The Kraków cosmic ray conference, which took place in 1947 provided an opportunity  to revive the project to study cosmic rays deep underground. Earlier, before the war, the renowned French physicist, prof. Pierre Auger suggested during his stay in Kraków that the salt mine in Wieliczka near Kraków was an ideal place to study cosmic ray shower after traversing a thick layer of soil. Although the World War II interrupted the common research, after the war the original idea was revisited.

At the conference, results of research by L.Janossy were presented on properties of penetrating showers. Prof. P.Auger claimed that cosmic radiation at large depths underground consist mainly of penetrating particles, i.e. muons. Professors Barnothy and Forro from Budapest presented a different point of view. They claimed that deep underground, apart from the muon component, they observed another kind of radiation: a weekly ionizing radiation of unknown nature. It was postulated that this radiation was due to interactions of neutrinos.

 

Unlike the muon radiation, which is collimated predominantly along the vertical direction, the weekly ionizing radiation was observed to be isotropic and strongly absorbed by lead. In 1948 a team lead by Prof. Marian Miesowicz began the research in the Wieliczka mine. The results confirmed existence of the week radiation. The Kraków team interpreted it differently however. They found that the effect was due to natural radiation of the ambient medium. The measurements in Wieliczka lasted for about a year. They were quite tedious, not only due to necessity to descend daily into the mine in order to read out the detectors. Especially annoying was curiosity of the Bureau of Security. It was difficult to explain to its officers what actually the scientists were doing in the mine. The numerous appeals of Prof. M. Miesowicz were often aided by Prof. Walery Goetel, the rector of the Mining Academy in Kraków. 

The results of this results were published in Physical Review journal and were later cited many times in review articles and books. 

The Crystal Cave in the Wieliczka salt mine

 Fragment of the underground system of stairs and corridors

Blessed Kinga chapel in the Wieliczka salt mine, located 101 m under the surface. This chapel was entirely forged in salt: walls, ceiling, floor, sculptures and even chandeliers are made of crystal salt.

 

Prof. Marian Miesowicz and Prof.L.Jurkiewicz preparing their counters for the underground experiment in Wieliczka.