🪴 GoDeep
Search
← University Challenge
Portrait of Neutrinos

Science · Physics

Neutrinos

proposed 1930; detected 1956

Physics — particle physics

Electrically neutral, almost massless fundamental particles that interact only through the weak force and gravity, so they pass through matter almost unhindered — about 65 billion from the Sun cross every square centimetre of your body each second. Wolfgang Pauli postulated one in 1930 to rescue energy conservation in beta decay, calling it a desperate remedy; Enrico Fermi gave it its Italian diminutive name. Clyde Cowan and Frederick Reines detected them in 1956 beside a nuclear reactor. They come in three flavours and change from one to another in flight, which proved they have mass and won the 2015 Nobel Prize.

How to spot them

  • ▸Postulated in 1930 to save energy conservation in beta decay, in a letter to 'radioactive ladies and gentlemen'
  • ▸Its Italian name, given by Fermi, means 'little neutral one'
  • ▸About 65 billion from the Sun pass through each square centimetre of you every second
  • ▸Detected in a tank of water at a South Pole observatory called IceCube, and in a mine under Mount Ikeno

Key facts

Proposed in a 1930 letter opening 'Dear radioactive ladies and gentlemen' (1930)

Wolfgang Pauli, writing to a meeting in Tübingen he was skipping for a ball in Zurich

Fermi's 1934 name for it, an Italian diminutive meaning 'little neutral one' (1934)

Coined to distinguish it from Chadwick's newly found neutron

The 1956 reactor experiment at Savannah River, codenamed Project Poltergeist (1956)

Cowan and Reines; Reines received the Nobel Prize in 1995

The shortfall in the count from the Sun that puzzled Ray Davis's tank of dry-cleaning fluid (1968)

The solar problem: only a third of the expected number arrived

The flavour-changing in flight confirmed by Super-Kamiokande and Sudbury, rewarded in 2015 (1998–2001)

Oscillation, which requires the particles to have mass

About two dozen arrived from supernova 1987A, hours before the light did (1987)

Detected at Kamiokande II, IMB and Baksan

The 2011 claim that they had beaten light from Geneva to Gran Sasso, undone by a loose cable (2011)

The OPERA result, traced to a badly seated fibre-optic connector

Key ideas

  • In beta decay the emitted electron carries a variable energy; Pauli restored the books by positing an unseen third particle that carries away the remainder.
  • Because the flavour states are mixtures of states with slightly different masses, a beam born as one flavour arrives partly as another — which is only possible if at least two of the masses are non-zero.

Quick-fire facts

  • •Wolfgang Pauli proposed the particle on 4 December 1930 in a letter addressed 'Dear radioactive ladies and gentlemen', calling it a desperate remedy
  • •He first called it the 'neutron'; Enrico Fermi renamed it the neutrino, 'little neutral one', after Chadwick's 1932 discovery took the other name
  • •Clyde Cowan and Frederick Reines detected antineutrinos at the Savannah River reactor in 1956; Reines shared the 1995 Nobel Prize
  • •Three flavours exist — electron, muon and tau — matching the three charged leptons
  • •The muon neutrino's discovery brought Lederman, Schwartz and Steinberger the 1988 Nobel Prize; the tau neutrino was seen at Fermilab in 2000
  • •Raymond Davis Jr and Masatoshi Koshiba shared the 2002 Nobel Prize for detecting cosmic neutrinos
  • •Takaaki Kajita and Arthur McDonald shared the 2015 Nobel Prize for oscillation, proving non-zero mass — the Standard Model had assumed they were massless
  • •The solar 'problem' of the 1960s was not a faulty Sun model but flavour change en route
  • •Detectors include Super-Kamiokande in the Kamioka mine, SNO in a Canadian nickel mine, and IceCube, a cubic kilometre of Antarctic ice
  • •In 2011 the OPERA experiment appeared to measure faster-than-light travel from CERN to Gran Sasso; a loose fibre-optic cable was to blame

Drill it — 9 cards

1 / 9new card

Sources