Abstract
Since the presence of neutrinos cannot be detected by ionization effects, which serve to detect other elementary particles (as well as $\gamma$-rays), the only method here is the use of certain nuclear reactions.
Full Text
FROM CURRENT LITERATURE
ATTEMPTS TO DETECT NEUTRINO ABSORPTION1
Since the presence of a neutrino cannot be detected by ionization effects, which serve for the detection of other elementary particles (and also of γ-rays), the only method here is the use of certain nuclear reactions. Recently Crane undertook such an attempt, based on the reaction
\[ {}^{35}\mathrm{Cl}+\mu \to {}^{35}\mathrm{S}+e^{+} \]
(where \(\mu\) denotes the neutrino).
The radioactive sulfur \({}^{35}\mathrm{S}\) obtained as a result of this decays, returning to the initial product—chlorine—with emission of a negative electron and a neutrino,
\[ {}^{35}\mathrm{S}\to {}^{35}\mathrm{Cl}+e^{-}+\mu . \]
Thus these transformations have a cyclic character and in the final analysis reduce only to the emission of electron pairs.
It follows from these equations that the energy of the neutrino capable of producing the required transformation must be not less than
\[ 2mc^{2}+W_{0}, \]
where \(W_{0}\) is the upper limit of the β-spectrum of the radioactive isotope produced.
Breit made an approximate calculation of the effective cross section for this interaction, which turned out to be about \(10^{-46}\ \mathrm{cm}^{2}\). Crane had the possibility of carrying out an experiment that would give a positive result with a much larger cross section (\(\sim 10^{-30}\ \mathrm{cm}^{2}\)). He considered it worthwhile to carry out such an experiment, since establishing the absence of the effect would also be of significance for certain questions of astrophysics.
Since \({}^{35}\mathrm{S}\) has a β-spectrum with an upper limit of about 0.3 MeV, the minimum neutrino energy required for the above reaction must be 1.3 MeV; therefore, as a source of neutrinos one could use mesothorium with the products of its decay. The experiment consisted in the following: inside a mass of 1.2 kg of NaCl a capsule containing 1 millicurie of MsTh was placed, and after 90 days of irradiation the dissolved salt was treated with \(\mathrm{H}_{2}\mathrm{O}_{2}\) (to oxidize the sulfur). All the sulfur contained in the NaCl was precipitated (in the form of barium sulfite). The resulting precipitate was tested for β-activity with a counter capable of detecting 10 electrons in 1 sec. No activity was found.
-
H. R. Crane, Phys. Rev., 55, 502, 1939. ↩