Chronology of Milestone Events in Particle Physics - COWAN 1956
Chronology of Milestone Events in Particle Physics

  Nobel prize to F. Reines awarded in 1995 "for the detection of the neutrino''. Co-winner M. Perl "for the discovery of the tau lepton''  

COWAN 1956

Cowan, C.L.; Reines, F.; Harrison, F.B.; Kruse, H.W.; McGuire, A.D.;
Detection of the Free Neutrino: A Confirmation
Science 124 (1956) 103;

A tentative identification of the free neutrino was made as an experiment performed at Hanford in 1953. In that work the reaction: p+ + n0 (1) was employed wherein the intense neutrino flux from fission-fragment decay in a large reactor was incident on a detector containing many target protons in a hydrogenous liquid scintillator. The reaction products were detected as a delayed pulse pair; the first pulse being due to the slowing down and annihilation of the positron and the second to capture of the moderated neutron in cadmium dissolved in the scintillator. To identify the observed signal as neutrino-induced, the energies of the two pulses, their time-delay spectrum, the dependance of the signal rate on reactor power, and its magnitude, as compared with the predicted rate were used. The calculated effectiveness of the shielding employed, together with neutron measurements made with emulsions external to the shield, seemed to rule out reactor neutrons and gamma radiation as the cause of the signal. Although a high background was experienced due to both the reactor and to cosmic radiation, it was felt that an identification of the free neutrino had probably been made.
To carry this work to a more definitive conclusion, a second experiment was designed, and the equipment was taken to the Savannah River Plant of the US Atomic Energy Commission, where the present work was done. This work confirms the results obtained at Hanford and so verifies the neutrino hypothesis suggested by Pauli and incorporated in a quantitative theory of beta decay by Fermi.
In this experiment, a detailed check of each term of Eq.1 was made using a detector consisting of a multiple-layer (club-sandwich) arrangement of scintillation counters and target tanks. This arrangement permits the observation of prompt spatial coincidences characteristic of positron annihilation radiation and of the multiple gamma ray burst due to neutron capture in cadmium as well as the delayed coincidences described in the first paragraph. (Extracted from the introductory part of the paper.).

Accelerator REACTOR Detectors CNTR

Related references
See also
F. Reines and C. L. Cowan, Phys. Rev. 90 (1953) 492;
C. L. Cowan, F. Reines et al., Phys. Rev. 90 (1953) 493;
F. Reines and C. L. Cowan, Phys. Rev. 92 (1953) 830;

  e p n e+ 1.8-6.0 MeV (Elab) cs

Particles studied
  e ex
  e ex

Record comments
Confirmation of the detection of the e.
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