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Rare radioactive decay captured by dark matter detector

  • Category
    Science & Technology
  • Published
    10th May, 2019

Scientists have found the first direct evidence of a rare radioactive decay reaction, known as the two neutrino double electron capture.


Scientists have found the first direct evidence of a rare radioactive decay reaction, known as the two neutrino double electron capture.


  • There are four fundamental forces in the Universe: gravitational force, electromagnetic force, strong forces and weak forces.
  • Among these, the weak forces act at the shortest distance and aid in the disintegration of atomic nuclei. This happens through a process known as beta decay.
  • One of the processes of beta decay is an electron capture — in which the nucleus captures an electron, in turn converting a proton in the nucleus into a neutron and emitting a neutrino.
  • The disintegration of some atomic nuclei happens through a double electron capture (two electrons are captured by the nucleus instead of one) which is very slow, and hence the longer half life.


  • The observation was made in the decay of xenon 124 nuclei, which were part of the XENON1T dark matter detector experiment, to tellurium 124.
  • This detection is an important step towards knowing the constituents of dark matter, which makes up 27 per cent of the Universe.
  • Researchers have theorised that dark matter could be made up of yet unfound particles known as Weakly Interacting Massive Particles (WIMP).
  • Such particles will display rare radioactive reactions such as neutrino-less double beta decay, one example of which is a neutrino-less double electron capture.
  • The current observation of a neutrino double electron capture is the first step towards the neutrino-less version of the reaction.

Dark Matter-

  • Everything else, on Earth or elsewhere that we can see and observe constitutes less than 5 per cent of the Universe. The rest of the Universe, around 68 per cent, is dark energy and remains unknown.
  • Scientists have come to this conclusion as the rate of expansion of the Universe cannot be explained with the existence of ordinary matter alone.
  • Only by taking dark matter and dark energy into account can this rate be explained. But apart from this, not much is known about these two mysterious entities.
  • The majority of dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles.
  • Its presence is implied in a variety of astrophysicalobservations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. 

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