Further Results on Neutron Production by Cosmic-Ray Particles at Sea Level

Abstract

Further measurements at sea level on neutrons coincident with charged cosmic-ray particles are reported. It is shown that the coincident neutrons are neither incident from the air nor produced in the neutron detector; they are produced in the Pb in our experimental arrangement. The earlier evidence for neutrons associated with the stopping in Pb of charged particles filtered by 12.7 cm Pb is confirmed. Evidence is presented for a second effect-neutron production in Pb in some kind of penetrating ionizing event. These neutron-penetrating particle coincidences may well be related to those discovered by Tongiorgi in penetrating showers; their bearing on the interpretation of neutron-stopped particle coincidences is discussed. With increasing thickness of the Pb filter above the G-M tube telescope, the frequency of the latter is essentially constant, while the frequency of the "neutron showers" increases steadily. Intensity considerations indicate that the bulk of the neutron-stopped particle coincidences are due to $\mu$-mesons stopped in the Pb; the neutron penetrating particle coincidences may well be due to incident nucleons. A very crude estimate of the average number of neutrons per stopped negative meson gives 2 or 3; the systematic errors are so uncertain that we can only conclude that the multiplicity is with high probability less than about 5.