It used simply water and in water you have of course electrons and the neutrinos can collide with the electrons and simply bring the electrons to high velocity and then you have a high energy electron which goes through the water and as it does so it emits Cerenkov Radiation which can be observed by photomultipliers which you put around the water tank. Well, the Kamiokande experiment I think has something like 7000 tons of water of which only 2000 are useful because the outer ones can be subject to particles coming from.. from the... container. But the inner 2000 tons are useful and you observe the Cerenkov radiation coming from those and with Cerenkov radiation you have the great advantage of observing these neutrinos as they are actually captured in... in the water and therefore you can determine not only the time of arrival but also the direction of arrival. And the Kamiokande people were able to show that... that many of these neutrinos came from an angle close to the direction of the sun. So it was really well established that these neutrinos really come from the sun.