Nuclear Power Plants : Neutrinos or Anti-Neutrinos ?

In 1946, Bruno Pontecorvo, then in Canada, proposed to use the inverse beta-process (ν + Z → e⁻+ [Z+1]) to detect the neutrinos, mentioning the famous chlorine-argon reaction (νe+ 37Cl →e⁻+ 37Ar) followed by the observed 37Ar decay [Pon46], and quoting nuclear reactors (and the Sun) as significant sources of “neutrinos”. In 1949, Alvarez proposed an experiment based on this reaction but did not realize it [Alv49].

In 1954, Ray Davis built a first detector based on this principle (observation of 37Ar decay in a chlorine target). He already noted [Dav55]: “A nuclear reactor emits antineutrinos which arise from the negative beta decays of fission products. In our experiment an attempt is made to observe an inverse electron capture process which requires neutrinos, using a source emitting antineutrinos. If neutrinos and antineutrinos are identical in their interactions with nucleons one should be able to observe the process upon carrying the experiment to the required sensitivity. However, if neutrinos and antineutrinos differ in their interactions with nucleons one would not expect to induce the reaction νe+ 37Cl →e⁻+ 37Ar“. Operating close to the Brookhaven reactor, Davis did not observe anything [Dav55], first experimental proof that neutrinos were not identical to antineutrinos, when interacting with nucleons. He has been more successful later to search for solar neutrinos (νe and not νe) [Dav64,Dav68].


Pon46B. Pontecorvo Inverse beta process Report PD-205 of the National Research Council of Canada, Division of Atomic Energy, Chalk River, Ontario, Nov. 13, 1946 (available in *Winter, K. (ed.): Neutrino physics*, p.25, in *Pontecorvo, B.: Selected scientific works*, p. 21, in *Bahcall, J.N. (ed.) et al.: Solar neutrinos* 97-106) - Reprint in “Neutrino Physics”, ed. by K. Winter, Cambridge University Press, 1991
Alv49L.W. Alvarez A proposed Experimental Test of the Neutrino Theory UCRL Report 328 (1949)
Dav55Raymond Davis Jr. Attempt to Detect the Antineutrino from a Nuclear Reactor by the 37Cl(neutrino,e-)37Ar reaction Phys. Rev. 97 (1955) 766
Dav64R. Davis, Jr. Solar neutrinos. II. Experimental Phys. Rev. Lett. 12 (1964) 303
Dav68R. Davis, D.S. Harmer, K.C. Hoffman Search for neutrinos from the Sun Phys. Rev. Lett. 20 (1968) 1205