Neutrinos – present in vast numbers but barely interact with matter

The sun emits vast numbers of neutrinos which can pass through the earth with little or no interaction. Solar neutrinos shine down on us during the day, and shine up on us during the night after passing through the earth almost no absorption. Bahcall’s modeling of the solar neutrino flux led to the prediction of about 5 x 106 neutrinos/cm2s.

Since a typical adult has a cross section of about 30 cm x 100 cm i.e 3000 cm2, there are over 1 billion neutrinos from the sun passing through our bodies every second.

Ten neutrino events were detected in a deep mine neutrino detection facility in Japan which coincided with the observation of Supernova 1987A. They were detected within a time interval of about 15 seconds against a background of lower energy neutrino events. A similar facility, IMB in Ohio detected 8 neutrino events in 6 seconds. These observations were made 18 hours before the first optical sighting of the supernova.

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