Cosmic Spray

Working with "coincidence counters" last year, the University of Padova's Professor Bruno Rossi, foremost of Italy's cosmic ray researchers, thought he had snared in his apparatus the trace of a radiation that came neither from outer space nor from earth's radioactive substances. It seemed to Professor Rossi that in darting through sheets of metal the primary cosmic rays gave birth to a secondary radiation of electric particles. Two other physicists got on the scent, found that the secondary particles were generated in the form of showers--like spray from the splash of passing cosmic rays. Then Professor Rossi hooked up a new arrangement of coincidence counters, made further discoveries about the spray, which last week he reported. Coincidence counters are multiple arrangements of individual counting-tubes. Arranging three tubes in the form of a triangle, Professor Rossi was able, by recording simultaneous discharges in the three tubes, to pin down the secondary rays as originating in the neighborhood of the triangle. He found that the splash rays differ from the primary rays in penetrative power. Up to a certain point the showers were more frequent as the thickness of the lead sheet was increased; the maximum shower production was observed in lead of such thickness that it weighed 20 grams per square centimetre. Beyond this thickness the number of triple coincidences dropped sharply, from which Professor Rossi concluded that the secondary rays are stopped after traveling a few centimetres in lead, whereas cosmic rays can traverse many feet of that metal. Professor Rossi found the showers most frequent in metals of high atomic number, metals in which the atomic nuclei have large cohorts of electrons. Lead (82 electrons) furnished twice as many showers as iron (26 electrons), four times as many as aluminum (13 electrons).

This file is automatically generated by a robot program, so reader's discretion is required.