past, it was thought that flux of cosmic radiation remain constant over time but recent researches suggested that 1.5 to 2 fold millennium-timescale changes in cosmic radiation flux in past 40,000 years. Well, it is thought that cosmic radiations are very dangerous for humans. Yes it is true, since cosmic radiations are charged so they are capable of changing your DNA by hitting individual cells inside your body.
Are cosmic rays harmful?
Cosmic rays permeate our bodies, passing right through us. Cosmic rays, which are made up of tiny atoms, are one such mystery. These rays, which are currently moving through us, are not harmful to us or any other life on the planet’s surface. Because of their unique properties, beams of charged particles, similar to those encountered in space, they can be used to destroy deep-seated tumors while minimizing damage to surrounding tissues. They also enable us to improve radiation protection in space and to overcome the current limitations in predicting health risks for long-duration space travel.