New Evidence for the Existence of Penetrating Neutral Particles

An experiment of the Rossi-Hsiung type was performed at an altitude of 14,200 ft. with a fourfold coincidence array of Geiger-Müller tubes in a vertical position. Thicknesses of 12.7 to 17.3 cm of lead served as absorber between the counters. Additional varying thicknesses were placed alternately above and between the counters, i.e., in positions $A$ and $B$. For small thicknesses the ratio of the counting rates with the lead in position $A$ to that for position $B$ was very little greater than unity. This means very slight production of barytrons by photons at this altitude. For greater thicknesses (19 to 23 cm), however, the ratio $\frac{A}{B}$ becomes 1.06±0.02. Working at sea level, and having the bottom tube shielded with 25 mm of lead, Hsiung obtained the same results. Maass, using no shield for the tubes, found the ratio $\frac{A}{B}$ equal to 1.2. The most reasonable interpretation of the fact that this ratio is greater than unity seems to be the production of barytrons by non-ionizing primaries. In view of the great thickness of lead required to give the maximum effect, these non-ionizing particles must be much more penetrating than photons. This high penetrating power suggests their identification with the neutrettos (neutral particles having mass and other properties similar to the barytron) postulated by Heitler.