We take a 1500 meters length, supposing the bubble chamber at 100 meters beyond the filter's end. Of course, the number of neutral kaons stopped inside the filter is enormous , but the possibility or probability that a few of them will reach the bubble chamber is significant. Its mechanism is very special, as is shown in what follows. The neutrino, and the secondary emission, is emitted, in its center of mass, in all directions, that is, the neutrino is emitted between 0 and 360 degree with respect to its line of flight. Another fountain of neutral particles, is the enormous neutron quantity yielded in the target.
Various phenomena yield the same reaction, as was explained.
Many particles, of the total produced, will collide with the nuclei inside the filter. Such reactions also produce neutrons and gamma rays. Sooner or later, if the filter is too long, the reaction in the bubble chamber will cease to be neutrino-like, and the neutrino business will cease to be a successful enterprise. Brookhaven National Lab. Pion Beta Decay Experiment.