Positron

In News 

Researchers from the Raman Research Institute (RRI), Bengaluru, have resolved the mystery of the antimatter counterpart of the electrons called Positron and Positron Excess Phenomenon.

About Positron 

• It is a positively charged subatomic particle having the same mass and magnitude of charge as the electron and constituting the antiparticle of a negative electron. 
• It is also called a positive electron.
• Positrons were discovered by Carl David Anderson in cloud-chamber studies of the composition of cosmic rays (1932).

Positron Excess

• Over the years astronomers have observed an excess of antimatter counterpart of the electron or positrons having an energy of more than 10 giga-electron volts, or 10 GeV.
• For an estimate, this is the energy of a positively charged electron accelerated across a 10,000,000,000 volt battery.
  • Positrons with energy more than 300 GeV, however, are lower in comparison to what astronomers expect. 
    • This behaviour of positrons between 10 and 300 GeV is what astronomers call the ‘positron excess’.

RRI’sStudy 

• The Milky Way consists of giant clouds of molecular hydrogen. They are the seats of the formation of new stars and can be as massive as 10 million times the Sun’s mass.
  • They can extend up to 600 light-years, the distance that would take light 600 years to travel. 
• Cosmic rays, produced in supernovae explosions propagate through these clouds before they reach the Earth. Cosmic rays interact with molecular hydrogen and can give rise to other cosmic rays.
  • As they propagate through these clouds, they decay from their original forms and intermix, lose their energy by energising the clouds, and may also get re-energised. 
• The researchers from RRI studied all these astrophysical processes via a code they set up on the computer, using a publicly available code.

Code

• The code considers 1638 molecular hydrogen clouds in the Milky Way that other astronomers have observed across different wavelengths of the electromagnetic spectrum.
• They have followed three different catalogues to construct a comprehensive one.
  • The combined catalogue consists of ten molecular clouds in the immediate neighbourhood of our Sun. 
  • These galactic clouds provide the astronomers with a crucial input –– the number of giga-electron volt cosmic rays.
  • These help them determine the excess number of positrons that reach the Earth. 
• The computer code the researchers used, by taking into account the exact number of nearby galactic molecular clouds and it was successfully able to reproduce the observed number of positrons at giga-electron volt energies. 
• Researchers consider all mechanisms via which cosmic rays interact with the molecular clouds to show that nearby molecular clouds can be a viable contributor to the positron excess phenomenon.
  • Not only the positron excess, the computer code accurately reproduces the spectra of protons, antiprotons, boron, carbon, and all other components of cosmic rays and their method explains all the observed numbers without running into any contradiction.

RRI proposal

• Their proposal is simple –– cosmic rays while propagating through the Milky Way galaxy interact with matter producing other cosmic rays, primarily electrons and positrons.  
  • These new cosmic rays are the origin of the ‘positron excess’ phenomenon.

• All mechanisms via which cosmic rays interact with the molecular clouds to show that nearby molecular clouds can be a viable contributor to the positron excess phenomenon.

Source :PIB