The reconstruction of the hydrogen fusion mechanism is certainly very reliable, but there are several other aspects which still remain a mystery. This uncertainty is related to one of the greatest discoveries in the world of physics in this century: a tiny particle with amazing properties - the neutrino. Everything started at the beginning of the Thirties. The Austrian physicist Wolfgang Pauli had found that things didn't add up in a certain type of radioactive decay, because a part of the energy available was mysteriously lost. At that time, Pauli thought that the "deficit" was caused by the release of a particle that had never been observed, but that had to have very specific characteristics: nearly zero mass, no electric charge (neutral), but that moves at almost the speed of light. What name could be given to such an elusive particle? The term neutron ("neutral particle") had already been used for quite some time when physicists seriously began to consider Pauli's hypothesis, and so Enrico Fermi suggested to call it the neutrino: a very small neutron. With zero mass and no electric charge, the neutrino was difficult to detect in the laboratory and for many scientists was considered to be a kind of ghost: did it really exist or was it only a way to make things come out? The best way to discover the truth was to see if the Sun, where the same nuclear processes took place on such a vast scale, emitted the mysterious particle. In the Fifties, physicists went hunting, preparing an ingenious trap. The trap was based on the fact that when a high-energy neutrino collides with a chlorine atom, that atom might be transformed into an argon atom. If the transformation occurs, the neutrino exists. And so, about twenty years ago, an American physicist, Raymond Davis, built a "neutrino telescope", a large tank containing 378 000 liters of chlorine detergent. To make sure that the other particles coming from space, with less penetrating power than neutrinos, would not interfere with the experiment, he placed the tank deep down inside an old gold mine in South Dakota, in the United States, at a depth of almost 1 500 meters. The hunt was a success: a certain number of chlorine atoms were transformed into argon. But the number of neutrinos detected was much less than expected, if the theorized atomic reactions inside the Sun were correct. At this point, scientists didn't know what to think: either the solar energy production system reconstructed to this point was incorrect, or the Sun was undergoing a period of "weakness", or neutrinos behave differently than what was first believed. In other words, something wasn't right and it seemed certain that something fundamental had to be corrected in our knowledge of solar physics and, in particular, nuclear physics in general. Italy tried to make its contribution in this field by building a laboratory inside two emergency garages in the Monte Bianco tunnel, shielded by two and a half kilometers of rock. But, for the moment, neither we have obtained sure results: the neutrino seems to exist, but its essential nature continues to elude us.
The reconstruction of the hydrogen fusion mechanism is certainly very reliable, but there are several other aspects which still remain a mystery. This uncertainty is related to one of the greatest discoveries in the world of physics in this century: a tiny particle with amazing properties - the neutrino. Everything started at the beginning of the Thirties. The Austrian physicist Wolfgang Pauli had found that things didn't add up in a certain type of radioactive decay, because a part of the energy available was mysteriously lost. At that time, Pauli thought that the "deficit" was caused by the release of a particle that had never been observed, but that had to have very specific characteristics: nearly zero mass, no electric charge (neutral), but that moves at almost the speed of light. What name could be given to such an elusive particle? The term neutron ("neutral particle") had already been used for quite some time when physicists seriously began to consider Pauli's hypothesis, and so Enrico Fermi suggested to call it the neutrino: a very small neutron. With zero mass and no electric charge, the neutrino was difficult to detect in the laboratory and for many scientists was considered to be a kind of ghost: did it really exist or was it only a way to make things come out? The best way to discover the truth was to see if the Sun, where the same nuclear processes took place on such a vast scale, emitted the mysterious particle. In the Fifties, physicists went hunting, preparing an ingenious trap. The trap was based on the fact that when a high-energy neutrino collides with a chlorine atom, that atom might be transformed into an argon atom. If the transformation occurs, the neutrino exists. And so, about twenty years ago, an American physicist, Raymond Davis, built a "neutrino telescope", a large tank containing 378 000 liters of chlorine detergent. To make sure that the other particles coming from space, with less penetrating power than neutrinos, would not interfere with the experiment, he placed the tank deep down inside an old gold mine in South Dakota, in the United States, at a depth of almost 1 500 meters. The hunt was a success: a certain number of chlorine atoms were transformed into argon. But the number of neutrinos detected was much less than expected, if the theorized atomic reactions inside the Sun were correct. At this point, scientists didn't know what to think: either the solar energy production system reconstructed to this point was incorrect, or the Sun was undergoing a period of "weakness", or neutrinos behave differently than what was first believed. In other words, something wasn't right and it seemed certain that something fundamental had to be corrected in our knowledge of solar physics and, in particular, nuclear physics in general. Italy tried to make its contribution in this field by building a laboratory inside two emergency garages in the Monte Bianco tunnel, shielded by two and a half kilometers of rock. But, for the moment, neither we have obtained sure results: the neutrino seems to exist, but its essential nature continues to elude us.
