Back in the 1950s, when the neutrino was still a hypothesis but iron curtain was a reality, A. Szalay in Hungary had an idea to take a snapshot of an event that would prove the existence of the neutrino. During his research at Cavendish Laboratory (United Kingdom), he became acquainted with the latest techniques for research in nuclear physics, and decided to investigate the decay of 6He, a short lived isotope. He recruited J. Csikai, then a young scientist, and together they built a cloud chamber with a sophisticated stereo-camera system.
Forget about megapixels, data acquisition system, everything was hardwired. Still, from the tracks of the residual 6Li and of the emerging electron, it became evident that there was an invisible third party that steals momentum, or in other words, the conservation of momentum was violated.
Thus, the neutrino, the thief of the missing momentum was caught in the act. This evidence was sent to Nuovo Cimento in 1956 (the original article can be found in this archive), in the year where Hungary became famous more for the actions freedom fight there rather than its achievements in physics.
Epilogue: The iron curtain has become history now, and so is the place where this experiment was performed. The main building of MTA Atomki, Debrecen, joined the EPS Historic Sites in October 2013.
More information on the EPS Historic sites is available on the EPS website.